TWICS 2011 concluded - now the data analysis begins!

As of this afternoon, the TWICS-2011 experiment has concluded. We had planned to continue attempting to take data through the weekend, but this afternoon, the NOAA team has been notified that their schedule for a large experiment later this summer has been accelerated dramatically, and so they will need to remove HRDL from the NWTC tomorrow (Wednesday ~ 1pm) to prepare for international sea-bound deployment.

Although we would certainly be pleased to collect more data, and we hope to do so in future HRDL deployments at the NWTC, TWICS 2011 undoubtedly was a succcess. We have unprecedented measurements of turbine wakes, including valuable information on how far downwind they persist, how rapidly they expand in the cross-stream direction, and how these behaviors are modified by atmospheric stability.  TWICS 2011 has also demonstrated the strength of collaborations between NREL, NOAA, and CU (and Siemens!) as we work together to address critical issues for large-scale wind energy deployment.

Please let me know if you have any questions. Plans for a post-TWICS celebration are pending and will likely include the Southern Sun.

Siemens 12Z WRF Forecast, NAM Initialization

Siemens 12Z WRF Forecast initialized by NAM shows an increase in windspeed headed into Wednesday evening and Thursday. Also, note the windshifts. Times are in UTC.

20z 10 May 2011 Forecast Discussion

Today's SE winds should back to become northerly tonight as southern end of the major western US trough makes it's way east and then northeast, inducing surface cyclogenesis eastern NM and southeast CO. Pcpn (probably mostly snow on the flats) is expected to begin late tonight and end by late afternoon tomorrow, Wednesday. Following that, as the surface low moves east and northeast, surface winds on the flats are likely to back into the NW or WNW, and increase. So, it looks as if there might be another promising observing period setting up for Thursday evening and overnight, possibly continuing into Friday.

John B.

01Z Tu 10 May 2011 Forecast Discussion

See previous blog for this evening's weather. Outlook beyond 12z Tu 10 May:

The overnight wind Monday night will be weakening after midnight, but will hold from the W-WNW. Winds are not likely to continue over 10m/s from the west past about 14z Tuesday morning, and the rest of the day likely will see some increase in clouds and no wind of interest. The next chance of winds from the W - NW looks to be the wee hours of Thursday morning, as the remains of the upper trough shift slowly eastward. If this materializes, it could be a fairly strong event, as the direction of the upper flow will favor the flats over areas farther N.

John B.

00Z Tu 10 May 2011 Forecast Discussion

Situation evolving not too differently than suggested by yda's forecasts ... deep surface low is nearby, with winds on the flats having veered from SSE to SW previous hour with some blowing dust visible on the Siemans cam.

Expect surface circulation will continue to take shape near the CO-WY-NE triple point next couple hours and that as this happens winds on the flats will continue veering into the W. Whether they will continue to veer and go into the WNW is possible; winds are likely to continue quite strong over the next few hours, peaking early to mid evening. Another uncertainty is pcpn ... there is widespread shower activity on the western slope attm, as well is in SE WY. I am less optimistic about pcpn on the flats than yda, as it looks as if the showers are going to stay mainly W of the Divide S of Berthoud Pass. This puts the flats on the southeastern edge of the shower activity, as cells from the western slope cross the Divide mainly north of Berthoud Pass and dissipate as they move off the Divide. I put the likelyhood of measurable rain on the flats between now and midnight as 30%, chance of some pcpn at all during that same period, including very light from small drops, as 60%.

Probability of M2 peak gusts exceeding 15m/s ........... 25m/s

00-06z ............................................. near 100% ...... 60%

06-12z .............................................. 60% ................ 30%

03z M 9 May 2011 Forecast Discussion

After hanging in from the east most of the day, the wind here in Boulder finally turned into the W < 25mph about 01z. M2 is still not available, but the Siemans turbine is barely turning, so I presume winds are lighter on the flats than they are here in Boulder this evening.

This evening there is rather low pressure at the surface over much of the West. The boundary between the north Pacific air that has come in over the Pacific Northwest and much of California at 02z lies from near the WY-SD-NE triple point to just south of Casper to the northwest corner of CO across UT to northwest of Desert Rock NV. It appears to be slowly edging its way eastward. Aloft, the associated cold trough has its axis north-south across eastern WA southward across extreme western NV and thence offshore near Santa Barbara. It appears to me that there is a well-marked embedded short-wave feature aloft that is coming across central and southern CA attm. It is this feature that offers the next possibility for appreciable wind on the flats.

The models seem to be coalescing about the evolution suggested by the Europeans yda, namely, that this prominent short-wave feature now approaching central and southern CA will rotate around the bottom of the trough and approach us from the SW, passing near us in the 00-03z time frame. It will be accompanied by development of a surface low in northeast CO / southwest NE Monday afternoon. This argues for probability of W wind beginning on the flats, say, early to mid afternoon on Monday and continuing for a time Monday night and possibly into Tuesday. The chief concern I have attm is that the overall flow may be a bit too southwesterly for optimum conditions on the flats, but I consider this to be a low enough risk that this opportunity should not be shunned.

Following this, it is pretty certain that the main trough will remain to the west, and that another high-plains surface development will occur on W or Th. Timing of this is uncertain, but I anticipate that there will likely be a gap of 24h or so between the end of the first wind event and the start of the second, assuming the latter materializes.

As the westerlies develop with the frontal passage M afternoon or early evening, light pcpn is likely from a highly convective Foehn cloud over the Divide that contains weak, glaciated Cbs that dissipate as they move off the Divide toward the plains. If the wind really cranks up, I think this precipitation will be fairly short lived, and be toward the beginning of the wind event. Nevertheless, I put the probability of measurable pcpn in Boulder between 18z M and 00z Tu as 70%, and between 00 and 06z Tu as 50%, this latter most likely early in the 00-06z period. The pcpn is not likely to be continuous if wind is blowing hard from the W-NW, but to come in occasional bursts associated with individual convective elements coming off the Divide.

Between the first and second wind event, assuming both occur, I think a period of lighter winds, probably mainly from the NE, is likely, and pcpn is likely as well during the wind remission. There is some possibility of pcpn with a deep convective Foehn cloud on the Divide with the second wind event as well as with the first.

Probability of M2 max gusts exceeding ... 15m/s .......... 25m/s

00-06z M 9 May ..................................... 20% ............ near 0%

06-12z M 9 May ......................................20% ............. near 0%

12 - 18z M 9 May ..................................... 40% ............ near 0%

18z M 9 - 00z Tu 10 May .........................70% ............. 20%

00-06z Tu 10 May ..................................70% ............. 20%

No IOP Saturday

Although the winds teased with us and pulled to the southwest, they don't seem to be rotating to the northwest at all (see Windcube obs below, time is in MST). Bob and I decided to not try for an IOP tonight. Next prospects are Monday...

Windcube obs of wind shift to SWly

The wind shift that John observed (below) was ~ fifteen minutes later at the NWTC according to the Windcube Obs (see below, time in MST). Wind speeds are still quite low.

It seems that M2 is undergoing some maintenance and so data is not streaming right now. I'll keep monitoring the windcube and post updates. You can also check the Triton sodar via www dot skyserve dot net, login and password in comments below, location 112-7. It is currently showing southerly winds. The windcube is behind a VPN firewall, or else I would provide a link to its datastream. -- Julie

20z 7 May 2011 Forecast Discussion

Today has been a bit frustrating ... the heating-induced Cu are moving out of the W - WSW, but slowly, and wind hung in from the SE - SSE at NOAA Bldg 33 in Boulder till 1920z, when it abruptly shifted into the W-WSW. This continues as I write this. So, maybe there is yet hope for today.

