185 
fxus65 kbou 202228 
afdbou 


Area forecast discussion 
National Weather Service Denver Colorado 
328 PM MST Thursday Nov 20 2008 


Short term...upslope flow weakening as noted by latest surface observation 
and Platteville profiler. Satellite still showing status across much 
of plains and along foothills...though ceilings mainly MVFR. Web 
cams...observations and radar indicating precipitation has ended. 
Advisories for freezing drizzle have since been cancelled. Drier air 
continues to move across plains from the Northeast. Boundary layer 
wind and humidity forecasts keep considerable moisture across foothills 
and plains this evening...sliding the moisture further east after 
midnight as winds shift to the southwest. With the drier air working 
into area...precipitation chances none and will drop from the grids. Will 
keep some fog along foothills and adjacent plains this evening. 
On Friday...models continue to show shortwave moving across Wyoming. 
Cross sections show minimal moisture through the day. Despite some 
weak qg ascent during the afternoon...airmass looks too stable for 
any snow to generate as lapse rates of around 4 c/km are prognosticated 
through the day. So...have taken out any mention of snow for the 
mountains during the day. Westerly gradient increases by 18z with 
Cross Mountain flow nearing 50 kts. A bit of a mountain top 
inversion shows up on cross sections and forecast soundings. 
Sangester wind forecast program shows very low chance for winds 
reaching high wind criteria. Grids already have gusty winds. Will 
include some gusts to 50 miles per hour over the higher terrain. Temperature 
and thickness forecasts answer well as guidance suggest highs in the 40s 
across the plains. This looking reasonable. Current temperature 
grids in line with guidance...little changes needed. 


Long term...pretty good model agreement now through early next 
week. A weak upper trough will move across the northern plains 
Friday night with the only effect a bit more wind in the mountains 
and some high cloud cover. The next trough is stronger but follows 
the same path on Sunday. This should bring more cooling but again 
looks to be too dry for precipitation. Models begin to diverge with 
the amount and location of ridging on Monday and Tuesday but 
everything looks dry with the consensus a bit warmer than what we 
had so I raised temperatures a little...if the warmer solutions are 
right we will be back in the 60s as the ridge axis passes. 


There is also model agreement on the West Coast trough developing 
and a tendency toward split flow. Latest GFS and European model (ecmwf) solutions 
showing more of a shortwave in the northern stream dropping into the 
Midwest by Thanksgiving day. 12z GFS was an outlier with this 
bringing sharp cooling to Denver...but European model (ecmwf) solution with a little 
cooling seems plausible. Still many runs with the southern stream 
troughing over the southwest or off California dominating with 
milder southwest flow over Colorado. These solutions would have 
lesser cooling...or none depending on cloud cover. Chance of 
precipitation remains low through Thanksgiving with some possibility 
of light mountain snow. Some possibility of something coming out of 
the western trough later in the weekend...but not looking like too 
favorable of an environment to start with. 


&& 


Aviation...drier air working into area from the northeast...no 
precipitation expected. MVFR ceilings to persist through 06z...then improve 
as surface winds shift to the southwest. Patchy fog could develop 
across area this evening...visibilities should remain VFR. VFR 
conditions Friday with surface winds becoming westerly by 18z. 


&& 


Bou watches/warnings/advisories...none. 


$$ 
D-l/cmg