Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 290510
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1010 PM MST Fri Feb 28 2020

.SHORT TERM...This evening through Sunday
Issued at 220 PM MST Fri Feb 28 2020

Dry weather tonight and tomorrow with breezy to windy areas in the
central wind corridor as well as in parts of NW WY. Light wind
elsewhere. Lows tonight will vary widely again with single digits in
the western valleys and basins to as mild as the lower 30s in some
mixed locations. Saturday looks dry for most of the region with mild
high temps for many places. Some light snow may develop in the NW WY
mountains Saturday afternoon.

Saturday night, the snow increases in the west. East of the divide,
snow develops over the north as the cold front sags south into this
area as the weather system moves over the area. The cold front and
snow should be into the central zones around 12Z Sunday. Low temps
Saturday night will be in the teens and 20s. Sweetwater County could
see some light snow by 12Z but the moderate to heavy snow and
stronger winds should hold off until after 15Z. Models are still
picking up on a 700mb circulation pushing down into southwest
Wyoming early Sunday. The resulting flow could lead to some good
upslope conditions for the Lander Foothills and the eastern Wind
River Mountains, especially South Pass. the front will also bring
strong northeast winds from South Pass into eastern Sweetwater
County. We have issued a Winter Storm Watch for these areas,
starting early Sunday morning, due to the moderate to heavy snow
and/or wind gusts up to 40 MPH.

.LONG TERM...Sunday night through Friday
Issued at 220 PM MST Fri Feb 28 2020

The snow will decrease in intensity across central Wyoming Sunday
evening as the best northern stream jet energy shifts east and the
upslope begins to wane. The best low-level lift will shift to
Sweetwater County as it appears the front will hang up across
southern Wyoming Sunday night. Post-frontal northeast wind of 20 to
30 mph is likely within the I-80 corridor which will impact travel
through at least midnight. Snow amounts in this region remain in
question. However, even one to two inches of snow in combination
with the wind will be hazardous, especially after sunset Sunday.
Generally, cloud cover will dissipate first in the north and
eventually central Wyoming by sunrise Monday. Given fresh snow
cover, clearing skies, and a lingering mid-level cold pool, Sunday
night low temperatures may need to be knocked down a notch or two.

Monday will be generally dry through midday before a shortwave dives
south out of Montana in northwest flow aloft late in the day. Clouds
will increase out of the northwest and spread across the region by
sunset. Adjustments were made to increase snow chances across
portions of the Bighorn Basin, Fremont, Natrona, and Johnson
counties Monday evening and overnight. The overall pattern would
favor a quick inch or two in the southeast Bighorn Basin and around
Casper. The left exit region of a 100-120kt 300mb jet could also
provide assistance Monday evening. The other player here could be
snow bands. Mean layer northwest wind 30-40kts coupled with a moist
atmosphere, cyclonic flow, and lapse rates around 8C/km could lead
to snow banding Monday evening. Favored locations in northwest flow
could also see gusty northwest wind Monday evening. This would
include northern portions of Johnson and Fremont counties and
potentially Big Horn County. The northwest flow lingers through
Tuesday with persistent light snow across the northwest mountains.

Cooler northwest flow continues Wednesday with the moisture
generally pinpointing the northwest mountains. Other areas will be
drier and temperatures will moderate from those see Monday and
Tuesday. The upper flow will become more zonal with ridging possible
by Friday. Overall, the end of next week looks warmer as 700mb
temperatures rise to around +1C by Friday. Increasing southwest wind
will make for a windy day Friday from eastern Sweetwater County up
through Natrona County. The combination of warm air advection and
gusty southwest wind could lead to temperatures 5 to 10 degrees
above normal within this wind corridor and along the east slopes of
the Bighorn and Absaroka mountains.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1007 PM MST Fri Feb 28 2020

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

Cloud cover will gradually increase from the northwest through the
day Saturday, but conditions will remain VFR for most of the period.
KJAC will see vicinity snow showers by 23z, with snow beginning at
the terminal around 03z. KBPI and KPNA will see vicinity snow
showers around 01z. Snow will increase after 06z across all
terminals.

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

All terminals will be VFR through Saturday afternoon, with mid
and high clouds increasing from the west-northwest. KCPR can
anticipate a persistent southwest surface wind at 20-28kts
throughout the forecast period. A westerly wind of 10-20kts is
expected at KCOD overnight with similar speeds prevailing Saturday
ahead of an approaching cold front. Vicinity snow showers
expected at KCOD by 02z, and at KCPR and KWRL by around 05z. Snow
will increase at all terminals during the next period.

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 220 PM MST Fri Feb 28 2020

Seasonal temperatures and dry conditions will prevail for most
locations through much of Saturday. A cold front will approach from
the northwest late Saturday with light snow breaking out across the
northwest mountains prior to sunset. The cold front and associated
snow will spread across northern and western Wyoming Saturday night
and across central and southwest Wyoming Sunday. Significant
snowfall is possible in the central and western mountains with
accumulating snow across almost all of the lower elevations.
Conditions will gradually dry from north-to-south Sunday night.
After a dry day Monday, a quick-hitting weather system will sweep
through the state Monday night and Tuesday. This could bring
accumulating snow to portions of the Bighorn Basin and I-25
corridor, with the best chance of snow remaining across the
northwest mountains. Areas favored for northwest wind could see at
least breezy conditions Tuesday in the wake of this system.
Temperatures will be below normal Sunday through Tuesday before a
warming trend begins later in the week. These warmer temperatures
and increasing west to southwest wind will generate improved smoke
dispersal.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Sunday morning through late Sunday night
for WYZ030.

Winter Storm Watch from late Saturday night through Sunday
evening for WYZ019.

Winter Storm Watch from Saturday evening through Sunday evening
for WYZ015-018.

&&

$$

SHORT TERM...Hulme
LONG TERM...Jones
AVIATION...Myers
FIRE WEATHER...Jones



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