The overall pattern presents some fascinating forecast dilemmas ... a little bit like a week ago Friday. Basically, we have a deepening cold trough aloft approaching the west coast, and turning the winds aloft more into the southwest. This trough has the potential to cut off over the intermountain region, or, it may stay more connected with the westerlies as the GFS from this morning suggests, or we may have a piece of the trough hang back over the southwest, and the main part come out, as the Europeans suggest. How this all evolves will determine prospects for winds of interest next week. The bottom line: there is a chance for strong "howling" W to NW wind at some point next week, sometime between Monday evening and Friday.

But ... ahead of all this there is a weak short-wave feature evident on the satellite water-vapor imagery over WY and moving eastward. This is of relevance for Sunday. It appears that this is inducing a weak surface low in northeast WY, and allowing some of the cooler air from the Northwest to filter across the mountains into parts of WY. This complicates the forecast for Sunday, as the GFS and NAM suggest that we might have a chance for daytime downward mixing of momentum once again. On the other hand, if some shallow cooler air sneaks across WY and then down the high plains of CO, we will stay cool with light northerly winds on the west side of a Denver Cyclone, perhaps preceeded by a Longmont Anticyclone with E - SE wind on the flats. Right now, I see it as about 50-50 on the cooler air getting in here on Sunday.

M2 wind gust probabilities (still no web updating at this writing)

> 15m/s ............ > 25m/s

18z 7 - 00z 8 May ..... 50% ............ near 0%

00-06z 8 May .......... 30% ............ near 0% wind likely dying toward dusk

06-12z 8 May ........... 10% ............ near 0%

12-18z 8 May ........... 30% ............ near 0% wind most likely closer to noon

18z 8 - 00z 9 May ..... 40% ............ 10% wind gusts from high based convection possible; pcpn unlikely.

John B.

Wind shift to west at NOAA Bldg 33

FYI ... Wind shifted to west gusting 20-25mph about 1920z, just a couple minutes ago, after blowing mostly SE all mrng. I'm not getting any M2 tower data over the web, so don't know what might be happening out that way. ... john b.

23Z F 6 May 2011 Forecast Discussion

We finally got some west winds just before noon, and winds have continued from the west this afternoon. However, it appears we may have a break in west wind on the flats this evening as one short-wave trough aloft is passing on to the east. There is a weak surface wind shift from NW to N in SE WY attm, and I think it likely that this will hold together this evening as it moves south down I-25, to arrive on the flats mid-late this evening. Even before this we may see slackening of the wind as the incident solar radiation at the surface diminishes, partly due to the persistent cloud cover. So, I anticipate the nighttime hours after, say, 11pm MDT will see light winds.

This evening's cool push is much less substantial than the one that came down on Wednesday, and I expect that if it makes it down this far, it will rapidly be mixed out on Saturday unless cloud cover is more opaque than I anticipate. Accordingly, I look for a deep mixed layer, with sufficient vertical mixing of momentum to allow breezy conditions, to develop by late morning Saturday. As the flow aloft is going to be backing into the SW over the next 36h or so, winds are likely to be more from the W = SW Saturday afternoon than they have been this afternoon. There is a possibility that such conditions could repeat Sunday as well.

Peak gust probabilities on M2 ...... > 15m/s ............ > 25m/s

00-06z 7 May: ................................ 50% ............... near 0%

06-12z 7 May: ................................. 20% ............... near 0%

12-18z 7 May: .................................. 30% ............... near 0%

18-24z 7 May: ................................. 40% ............... near 0%

NWTC observations

Yesterday's upgrades on the 135 m meteorological tower bought some great improvements. We are now getting data at a solid 20 Hz, and the instrumentation look to be behaving well. I've spent some time today trying to get an overview of the data and I'm pretty pleased, so far. Once I am a bit more certain about data quality I will post some info here.

As far as conditions on site are concerned, winds are slowly picking up but remain gusty. They've swung slowly to the WNW over the last two-and-a-half hours, say since 10:00 local. Details are in the plot below.

Friday 6 May IOP

The westerlies are blowing at the site and we will begin taking data a little before the Siemens turbine comes back up by 1:30. John Brown observed that this is a trapped lee wave situation, which means that the winds could be variable in direction and speed at the site as the waves propagate along, but as the mountain ridges heat up during the afternoon, that could change the atmospheric stability enough to make the waves go away and give more steady westerlies this afternoon, although still gusty.

The plan is to "take data until the westerlies stop," since the flow is so hard to predict now. We're prepared to work through the night, but will stop if the favorable winds end -- stay tuned.

23Z Th 5 May Forecast Discussion

Well, I was clearly too optimistic about downward mixing of westerly momentum today. Someone sent me a pix from the top of either Green Mtn or Bear Peak about 3pm MDT showing evidence for a vertically propagating wave launched by the Divide, and in the foreground a 20mph or so west wind based on tree appearance. So, one doesn't have to go up too far to get into the westerlies.

So, what's going to happen? You can get an idea of my confidence by looking at the probability numbers below. Suffice it to say that I think we were real close to getting that desired mixing of westerly momentum down to the surface today, but close doesn't count in this business. Nevertheless, the overall airmass has warmed considerably between 3 and 6km MSL today due to advection from the west. I suspect that with the westerlies not that far overhead, the reversal of the diurnal upslope flow as the sun sets below the mountains will bring the westerlies down to the surface between 6 and 8pm MDT. But, I don't expect strong wind. And, I expect the wind, through the night, will be variable, blowing from the W at gusts to 10-15m/s for perhaps 10-30min, then becoming variable in direction with speeds down to 3-8m/s for awhile. There is a slight hint that the wind might become more persistently W later in the night or into the wee hours, but I say this with low confidence.

Friday morning is no easier. If the wind pretty well dies down near the surface during the wee hours, the heating by the sun in early morning may produce downward mixing of momentum from 300-500m above the surface in the early morning, resulting in an hour or two of west winds of interest. This is not unusual this time of year. In any case, downward mixing of momentum is likely from late morning on, and west winds gusting in the 10-15m/s range will result. I will try to give an update on this if time allows in the morning.

As Bob Banta pointed out in an earlier email, winds aloft will trend toward a less favorable Rocky Flats direction by Friday night or Saturday, although overall strength of flow aloft is likely to increase.

Probability of M2 wind gusts exceeding ..... 15m/s ............ 25m/s

00-06z F 6 May ......................................... 30% .............. near 0%

06-12z F 6 May ......................................... 50% .............. near 0%

12-18z F 6 May .......................................... 50% .............. near 0%

18z F 6 - 00z 7 May .................................... 60% .............. near 0%

John b.

Siemens 18Z windspeed forecast (hopefully soon)

Everyone,

I am executing an 18Z Boulder Turbine run right now. It should be done in ~2 hours. I hope to post an updated windspeed plot to the TWICS blog.

From my brief look at the conditions, the timing of the wind shift and increase is hard to say, but it looks to me around 0300 MDT.

I just talked with Peter a moment ago. The turbine shutdown should occur tomorrow (Fri.) morning and Saturday morning, according to him.

