Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 250359
AFDBOU

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

.UPDATE...
Issued at 859 PM MST Fri Feb 24 2017

Satellite continues to track the weak short wave which is now
into west central Colorado. This will keep snow showers going in
the mountains through this evening with another inch or so.
Meanwhile, orographic component is increasing slightly overnight
into Saturday morning, so forecast of lingering showers in the
high country is on track.

On the plains, there was one small area of light snow on the
Palmer Divide, and this may continue through midnight before
downsloping takes hold. Farther north, just a slight chance of a
passing light shower but overall the increasing downslope
component and passage of the weak weather disturbance will bring
clearing skies later tonight.

&&

.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
elevations.

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 06Z TAFS through 06Z Saturday night)
Issued at 859 PM MST Fri Feb 24 2017

Last of the low clouds departing the Denver Metro area airports.
There is some light snow grazing by through Douglas county but
that should stay south of KAPA over the next couple hours. VFR
conditions will then prevail through the night with gradual
clearing. No fog threat with sufficient south/southwest drainage
winds developing. On Saturday, mainly light winds should prevail
with a better chance of westerlies to around 15g22kts spreading
off the foothills and affecting mainly KBJC after 19-20Z.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

UPDATE...Barjenbruch
SHORT TERM...Entrekin
LONG TERM...Baker
AVIATION...Barjenbruch


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