Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 200832

Area Forecast Discussion
National Weather Service Riverton WY
232 AM MDT Tue Mar 20 2018

.SHORT TERM...(Today and tonight)
Issued at 158 AM MDT Tue Mar 20 2018

A weak shortwave will be tracking southeast across the area early
this morning. Light snow will linger in the far west as this
feature tracks across the area. A similar weak wave will follow
late today within the west northwest flow along with a continuation
of light snow or flurries in the far west today ahead of and
during the troughpa. Then a flat ridge will build into the area
through the middle of the week ushering in milder temperatures.
With the flow streaming in off the Pacific within the flat ridge
along with an increasing gradient, upslope rain and snow will
increase in the far west Wednesday and Wednesday night. The
heaviest precip will fall Thursday and Thursday night in the west
as the flow backs and becomes more difluent along with an increase
in upslope flow. In addition, a lead shortwave will track wsw to
ene enhancing precip in the west during this time frame. Sub
advisory amounts of snow are expected in the far west Wed/Wed
night. We are looking at advisory amounts for Thu/Thu nt for the
western mtns along with some rain in the valleys, but there is
plenty of time to interrogate the potential for any hilites
regarding this. There could even be some isold thunder Thu
afternoon in the west. The general trend will be for a warming
trend through the week as the ridge builds in along with 60s east
of the divide by Thursday and 40s west.

.LONG TERM...(Friday through Tuesday) Issued at 158 AM MDT Tue
Mar 20 2018

Medium range period starts out with a shortwave moving east
across the area. Timing is a little more in line with the latest
GFS and ECMWF runs. Euro is still a few hours slower but not as
much as the 12z run. Current timing shows the system hitting the
west Thursday night into Friday morning and then shifting east of
the divide around midday and clearing the ern zones by around 00z
Saturday. A decent shot of mountain snow will likely continue in
the mountains west of the divide with a rain/snow mixture possibly
turning to all snow briefly in the wrn valleys. Windy and turning
cooler east of the divide in the afternoon with a few showers and
possibly an isold tstm along the track of the system. Best chance
will be over the higher terrain. Otherwise, a chilly west wind.
The main wrn U.S. upper low then moves on the coast Friday night
and moves east across us Saturday night into Sunday night. Snow
develops in the west later Friday night and continues through the
day Saturday as colder air rushes in with the large upper low.
Strong cold front blasts east of the divide Saturday afternoon
with a chance of showers along it, especially near the higher
terrain, I80 corridor and the far nrn Bighorn Basin. Models start
to diverge quite a bit as to what happens to the upper low as it
moves towards us though over the weekend. The GFS has a large part
of the upper low moving across the area into Sunday night. The
Euro stalls it out and then shears it apart next Monday. The GEM
is the slowest of the models and doesn`t actually have the trough
arrive until Sunday night and Monday with some shearing also
showing up Monday like the Euro. The GFS 5-wave gradually takes
the mean trough from along the west coast early in the weekend to
over the Rockies on Monday (albeit much flatter). This would
generally support something closer to the OP GFS. After the trough
weakens or passes across us, we get an unstable nw flow early
next week with snow showers in the nrn mountains likely. The
potential stronger clipper in this nw flow Tuesday may produce a
swath of snow across the nrn lower elevations also.


.AVIATION...(For the 12Z TAFS through 12Z Tuesday night) Issued
at 158 AM MDT Tue Mar 20 2018

Isolated to scattered snow showers will continue over the western
mountains through tonight. Areas of MVFR to IFR conditions will
occur vcnty the mountains. KJAC terminal will have VCSH through
02Z Wed. Otherwise, VFR conditions will occur at the terminal


Issued AT 158 AM MDT Tue Mar 20 2018

Isolated to scattered snow showers will continue over the
northwestern and northern mountains early this morning.
Precipitation will be in the form of rain mixed with snow (along
the foothills of the Absarokas and Bighorns). Elsewhere,
conditions will mainly be dry across the area, with seasonal
temperatures and gusty winds across the south. A warming trend
will begin today and continue through the week. Gusty winds will
also return across wind prone locations (mainly during the
afternoon) today through Thursday. At the same time, mixing
heights will also continue to increase through the week. Smoke
dispersal will also be fair to good.




LONG TERM...Skrbac
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