023 
fxus65 kbou 190948 
afdbou 


Area forecast discussion 
National Weather Service Denver Colorado 
340 am MDT Friday Mar 19 2010 


Short term...at present time...principle upper level trough to our 
west-northwest with a closed 500mb low just moving over the 
northwest corner of Colorado. Upstream from this feature is a 
shortwave trough now forming over western Wyoming which the RUC and NAM 
show diving south and being absorbed into the main trough...causing 
the upper low to deepen further. This also causes the main trough to 
Arch westward a bit more which shifts the center of strongest qg 
ascent over areas west of the Continental Divide. Not to worry if 
you are a snow lover. Stronger height falls to our west will only 
tighten the upslope gradient over US. At this hour Platteville 
profiler and VAD winds off kftg and tden radars indicate 10-20kt 
northeasterly flow up to 600 mb. Surface observations across northestern Colorado also 
indicate 10-20kt northeasterly winds with gusts 30kt. Surface dewpoints have 
continued to rise increasing 3c at dia in the past few hours. 
Whereas surface temperatures along the Front Range have remained fairly 
steady around 0c. Precipitation in the area thus far has been rain 
or drizzle. Although the change over to a rain/snow mix or all snow 
has begun. Across the high country light to moderate snowfall has 
become widespread with many mountain passes reporting snow covered and/or 
slushy Road conditions. At last check heavy snow was being reported 
at Lake George in Park County. 


During the next 12 hours...as the deepening upper trough/low swings 
to our west-southwest...should see snowfall becoming widespread east 
of the mountains with the heavier snowfall/greatest snowfall rates 
associated with banded showers aligned with the upper level jet/ 
shear axis now draped across northwestern Colorado/southeastern Wyoming. At it/S 
present forward progress should see this zone of enhanced snowfall 
sliding over the Denver metropolitan area sometime between 13z-17z this 
morning. East-northeast upslope flow will also be at its strongest/ 
deepest at this time. Foothill areas could see snowfall rates 
approaching 4 inches per hour during this period...with upwards of 
2 inches per hour with the heavier snow bands passing over the I-25 
urban corridor. Farther out across the plains...upslope flow will be 
of less importance so snow totals/snowfall rates nowhere as great as 
those over and along The East Slope of the Front Range. 


By this evening the main area of large scale lift to be passing to 
our south/southwest...and upslope lift will be on the decline. 
Should still continue to see snowfall through most of the tonight... 
but any additional accumulation should be light and confined mainly 
to the high terrain and nearby plains...including the Palmer Divide. 
As for total snow accumulations by 12z/Saturday...plan to make only 
small adjustments in the high country and along the base of the 
foothills. Will hang onto the same amounts on the plains. All winter 
weather highlights will remain in place. 




Long term...improving weather trends for Saturday as the storm 
system deepens over the southern High Plains and pulls away from 
Colorado. There is still some lingering low level moisture across 
southern portions of the County Warning Area and will continue to leave some chance 
probability of precipitation for lingering light snow and even some fog possible. Any 
additional accumulations would be under an inch. High pressure aloft 
will build across the region through Sunday before flattening on 
Monday/early Tuesday ahead of next storm system. Cross sections show 
some gusty west winds developing over the east slopes Sunday 
night/early Monday with possible gusts in the 40-50kt range over 
higher east slopes. With this downslope flow should really see temperatures 
rebound with readings near 60 degrees over lower elevations as 
lingering snow cover diminishes. 


Attention then moves towards next developing storm system expected 
to influence our weather in the late Tuesday/Wednesday time frame. The 00z 
European/GFS/Gem are amazingly similar with all models showing a 
closed low near the 4 corners by 12z Wednesday before sliding across 
northern New Mexico on Thursday. This storm also bears watching as this 
one even taps Gulf moisture and warps it back into Colorado. There 
also appears to be enough cold air for snow as well. Both 
European/GFS are producing huge quantitative precipitation forecast numbers across eastern Colorado. 
Still...a bit early to get too excited yet. Current grids already 
have chance probability of precipitation for the east slopes and this is sufficient for now. 
Mainly just minor changes to out periods. 


Aviation...ceilings below 600 feet above ground level and visibilities below 2 miles 
will prevail during the day with occasional ceilings below 200 feet 
above ground level and visibilities below 1/4 mile with the heavier snow bands. 
Conditions will gradually improve through the evening with marginal 
VFR conditions developing after 06z tonight. 


&& 


Bou watches/warnings/advisories...Winter Storm Warning midnight 
tonight until midnight Friday night for the Front Range 
mountains...foothills...and adjacent plains including the Front 
Range urban corridor and Palmer Divide...zones 33>36..38>41. 
..Winter Weather Advisory for the northeastern plains of 
Colorado...zones 42>44..and 48>51. 
..Winter Weather Advisory for the eastern plains of Colorado... 
Zones 45... park and the park/Gore Mountain ranges...zones 
31..37. 


$$ 


Baker/entrekin