418
FXUS65 KRIW 230312
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
812 PM MST Sat Feb 22 2025

.KEY MESSAGES...

- Seasonal temperatures tonight with mainly dry conditions.

- Strong winds Sunday through Tuesday afternoon, especially
  across the Absaroka Mountains and into the Cody Foothills. A
  High Wind Warning is in effect for these areas Sunday and
  Monday.

- Snow moves into western Wyoming Sunday morning, continuing
  through Tuesday, though the heaviest snow falls Sunday
  afternoon through Monday morning. Western lower
  elevations/valleys could see rain or rain/snow mix.

- Continuing to watch for the possibility of ice jamming and flooding
  Sunday through Tuesday across the Bighorn Basin and Johnson
  County. This is due to warming temperatures and current
  snowpack in those areas.

&&

.UPDATE...
Issued at 811 PM MST Sat Feb 22 2025

It remains quiet this evening, with gusty wind in a few
locations across the area. Mid-level clouds (5k-8kft) have
developed over northwest Wyoming this evening and will linger
into Sunday. Skies have cleared out for the rest of the forecast
area, so diurnal cooling will cause temperatures to drop into
the teens and twenties by sunrise Sunday. A northwest drainage
wind in the Wind River Basin has kept the atmosphere mixed this
evening, which has kept temperatures a little warmer from
Crowheart to Riverton. This wind should subside overnight and
allow temperatures to drop.

&&

.DISCUSSION...
Issued at 254 AM MST Sat Feb 22 2025

Current (09Z) water vapor imagery shows broad upper-level ridging
building into the Intermountain West. A fetch of Pacific moisture
rounding the periphery of the ridge is allowing for increasing upper-
level clouds to make its way into Wyoming. Cloud cover today will
limit insolation across the area and keep temperatures slightly
cooler compared to yesterday. Despite this increased moisture,
height rises and a lack of forcing will keep most of the area dry
today. However, I cannot rule out light snow this afternoon in
higher elevations of the Western Mountains. Snow amounts will be
minimal with the highest amounts being up to 0.5 inch.

Tonight, the ridge will continue to expand with mostly zonal flow
returning to the region. A 700mb wind maximum situated over Montana
will shift south into northern Wyoming and bring with it Pacific
moisture by Sunday afternoon. The deep zonal (westerly) flow is
favorable for snow chances across the Western Mountains through mid-
week. In the Western Mountains, there is a 70-80% chance of snow
amounts greater than 6 inches (minimum amount for a Winter Weather
Advisory) through early Tuesday morning. Snow amounts greater than
10 inches drops considerably to around 30% through Tuesday morning.
Snow will be confined to the higher elevations as temperatures
across the western Valleys are forecast to be in the upper 30s to
low 40s. Therefore, liquid precipitation can be expected in the
western Valleys.

Locations east of the Divide Sunday through Monday afternoon can
expect mainly dry weather with wind. The westerly 700mb wind
maximum, a tight pressure gradient, and a sharp 700mb temperature
gradient across northern Wyoming will allow for high wind potential
Sunday through Monday afternoon across the Absaroka Mountains and
the Cody Foothills. A High Wind Watch has been issued for these
areas for west winds 30 to 40 mph and gusts up to 70 mph. The watch
is in effect from early Sunday morning through Monday afternoon.
Strong winds cannot be ruled out for South Pass, over mountains, and
the Wind Corridor during through Tuesday. However, confidence is
much lower in reaching High Wind criteria due to not as favorable
flow.

Confidence is high in warmer temperatures east of the Divide with
highs in the 50s for lower elevations Sunday through Tuesday. This
brings continued concern for ice jamming and flooding for areas
across the northern Bighorn Basin and Johnson County.

There is consensus amongst guidance in a shortwave dropping through
Wyoming Tuesday into Wednesday. With the available Pacific moisture,
this brings the next chance for precipitation (both frozen and
liquid) to western and northern Wyoming. High elevations can
anticipate snow and the Bighorn Basin will see rain chances with
this system. Ensemble guidance is in agreement in ridging builds
back into the region Wednesday through the end of the work week.
This ridge will cut off available moisture for the Intermountain
West and keep precipitation chances very low (less than 10%
chance).

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 340 PM MST Sat Feb 22 2025

Cirrus continues to pour across the state, with some thinning
noted upstream across Idaho this afternoon. This should keep
most areas mostly clear overnight. Increased wind aloft tonight
will keep some mixing going in the vicinity of KJAC, so low
cloud deck is less likely than the pesky deck this morning. The
next winter system moves into the western sites late morning,
with increasing snowfall impacting KJAC through most of the
afternoon and evening. Snow may briefly drift into the vicinity
of KBPI/KPNA in the afternoon, but chances are too low to add
into the TAF at this time. Other aviation concern is gusty winds
tonight and tomorrow. KCPR/KRKS/KCOD/KDUB have been gusting
above 30kts this afternoon, and most of this energy should
continue overnight tonight, with only minimal decreases noted.
After sunrise, higher gusts return during the day, and continue
beyond 00Z/24.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 11 AM Sunday to 11 AM MST Monday
for WYZ001-012.

High Wind Warning from 5 AM Sunday to 5 PM MST Monday for
WYZ002-003.

&&

$$

UPDATE...Rowe
DISCUSSION...Gerhardt
AVIATION...Straub