Best regards,

--Paul Quelet

Siemens WRF 06Z forecast, NAM initialization

4.4 Met Tower offline

We're taking the 4.4 met tower offline this morning for some upgrades.

01Z W 4 May 2011 Forecast Discussion

The cold front finally made it through here about 9am MDT this morning, followed by brisk E - SE flow locally, part of a strong Longmont Anticyclone.

The forecast for Thursday has turned out to be more difficult than I thought it would be, particularly on the timing of the onset of winds from the westerly quadrant. I think that by early to mid-afternoon there are likely to be west winds, driven mainly by vertical mixing of WNW flow aloft, mainly above 700mb. It is possible but unlikely that westerly winds will begin as early as 8am MDT; best estimate attm is for a noon west-wind start. If the onset of the west wind is of interest, then starting observations before noon is advised. Wind gusts at 10m appear to me unlikely to get above 15m/s, so this will not be a high-wind event.

Ambient wind at mountain-top level on the Divide looks to not be strong enough to maintain a vertically-propagating mountain wave that would have the proper configuration to favor continuously windy conditions Th night. However, there may be occasional breezy periods from the west overnight, as shear in the nocturnal boundary layer temporarily breaks down to allow some westerly momentum to penetrate close to the surface.

If there is W-quadrant wind on F, it will again most likely be due to vertical mixing of momentum, as I expect the mixed layer will grow deep enough to entrain westerly momentum aloft.

Probability of max gusts on M2 .......... >15m/s .................. > 25m/s

00-06z Th 5 May ................................ near 0% ................. near 0%

06-12z Th 5 May ................................ near 0% ................. near 0%

12-18z Th 5 May ................................. 20% ....................... near 0% most likely late

18z Th 5 May - 00z F 6 May ................ 40% ....................... near 0%

00 - 06z F 6 May ................................ 20% ....................... near 0% most likely early

Siemens WRF 12Z forecast, NAM initialization

Turbine down Thursday

The turbine operators need to bring the turbine down Thursday, starting 9am. They will update us when their changes are completed (scheduled by 4pm). Similarly, there will be down time Saturday morning 8:30-10am.

No IOP Wednesday

Winds Wednesday will be light and variable, so no TWICS IOP. Thursday should have strong zonal flow aloft; we are keeping fingers crossed that Thursday daytime mixing will bring some of that down to the surface so that we can make some TWICS observations. Friday might be even better. We will have an email discussion Wed pm - Thurs am noon to make a decision for Thursday afternoon and evening TWICS activities; look for an update by 10am 2pm Thursday. (Edits added after we learned new information about turbine activities.)

00Z W 4 May 2011 Forecast Discussion

Today's "event" appears to have been pretty much of a dud from my perspective, in part due to the thick wave cloud that limited vertical mixing of stronger westerly momentum from aloft. The more interesting winds occurred before dawn.

The front that I have been anticipating tonight is currently still in northern WY, having passed Gillette at 2255Z. This means it will not get here till the wee hours at the earliest; the HRRR and RR suggest passage about 5am. This will not be a strong frontal passage. Prior to then, I anticipate some west to north winds on the flats. These will likely be intermittent at 10m, with low-level stability and weak winds alternating with periods of breezy conditions.

Wednesday looks to be partly to mostly cloudy with a chance of a little drizzle in the morning, and a slight chance of a shower in the afternoon. Winds will be < 10m/s and likely from the NE quadrant in the morning, and E to SE in the afternoon.

The Wednesday night outlook is for light winds, dominated by drainage flows if cloud cover dissipates, which I anticipate it will. By Thursday the cool air of Wednesday will be displaced by weak downslope and the likelihood of a deep mixed layer developing. This will be sufficient to mix westerly or northwesterly momentum aloft down to the surface, but no strong winds are expected. It appears likely that the possibilities for stronger winds become larger as we approach Friday night into Saturday, but no repeat of the winds of last Friday is anticipated.

Probability of gusts on M2 exceeding 15m/s ................25m/s

00-06Z W 4 Feb ............................... 30% .................near 0%

06-12Z W 4 Feb ............................... 40% .................near 0%

12-18Z W 4 Feb ............................... 10% .................near 0%

18Z W 4 through 06Z Th 5 Feb ......... near 0% ..........near 0%

Tuesday IOP

Starting around 8-830 MDT Tuesday, we will have HRDL operations until the northerly surge that John B. forecasts in the nighttime hours Tuesday. (This case does not look as ideal as previous, but Wednesday and Thursday look even worse!)

18Z M 2 May Forecast Discussion

The rest of today, Monday, should see light winds, except for a few gusts to up to 10m/s in vicinity of the light showers. The threat of showers on the flats will end by 4pm MDT, and clouds will dissipate by sunset.

Monday night will see warming and drying conditions aloft and downslope developing between midnight and dawn. I foresee a pretty good chance of west wind toward dawn on Tu, probably continuing through much of the afternoon on Tu. Assuming west wind does kick in by dawn, there is likely to be a transition during the morning toward a more gusty character to the west wind as the boundary layer becomes convective. Although wave clouds (induced by both vertically propagating and trapped lee waves) are expected for most of the day, no pcpn is anticipated.

A weak surge from the N is likely during the Tu-W nighttime hours, most likely after midnight, and W looks to be a day of light to moderate winds, most likely beginning from the N - NE and then veering to E - SE by noon. Low clouds are likely in the morning at least, and I wouldn't rule out the possibility of some morning drizzle or afternoon showers.

Later in the week looks favorable for more daytime west winds due to mixing down of momentum aloft as afternoon deep daytime mixed layers are likely.

Chances of peak wind gusts on M2 .....>15m/s ................ > 25m/s

18Z M 2 May through 06Z Tu 3 May............ near 0%

06-12Z Tu 3 May ...................................... 40% ................ near 0%

12-18Z Tu 3 May ...................................... 60% ................ 10%

18Z Tu 3 - 00Z W 4 May............................ 60% ................ near 0%

00-06Z W 4 May ...................................... 40% ................ near 0%

No IOP Monday

There will not be TWICS operations Monday. We hope for westerly winds starting Tuesday morning, so stayed tuned for an email update after 8pm MDT Monday night for a plan for Tuesday. Yelena and I will review John's evening forecast discussion and make a call for Tuesday.

01Z M 2 May 2011 Forecast Discussion

The cold upper-level trough presently over the region will slowly shift eastward, likely to be replaced by generally westerly flow aloft from Tuesday through Friday or so. Overall strength of the mobile troughs and ridges will be weaker than what has been typical of the first half of TWICS, and conditions are likely to be drier than typical for this wettest time of year on the flats.

Monday should see light winds, dominated by mountain-valley flows. Residual moisture and cold air aloft will remain, but with a drying and warming trend by afternoon. I expect that the present cloud cover will largely dissipate overnight, but we should see rapid development of a mixed layer, with Cumulus over the foothills and mountains and winds likely into the SE - E by mid-morning. With cold air remaining over the region through noon, clouds should glaciate readily and there is a chance of the resulting virga reaching the ground as very light rain or graupel-like snow. However, measurable pcpn is unlikely.

Monday night and Tuesday will see warming and drying conditions aloft and weak downslope developing. There is a chance of some west wind toward dawn on Tu, and, also during late morning and afternoon on Tu. The latter west winds will be due to vertical mixing of westerly momentum from aloft. A weak surge from the N is likely during the Tu-W nighttime hours, and W looks to be a day of light winds, most likely from the SE during daytime hours. Later in the week my suspicion we may have more daytime west winds due to mixing down of momentum aloft as deep daytime mixed layers are likely each day through Friday.

