Weather

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Area forecast discussion 
National Weather Service Denver Colorado 
350 am MDT Monday Oct 13 2008 


Short term...the word for today is drying. At low levels drier air 
is filtering in from the north...eroding the low clouds. Meanwhile 
sharp middle level front is finally shifting east with sharp drying and 
cooling on the west side. As a result clouds will dissipate from 
west to east this morning. Some question about how far east this 
frontal zone will shift as the upper level trough is still stretched 
over US...so will hedge on the clearing near the eastern Colorado 
border. Despite the sunshine it will probably not be any warmer due 
to the cooling aloft. Models are generating clouds and precipitation 
rather quickly as the bottom of the trough closes out and begins to 
generate some isentropic lift from about Interstate 70 southward 
tonight. This seems overdone given the extreme dryness of the air 
aloft edging eastward this morning and less pronounced drying in the 
low levels east of the mountains. Easy to see this development in 
the moisture further east. I will hang on to some clouds and a low 
chance of precipitation in our southern tier of counties...but the 
whole thing could be further south and east in which case it may be 
clear most of the night. Finally...a few spots on the Cheyenne and 
Palmer ridges barely below freezing this morning. We should have a 
fairly widespread freeze tonight. 


Long term...models have the strong southwesterly flow aloft for the 
forecast area early Tuesday. The upper trough axis moves eastward 
over US from middle Tuesday afternoon through Tuesday evening. There 
is a closed circulation at the bottom of the trough near The Four 
Corners around middle day Tuesday. Models have this weakening 
significantly by Tuesday night as the trough moves eastward. From 
06z Tuesday night into Thursday morning west-southwesterly flow 
aloft is prognosticated over the forecast area. There is upward motion 
prognosticated over the forecast area much of Tuesday...with weak downward 
vertical velocity the rest of the Tuesday night and Wednesday. The 
low level pressure gradient is fairly weak over the forecast are 
through the periods. There should be some downsloping flow in the 
boundary layer late Tuesday afternoon and evening with the upper 
trough passage...otherwise normal diurnal wind patterns will 
prevail. For moisture...there is some in the middle and upper levels 
on Tuesday...but little in the lower levels. There is a bit of middle 
level moisture over the eastern half of the forecast area Tuesday 
night. Wednesday and Wednesday night are pretty dry. Will leave 
minimal probability of precipitation on over the southeastern forecast area Tuesday 
morning...that's it. Otherwise no probability of precipitation through Wednesday night. 
For temperatures...tuesday's highs are 3-5 c warmer than today's. 
Wednesday's warm up 2-4 c from tuesday's. For the later days... 
Thursday through Sunday...models have zonal flow...then upper 
ridging form Friday Onward. It looks dry with temperatures getting 
at or a bit above seasonal norms. 


&& 


Aviation...ceilings should dissipate this morning. There is a 
chance of clouds redeveloping late tonight with a 20 percent chance 
of MVFR ceilings in the Denver area after 06z. 


&& 


Bou watches/warnings/advisories...none. 


$$ 
Gimmestad/rjk