Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 222215

Area Forecast Discussion
National Weather Service Riverton WY
315 PM MST Fri Feb 22 2019

.SHORT TERM...This afternoon through Saturday night

Snow has ended across the area, with skies continuing to clear over
eastern Sweetwater and Natrona counties. Expect dry and calm
conditions through the rest of the day and into tonight.

Clouds will begin to increase across the far west early Saturday
morning before sunrise, spreading across the western mountains by
the noon hour. Light snow will accompany these clouds, with
increasing chances of snow as well. Light to moderate snow will then
be ongoing through Saturday afternoon and continue into Saturday
night. This will begin a period of prolonged snowfall across the
west, which will include Yellowstone, western portions of the
Absarokas and Wind River Mountains, Tetons, Gros Ventres, Salt and
Wyoming Ranges, Jackson Hole, Star Valley and the Upper Green River
Basin near Bondurant. A Winter Storm Watch was issued earlier this
morning beginning Saturday evening through Tuesday (for now). The
potential for several feet of snow to fall in the mountains and at
least 6 to 12 inches in the valleys is likely. Further details of
the storm from Sunday onward will be expounded upon below.

East of the Divide will remain dry tonight through Saturday.
However, there will be a chance for snow over northern portions
Saturday night. Accumulations look to be minor for now. Also, gusty
west to southwest winds will redevelop early Saturday morning from
Rock Springs to Casper. These winds will expand to include southern
Lincoln County and the mountains by the afternoon. These winds will
slowly subside Saturday night over much of these areas, but will
remain high over the mountains into Sunday morning.

.LONG TERM...Sunday through Friday

Will continue with the trending of snow Sunday through Tuesday
across the west. With continued timing difficulty due to the
several pieces of shortwave energy that will be moving through
there could be some lulls, but to be a fairly continuous event.
Will continue with slight/chance pops mainly along and slightly
east of the Divide through Tuesday. The Upper Wind River Basin and
Northern Bighorn Basin will see the most of this activity Sunday
though snow totals will remain low. The combination of zonal flow
at 500 millibars and good mid-upper level jet support on Monday,
should result in decent snow rates on Monday into Monday evening.
Could be some decent blowing and drifting of snow due to the
expected mixing downward of mid-upper level jet into the western
mountain areas also during the Monday time frame.

GFS/ECMWF models continue to indicate that there may be some snow
making it eastward of the Continental Divide also on Monday, a
bit still spilling over the divide, mainly in the north. The west-
southwest flow will further usher in warmer and more pacific air
into the region by Tuesday and will play a wait and see a little
longer involving model guidance temps in the extended. Everything
will depend upon the warmer 700-500 millibar temps mixing down and
breaking through the inversion across the forecast area. We stuck
with snow in the west due to -6 to -8 H7 temps aloft but as the
models keep pushing surface temps higher into the 30s we may be
looking at a change over during the afternoon for the valleys.

Between Wednesday and Thursday, the models differ involving the
upper pattern. Both models to differing degrees, indicate that a
west to northwest upper level flow will set up over the western
part of the U.S. with slightly cooler temps expected through the
end of the forecast period. Temps for Wednesday and Thursday will
still remain nearly 10 degrees below normal for this time of the
year. Will continue with at least chance pops for mainly snow in
the west and keep conditions for now, dry east of the Divide.


.AVIATION...00Z Issuance

VFR conditions will continue through much of the forecast area
through the TAF period. Clouds will increase over the far west
tonight, with overcast skies expected by sunrise. Mountain
obscurations and snow will be in place over the western mountains
by 18Z Saturday. -SN and MVFR conditions are expected at KJAC
after 15Z Saturday and will continue through the rest of the day.
The remaining terminals will be dry, VCSH possible at KPNA and
KBPI. Winds will increase at KCPR and KRKS between 15Z and 18Z
Saturday, remaining gusty through the rest of the period.



Dry conditions with light to moderate winds will continue this
afternoon and tonight. Light snow will return to western portions
Saturday morning, marking the beginning of a prolonged period of
snow. This is expected to last through at least Tuesday. Gusty
west to southwest winds will return to the Wind Corridor early
Saturday morning, expanding to include southern Lincoln County and
the mountains by the afternoon. These winds are expected to last
through much of the night Saturday night.


Winter Storm Watch from Saturday evening through Tuesday
afternoon for WYZ001-002-012>014-023>025.



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