Chances of wind gusts on M2 > 15m/s near zero before 06Z Tu.

I have another commitment at 8 on Monday and so will not be joining the telcon.

John B.

No IOP Sunday

With the extremely light winds (from the wrong direction) and chances of precip in the forecast, we do not need to consider an IOP for tonight. Please join the regularly-scheduled conference call Monday morning at 8am MDT to discuss the possibilities for Monday/Tuesday.

01Z 1 May 2011 Forecast Discussion

Julie, in the F am telcon, indicated there were 3 situations under which she would like to gather data (Julie, please correct if I have this wrong):

1. A day that has strong surface heating and light winds (without pcpn, of course);

2. Morning transition under some wind, e.g., stable conditions at 6m/s to (dry) convective at 8m/s;

3. Howling wind (I assume meaning gusts > 25m/s).

At this writing, it looks as if Monday, particularly before noon, might qualify for candidacy under #1. Winds aloft should be fairly light as the upper trough now to our southwest slowly pulls out, and any pcpn (likely snow) should be over by then. I will look at this again late Sunday and report.

John b.

NWTC met towers

On the NWTC there are several sources of meteorological data. NREL operates two towers;

• The M2 tower. This has sensors up to 80 m a.g.l. and is the reference data set for the site, having been operational from the mid 1990's on. It's about 250 m WSW of the HRDL at the moment, an 1 KM west of the large turbine test stands on row 4. We have continuous data from this tower, and it's publicly available online at http://www.nrel.gov/midc/nwtc_m2/
• A tower in front of the CART turbine, which is the two-bladed turbine on row 4. When the CART is not operational, we have data coming off a 58m tower, including a sonic at 36 m. This tower also has wind speed, direction an temperature at 3, 15, 36 and 58 m. We're working out what data is available during the TWICS IOPs.

We're in the process of commissioning a new, 135 met tower at site 4.4, directly upwind of the turbine. That tower was instrumented earlier this year, and the termination to our data acquisition systems was completed in April. Since then, we have been working to check the data coming off the tower. For those who aren't familiar with this, the data collection process goes something like this;

1. The physical property of interest is converted into a signal of some sort by an instrument. So, wind speeds are measured by cup anemometers, which generate a pulse every time they rotate. The speed of rotation is then a function of the wind speed. Wind directions are measured by vanes, where the rotation of the vane into the wind changes a resistance and so we get a voltage signal which is proportional to wind direction. And so on, for temperatures, pressure and whatever else is of interest.
2. These signals are transmitted down the tower to our computers, where we use a variety of hardware to convert the signals into something that a computer can read.
3. Then we scale the signals that the computer reads, back into so-called 'engineering units'. This is the opposite of what is done by the instruments; we convert voltages back to wind directions, frequencies to speed, and so on.
4. Then we save the data on the local computer. To keep file sizes down, we use a binary format. We have more than 70 data channels that we record at 20 Hz, so this is an essential step.
5. Next, data moves to the server. We now have two copies of our data in seperate locations.
6. Then we load the data and reduce the 20 Hz data to 10 minute data so that we can get a quick look at what's happening, and save this data for reference.
7. In future, we can revisit the high-frequency data for interesting events.

So, 'commissioning' means that we check every step of the above process. Are our voltages and frequencies right? Are we picking up the right piece of data and associating it with the right instrument? Do our files look right? And so on, ad nauseum.

Let me give you a flavour of where we are now, and the kind of things we are dealing with.

1. The wind vane orientation is being checked and adjusted. This means that any data from earlier will have to be adjusted slightly, but by an amount that we can quantify.
2. Accelerometers that show how much the sonic anemometer booms are vibrating are showing a drifting offset from the values they should show. I'm not going into the technical reasons for this, but it's annoying.
3. We're checking the process of converting data to binary and back again.

In terms of instrumentation and data, we have the following

1. Sonic anemometer data should be OK by now, but we have questions about how large the boom vibrations are.
2. Wind speeds look OK, but wind directions are not calibrated at all heights (we've done to 26 m a.g.l up to now).
3. Ground pressure is fluctuating quite severely, which may or may not be realistic.
4. Temperatures look reasonable.

I'll provide updates as we go along, but it's worth keeping in mind that this kind of thing can last a while. My gut feeling is that we're close, although there are always things that pop up when doing this kind of work.

Siemens WRF vs. NREL M2 April 27th

I've learned, thanks to Paul's impeccable eye for detail, that the reference lat/lon points for our WRF domain were actually somewhere near Loveland. Obviously, comparing our WRF output to the NREL M2 tower in this case would be fruitless. I have since improved our script and I think the results are at least interesting, if not slightly reliable.

I have plotted a simple time-series comparison for 12Z on Wednesday to 06Z Today. I do notice that WRF discovers the structure that caused a drop in wind speed and change in direction around 13Z on Thursday, however WRF settles on a WSWly direction while the M2 measured a NNEly direction. I don't know why this is - except possibly WRF's inability to find the correct SFC high distribution. In spite of that discrepancy, both modeled and observed wind speeds are fairly nice. Before the 13Z shift, I can't say what small structure was associated with the observed fall in wind speeds overnight. WRF on the other hand expected a higher winds.

I do not claim to be a brilliant scientist, so if any of you have feedback, please feel free.

No IOP Friday - Sunday

Given the very uncertain situation regarding how this front will move through and how/if precip will occur, and the "in commissioning" status of the meteorological tower, TWICS will NOT take measurements Friday or Saturday. Please check in Sunday afternoon for an update then. And have a wonderful weekend!

01z F 29 Apr 2011 Forecast Discussion

Very interesting forecast challenge for Friday night into Saturday....this is a classic example of what makes forecasting such a challenge around here!

The next system aloft is crossing the west coast at this writing, with a good surface low and cold front into Nevada. Some critical information is still offshore, mostly unobserved. So, the question remains, snow (or rain) or blow on Friday night. I think this will be obvious by late morning tomorrow, but probably not much before.

At present the most likely scenario is for variable amounts of cloudiness daytime Friday, but with enough daytime heating to allow strong winds from the S to WSW to develop on the plains, particularly E of I-25.

On the flats, I anticipate variable shifting winds, but predominantly from the SW - W, during daytime hours on Friday. Then, sometime in early evening this will be followed by a well marked frontal passage from the N, followed by good winds out of the N for a few hours and with pcpn beginning soon after frontal passage.

The alternative scenario also includes the daytime gusty winds mentioned above, but rather than these terminating with a frontal passage from the N, they would end with a frontal passage from the W, likely also in early evening, and accompanied by a brief shower and short period of strong W wind. Following the frontal passage would come a period of 0.5 to 2h of weaker wind, followed later by strong winds from the W - NW, likely persisting much of the night. I put the likelihood of this scenario about 1 in 3.

What happens beyond Friday night is also not real clear at this point, but the prospects for W to NW wind seem fairly low, and the threat of rainy or snowy periods continuing through Sunday to be fairly high.

John B.

IOP concluded

The winds have rotated to the SE already and so the TWICS IOP is now concluded. The forecast for the weekend is uncertain, but if the forecast for precipitation Friday night holds, we would not have an IOP at that time. The situation is evolving, however, so please stay tuned for John B's forecasts and join the call Friday morning for an update. The tower status is still evolving as well.

