047
FXUS65 KRIW 160949
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
349 AM MDT Tue Sep 16 2025

.KEY MESSAGES...

- Showers and thunderstorms will continue to drift around the
  region through the next 36 to 48 hours, with significant
  accumulation possible across central Wyoming.

- Freeze Warnings continue this morning for the lower elevation
  basins west of the Divide.

- More tranquil conditions for the latter half of the week into
  the weekend.

&&

.DISCUSSION...
Issued at 207 AM MDT Tue Sep 16 2025

Morning WV imagery shows the latest H5 trough spinning across
the northern Rockies, generally centered on YNP. With this
system blocked from progressing, the system will produce
widespread showers and thunderstorms across western WY today
through Wednesday evening. Some midlevel enhancement is already
sparking showers and thunderstorms across Sweetwater County,
which is quickly spreading NE into Natrona County. This will be
one of two main focus areas for precip today. The other is
closer to the center of the trough, bringing precip across far
NW WY this afternoon. While the main enhancement remains just to
the north in souther Montana, enough energy will be available to
produce precip for the Absarokas, the Parks, and down the Winds
through this afternoon. Once daytime heating kicks in, showers
will also build along the Bighorns. Precip will likely not fade
off overnight, with chances remaining above 50% for all except
far western WY through sunrise.

As the trough slowly nudges east Wednesday, this puts the
circulation over central WY. Models continue to indicate
widespread rainfall east of the Divide, focusing on Johnson and
Natrona Counties. Latest forecast probabilities for rain
accumulations above a half inch remain 50 to 60 percent along
I-25, and around 35 percent probability of a full inch of rain
for Natrona County.

After Wednesday, the trough nudges just far enough east to
loosen its grip on western Wyoming weather for the remainder of
the week. Temperatures will rebound back into the 70s and low
80s into the upcoming weekend.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 343 AM MDT Tue Sep 16 2025

There is around a 1 in 5 chance of patchy fog in vicinity of
KJAC through around 16Z this morning but with the chance only
around 1 out of 5 we have elected to keep the low cloud group
only at this time. A few rain showers will continue through
around 15Z roughly along and east of a line from East of Rock
Springs through Casper. Scattered low clouds are possible at
KCPR with these showers and this potential is reflected by a
FEW015 cloud group. Scattered showers and thunderstorms are
forecast to develop across much of the area 20Z Tuesday with
PROB30 groups covering most likely timing. Most locations will
have at least a 1 in 4 chance. We can`t rule out a shower or
thunderstorm in vicinity of KBPI and KPNA but with the chance
less than 1 out of 5 we elected to leave convection out of the
forecast. Conditions are expected to stay VFR with any showers
and thunderstorms; however, a brief period of reduced flight
conditions cannot be ruled out in a heavy shower or
thunderstorm. Areas that see significant rain may see fog after
06Z Wednesday but not enough confidence to pinpoint at this
time.

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

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Freeze Warning until 7 AM MDT this morning for WYZ013-023-025-
026.

&&

$$

DISCUSSION...Straub
AVIATION...Hattings