149
FXUS65 KRIW 240350
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
950 PM MDT Thu May 23 2024

.KEY MESSAGES...

- Light to moderate mountain snow and lower elevation rain/snow
  showers will continue through the afternoon.

- Gusty winds continue for much of the area through the afternoon.

- Precipitation and wind will end after sunset. Most areas will see
  a frost or freeze tonight.

- Warmer and drier Friday before unsettled conditions return for
  the weekend.

&&

.DISCUSSION...
Issued at 324 PM MDT Thu May 23 2024

Cooler and wetter conditions are ongoing today as a low pressure
system rotates across northern Wyoming. The precipitation focus last
evening was across the western mountains, with 6 to 10 inches of
snow noted on area webcams. That focus has now shifted to northern
areas as the low moves farther east. Precipitation will continue
through the afternoon, though the heaviest amounts will generally
remain along and north of the Wyoming/Montana border. Snow will
be heaviest across the upslope favored, north facing slopes,
including in the northern Absarokas and Bighorns. The main
impact from snow will be slick roads in spots, especially over
Teton, Togwotee, and Granite passes. A Winter Weather Advisory
remains in effect through most of the afternoon for the Tetons,
Gros Ventres, and Bighorns.

Otherwise, rain showers will move farther south toward the
Continental Divide through the afternoon, though again most of this
will fall in the Bighorn and Powder River basins. The other aspect
with the system today is wind, with gusts of 35 to 45 mph noted
across much of the area this afternoon. This will continue for the
next several hours, with a few isolated gusts over 50 mph likely
(70%) within the Wind Corridor from Rock Springs through
Casper.

Both precipitation and wind will quickly decrease from west to east
after sunset as the system moves away. With clearing skies overnight
it will make for a chilly morning. Lows around or just under the
freezing mark are expected for much of the Bighorn Basin; given that
they are past the average last freeze date, we will be upgrading the
Freeze Watch to a Warning.

Friday will be warmer and drier as a weak transitory ridge takes
over, though still about five degrees below normal for this time of
year. Returning southwest flow near the surface will make for a
breezy afternoon for most locations while mixing down drier air
moving in aloft. This will return slightly elevated fire
weather conditions to much of central and southern areas where
humidity will drop below 20 percent.

Unsettled conditions will then return Friday evening as the next
shortwave arrives. This will bring light showers across southern
areas through Saturday morning, followed quickly by the arrival of a
weak trough axis connected to a low positioned well to our
northwest. This feature appears likely to bring another round of
showers from west to east across the area through Saturday. Amounts
do not look very impressive right now, and will likely fall as
scattered light rain showers given the warmer temperatures of this
system. Guidance then shows the low clipping northern Wyoming on
Sunday, with showers focused more east of the Divide.

Memorial Day will be warmer and dry as stronger ridging returns to
the area. Further out, ensemble guidance generally favors ridging
persisting through midweek before weakening by the weekend. This
would keep drier conditions and temperatures around or above normal
through much of next week.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 948 PM MDT Thu May 23 2024

VFR conditions expected to prevail through the period, with
decreasing cloud cover and winds tonight. Winds pick back up Friday,
with gusts 20 to 25 knots possible for some sites in the
afternoon and evening. Precipitation chances begin moving into
the southern part of Wyoming towards the end of the TAF period,
with KRKS the first to be impacted. Increasing clouds occur for
all sites ahead of this.

At KJAC, there is some uncertainty with how much clouds clear
tonight. Have kept scattered mid-level clouds in for now. Some
guidance is showing the northerly wind form overnight, while other
models keep a southwest flow in. Have kept southwest flow in the TAF
for now, but may need to change should a northerly wind develop. In
either case, southwest flow develops for Friday. An occasional gust
around 15 to 20 knots is possible in the afternoon.

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...
Freeze Warning from 2 AM to 8 AM MDT Friday for WYZ003>006.

&&

$$

DISCUSSION...Myers
AVIATION...Wittmann