332
FXUS65 KRIW 181833
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1233 PM MDT Fri Apr 18 2025

.KEY MESSAGES...

- Light snow continues through this evening. Snow showers this afternoon
  may bring locally higher amounts.

- Gusty north to northwest winds across Sweetwater County
  diminish this evening.

- Cool through the weekend, though will warm some. Next weather system
  comes Sunday and Monday.

&&

.UPDATE...
Issued at 1232 PM MDT Fri Apr 18 2025

Clouds have been slowly dissipating through the morning. This trend
continues this afternoon as snow chances decrease across the area.
Some instability, and upper-level support, will help bring some snow
showers around through the afternoon, with current radar showing
just that.

Clouds should be mostly gone by tonight, with a clear to mostly
clear sky overnight and into tomorrow morning. This will help to
keep temperatures cold tonight, with lows potentially in the single
digits for some. The low temperature forecast tonight was lowered a
bit as models tend to be too warm in these situations.

The other concern with a clearing sky and recent snowfall is fog.
Models at this time are showing almost no signals for fog, but
conditions will be favorable for fog formation. Favored areas would
be basins that just received ample moisture in the form of snow, as
well as low-lying areas like near rivers.

&&

.DISCUSSION...
Issued at 210 AM MDT Fri Apr 18 2025

The large amplitude trough is currently stretched generally
across western WY this morning, and continues to slowly shift
southward across the Rockies. This is keeping winds aloft from
the southwest, keeping moisture in place in the region. At the
sfc, the north to northeast winds behind yesterday`s front
continue to dig underneath the SW flow aloft, helping to lift
the moisture to continue the snowfall across the region. As the
trough shifts southward today, the winds sfc and aloft will
align better, decreasing the overall lift near the sfc, bringing
most precip to an end through the afternoon. Models show the
precip will transition this afternoon from the overrunning
pattern to a more convective pattern with streamer showers off
higher elevations into central WY. Overall snow accumulations
could still reach 1 to 3 inches through sunset, but should be
complete by that time. Other issue is the gusty north to
northeast winds at the sfc, which will still be gusting 30 to 40
mph across Sweetwater County today. This will continue the
hazardous conditions most of the day along I-80.

Dry air wraps in this evening from the north, bringing quickly
clearing skies across the state. With the clear skies and cold
pool still in place behind the front, temps tonight will drop
considerably, with most areas falling into the lower teens and
upper single digits. Most of the day Saturday will be chilly
for April, generally still in the 40s. Some areas in the Bighorn
Basin and Johnson County that have little to no sfc snow may
reach the 50s before peak heating decreases.Another midlevel
trough sweeps in late Saturday night into Sunday morning,
bringing a brief push of light snow to the western mountains.
Probabilities of snowfall above 2 inches remain low for the
western mountains (<20%).

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1158 AM MDT Fri Apr 18 2025

The spring snowstorm that has been producing impacts at terminals is
now in its final phase. Prevailing MVFR to IFR impacts have mostly
ended, and the main driver of impacts through the rest of the
afternoon will be of the convective kind with much more spotty
coverage. The locations most favored for brief MVFR/IFR impacts will
be KCPR, KLND, KRIW, and KWRL, especially at the beginning of the
period. KRKS will continue to see a northeast wind gusting to 30
knots this afternoon, subsiding by sunset. Conditions are expected
to improve everywhere by later this afternoon with VFR conditions
prevailing overnight. However, one caveat to this will be the
potential for fog before sunrise owing to the fresh snow and
clearing skies. Confidence is not high on this for now, but have
introduced low scattered ceilings and/or VCFG at locations most
favored to see fog tonight.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on icing and turbulence forecasts.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

UPDATE...Wittmann
DISCUSSION...Straub
AVIATION...Myers