Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 182220

Area Forecast Discussion
National Weather Service Cheyenne WY
320 PM MST Sat Feb 18 2017

.SHORT TERM...(This evening through Monday)
Issued at 220 PM MST Sat Feb 18 2017

The very warm February will continue through early next week.
Highs today have climbed into the upper 50s and 60s to the east of
the Laramie Range, this is around 20 degrees above normal for mid
February. The weather will remain rather quiet through tomorrow
afternoon with occasional mid to high lvl clouds streaming into
the region from the south. Temps tomorrow will be very similar to
today and generally light south to southwesterly winds will
prevail. Upper level low over the Southwestern United States will
weaken and lift northeastward into Colorado by Sunday night.
Increasing 700-500 mb moisture combined with weak dynamics will
cause at least a slight chance of of rain/snow showers over much
of the CWA by late aftn into the evening. Snow accumulations
across the Sierra Madre and Snowy Ranges will be generally less
than 4 inches owing to the progressive nature of the upper level
shortwave trough.

Still expecting winds to increase by Sunday night across southeast
WY as the sfc trough moves eastward into the western Nebraska
Panhandle and the llvl gradient comes up. The 12Z GFS shows the
strongest llvl gradient and winds aloft. It is interesting that
the 850 mb CAG-CPR gradient off the 12Z GFS has come down from
previous runs (60-65 meters compared to 80 meters yesterday). The
12Z NAM only shows 40 meters for the 850 mb CAG-CPR gradient,
quite the difference. With uncertainty on how the southern stream
shortwave merges with the upper wave moving across WY, decided to
hold off on any High Wind Watches at this point. It will
definitely be something that future shifts will have to consider
across the wind prone areas. With good mixing during the day on
Monday, winds will remain elevated even as winds aloft come down
some through the aftn.

.LONG TERM...(Monday night through Saturday)
Issued at 220 PM MST Sat Feb 18 2017

Monday night/Tuesday...Another quite mild day on tap Tuesday with
brisk zonal flow aloft and surface lee troughing producing downslope
warming west winds. Maximum temperatures well into the 60s to lower
70s east of I-25 based on thicknesses and 700 mb temperatures. May
see near high wind criteria winds across our wind prone locations
based on low and mid level gradients.

Wednesday...Southwest flow aloft strengthens with falling heights
suggesting a cooler day, through still with above normal
temperatures. With moist flow aloft, will see scattered showers
develop in the afternoon along and west of I-25, and north of a
Wheatland to Scottsbluff line.

Thursday...Models continue to show a progressive shortwave trough
and strong cold front advancing across our forecast area, and with
adequate low and mid level moisture, will see scattered to
widespread coverage of precipitation mainly in the form of snow.
Much colder temperatures in the wake of the cold front.

Friday...Progressive pattern aloft continues with a transitory ridge
aloft moving overhead. Low level upslope winds will continue with
surface high pressure residing across the plains states to our east
and with 700 mb temperatures near -14 Celsius, high temperatures
will be at or below freezing at most locations. Mostly dry
conditions expected due to minimal low and mid level moisture.

Saturday...Fast zonal flow aloft continues with a slow warming trend
developing based on thicknesses and 700 mb temperature trends. Aside
from a few orographic snow showers over the Snowy and Sierra Madre
Ranges, it looks dry with mostly dry low and mid levels.


.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 318 PM MST Sat Feb 18 2017

Wyoming TAFS...VFR, except MVFR at Rawlins from 09Z to 15Z.
Winds gusting 20 to 30 knots after 15Z Sunday.

Nebraska TAFS...VFR. Wind gusts to 20 knots after 15Z Sunday.


Issued at 220 PM MST Sat Feb 18 2017

Minimal fire weather concerns through early next week. West to
northwest winds will be breezy to windy on Monday and Tuesday.
Some locations to the east of the Laramie Range will see minimum
afternoon humidity values drop to around 20 percent by early next




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