Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 202016
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
116 PM MST Tue Feb 20 2018

.SHORT TERM...Tonight through Friday

Our storm has moved off leaving us with a bitter cold airmass that
will be slow to move out this week. Temperatures will be just as
cold if not colder tonight, especially for the central basins where
a full night of clear skies will occur. Not as cold most likely
around Casper with some sw breeze. If that dies though, temps will
plummet. Otherwise, some light snow or flurries will persist out
west off and on the next couple days with cold, somewhat moist flow
and several embedded disturbances like the one this morning.
Temperatures overall will show a slow rebound but it`ll be slow. The
next system that has a shot of spreading snow east of the divide
will likely be the later Thursday night into Friday system. This
system is currently up in Alaska and will be diving swd towards us
the next couple days. The nrn extension of this upper low will aid
in a strengthening surface high that drops into MT early Friday
providing some shallow upslope east of the divide. Weak qg forcing
spreads nwd Thursday night into Friday from our new NV upper low.
The chance of light snow will spread nwd with it. How far north it
makes it right now is more of a question mark. Some of the guidance
like the NAM and SREF produce light qpf up to the Wind River Basin
by early Friday. The GFS keeps it just to the south. Will likely put
more pops in the area from this system with at least a slight chance
up into the central zones.

.LONG TERM...Friday night through Tuesday

The Friday system that may bring some light snow to portions of the
area is expected to move out Friday evening with mainly dry
conditions later at night. Below normal temperatures will continue,
but with the late February sun the airmass will modify somewhat so
not as cold as today but still below normal.

The next system looks to impact western Wyoming on Saturday
afternoon into Saturday night. At this point, this one looks to be
more of a Pacific origin than Arctic so we do not expect much
reinforcing cold air moving in behind it. It does have a decent
amount of moisture with it though so some highlights will certainly
be possible. As for East of the Divide, the GFS has a bit more
precipitation than the European but both have very little QPF. As a
result, we have only low POPS in the grids and any snowfall would
likely be light. There could be some mixing as it moves through
however and may give temperatures a bit of a boost, but likely still
remain below normal.

Sunday and Monday look to be different across the area. For West of
the Divide, the weather continues to look unsettled with a couple of
systems moving in from the west and bringing some rounds of snow.
Meanwhile, dry weather will likely hold East of the Divide through
Monday and even into Monday night. Temperatures may be tricky,
especially in the typically breezier areas where things could warm a
bit, especially given the increasing sun angle.

The next decent chance of snow for all areas now appears to be
Tuesday or Wednesday. Both the GFS and European have a decent system
moving in. However, as is expected a week out, they differ on the
details, especially timing. For now, we have put in slight to chance
POPS for Tuesday night until things become clearer. Definitely
something to watch however.
&&

.AVIATION...00Z Issuance

West of the Continental Divide...KJAC, KPNA, KBPI and KRKS

Mainly VFR conditions are expected through 00Z. The exception will
be some occasional mountain obscurations from spotty snow showers,
especially in vicinity of KJAC. Patchy fog may form after
09Z Wednesday but not enough confidence to pinpoint at this time.

East of the Continental Divide...KCPR, KCOD, KRIW, KLND, and KWRL

Largely VFR conditions will occur across the area through 18Z
Wednesday. Patchy fog may form in the valleys after 08Z tonight. At
this time, we will include vicinity for near KWRL and KRIW but not
enough certainty to prevail it at this time. A gusty breeze will
redevelop in vicinity of KCPR after 18Z Wednesday.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on icing and turbulence forecasts.

&&

.FIRE WEATHER...
Issued AT 100 PM MST Tue Feb 20 2018

A bitter cold airmass will encompass much of the region through
midweek. Some light snow or flurries will fall in the western
mountains and valleys at times. Some breezy to windy areas will be
noted from Jeffrey City to Casper each afternoon and evening. Some
of the higher mountains and foothills will also see a return of
locally gusty west to southwest wind. Smoke dispersion will be poor
to fair across the area with locally good in breezy areas.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Wind Chill Warning from 5 PM this afternoon to 10 AM MST
Wednesday for WYZ019-020.

&&

$$

SHORT TERM...Skrbac
LONG TERM...Hattings
AVIATION...Hattings
FIRE WEATHER...Skrbac



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