Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 010020 AAA

Area Forecast Discussion...UPDATED
National Weather Service Cheyenne WY
520 PM MST Wed Nov 30 2016

.SHORT TERM...(This evening through Friday)
Issued at 250 PM MST Wed Nov 30 2016

Latest water vapor loop is showing the weak upper level trof
continuing to push southeast from the northwest. This trof will
broaden the upper level influence across the western portions of
the forecast area tonight through Friday morning, as the trof
dives into the desert southwest by Friday evening. This will
continue to set the stage for scattered snow showers in that
region during the next 48hrs. Very little if any snowfall
accumulation is expected in the lower elevations, but it may
produce a few inches of snow in the mountains. Otherwise, it will
continue to be a bit breezy and chilly with afternoon highs not
climbing out of the 20s and 30s.

.LONG TERM...(Friday night through Tuesday night)
Issued at 250 PM MST Wed Nov 30 2016

The main story in the long term continues to be the next significant
Pacific storm system bringing snow and very cold temperatures to the
forecast area early next week. To start, the weekend looks to warm
up a bit with highs in the 30s/40s by Sunday. Windy conditions will
return in the wind prone areas along and west of the Laramie Range
on Saturday and Saturday night as high pressure builds in from the
west. Could be flirting with high wind thresholds Saturday morning
with 700-750 mb winds progged to range 40-50kts, so will have to
keep an eye on that timeframe for potential wind highlights.
Winds will diminish some and turn to the south-southwest for
Sunday as a leading vort max in the aforementioned Pacific system
tracks across the northern Rockies and induces leeside
cyclogenesis over northern Wyoming.

12z models are in better alignment with this system, digging a
second strong vorticity anomaly south along the California coast as
the initial wave continues to move northeast into Canada.
The initial cold front looks to move south through the forecast area
late Sunday night through Monday morning, opening the door for very
cold Canadian air to rush south and invade our region thru midweek.
Overnight lows will drop below zero out west Tuesday night, with
single digits over the plains. Afternoon highs may only peak in the
teens to low 20s on Tuesday.

Regarding snow chances, much uncertainty remains with this storm
regarding track and timing. Some light snow will accompany the cold
front on Monday, then the potential for more widespread and heavier
snow ramps up Tuesday morning from west to east. 12z GFS is faster
and further north than the ECMWF, and paints light/moderate snow
accumulations across most of the forecast area. The ECMWF keeps the
heaviest snow south into Colorado, with light snow targeting the I-
80 corridor and points south. Bottom line, confidence is low still
regarding where and when the snow will affect our counties, so
maintained chance PoPs.


.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 511 PM MST Wed Nov 30 2016

VFR outside the mountains where occasional snow showers will cause
obscurations tonight. Westerly winds 8-15 kt will prevail through
Thursday. Occasional ceilings between 5000 and 10000 ft AGL west of
Laramie Range and across the northern NE panhandle tonight.


Issued at 250 PM MST Wed Nov 30 2016

Fire weather concerns will be low through the near term. Breezy
west-southwest winds today will diminish this evening, remaining
relatively light over the next couple of days. Temperatures will
remain below average for this time of year through the rest of the




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