Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 192013

Area Forecast Discussion
National Weather Service Riverton WY
113 PM MST Sun Jan 19 2020

.SHORT TERM...Today through Monday night

Mostly sunny skies and lighter winds will continue this afternoon.
With the ridging building in today most afternoon highs will be a
bit warmer than yesterday, except for most valleys and basins
where lingering cold air will remain trapped under the usual
inversions. These inversions will persist through Monday with
continued warming elsewhere. KBYG is expected to reach 50 along
with highs in the 40s in the Casper area Monday. Highs will remain
below freezing in the basins, except the Big Horn Basin will
manage to reach 40 in some areas as there is a lack of snow cover
there. The Cody Foothills could also reach the low 50s Monday as

The upper ridge will shift east Monday night as a weak shortwave
enters the Intermountain West. Late Monday night will mark the
early beginnings of the west`s next round of snow. This period of
snow will be light and mainly confined to the mountains but will
intensify and spread during the extended period.

.LONG TERM...Tuesday through Saturday

Models remain in good agreement with an upper low moving onshore
over the PACNW Tuesday. Ahead of this system, a weak and open
shortwave will move across the area. This, in addition to weak
isentropic upglide and some diffluence will result in good
chances of light snow over the far west Tuesday.

There is not much difference between today`s 12Z model run and
last nights 00Z run. The ECMWF and GFS continue to differ
significantly in the track of this upper low Tuesday night thru
Wednesday night. The ECMWF doesn`t dig the system as much, as it
moves over the region Wednesday. It also depicts the ridge that
builds behind the trough to be a much stronger influence. The GFS
continues to have the upper low/trough pulling east-southeast
into the central/northern Rockies by 00Z Thursday. The GFS
continues to show several shortwaves in the overall trough, with
leeside cyclogenesis strengthening the upper low over the High
Plains by 12Z Thursday. A cold front and associated trough will
bring snow east of the Divide during the day Wednesday, with snow
continuing Wednesday night. Once the system shifts east of the
Divide, models are showing the heaviest snow to be over the east
sections of the forecast area. Snow could possibly linger into
Thursday morning. The system has potential to have advisory
amounts of snow, and will continue to be monitored. Forecasted
high temperatures continue to trend high, with readings in the low
to mid 40s in the Bighorn Basin and east sections.

In wake of this system, late Thursday into Saturday looks to be
mainly dry with weak ridging. The next Pacific storm system could
impact the forecast area Sunday into Monday.


.AVIATION...For the 00Z TAFS through 00Z Tuesday

Clouds will begin developing over the basins after 00Z, with mid
to high clouds increasing over the area after 12Z. Winds will
remain light, except at KCPR, where gusty southwest winds will



Dry conditions with light winds and clear skies will occur across
the area today. Gusty southwest winds will continue over zones 280
and 289 today through Monday. High clouds will increase over the
area from the west late tonight into Monday morning. Temperatures
will remain cold, except in the Bighorn Basin and zone 281, where
highs will rise into the low to mid 40s.




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