Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 210918

Area Forecast Discussion
National Weather Service Riverton WY
318 AM MDT Wed Mar 21 2018

.SHORT TERM...(Today through Friday night) Issued at 209 AM MDT
Wed Mar 21 2018

A flat ridge of high pressure, albeit amplifying, will be
building into the area from the west through Thursday. Some
Pacific moisture will be streaming through the ridge today and
tonight. The moisture along with some isentropic lift will
produce sub advisory snow amounts to the far west today and
tonight. Then by Thursday, the amplified ridge axis will move off
to the east putting us under southwest flow ushering in milder
air, with the jet to the north of Wyoming. As a result,
temperatures will climb to the 60s at the lower elevations east of
the divide, with 40s west Thursday afternoon. An increasing
southwest upslope flow along with increasing diffluence ahead of
an approaching prominent shortwave will result in intensifying
snowfall for the western mountains Thursday and Thursday night,
resulting in likely advisory amounts. Rain will likely fall in the
western valleys Thursday and then turn to snow Thursday night and
Friday morning where a few inches of snow will also fall. Light
snow will continue Friday afternoon and evening between shortwaves
before the next shortwave in the southwest flow, all within the
same long wave trough off the Pacific coast, approaches Wyoming
with snowfall increasing after midnight Friday night in the west.
West southwest winds will increase in wind prone areas toward the
end of the week.

.LONG TERM...(Saturday through Wednesday) Issued at 209 AM MDT
Wed Mar 21 2018

Cold front and shortwave moves east across the area Saturday
ahead of the main upper low. Widespread snow will fall in the
west. East of the divide, strong wind will likely occur with fropa
and behind it with an increasing chance of mixed rain and snow
showers in our sern zones. The main concern east of the divide
will be Sunday into Monday. It now looks like the upper low will
move in Sunday and slowly weaken on top of us through the day
Monday before gradually shearing and filling by Monday night. This
scenario looks closer to the Euro from last night and increases
the threat of accumulating snow east of the divide in this period.
Combination of a mid level low in Central WY with increasing
upslope and potential jet streak support increases the potential
for accumulating snowfall developing Sunday and continuing into
Monday. Temps are more than cold enough east of the divide with
temps falling from -7 to -10C at H7 Sunday and possibly colder yet
Monday. As the low shears apart Monday night a new upper low
forms in the Desert SW and we await a developing nw flow that
right now the models are keeping the energy ne of us on Wednesday.
Worth watching though with time as the GFS 5-wave shows the
developing nw flow with the ridge axis out near 140W. Otherwise,
Tuesday will likely be a cool day, especially where fresh snow is
on the ground. Wednesday could see some warming if the nw flow
doesn`t get us by then. Guidance shows temps recovering Wednesday
right now with some 50 degree potential east of the divide and 40s


.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 209 AM MDT Wed Mar 21 2018

West of the Divide...KBPI/KJAC/KPNA/KRKS Routes

VFR conditions will prevail at the terminal sites through the
period. Scattered rain and snow showers will occur in southwest WY
after 12Z through 21Z with local MVFR conditions. Then a new batch
of rain and snow showers will occur over northwest WY from 00Z Thurs
through 12Z Thurs. MVFR to IFR conditions will occur in this area
with mountains frequently obscured.

East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Routes

VFR conditions will occur through the period.


Issued AT 209 AM MDT Wed Mar 21 2018

Slightly warmer across the forecast area today, but otherwise similar
weather results to those of Tuesday with periods of rain and snow
in the far west today and tonight. Thursday through Thursday
night and into Friday morning, significant snowfall can be
expected in the western mountains. Rain and snow in the western
valleys Thursday will turn to all snow Thursday night and continue
into Friday morning where a few inches of snow will also accumulate.
Temperatures will gradually warm through the end of the week.




LONG TERM...Skrbac
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