874
FXUS65 KRIW 090227
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
827 PM MDT Tue Jul 8 2025

.KEY MESSAGES...

- Very hot conditions with widespread 90s and some locations
  getting close to the triple digit mark Wednesday. The lowest
  elevations of the Bighorn and Wind River Basins have a 40-70
  percent chance of 100 degree highs Wednesday.

- Elevated fire weather conditions continue Wednesday. Humidity
  will be very low, but wind gusts will be limited through the
  afternoon.

- Isolated virga showers will also be possible Wednesday. Wind
  gusts of 55 to 60 mph will be the main threat from any shower
  that forms.

- Another round of showers is possible for southern WY near dawn
  Thursday morning, spreading north and east during the
  afternoon. Overall chances of any accumulation remain low. A
  trailing trough from Canada brings cooler temperatures for
  Friday.

&&

.DISCUSSION...
Issued at 100 PM MDT Tue Jul 8 2025

The current H5 ridge centered on the Four Corners will continue
to provide hot temperatures into the day Wednesday. H7 temps
will be 15 to 18C during the afternoon tomorrow, which
translates down to sfc temps in the mid to upper 90s, especially
for the Wind River and Bighorn basins. An approaching shortwave
trough will nudge down the ridge during the afternoon, bringing
enough instability for some isolated showers during peak heating
Wednesday afternoon, mainly along the highest elevations. Sfc
dry air remains low, so getting showers to the sfc will be
tough, but some gusty winds may accompany any showers. The
approach of the trough will also bring some higher wind gusts in
the afternoon, bringing a fire weather threat (see below).

The trough succeeds in chopping off the top of the ridge,
bringing some increased moisture late Wednesday night. Enough
instability comes along with the trough for some showers for SW
WY Thursday morning. The showers then spread north and east
during the afternoon. Most accumulations will remain light, so
some dry lightning could be an issue for SW WY.

Following along behind this system will be a secondary trough
dropping southeast out of Canada Thursday night into Friday.
Showers and thunderstorms will be possible along the cold front
as it sweeps south, mainly east of the Divide. The most
noticeable difference will be the change in temperature, as
highs Friday will be a good 20 to 30 degrees cooler than the
dry desert heat of Wednesday east of the Divide. The colder
temps will likely not reach south and west of the Divide, so
areas from KJAC to KRKS will again reach the lower to mid 80s
Thursday and Friday.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 354 PM MDT Tue Jul 8 2025

VFR conditions will prevail through the next 24 hours. Any lingering
shower or virga shower activity with outflow wind impacts should
quickly taper off at the start of the period. SKC and light winds
(less than 10kts) will then prevail through the rest of the TAF
period for all terminals. Wednesday afternoon, a few showers may be
possible, but should be mostly virga with gusty outflows being the
main concern.

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

&&

.FIRE WEATHER...
Issued at 137 AM MDT Tue Jul 8 2025

Widespread elevated fire weather conditions return Wednesday as
temperatures increase and critical RHs spread. Wednesday will
be the hottest and driest day, with widespread afternoon RHs 8
to 15 percent. Gusty winds will increase ahead of the next
trough, with frequent gusts reaching 20mph, with higher gusts in
the higher elevations. Red Flag Warnings currently look
unlikely, due to the lack of dry air, gusty winds above 25 mph,
and cured fuels in the same locations.

Overnight Wednesday night, the trough moves into southern WY,
bringing some scattered thunderstorms. Surface humidity remain
fairly low, so some of the lightning may occur outside of any
wetting rainfall areas.

&&

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

&&

$$

DISCUSSION...Straub
AVIATION...Hensley
FIRE WEATHER...Straub/Wittmann