IOP continuing until Th morning

Despite a (very odd) quiescent period around 2300 MDT, winds are now ideal, from the NW ~ 8 m/s. The IOP will continue until 0930 Thursday unless winds rotate to southerly or drop below 3 m/s again for an extended period of time.

01z Th 28 Apr 2011 Forecast Discussion

Present persistent windy conditions are expected to become more intermittent next few hours as darkness sets in. I think there continues to be a potential for gusts > 15m/s through the evening, as winds aloft continue out of the NW. After midnight overall conditions appear likely to become less favorable, although gusts near or in excess of 10m/s may continue through the night.

Winds at mountain-top level will become W to WSW by sunset on Th 28 Apr. With bright sunshine likely, there will be opportunity for vertical mixing of momentum, and I anticipate that after a slack period from dawn through mid-morning, wind will pick up again and be fairly gusty. Winds are not likely to be stronger than today.

The shift of wind direction to south of west during the day Th ushers in a period of winds aloft from the SW quadrant, normally not as favorable a direction for the flats. Friday is likely to see more downward mixing of momentum during the daytime hours, but with more clouds also, and a possibility of virga-producing high-based convection moving off the hills in the afternoon (read the possibility of ramps). Looking farther ahead, this weekend looks similar to last: lots of clouds, threats of pcpn (rain), and light wind.

Probability of wind at M2 exceeding 15m/s................25m/s

6pm to midnight W 27 Apr ............ 100% .................10% ... gusts > 15m/s have already occurred

Midnight to 6am Th 28 Apr ........... 50% ................. near 0%

6am to noon Th 28 Apr ................. 50% ................. near 0% windier late in period

noon to 6pm Th 18 Apr ................. 70% ................. near 0 %

6pm to midnight Th 18 Apr ........... 40% ................. near 0% wind dying after sunset

01z Th 28 Apr 2011 Forecast Discussion

Present persistent windy conditions are expected to become more intermittent next few hours as darkness sets in. I think there continues to be a potential for gusts > 15m/s through the evening, as winds aloft continue out of the NW. After midnight overall conditions appear likely to become less favorable, although gusts near or in excess of 10m/s may continue through the night.

Winds at mountain-top level will become W to WSW by sunset on Th 28 Apr. With bright sunshine likely, there will be opportunity for vertical mixing of momentum, and I anticipate that after a slack period from dawn through mid-morning, wind will pick up again and be fairly gusty. Winds are not likely to be stronger than today.

The shift of wind direction to south of west during the day Th ushers in a period of winds aloft from the SW quadrant, normally not as favorable a direction for the flats. Friday is likely to see more downward mixing of momentum during the daytime hours, but with more clouds also, and a possibility of virga-producing high-based convection moving off the hills in the afternoon (read the possibility of ramps). Looking farther ahead, this weekend looks similar to last: lots of clouds, threats of pcpn (rain), and light wind.

Probability of wind at M2 exceeding 15m/s................25m/s

6pm to midnight W 27 Apr ............ 100% .................10% ... gusts > 15m/s have already occurred

Midnight to 6am Th 28 Apr ........... 50% ................. near 0%

6am to noon Th 28 Apr ................. 50% ................. near 0% windier late in period

noon to 6pm Th 18 Apr ................. 70% ................. near 0 %

6pm to midnight Th 18 Apr ........... 40% ................. near 0% wind dying after sunset

Siemens WRF 12Z forecast, NAM initialization

Tower update

From Andy: Tower looking better, cups up, vanes below 26m calibrated. Still in troubleshooting mode.

Julie: Given that we have ~ 18 days left before HRDL leaves, we cannot wait for the 4.4 tower, so we should continue with IOPs if we have NWly winds with no precip.

TWICS IOP starting 0930 MDT Wed 27 April

Hi all,

The precip cleared out faster than expected! Given the perfect WNWly conditions and the likelihood of stronger winds later today, we are starting HRDL up as soon as possible this morning and will take measurements through the evening, possibly to midnight or later if the winds hold. It will be a challenge to determine when to end the IOP if the winds hold up.

00z W 27 April 2011 Forecast DIscussion

The present cold upper trough has moved slower and tracked across the Rockies farther to the south than I anticpated, resulting in a delay in the onset of wind and more pcpn today (though still only a trace at NOAA) than I was looking for in last evening's update. A deep surface low is now in the TX panhandle, and the upper PV anomaly is passing over our heads here in Boulder as I write this. This means that tonight will be windy in most areas, with an end to pcpn on the lower foothills and plains (no further pcpn is expected on the flats this evening through Wednesday). Flow aloft will be primarily from the NNW by mid evening today. Strong winds are likely to persist on the plains all night, particularly east of about US287 and north of I70. Anticipating what will happen at Rocky Flats tonite is decidedly tricky, but I think there is a chance of high winds, particularly from 10pm MDT on. Further, the chances of high winds on the flats with flow aloft from the NNW is appreciably higher than the chances in Boulder, particularly north of Table Mesa Drive. These winds are likely to continue through the daylight hours tomorrow, but become more gusty and variable under the influence of surface heating. Flow at mid levels is likely to be weakening by late afternoon tomorrow.

FWIW, here are some probabilities for M2 max gusts for 6-h periods

> 15m/s > 25m/s

6pm - midnight Tu 26th 70% 20% most likely after 10pm

midnight - 6am W 27th 80% 40%

6am - noon W 27th 90% 30%

noon - 6pm W 27th 80% 20%

6pm - midnight 27th 60% 10% most likely early evening

Flurry of press releases

Hi all,

For your amusement:

http://www.noaanews.noaa.gov/stories2011/20110426_windwakes.html

https://www.llnl.gov/news/newsreleases/2011/Apr/NR-11-04-06.html

http://www.colorado.edu/news/r/de4f104b4d5944697247ebe3a76cb5a5.html 

And we'll probably be in the Camera tomorrow.

Julie

No IOP Tuesday, possibly Wednesday PM

Given the likelihood of precipitation at the NWTC today and tonight, we will not schedule an IOP for Tuesday. If the precip moves out Wednesday morning, we may consider one for Wednesday night/Thursday, but will discuss that in the Wednesday morning call. John, thanks much for your forecasts - any refinement you can offer on precip would be very helpful as that seems to be our constraint right now.

01Z Tu 26 Apr 2011 Forecast Discussion

From the lack of blog activity I gather that no data was collected today. The strongest 10m gusts I saw were between 12 and 15m/s, and these are continuing. This aftn a Cirrostratus / Altostratus overcast has overspread the area, harbinger of the next in this seemingly unending series of systems parading across us. This one does appear to have potential to bring a good wind event, especially for so late in the year.

Indications favor weak to moderate cyclogenesis on the plains as this short-wave trough crosses the Divide Tuesday morning 26 Apr. There appears to be a tracable Pacific front currently in eastern UT, with some precipitation on Colorado's western slope ahead of it. The current winds in Boulder may be partly augmented by evaporational cooling from this pcpn; if so, then we can expect the current breezy conditions to continue well into the evening, but then quiet down through most, if not all, the remainder of this Monday night. However, after the Pacific front passes, most likely soon after dawn, we can expect winds to pick up, augmented as so commonly this time of year by vertical mixing of westerly momentum as the daytime mixed layer behind the front deepens rapidly. I look for winds to reach gusts of 18-20m/s by noon Tuesday at M2, and continue strong, at least intermittently till W mrng 27 Apr. Strongest winds right now look to be Tu aftn and evening, with probability of peak gusts on M2 > 18m/s during the noon to 6pm period being 80%, and probability of gusts exceeding 25m/s being 30%. Similar probabilities apply for the 6pm to midnight period.

