FXUS65 KRIW 150804
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
204 AM MDT Wed Apr 15 2026

.KEY MESSAGES...

- A potent late winter storm will sweep across Wyoming through
  the rest of the week, bringing widespread snowfall to most of
  the state. Winter Storm Warnings are in effect for the
  northwest mountains tonight through Friday.

- Cold air moves in with the winter storm, with temperatures
  likely falling below 28 degrees both Friday morning and
  Saturday morning (90% +). Extent of temperatures below
  freezing could reach 12 to 15 hours Friday night into Saturday
  morning.

&&

.DISCUSSION...
Issued at 109 AM MDT Wed Apr 15 2026

For most of the state, the mild temperatures will belie the
abrupt and shift weather shift approaching. Most of the state
will again see mild temperatures and gusty winds today, with
highs in the 60s.

And then the bottom falls out of the forecast. The next winter
system is coming ashore along the PacNW this morning, and will
already start to spread snowfall into the NW mountains by this
afternoon. This snowfall will only increase through the night
tonight as the cold air pushes into the state. The main cold
front will race across the state during the day Thursday,
bringing a stunning drop in temperatures from the low to mid 50s
around noon to the upper 30s by 6PM. As the front sweeps
through, precipitation will come along as well. Precip will
start as rain for the lower elevations briefly, before switching
to all snow by early evening. Snow will continue across the
state through the night into Friday, continuing through sunset
before tapering off. Main forecast issue is how much of the
initial snowfall will melt off, due to ground temperatures
already being very warm. Putting all these factors together,
Have gone ahead and upgraded current Winter WAtches to Winter
Storms Warnings for the NW Mountains, including the Wind River
Range. Will need to closely monitor the snow forecast for the
Bighorns, along with lower elevations of Johnson, Natrona, and
Fremont Counties for last minute model shifts for accumulations.

As this system sweeps southeast, skies will gradually clear west
to east Friday night. The cold pool moving in behind the system
is particularly cold for this time of year, and a couple factors
will determine just how cold temperatures fall. First is how
fast cloud cover clears out, allowing better radiational
cooling. Second is if there's any considerable sfc snowpack
insulating the cold pool as it moves through. Current forecast
is for lows in the mid to upper teens. with clouds clearing sell
before sunrise, and snowpack holding for most areas. Current
forecast has temperatures in most lower elevations falling
below 28 degrees (hard freeze) for 9 to 12 hours. This will have
a significant impact on already flowering plant life, animals,
lawn sprinkler and irrigation systems, and the like. Please take
any and all precautions for a late-season cold snap.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 946 PM MDT Tue Apr 14 2026

VFR conditions prevail through Wednesday afternoon. A weather system
will approach from the west during the TAF period, with increasing
clouds Wednesday morning through Wednesday evening. Rain and
mountain snow will move into western Wyoming Wednesday morning, with
light rain at KJAC by 20Z. As rain transitions to a mix Wednesday
evening reductions to MVFR may occur at KJAC. Have added PROB30
groups at KBPI and KPNA from 03-06Z Thursday for MVFR conditions and
-SHRA. Little to no precipitation will make it east of the
Continental Divide through the TAF period.

Wind will remain quite breezy at KRIW until 10Z when the gusty
northwesterly drainage wind should subside. Wind will increase by
mid to late morning Wednesday for most terminals and certainly by
early afternoon for all terminals. Wind will be strong from the
southwest, which is typical ahead of a weather system. Mountain
obscuration will become more prevalent Wednesday afternoon, mainly
around western mountains.

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...
Winter Storm Warning from 6 PM this evening to 6 AM MDT Friday
for WYZ001-002-012.

Winter Storm Warning from 6 PM this evening to 6 PM MDT Friday
for WYZ014-015.

&&

$$

DISCUSSION...Straub
AVIATION...Rowe