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FXUS65 KBOU 242204

Area Forecast Discussion
National Weather Service Denver/Boulder CO
304 PM MST Fri Feb 24 2017

.SHORT TERM...(This evening through Saturday)
Issued at 231 PM MST Fri Feb 24 2017

Radar and satellite imagery showing convective snow shower 
development over the mountains and foothills this afternoon. This 
will continue through early evening with main focus shifting over 
the Palmer Divide. With the convective nature, could see a quick 
1/2 to an inch of snow with the heavier embedded showers. Water 
vapor imagery does show an upper level feature/circulation across 
Northeast Utah which will move across Colorado this evening. 
Airmass dries out later tonight with clearing skies expected on 
the plains. The flow aloft will become northwest, so with 
lingering moisture and orographic flow expect scattered snow 
showers through the night. 

As the flow aloft increases, cross sections showing increase
downslope flow later tonight through mid day on Saturday. Nothing
high wind, but could see some gusts in the 30-50 mph range. With
the increasing downslope flow and return to drainage winds will
not include any fog for the plains. Could be a few patches over
low lying areas but coverage expected to be quite small. 

Mid level drying over the mountains Saturday morning but then
moisture increases in the afternoon with a return to snow showers
and some light accumulations. Dry conditions on the plains with
warmer temperatures during the day. 

.LONG TERM...(Saturday night through Friday)
Issued at 231 PM MST Fri Feb 24 2017

Progressive mid-level shortwave trough upstream over Idaho 
Saturday evening is proceeded by an increasing moist zonal 
flow which models show showing over western Colorado. 7-8deg/km 
700-500 mb lapse rates over the nrn mtns and favorable orographic 
forcing should continue to generate scattered to numerous snow 
showers over high elevations generally west of the Continental 
Divide through midnight. After which time, models show this plume 
of moist rising air translating southward causing a steady 
reduction in snowfall chances across the high country later that 
night. Areas east of the mtns will remain dry. On Sunday, the 
shortwave trough sweeps across the forecast area during the 
morning hours as per the models and with its passage arrives drier
air, but not necessarily warmer air. Sunday night into Monday 
morning, moderately strong zonal flow aloft gradually transitions 
to southwest flow by Monday morning with a shortwave ridge 
building over the western Great Plains. Flow aloft is progged to 
strengthen through the day with swly mtn top flow winds around 
40kts in the afternoon. Some of this momentum is projected to mix 
downward onto the foothills, adjacent plains and Palmer Divide 
causing dewpoints to fall and gusty swly sfc winds to form. 
Combination will elevate the wildland fire danger in these areas, 
however do not see red flag warning criteria being met. This same 
flow will moisten and destabilize the west slope atmosphere 
leading to a steady increase in clouds and shower coverage. Snow 
levels will start out high as temperatures will with the freeze 
level up around 10500 feet during the day. By Monday night...steep
mtn top lapse rates will support upright convection potentially 
resulting on pockets of moderate to heavy snowfall at higher 

The airmass over Colorado is forecast to become increasing moist 
and unstable, almost spring-like, on Tuesday with moisture 
continuing to flow up from the Four Corners region ahead of the 
large upper level trough still west of Colorado at that time. 
Good bet we'll see scattered to numerous snow showers of moderate
intensity in the high country. Some of this shower activity 
may move off the Front Range and over the adjacent plains during
the afternoon. Rain or a mix of rain and snow possible at lower
elevations. Do not expect to see any snow accumulation as daytime
temperatures should remain well above freezing. For the period 
Wednesday and Thursday, models indicate a return to drier and 
warmer conditions with northwest flow aloft with a large upper 
ridge building to our west. Temperatures are forecast to be near 
average both days. 


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 231 PM MST Fri Feb 24 2017

Scattered, convective snow showers developing this afternoon with
most likely candidates BJC/APA. Could see a quick 1/2 inch of 
snow with the showers. Snow should end between 01-03z this evening
with clearing skies overnight. Given a return to drainage,
southerly winds overnight have opted for no fog development. Most
of the high res models do not have any fog except the NAM.
Something at least to watch out for increase drainage winds are



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