380
FXUS65 KRIW 141900
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
Issued by National Weather Service Cheyenne WY
100 PM MDT Mon Sep 14 2026

.KEY MESSAGES...

- Any showers ending early. This will be followed by a windy and
  cooler day with elevated to critical fire weather across most
  of the area.

- A mainly dry day on Tuesday, with any showers confined to the
  southern third of the area.

- Increasing moisture will bring an increased chance of showers
  and thunderstorms Wednesday through at least Friday, although
  details on timing and placement of the most numerous and
  heaviest showers remains highly uncertain.

&&

.UPDATE...
Issued at 100 PM MDT Mon Sep 14 2026

IR continues to depict clearing skies behind the system that pushed through
last night. Gusty winds in its wake continues, especially through the
Absarokas to the Cody Foothills still pushing 40 to 50 mph. 30 to 40 mph
will be common across the wind corridor from eastern Sweetwater to Natrona
Counties where the Red Flag Warning remains for the rest of the afternoon
and evening hours. Winds will diminish towards sunset with radiational cooling
under mainly clear skies. This will bring the coldest start to the morning for
Tuesday but with a slight warming trend for the rest of the work week. The
next system still on track with no major changes that will push in Wednesday
night west of the Divide before pushing to the east that will bring scattered
storm chances for much of the CWA Thursday and Friday. Stay tuned for details
in the coming day or two going forward.

&&

.DISCUSSION...
Issued at 240 AM MDT Mon Sep 14 2026

In last night`s discussion, I made a reference to a rather old song
from the 80s. Tonight, we are going even further back, to when I was
a little kid, the 1970s. And this song, and this band, are very
appropriate for today, at least after any showers end shortly after
sunset. The song is September, and the band is Earth, Wind and Fire.
Meaning on earth (at least in western and central Wyoming), the wind
impacts today will be from wind and fire, and it is occurring in
September. Just not on the twenty first night, but on the fourteenth
day of the month.

The culprits for this are an upper level low now spinning over
northern Idaho that will move eastward today. Most of the moisture
should be gone by shortly after sunrise, with dry weather returning
for the entire area after that. The low will be close enough to
keep a decent pressure gradient across the area as well. A jet
streak will be moving across the northern portions of the state as
well. All this adds up to a rather windy day across most of the
area. Most of western and central Wyoming has at least a 2 out of 3
chance of wind gusts over 30 mph today, with a greater than 1 out of
2 chance of gusts over 45 mph in the windier portions of the area.
As for the high wind warning, we will leave it up, but it looks
borderline. The best chance would be in areas like near Clark and
to the west of Cody, where there is around a 1 in 2 chance of wind
gusts over 55 mph. There is still the chance of a mountain wave in
places like Cody and possibly Dubois or even Lander, but not enough
confidence to add to the warning. The strongest wind in the north
should be over by around noon, but gusty wind will continue through
the day before decreasing tonight as the jet streak moves away and
the atmosphere decouples.

The other concern is fire weather. There will certainly be plenty of
wind across the area, so that is a slam dunk. The area for low
humidity also looks solid, covering areas mainly south of the Owl
Creek and Bridger Range as well as Sweetwater County. If there is a
mitigating factor, it is that some areas received a decent rain
tonight, which should wet fuels at least initially. It has been
spotty though, so we will keep it as is. Elsewhere, relative
humidity should remain above critical levels. However, elevated fire
weather will be likely everywhere as most locations will see
humidity under 25 percent this afternoon. As for temperatures, it
will be cooler behind the front, with highs fairly close to
seasonal normals for the middle of September.

Tuesday looks like a fairly quiet day for most with sunshine mixing
with some clouds. Some increased moisture may try to return to far
southern Wyoming and could bring a stray shower or thunderstorm.
Most activity should hold off until after sunset though. Moisture
may push through the southern third of the area to bring a spotty
shower or thunderstorm, but most areas will not see one.

The reasoning for the rest of the week remains similar to the past
couple of days. And upper level low will move from the Pacific
Northwest to the northeast and eventually to the east. There is a
bit of more model consensus this morning in taking the low over
Montana late in the week rather than into Wyoming. However, there
are still some differences in the exact position as well as the
speed in which it moves through. Southwest flow will keep some
monsoonal moisture moving into the area, as well as bring a return
of above normal temperatures. With the increased moisture, there
will be a chance of showers and thunderstorms each day from
Wednesday through Friday and possibly into Saturday as well. At this
point, Thursday and Friday may be the most active days. However,
there is still a ton of model spread regarding the placement of
timing of the most numerous showers and storms. As a result, we kept
largely broad brushed the POPs. At this point, drier air looks to
return for the second half of the weekend.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1113 AM MDT Mon Sep 14 2026

VFR conditions prevail through the period. Gusty west winds occur
over much of the area today in the wake of last nights cold front.
Gusts 15 to 30 knots will be common across the area, generally
decreasing this evening. Some afternoon cumulus and high cirrus
clouds occur, but otherwise a mostly clear sky remains.


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

&&

.FIRE WEATHER...
Issued at 240 AM MDT Mon Sep 14 2026

Much drier air will move into the area today with any showers
ending early. In much of Natrona, Fremont and Sweetwater County,
a gusty to strong wind will combine with humidity falling below
15 percent to bring critical fire weather this afternoon.
Elsewhere, humidity should remain above critical levels.
However, a gusty wind will bring periods of elevated to near
critical fire weather, especially in the afternoon.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
High Wind Warning until 2 PM MDT this afternoon for WYZ002-003-
016.

Red Flag Warning until 8 PM MDT this evening for WYZ279-280-
283-289-300.

&&

$$

UPDATE...Lowe
DISCUSSION...Hattings
AVIATION...Wittmann
FIRE WEATHER...Hattings