Wind is likely to become more intermittent in the evening and through the night.

Looking farther ahead, I suspect we may see some gusts at M2 W late morning through late aftn as a result of vertical mixing of momentum. There is a possibility of more windy afternoons after W.

No IOP Monday, probably none on Tuesday

Given the precip in the forecast today, we will NOT have a TWICS IOP. Stay tuned Tuesday morning for an update regarding any activity Tuesday. In general, precip will mean that we will stand down, which makes now through Wednesday not particularly appealing. - Julie

21Z Sunday 24 Apr 2011 Forecast Discussion

Broad trough aloft continues over the area and will slowly pull eastward Sunday night and Monday, to be replaced by another, rather poorly defined short-wave trough over the area Monday night and early Tuesday. So, our active weather pattern continues. I don't have a lot of confidence in details (timing or intensity) of what follows, especially beyond Monday. It looks as if the strongest surface-wind-relevant flow aloft will remain south of us through daytime Tuesday.

Tonight should continue uninteresting, with partly cloudy conditions, possibly a little light pcpn (mostly early) and little wind. What wind there is will most likely come out of the north, < 10m/s. Monday I think will see drying and better chances of winds of interest, as flow at mountain-top level becomes more NW to NNW. It will be a tug of war between a Longmont Anticyclone (SE flow on the flats) and vertical mixing of NWly momentum from above. This means that if there are northwest winds, they will be gusty during the daylight hours. Probability of gusts on M2 > 15m/s: 60%.

If there are winds during the day on Monday, they will likely die down near dusk. Right now, I see Monday night and early Tuesday as likely to have winds < 10m/s on the flats, but with a definite possibility of stronger W - NW winds on the flats again by Tuesday afternoon. Beyond this, I see possibilities of windy periods extending through the week, but of the details I have low confidence at this point. Since youall have the ability to react fairly quickly, I won't waste time engaging in speculation at this point.

Next update Monday afternoon.

John B.

Great IOP2 concluded 6 UTC 23 April

IOP2 concluded at 11:37pm MDT tonight (just before 6 UTC 23 April). From about 8pm to 10:30pm we had some absolutely beautiful wakes in the right orientation; we have some great data to work with now. John's forecast was right on.

With possible precip Sat and Sun we will not consider an IOP through the weekend, but stay tuned and join the Mon AM call to discuss whether or not Monday's downslope winds will be accompanied by enough precip to block an IOP.

Peace,

Julie

IOP Friday through midnight

We have the right wind direction; there may be gusty winds today, but we should have ideal conditions now until potentially midnight or so. After a small hardware repair is made to HRDL this morning, we will start an IOP (unless we hear from Siemens that they are turning off the turbine for some reason). It's a beautiful day!

00Z F 22 April 2011 Forecast Discussion

Upper trough over Great Basin attm will move eastward and the 500 mb trough axis pass overhead by about 12Z Friday morning, accompanied by cyclogenesis over the high plains. This is a favorable pattern for wind, as noted in yda's discussion, and I expect that winds may not completely quit tonight, and pick up again near or a little before dawn on Friday, continuing most of the day, but with the strongest winds on the flats likely mid-late morning. Probabilities of > 15m/s on M2 80%, probability of > 25m/s 30%.

Winds are likely to die down a little in the afternoon, but continue at least to 6pm MDT. Attm it looks as if Friday night and Saturday will be fairly quiet, with winds for the most part < 10m/s. We continue in an active weather pattern, however, and periods of precipitation and periods of wind (usually not overlapping) appear likely for the next several days.

Next update: late Friday afternoon.

Siemens WRF 12Z Forecast, Boulder Turbine

Greetings everyone,

Similar to what John has posted on the forecast discussion, the 12Z Siemens WRF run for the Boulder turbine shows significant variability throughout the period. There is a general upward trend of windspeeds into tomorrow evening (Friday 22 April), with a significant windspeed decrease expected. Wind direction shows mostly westerly at hub height with strong variability overnight Friday into Saturday, changing to Southeasterly flow. Any thoughts or discussion?

Th 01Z 21 April 2011 Forecast discussion

Another tricky forecast ...

There are some indications that the cold air now over the plains may mix out or pull away from the foothills by noon MST on Thursday (21st). If the cold air does retreat eastward or mix out, we are likely to get enough vertical mixing of momentum from aloft to give breezy conditions from the west to southwest by late morning and continuing till dusk Thursday evening. I give this a 50-50 chance of happening. If it does, extreme gust on M2 is likely to be in the 15-20 m/s range.

I think Thursday evening is likely to see light winds, but it is possible that winds will come up again toward Friday morning, and Friday daytime looks more likely than Thursday to have winds in excess of 15m/s (I'll say 70%, i.e., not that much more likely). These winds will be more synoptically driven than Thursday, as cyclogenesis is likely on the plains this day, though not with the strength we saw a week earlier. But, the Friday winds are also likely to be augmented and made more likely during the daytime by downward mixing of momentum within a fairly deep mixed layer.

Indications currently are for little wind over the Easter weekend, but with an active weather pattern (that is, with intermittent vigorous flow aloft with the passage of short-wave troughs and ridges, and changeable conditions at low levels) , this outlook could easily change. I will attempt another update tomorrow afternoon.

John B.

01Z 20 Apr 11 forecast discussion

Well, things didn't work out quite as I envisioned for today. Today's Wx was more like I was anticipating for tmrw (W 20 Apr) at the time of my last blog Sunday evening. West winds have gusted to 39mph at 10m this afternoon on M2, and westerlies continue. These westerlies appear to be augmented locally by convection coming off the hills. However, I think this period of westerly low-level flow will end by midnight tonite or so,

as pressures are rising to the north relative to the south (this trend is expected to continue), and downward mixing of westerly momentum from aloft will diminish as conditions stabilize with the arrival of darkness.

Winds on Wednesday I expect to go into the southeast with a Longmont Anticyclone by morning, and then back into the north or NNW during the day tomorrow as a Denver Cyclone forms. Wind speeds at 10m should remain under 10m/s.

The next period of downslope flow I expect to start most likely near midnight Wednesday or the wee hours of Thursday, as lee troughing develops over WY. Confidence in this forecast is not high ... as the next system in the Pacific may well come in farther south than the models are indicating. I plan an update late Wednesday afternoon. If downslope winds do occur, I don't expect them to exceed 25m/s at 80m.

Looking farther ahead, this changeable Wx pattern seems likely to continue into the weekend.

I an unlikely to join the conference call tomorrow morning.

John B.

Siemens 19 April 2011 Windspeed / Wind Direction Forecast

Greetings everyone,

Here is the windspeed forecast. Times are in Z (UTC) and it was initialized from NAM at 12Z. The initialization looks good with Tuesday afternoon. WRF predicts the highest windspeeds will be in the morning, but then die down in the afternoon. It shows Wednesday night into Thursday, a slow gradual gain of windspeed with one period of lesser winds.

And here is the direction forecast. WRF predicts W or NW flow throughout most of the period, not surprisingly.

