Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 220906

Area Forecast Discussion
National Weather Service Riverton WY
306 AM MDT Mon Apr 22 2019

.SHORT TERM...(Today through Wednesday night)

The 500mb low appears to be spinning over Utah at the moment.
This low is progged to track well to our south as it propagates
back to Vegas later this morning, and then on to Southwest Arizona
by later this afternoon. The associated broad trough axis will
clear our area just after 00Z Tuesday will come through roughly
around 00Z this evening. Until then, some additional rain showers
will occur today, with snow showers above 6500 feet this morning,
rising to 7500 feet this afternoon east of the Divide and around
8000 feet west. The only additional snow accumulations are
expected to occur over the upper east slope of the Wind River
Mtns, where 1 to 3 inches of snow are expected today. Most of the
upper support will slip off to the south today. A weak mid level
circulation will track east along the southern Wyoming border
today where the negative lifted indices are expected through early
this evening for some enhanced convection there today.

Then a positively tilted ridge will build into the area tonight for
the start of a warming and drying trend. High temperatures will be
back up into the 60s Tuesday and then on Wednesday, 60s west and 70s

On Tuesday, a west northwest difluent flow will quickly develop
behind the ridge. West winds will increase at the surface by
Wednesday. There will be a weak ripple in the westerly flow with
resultant showers over Northern Wyoming as well as the Wind River
Mtns Wednesday afternoon and evening, given the increasing
instability, with precip likely falling as snow above 9000 feet
after dark Wednesday evening.

.LONG TERM...(Thursday through Monday)

Thursday will see isolated to widely scattered showers and
thunderstorms in the afternoon and evening with some instability
indicated and relatively low cape. Many locations will not see any
rain Thursday. Friday looks a little more active with rain and
mountain snow in the west. A chance of showers and isolated storms
east of the divide. Saturday will have isolated showers and
storms over the north and northwest with dry weather expected
elsewhere. The GFS and ECMWF models are in less agreement with
Sunday through next Monday. The GFS model brings in moisture to
the west and northwest in a moist southwest flow aloft for Sunday
and Sunday night. The ECMWF model has a west flow aloft with a
weather system cutting through Montana and a decent cold front
along the northern border. Thus it has higher precip chance over
the north and not much elsewhere. Have compromised and will have a
chance of showers and isolated storms over the west and north
with less activity in the central and south. Next Monday, the GFS
maintains a southwest flow aloft with enough moisture to generate
a chance of showers and storms over most of the region Monday
afternoon into the evening. The ECMWF model is dry over most of
the region Monday with isolated showers or storms along the
southern WY border. Have kept a chance of showers and isolated
storms over the north and west to match with others. Will go with
a lesser chance in the central and south zones for now. As for
high temps, mild on Thursday and Friday over the region, then
slightly cooler Saturday and Sunday, but still decent for late
April. Next Monday is potentially cooler all areas provided the
cold front timing remains.


.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)

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

Widespread MVFR conditions, areas of IFR conditions and mountain
obscurations will persist through 15z Monday, along with widespread
mountain obscurations.  However, areas of precipitation will
decrease in intensity and coverage through 15z, confined to mainly
the mountains and eastern foothills by 15z.  Snow levels will
generally be around 6500 feet.  Ceilings will gradually dissipate
18z-22z Monday.  Skies will clear Monday evening, allowing for
patchy fog to partially obscure terrain, primarily vicinity KRIW and

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

Widespread MVFR ceilings/mountain obscurations with areas of IFR
conditions will persist until 14z Monday.  Scattered to numerous
rain and snow showers, snow levels 6500-7000 feet, will continue
mainly vicinity and south of a KJAC-KDUB line through 14z.

Ceilings will then gradually lift from the north and west 14z-18z,
with some MVFR ceilings persisting vicinity KRKS into the early
afternoon.  Skies will then clear early Monday evening, allowing for
patchy fog to develop near all terminals 06z-12z Monday.



Isolated to scattered showers will continue across the area
today, with precipitation amounts much lower compared to Sunday.
Snow levels should range from 6500 feet this morning east of the
divide, and then rise to 7500 feet this afternoon. In the west,
the snow levels should be around 8000 feet today. A drying and
warming trend is expected through mid week. Some showers are
expected across the north half of the state Wednesday afternoon
and evening. Smoke dispersal will range from fair in the north
this afternoon to good in the south.





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