Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 081735
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1035 AM MST Mon Mar 8 2021

.SHORT TERM...(Today through Tuesday)
Issued at 455 AM MST Mon Mar 8 2021

Today the Cowboy State will see two seasons. The first half of the
day will be dry and warm as the ridges to the east starts to give
way. Temperatures are again expected to reach well above normal
temperatures, especially in southern and central Wyoming. This
afternoon a strong southwest wind will develop in the mountains and
the Wind Corridor from Rock Springs to southern Johnson. These two
factors combined with humidities around 15 percent will lead to
elevated fire weather conditions. A Rangeland Fire Danger Statement
has been issued for Sweetwater, Fremont, Natrona, and Johnson
Counties for this afternoon.

A shortwave will kick of some snow showers in the western mountains
and valleys late this afternoon. Snow accumulation remains fairly
low. The warmer temperatures will cause a number of areas to see a
mix of rain and snow to start, especially in the valleys. In the
mountains breezy conditions could cause some visibility issues at
times along the mountain passes.

Tonight a 120 knot jet is progged to push in from the southwest. As
the front right quad moves over Wyoming early morning Tuesday winds
will pick up across the area. We have increased winds in the lee of
the Winds and Absaroka Mountains, impacting mainly the Lander and
Cody Foothills. These winds do not currently look like they will
reach the high category, but should be watched closely. A cold front
will push through the area just before sunrise Tuesday shifting
winds to the northwest. This will also bring a quick blast of gusty
winds to the Wind River Basin and western Natrona County.

The early morning cold front will bring more seasonal temperatures
for the day Tuesday. Isolated to scattered showers in the west will
remain all snow. Winds will slow after noon, but will remain breezy
through the day east of the Divide. As the main upper trough pushes
into the Intermountain West showers will begin to push eastward. By
late afternoon most areas will see some showers. West of the Divide
and the northern mountains will be mainly snow, while the lower
elevations in central Wyoming will be rain.

.LONG TERM...(Tuesday night through Sunday)
Issued at 455 AM MST Mon Mar 8 2021

Tuesday night and Wednesday a weather system will move from
southwest to northeast across the region. The models continue to be
in good agreement with this snow event for some places along and
east of the continental divide. The models also show a band of
heavier snow from central Sweetwater county to southern Johnson
county. This is mainly due to good upper level dynamics and a jet
couplet that is forecast to occur. Plus a 700MB circulation is
forecast to move out of Sweetwater county Tuesday night and into
Natrona county Wednesday morning. The exact track of this
circulation may well enhance snowfall in some locations. A winter
storm watch has been posted for portions of central WY Tue night
through Wednesday afternoon. WPC QPF and snow amounts have been
consistent with this snow event as well, adding to my confidence.
The west and far north will only see scattered light snow Tuesday
night and Wednesday. High temps will be in the 30s for the most
part on Wednesday. Snow will be ending Wednesday night east of the
divide.

The models develop an upper low pressure system over the southwest
U.S. Thursday. Then this upper low gradually moves east Friday and
Saturday, ending up in southeast Colorado Saturday night, then out
into the central plains states on Sunday. The GFS and ECMWF
models have some precipitation moving into southern WY Thursday
night and Friday morning. Then they wish to spread precipiation
into the central and southern zones Friday afternoon through
Saturday afternoon. A lot of uncertainty in this period on just
where this upper low will go and how far north the precip will
advance. Was given low pops in the NBM for the central and south
and will not stray from this for now. High temperatures will be on
the cool side Thursday and Friday, then a little milder Saturday
and Sunday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday morning)
Issued at 1035 AM MST Mon Mar 8 2021

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

VFR conditions with variable mid and high level cloudiness are
expected at area terminals through the period. Southwest winds at
KCPR will increase by midday and continue overnight. KCOD and KLND
have the potential for low-level wind shear overnight with some
strong winds likely mixing down at times at the terminals. A strong
Pacific cold front will push eastward with strong west to northwest
winds developing at KCOD and KRIW by around 09Z Tuesday.

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

VFR conditions with considerable high-level cloudiness expected
through about 00Z Tuesday. Precipitation is expected to break out
across the far west between 01Z and 03Z. Although the precipitation
could begin as rain, it will turn quickly to snow. KJAC will be the
main terminal most impacted by this snow with a period of 2 to 4
hours of IFR conditions expected. Farther southeast including the
KBPI and KPNA terminals, will have VCSH in each terminal as
confidence is relatively low on the extent/timing of the snow at
those terminals. KRKS is expected to remain dry through the TAF
period. Strong west to northwest winds are expected around 09Z
Monday night as a Pacific cold front pulls across the area. Western
mountains will become obscured between 00Z and 03Z Tuesday, and
remain so through the forecast 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 455 AM MST Mon Mar 8 2021

Today will be very mild in the central and south with low humidity
and breezy to windy conditions. This will produce elevated fire
weather conditions, especially in the Wind Corridor from Rock
Springs to southern Johnson County. Scattered rain and snow
showers will occur in the northwest late this afternoon. Then snow
will occur tonight in the western mountains as a cold front moves
into this area. Expect strong winds in the Lander and Cody
Foothills overnight. A wind shift will occur to the northwest
during the early morning hours Tuesday, which will bring a quick
blast of strong winds to the Wind River Basin and western Natrona
County. Some light snow will occur in the far west valleys.
Tuesday will see cooler temperatures and higher humidity over the
region. Scattered snow showers will occur in the mountains on
Tuesday.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...

Winter Storm Watch from Tuesday evening through Wednesday
afternoon for WYZ007>011-015-018>020-022.

&&

$$

SHORT TERM...Hulme
LONG TERM...AR
AVIATION...Swanson/CNJ
FIRE WEATHER...Hulme


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