So what are the thoughts & opinions? Hope to talk to you all tomorrow on the call.

--Paul Quelet

No IOP until Wednesday pm at earliest

Based on John's forecast below, on our conference call today we decided to hold off on any HRDL operations until Wednesday afternoon at the earliest. John will update his forecast Tuesday afternoon, and we will discuss it on the Wednesday am call. We also decided that, for staffing issues, we will limit future HRLD tests to no longer than 48 hours. Today, tomorrow, and Wednesday, we'll be looking at the data collected thus far and decide if we need to change scanning strategies. Thanks everyone for all your hard work! We have a very unique dataset.

02Z M 18 Apr 11 Forecast Discussion

The present wind event is almost over, and a major, if maybe short-term change is in the offing. There will probably be a few breezy periods from the west tonight, but a cold front is likely to slide in from the north over the plains late tonight or during the morning tomorrow, along with an increase in clouds and the possibility of rain or rain changing over to snow tomorrow night into Tu.

The next possibility of synoptically-induced west-component winds looks to be late Wednesday into Friday morning. At this juncture, this possibility, if it develops at all, looks to be weaker in strength than what we just experienced the past several days. Preceeding it, there may be a Denver Cyclone developing by Wednesday morning.

Unless requested to do sooner, or unless I see a notable change to this scenario, my next update will be Tuesday,

probably late afternoon or early evening.

John B.

IOP concluded

Winds have dropped to less than 5 m/s at the Windcube lidar and the Siemens turbine is not spinning (although the DOE 1.5 is spinning slowly). Given the uncertainty in the forecast, the need to analyze Thursday-Saturday am scans, and uncertainty of the status of the Siemens turbine, Bob and I decided to conclude operations. If winds pick up again, we may revisit this decision. We plan to have the conference call Monday morning and Wednesday morning, and meet Wednesday morning to review some HRDL results and determine if our scanning strategy is fulfilling our requirements. Thanks everybody for your hard work!

01Z 16 Apr 11 forecast discussion

Northwest flow aloft will gradually back to westerly over the next 24h as the low pressure area that has been affecting our weather the past two days shifts eastward, and a weak ridge aloft builds in over the West. As a glance outside will tell you, moisture has dramatically increased far aloft the past 2h, and we will see increasing moisture at middle levels as well by Saturday. Likewise, we will see increased baroclinity at middle levels beginning Saturday morning.

These factors taken together argue for more of a tendency for trapped lee waves off the Front Range than we likely had today. Likewise the anticipated backing of the flow aloft into the west tends to be less favorable for high wind on the flats than northwest winds aloft. I therefore expect that the westerly winds will become more intermittent than during the past 24h, and there may even be periods of near-surface weak easterly flow, depending on the horizontal wavelength of the trapped waves, which is typically 10-15km. We should expect to see a strong diurnality to the winds as well, with perhaps several hours of light 10-m winds during nighttime,

but also perhaps some strong vertical wind shears at night at or above turbine height.

Looking farther ahead, it appears that this may be the last sustained windy period for awhile. By Sunday evening the prospects for synoptically-driven westerly 10-m winds decrease substantially, and a front from the north is anticipated to pass the area either Sunday night or Monday. The next possibility for a period (probably brief) of west wind at 10m is about Wednesday 20 Apr.

Siemens WRF 12Z forecast, NAM initialization

Everyone,

Here is the Siemens 12Z WRF run. Sorry this took so long to post. Anyway, we have both windspeed and direction plotted here. WRF reveals strong winds tomorrow as well as winds still from the NW and WNW. Any thoughts? These seem to verify with some accuracy so far.

Best regards,

--Paul Quelet & Padriac Fowler

Early Morning Operations, TWICS 2011, 15 April 2011 IOP

Hello everyone,

Padriac and I just returned to our office at Siemens after being at the site and thought we would offer an update.

0000 - 0300 MDT (0600 - 0900 UTC): Phenomenal winds and wake effects. See Julie's post earlier.

~0310 - 0320 MDT (0910 - 0920 UTC): Fault in the Siemens turbine, caused a shutdown, no wake from the Siemens turbine until later in the morning.

~0320 MDT (0920 UTC) (unfortunately...) a near density current?? (I, Paul Quelet, saw in the met tower overnight observations. Clear loss of windspeed and temperature.)

~0800 MDT (1400 UTC) Winds died down significantly at the site. Yelena and Scott mentioned flow reversal coming up from the canyon behind the turbines. (Root cause still unknown.)

~0930 MDT (1530 UTC) Siemens Turbine operational again. Possible troubleshooting needed, supposed to remain on all day for operations.

~1005 MDT (1605 UTC) Significant wind shift from 320 to 352 degrees. Also accompanied by winds gusts and windspeed increase. The Siemens turbine yawed about 10 minutes afterwards.


Since I was on-site and the HRDL trailer does not have internet access, I wanted to post recent developments before I forgot what happened. Hopefully, these are beneficial.

Padriac and I hope to have our NAM initialized WRF run posted in a few hours. Many thanks to all for welcoming us, the learning, and the participation.


--Paul Quelet

Great shakedown night

What a great night! There were a variety of conditions and wind speeds, including a slow-down and reversal of the flow to ESE for a bit that made us think we'd have to call off the rest of the night...but then flow sped up and reversed to NNWly,  giving us lots of beautiful wakes that persisted much further downwind than expected. Here's a sample. Looking forward to looking at this data in much more detail!

In the left panel we see velocities from HRDL, red is highest value. The turbine at ~ 1km is the white rectangle, and that long stream to the SSE of lower velocities (yellow) would be the wake.

Siemens Turbine Fault @ 3:10am MDT. Service enroute.

whoo-hoo!

I'm not out to the site yet, but I took a peek at the Windcube lidar data, and we have perfect conditions. At 8:41pm MDT in Table Mesa, we had a density current roll through around the same time the Windcube started picking up. Look at that shear! Maybe I won't need lots of coffee to keep me awake tonight....

Staff Schedule for IOP 0 (shakedown)

Hardware staff:

Alan Thurs 12pm-6pm
Raul Thurs 5pm - 1:30am
Scott Friday 1 am -9am
Alan Friday 8:30 - 5:30 pm *** RV meeting at 2pm
Raul Friday 5pm - 1:30am
Scott Saturday 1 am -9am

Science Advisors:

Thursday:  2 pm-11pm  Bob
                10pm-3am    Julie
 Friday:       5am- 1pm   Lena
                    1pm- 9pm  Bob  *** RV meeting at 2pm
                    9pm-12pm Julie.
                   12pm- 9am Lena

NWTC Observations - winds picking up

In the last half hour or so (13:00 local, onwards) winds measured at M2 have picked up, rising to 8-10 m/s at all levels up to 80 m above ground. Air temperatures have also increased 3-4 degrees at all heights. This is coupled with the wind swinging to 270 at 80 m, and a clearing of the sky from more or less 8/8 cover to 2-4/8 at a few thousand feet over Boulder depending on direction. There's still high cloud in evidence, but it would appear that we're seeing a fairly rapid change locally. Is this John's 2 PM MDT ramp?

Winds observed on the NWTC M2 tower on the morning of April 14, 2011. Times are in MST, i.e. 1 hour offset from MDT.

Siemens WRF 12Z forecast, NAM initialization

Everyone...the Siemens WRF run for today is posted. It looks like strong windspeeds are still forecasted for this afternoon into this evening. Note the times are in Z (UTC).

