484
FXUS65 KRIW 040359
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
959 PM MDT Sun Aug 3 2025

.KEY MESSAGES...

- Red Flag Warning posted for the southwest-quarter of Wyoming
  12 PM to 8 PM Monday. A warm, dry, and breezy week is ahead,
  which will keep fire weather concerns heightened.

- Thursday and Friday are likely to be the windiest days of the
  week as weather system moves into Wyoming from the Pacific
  Northwest.

- Isolated showers and thunderstorms over northwest Wyoming
  Monday afternoon.

&&

.UPDATE...
Issued at 1200 PM MDT Sun Aug 3 2025

A transient shortwave ridge will keep convection at bay for many
areas Sunday afternoon and evening as drier air filters into
the region from the Great Basin. The best chance for isolated
to scattered showers and thunderstorms will be across the
Absaroka and Bighorn Ranges downstream into the adjacent basins
between 2 PM and 7 PM. A few showers and storms will linger over
far northern portions of the Absaroka Mountains and Bighorn
Basin until sunset before fading. Otherwise, plenty of sunshine
with seasonal temperatures on this first Sunday of August. A
batch of mid-level cloud cover crosses the region late tonight
and early Monday morning. However, little more than virga, if
even that, is expected as the clouds progress eastward through
mid-morning Monday. However, the remnants of this moisture
combined with a shortwave traversing the Northern Rockies Monday
will reignite convection across the northwest mountains Monday
afternoon. This same shortwave will be responsible for
increasing westerly wind Monday afternoon along and west of the
Continental Divide. Speeds of 15 to 25 mph will be common. Dew
points crater across southwest Wyoming Monday afternoon as the
westerly wind transports very dry surface air into this portion
of the state. Abundant sunshine and 700mb temperatures surging
to +15C to +18C boost surface temperatures to about 3-5F above
normal. This results in single digit relative humidity for
almost the entire southern half of the forecast area. Red Flag
Warnings are in effect across southwest Wyoming, where winds
will be greatest, from 12 PM to 8 PM Monday. The overall trend
is for the warm, dry, and breezy conditions to persist through
Friday, especially across southwest Wyoming. EFI/SOT begin have
started to hint at an uptick in wind speeds Thursday/Friday.

&&

.DISCUSSION...
Issued at 230 AM MDT Sun Aug 3 2025

The H5 ridge continues to build across the greater Four Corners
region, but remaining local moisture will still bring some
showers during the afternoon. The next shortwave will be able to
tap enough remaining moisture to spark a few showers and
thunderstorms mainly for Teton and Park Counties during the few
hours around peak heating this afternoon. Some daytime CU will
also build along the Bighorns, but chances for accumulating
precip there will be minimal. The remainder of the area will see
mostly sunny skies and continued warm temperatures in the mid
to upper 80s.

After today, most of the state transitions into a drier, more
fire-weather concerning regime, as desert air pushes in from the
southwest. Shortwaves will continue to sweep around the northern
edge of the ridge, but will get pushed farther north. They will
be close enough, though, to tighten the gradient for gustier
southwest winds. Monday looking more likely for the combination
of these two for elevated to critical fire weather concerns.
Have opted to go straight to Red Flag Warning for southern WY
for Monday, as confidence in that period looks higher,
especially with humidity levels falling below 10 percent for an
extended period of the day. Tuesday is also looking very dry,
but winds currently forecast to hold back from Monday numbers,
so will not stretch the Red Flag beyond Monday.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 959 PM MDT Sun Aug 3 2025

VFR conditions are forecast over the next 24 hours. There could
be a few virga showers (and associated convective downdrafts)
overnight and Monday morning as mid-level moisture tracks east
across the forecast area, leading to weak rain showers that
evaporate before hitting the ground. This atmospheric moisture
lingers across northwest Wyoming ahead of a weather system that
moves through the Northern Rockies Monday afternoon. The
northwest quadrant of the state sees convection develop after
04/1900Z with KCOD again having the highest chance of being
impacted.

Gusty southwesterly surface winds develop for many terminals Monday
afternoon, with gusts 25 to 35 kt. These winds decrease after
sunset, but remain breezier than normal into the early
overnight hours as a upper-atmosphere weather system passes
through the state.


&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from noon to 8 PM MDT Monday for WYZ277>279-
288-289-414-416.

&&

$$

UPDATE...CNJ
DISCUSSION...Straub
AVIATION...VandenBoogart