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.