Padriac and Paul will plan on visiting the NREL/NWTC site tomorrow (Fri., 15 Apr.). Hopefully, we can be of some further assistance to the operations.

Wx forecast 18Z Th 14 Apr

Overall, surface low formed a little south and weaker than models were indicating, as yesterday's cold air penetrated farther south on the plains, limiting development somewhat. Locally we were insulated from the changes happening over our heads this mrng, as the Pacific cold front with it's wind shift from south to northwest slid over the cool air on the plains with little impact on the surface Wx except a cessation of the pcpn. I estimate that at 18Z today winds at top of Bear Peak are already probably strong NW.

The issue at hand is when the winds will break through on Rocky Flats. The low overcast near the top of the surface-based cool air is thinning notably as I write this at Bldg 33, and I anticipate that on the flats, NW wind will break through by 2pm MDT today, despite the snow cover.

Looking farther ahead, "occasional windy periods Th aftn through Sunday evening" is a good 0-order estimate for wind the next 80 hours. The chances of winds > 25m/s appear to me to be highest late this afternoon and early evening, but with everything farther south, I put the chances of an M2 10-meter gust > 25m/s between now and 2am F mrng as 30%, down a little from yesterday. Friday morning may well see a transition from light and variable winds or southeast winds early to west to northwest by late morning as the mixed layer develops and westerly momentum mixes to the surface. Overall, the most likely time for strong surface winds will be about 10am through 5pm Friday, Saturday and Sunday, with the usual loss of confidence the farther ahead in time. The nighttime hours could see some periods of strong vertical shear below 200m AGL (above ground level) over the Flats tonight through Saturday night, with a lot of intermittency as winds from the west to northwest continue aloft, and some trapped lee wave activity initiates at least intermittently off the Front Range. Friday will be cool, but Saturday and Sunday should see afternoon temps upper 60s.

No turbine tests Thursday night-Friday morning

Paul M has notified me that they do not plan any turbine tests through Friday morning, so we will be able to sample wakes all night if the winds cooperate: "You can expect that the turbine will be running continuously." Fingers crossed!

Go for Thursday-Friday

If the precip does indeed dry out by noon, then our plan holds to start HRDL ops around 1400 MDT Th and run as late as we have NWly winds. Neither the Paul/Paddy WRF or the NWS forecasts predict extended periods of ws > 25 m/s. 

Long-term, NAM has the winds dropping by 6Z Saturday, although upper levels are still westerly. It may in fact be the case that we have NWly winds from 1400ish Th through Saturday night.

How many staff do we have available to work in shifts? (I am the only CU person until finals are done, unfortunately.) And is there a hardware limitation for HRDL to be operating that long constantly?

Scans: I suggest we retain the environmental scans that Bob/Alan set up earlier in the week. The stares at the 4.4 tower are not of value with the tower not archiving data, so Th or Fri we could set up stares at the M2 tower (although that's not IEA standard mounting). In addition to the sector PPIs that Alan/Julie set up Tuesday, we can think about a series of vertical profiles (sector RHIs?) to get vertical profiles that will be more valuable for model assimilation/validation.

WRF Siemens 12Z run from NAM initilization

WRF 12Z Forecast for 80.5 m (approximately hub height). Times above show forecast valid time in UTC (Z). It looks like Thursday afternoon into evening is strong winds like we were talking about. The stronges winds look to be predicted for just past sunrise. Any comments or thoughts? Maybe there will be downward momentum mixing afterwards.

Wx forecast update 18Z W 13 Apr

This mrng's 1200 UTC model runs show trend toward more pcpn with this event and a shorter period of wind Th - Th evening. I'm still comfortable with the 2pm MDT start time, but am backing off on strong winds (i.e., gusts > 18m/s at 10m) continuing past mid-evening on Th.

For Friday, it is looking to me as if the westerly momentum available to mix down to the surface during the daytime hours will be more abundant late in the daytime hours, and that before late morning the 10m winds are likely to be < 8 m/s, possibly from the SE.

John B.

NWTC observations

This morning's winds have been predominantly from the N and fairly waek (3-6 m/s) up to 80 m above ground. We had very stable conditions overnight with a fair amount of wind direction shear, although it looks like winds at 80 m are picking up a little. This is based on the M2 tower observations, downloaded from http://www.nrel.gov/midc/nwtc_m2/

The larger turbines on site were operating when I came in the door.

It might be interesting to have TWICS look up and downstream of the mesa? We have some marked slope changes to the north of the site,  which may or may not lead to some flow separation -  I never cease to be amazed when this can occur!

Winds observed on the NWTC M2 tower on April 13, 2011. Times are in MST, i.e. 1 hour offset from MDT.

Wx fcst 0800MDT W 13 Apr 11

Looks like a lot of potential with this situation, but also a fair degree of uncertainty. Well defined upper trough near to just off W Coast attm is xpctd to move inland with no further southward deepening, and swing across CO on Thursday, to be followed by a 2-3 days of mostly W to NW winds aloft Friday into Sunday.

The Thursday trough passage aloft will be accompanied by marked deepening of a surface low on the plains, due to the overall low static stability, and the sharpness of the trough aloft. I anticipate that there will be passage of a Pacific front that will be trackable across the Great Basin today and tonight. This frontal passage, anticipated near dawn on Th, will likely be accompanied by some westerly wind and pcpn as it scours out the cooler moist upslope air that oozed in last night. Following that, as the surface low deepens, most likely initially over eastern CO and then moving into KS / OK + TX panhandles, there will be surface winds from W - N. Westerly winds are more likely if the surface low develops farther north, northerly if the low develops farther south. In any case, there is a definite threat of pcpn behind the Pacific front, mainly Th morning. Right now I see the best chance of high wind to be between 2pm MDT Th and 2am MDT F, but confidence is not as high as I would like. I put the chance of a gust > 25m/s during this period at the 10m level on the M2 tower as 50%.

Looking farther ahead, I think Friday there is likely to be cool air aloft with NW flow, and with April sun there will be opportunity for a deep mixed layer that will allow the higher-momentum air to mix down to the surface during daylight hours. Chances of 10-m gusts > 15m/s I put as 70% during daylight hours on F. A similar situation may prevail on Saturday. The possibility of a period of wave-induced strong (> 18m/s) wind on Friday night also cannot be ruled out.

I will take another look before 1300MDT today (W) and note on the blog.

WRF 3.33 km Siemens Boulder Turbine 72 hr. Forecast

This is the WRF output Meteogram for the 72 hr. forecast at hub height. You can see that the forecast is farily significant for Thursday evening in terms of windspeed.

Action Thursday through Friday?

Crossing my fingers, but we might have our ideal conditions in the next few days. NAM is indicating that winds should swing around to NWly Thursday. These forecasts are still a long way off (54hr and 60hr, respectively), but I like the way they look.

Thursday morning:

And Thursday evening:

On our Wednesday AM conference call, we should discuss shift availability starting Thursday afternoon and through to Friday morning, as well as whether or not winds might exceed 20m/s. Precip may still be an issue. Please post your comments below!

Test Post: science goals

Improved understanding and characterization of inflow conditions on turbines in complex terrain would help engineers better understand, model, and design for turbine loading, turbine performance, and power plant performance. This improved understanding can develop from an integration of advanced observational capabilities with innovative approaches to atmospheric simulation.