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.