575
FXUS65 KRIW 040900
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
300 AM MDT Thu Sep 4 2025

.KEY MESSAGES...

- A cold front will bring windy conditions to much of the area,
  with the strongest wind in northern Johnson County.

- Elevated fire weather is likely across much of the area today.

- After a cooler day Friday, the chance of showers and
  thunderstorms increases this weekend and may continue into
  next week.

&&

.DISCUSSION...
Issued at 257 AM MDT Thu Sep 4 2025

As compared to the last few days, things look a little busier today.
The culprit for this is a cold front that will be dropping southward
across the area today. The main concern is not convection though.
There will be a few showers and thunderstorms this afternoon and
evening but given the lack of moisture these look the remain
isolated (generally less than 1 in 4 chance) and largely confined to
the mountains. The main concern will be wind. And we need three
ingredients for strong wind in northern Wyoming. This front will
give the area it`s first taste of early autumn as it moves
southward. And, with it, some decent cold advection. Some areas,
like Johnson County, will see a 10 degree celsius drop in 700
millibar temperatures. This is the first ingredient. The second will
mid level flow. The ideal direction is northwest, and this is what
we have post frontal. The 700 millibar winds have ticked up as well,
with a few 50 knot barbs showing up on the 00Z NAM and up to 45
knots on the GFS. The third ingredient is a forcing mechanism. This
is a get, which is still to the east over the Dakotas but a bit
closer than yesterday. And, with decent mixing from the front, the
mid level wind should mix to the ground, especially in the early and
mid afternoon when mixing will be the strongest diurnally. And in
the world of the ensembles, the NBM ensemble is a greater than 2 in
3 chance of maximum wind gusts greater than 55 mph. With this, we
have hoisted a high wind warning for northern Johnson county, which
is most favored by this pattern. Chances are less in the Big Horn
basin but places like Greybull could see gusts close to 50 mph. Most
areas East of the Divide could see wind gusts past 35 mph, extending
down to Rock Springs this evening. As for temperatures, these will
be tricky depending on the speed of the front, a place like Buffalo
may stay in the lower 70s while the Wind River Basin should see
highs in the mid 80s again. And with the wind, elevated fire
weather is likely across much of the area. At this time though,
humidity should remain above critical levels. Wind should
decrease tonight as the front moves away and the pressure
gradient decreases.

Friday looks like the first taste of autumn across the area, with
highs staying in the 60s in Buffalo and many other areas in the
lower to middle 70s. And as for chances of convection, progression
of moisture continues to slow. There may be a few thunderstorm in
far southwestern Wyoming Friday afternoon but a vast majority of
locations should stay dry. Following that, chances of thunderstorms
begin to increase each day as some additional moisture from
Hurricane Lorena, which is moving into Baja California, may begin to
move northward into the area. The latest runs are showing more
inconsistency with details though in regards to timing and coverage.
Western Wyoming looks to have the best chance though. And, the taste
of autumn will be a brief one as flow turns southwest and brings
near normal temperatures back for Sunday and above normal
temperatures for much of next week. Temperatures don`t look record
breaking right now, but it will be consistently 5 to 10 degrees
above normal from Sunday into next week.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 945 PM MDT Wed Sep 3 2025

VFR conditions expected throughout the TAF period at all
locations. Mainly clear skies and light winds overnight into the
morning hours. A cold front will start to sag southward passing
through COD/WRL after 15Z, making its way south through RKS by
23Z as timing still looks on track. Winds were bumped up a bit
for some of the western sites at BPI/PNA as well as increasing
to 40kts at CPR between 00-02Z. The strongest winds behind the
front look to occur an hour of two after FROPA when the "cooler"
air advects through. Otherwise, winds will diminish at all but
CPR/RIW/RKS after 01-02Z towards sunset. The other locations
look to weaken into the next TAF cycle after 06Z into Friday
morning. Dry conditions expected with no indications for any
showers near TAF sites remaining over the Winds/Absarokas.

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...
Air Quality Alert until 11 AM MDT this morning for WYZ009>011.

High Wind Warning from 10 AM this morning to 6 PM MDT this
evening for WYZ010.

&&

$$

DISCUSSION...Hattings
AVIATION...Lowe