104
FXUS65 KRIW 021029
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
429 AM MDT Tue Sep 2 2025

.KEY MESSAGES...

- Another warm day today with isolated showers and thunderstorms
  in the northern mountains.

- A cold front moves through the area on Thursday, bringing
  windy conditions and cooler temperatures.

- Chances of showers and thunderstorms increase in western
  Wyoming Friday and spread across the rest of the area this
  weekend.

&&

.DISCUSSION...
Issued at 135 AM MDT Tue Sep 2 2025

Things are largely quiet on as we head into the post Labor Day
period at the humble Riverton weather abode. Radar does have
some echoes across northern Wyoming. However, with the large dew
point depressions, this is likely just virga or at the most a
couple of sprinkles. All in all, today looks fairly similar to
yesterday, with above normal temperatures and mainly dry
conditions. There will be a few showers and storms around, but
these should largely be confined to the northern mountains and
even here the chance is only around 1 out of 4. Any showers
should end fairly quickly after sunset. The main concern today
will be elevated fire weather. Humidity remains rather low,
falling to under 15 percent in some locations. However, wind
will remain light to moderate, so critical fire weather is not
anticipated.

The first of two cold fronts will approach the area late tonight.
This one looks like more of a glancing blow, with the coldest air
remaining well to the east of the area. It will being temperatures
down around 10 degrees in Johnson County, but effects elsewhere look
negligible, with only a few degree drop in temperatures. This
frontal passage also looks largely dry, with only a 1 in 10 chance
of a shower or thunderstorm. It will bring breezy conditions to
Johnson County, but maximum gusts should only be at most 30 mph.

The second front approaches the area Thursday, and this one looks to
be the more potent of the two. Once again though, moisture is rather
limited so the chance of convection again, looks small, at most 1
out of 5 with most areas remaining rain free. The main impact looks
to be wind. This is especially the case in the favored northwest
flow / cold advection regions, mainly the northern Bighorn Basin and
especially northern Johnson County. The NBA ensemble guidance gives
a greater than 3 in 5 chance of wind gusts past 50 mph on Thursday
afternoon, and a greater than 3 out of 5 chance of wind gusts past
40 mph in the northern Big Horn Basin. As for high wind, chances
look less than out of a 1 at this point. The 700 millibar wind is
around 40 knots, and I would like to see 50 knots there. Also, the
best jet forcing is further east in the Dakotas. However, it does
look like a windy afternoon for much of northern and even central
Wyoming. This front will bring cooler air, but timing at this point
shows most of central Wyoming having one more warm day before the
front arrives. As for fire weather concerns, humidity looks too high
for critical fire weather at this point but elevated fire weather
looks like a good possibility.

Friday will be a much cooler day, definitely feeling more early
autumn like with areas like Buffalo possibly remaining in the 60s.
On this day, ridging will push eastward and moisture will increase
from the west. The chance of thunderstorms will increase in the
west, but it looks isolated on this day. Coverage of showers and
storms than increases over the weekend as moisture spreads eastward,
but the best coverage of storms looks to be mainly over western
Wyoming.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 427 AM MDT Tue Sep 2 2025

VFR conditions prevail at all terminals through the forecast period
in northwest flow aloft. There is enough mid-level moisture to
again generate isolated late day showers and a thunderstorm or
two over the Absaroka, Wind River, and Bighorn Mountains
Tuesday. Steering winds lead to a few more clouds and the
outside chance at a shower at KCOD around 00Z/Wednesday but not
enough confidence to include in the TAFs at this time. Any
lingering convection should wane by 04Z/Wednesday. Wind should
remain at 11 knots or less at all TAF sites. A better northerly
surge reaches the far north after 09Z Wednesday.

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...
None.

&&

$$

DISCUSSION...Hattings
AVIATION...Hattings