738 
fxus65 kbou 191001 
afdbou 


Area forecast discussion 
National Weather Service Denver Colorado 
300 am MST Wednesday Nov 19 2008 


Short term...surface cold front early this morning was moving right 
along through the northern High Plains. Cold front is scheduled to 
reach the northeast corner of colordado around 15-16z and then back 
to Denver by 18z. Until then...we are starting the day quite mild 
so expect a quick warmup and early day high ahead of the front. 
Temperatures should steady out or slowly fall behind the front as 
low level cold advection is rather strong. 


By tonight...low clouds are expected to fill in as moist low level 
upslope flow develops from the surface up to 9000 feet mean sea level. With 
respect to drizzle and fog development overnight...I would like to 
see more in the way of low level moisture behind the front at the 
present time. Current ceilings behind the front are not that 
impressive either. However...the easterly low level flow is 
persistent through tonight so low levels should begin to saturate 
toward daybreak Thursday. Forecast soundings show that if we do get 
saturation...precipitation should be in the form of drizzle/freezing 
drizzle as temperatures greater than -10c in the moist layer are conducive 
to supercooled liquid water versus snow. 


Long term...we are still on track for a brief winter interlude on 
Thursday with moist upslope conditions across northeast Colorado. 
The extent of freezing drizzle is a question early Thursday...but 
will leave that in the forecast...then drizzle during the day as 
temperatures go above freezing. As flow becomes southerly Thursday 
night it does appear to dry out so another batch of freezing drizzle 
looks less likely and have dropped precipitation. 


Next trough moves quickly across Wyoming on Friday. The bulk of the 
dynamics and lift appear to be north of US...but the trough will 
pass close enough for some mountain snow showers in northern 
Colorado. There is still a fair amount of disagreement in the 
models with the main differences on whether a closed low develops vs 
an open trough and how far south the track will be. 


Another trough is foreast to dig across the northern rockies and 
wind up in the upper Midwest on Monday. The main impact on US will 
be another shot of cool air...but precipitation looks too far 
north. 


Heading towards Thanksgiving...an upper ridge will move from the 
Great Basin on Monday and across The Rockies Tuesday with 
southwesterly flow and moisture heading towards Colorado by 
Wednesday. Have take out mountain snow showers Monday and Tuesday 
as this period looks quite dry. Temperatures will also begin to 
climb a bit Tuesday into Wednesday. 


&& 


Aviation...cold front is still on track to reach dia and the Front 
Range airports around 18z today with easterly upslope flow behind 
the front. VFR conditions until low cloud development after 06z-07z 
tonight when airmass cools and moistens sufficiently. Ceilings should 
start off MVFR with a gradual lowering to IFR toward 12z Thursday 
morning. Light freezing drizzle and light fog with visibilitiies of 
1-3 miles also a threat late tonight through the Thursday morning 
rush. At this point...chance of visibilities 1/2 mile or less are 
quite low as surface moisture behind the front is somewhat limited. 
IFR/MVFR ceilings are expected to stick around through Thursday evening. 


&& 


Bou watches/warnings/advisories...none. 


$$ 


Barjenbruch/rtg