Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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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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