333
FXUS65 KRIW 031033
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
433 AM MDT Wed Sep 3 2025

.KEY MESSAGES...

- Another mainly dry and warm day across the area today.

- A cold front will move through the area on Thursday and bring
  gusty to strong winds for many locations.

- The chance of thunderstorms returns Friday across the west and
  becomes more widespread this weekend into early next week.

&&

.DISCUSSION...
Issued at 232 AM MDT Wed Sep 3 2025

It is another quiet night across western and central Wyoming. A weak
cold front will move through the area today. It has just passed
through Buffalo around 2 am with a wind shift to the northwest.
Effects look rather minimal though. The only impact will be
some local breezes as temperatures averaging about 5 degrees
cooler across far northern Wyoming. Otherwise, it will be
another warm and mainly dry late summer day across the region.
We will again have a few, emphasis on few, afternoon showers and
thunderstorms over the northern mountains, Mid levels are even
drier than yesterday, so chances are at most 1 out of 6 and will
be confined to the mountains with little chance to move far
from them. Temperatures elsewhere should be fairly similar to
yesterday. As for fire conditions, there could be locally
elevated fire weather is the central and southern Wyoming, but
wind should not reach critical levels.

Another cold front will drop southward into the area on Thursday,
and this one looks more interesting. Not in the precipitation
department though. There will be a few showers and thunderstorms
with it but most areas will see nothing. The main impact will be the
wind, and likely strong in some locations. Most areas East of the
Divide have at least a 1 in 2 chance of seeing wind gusts past 30
mph in the afternoon, when wind is expected to peak. The most
impacted areas will be usual suspects with northwest flow and cold
advection, mainly the northern Big Horn Basin. Both these area have
at last 1 in 2 chance of wind gusts past 40 mph. The question this
morning is about potential high wind though. And this would mainly
be in Johnson County. For now, we are leaning against it. The latest
NBM ensemble guidance is showing less than a 1 in 2 chance of wind
gusts past 50 mph in Johnson County. Deterministic guidance is
split, with the GFS MOS showing a period of sustained 40 mph wind
Thursday afternoon while the NAM and European keep sustained wind
under 35 mph. There are a couple of other factors though. One, 700
millibar wind is only 40 knots and I would prefer to see 50 knots.
The main jet energy is also further east in the Dakotas. So, we will
hold off on any highlights. If the wind trends up we can issue this
afternoon or tomorrow night. Wind should drop from north to south
Thursday night as the pressure gradient relaxes. As for fire weather
concerns, humidity looks to remain high enough to prevent critical
conditions. Elevated fire weather is certainly possible.

Friday looks like the first taste of early autumn across the area as
highs in the 70s look fairly widespread with places like Buffalo
remaining in the 60s. Our focus then shifts with an increasing
chance of thunderstorms as monsoonal moisture moves in from the
west. Most guidance shows the moisture being delayed somewhat,
so on Friday and storms would be largely confined to west of the
Divide and even here the chance is only 1 out of 5. Chances
then increase on Saturday as deeper moisture moves in and
spreads East of the Divide, especially on Sunday. The chance of
showers and storms looks to linger into early next week as well.
And with flow turning southwest, temperatures will likely climb
back to above normal levels by Sunday and stay there for much
of next week.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 429 AM MDT Wed Sep 3 2025

VFR conditions should continue at all terminals through 12Z
Thursday. A weak cold front may bring wind as high as 12 knots
to terminals East of the Divide as it passes through this
morning. Otherwise, wind should remain at 11 knots or less
except around KCPR where a period of wind gusts over 15 knots is
likely after 18Z. Areas of smoke may move into the area at
times, but any impact to visibility should be minimal. Isolated
afternoon showers and thunderstorms are possible but should
remain over the mountains and away from TAF sites. A stronger
cold front will likely bring a period of stronger wind on
Thursday afternoon, mainly East of the Divide and in vicinity of
KRKS.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Hattings
AVIATION...Hattings