495
FXUS65 KRIW 091041
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
441 AM MDT Wed Jul 9 2025

.KEY MESSAGES...

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

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

- Isolated virga showers will again be possible. 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 and western
  WY tonight. Some of these could reach areas east of the Divide
  Thursday morning. Overall chances of any accumulation remain
  low.

&&

.DISCUSSION...
Issued at 157 AM MDT Wed Jul 9 2025

The anticipated hottest day of the week has finally arrived. The
ridge that has been in place since Monday will continue its eastward
shift eastward this morning over the Cowboy State. 700mb
temperatures will be slightly higher today, ranging between 16C to
19C. 90 degree temperatures will be widespread once again, with
portions of the Bighorn Basin approaching 100 degrees. Winds
continue to look marginal for any fire weather highlights, however
gusts over 25 mph will occur at times (between 21Z and 00Z) over
areas with critical fuels. The atmosphere should be capped for most
areas, however isolated virga showers will be possible again in the
afternoon into the evening. Sweetwater County continues to look the
most likely location at this time, due a lead shortwave that will
move over the county from northern UT. Chances for these showers
will begin to increase after 21Z and move out of the area through
06Z Thursday. Wind gusts of 55 to 60 mph will again be possible, due
to the inverted-V sounding profiles in place.

A remnant low will approach the area through the overnight hours
Wednesday night, as it moves over southern ID. The aforementioned
lead shortwave will be ahead of this system. Increasing chances for
showers and isolated thunderstorms will become possible over western
portions after 06Z. Lightning chances are low, due to a lack of
moisture that is reflected in CAPE values of 100-200 J/kg.  These
chances for precip quickly spread east of the Divide by 09Z,
heading to the east-northeast. Precipitation chances associated
with this wave will exit Johnson County after 15Z, with
additional showers possible over Johnson and Natrona counties
through the afternoon. Little to no rain is expected from this
activity today and Thursday, due to a lack of moisture.
Temperatures will be about 10 degrees cooler across the CWA
Thursday as a result of the passage of this remnant low lowering
heights and suppressing the Four Corners high to the south (the
high will retrograde over the Desert Southwest at the same
time). Fire weather conditions will remain elevated as well, but
critical RH values will be isolated and confined to Sweetwater
County.

As expected, the timing from the trough dropping south from Canada
has slowed down and now looks to reach the MT/WY border Friday
morning. Any precipitation looks to be confined to northern portions
through the day Friday. Highs in the 70s east of the Divide is still
in the forecast, while areas west of the Divide stay in the low to
middle 80s.

Dry conditions then return for the weekend, with seasonal
temperatures on Saturday and highs in the 90s return for areas east
of the Divide on Sunday. Showers and thunderstorms could be possible
over far northern portions Monday afternoon, as another trough
drops south from Canada/British Columbia.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 428 AM MDT Wed Jul 9 2025

Mainly VFR conditions throughout the period for all TAF sites.
Winds and upper level clouds will increase for all locations
after 18Z to 20Z with daytime heating and mixing to the
surface. Most locations will gust up to 18 knots with KRKS the
highest, peaking close to 25 knots. Any shower activity will be
limited and not expected on station, but KRKS will have the only
real shot from a stray one and random stronger gust of wind in
the late afternoon/evening. The chance is less than 1 out of 6
though so we will not include in the TAFs at this time. Winds
will diminish after 01Z-02Z with nighttime cooling once again.
However, a couple models are indicating a stronger wind gusting
up to 30 plus knots at KLND after 03Z that are of higher
reliability. An approaching area of low pressure will bring the
chance of showers (about 1 in 4 to 1 in 3) to KRKS, KBPI and
KPNA after 05Z tonight. A few showers may spread East of the
Divide after 08Z but less confidence here. With the chance of
thunder, we have gone with a PROB30 group for KRKS, KBPI and
KPNA.

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 157 AM MDT Wed Jul 9 2025

Widespread elevated fire weather conditions continue as
temperatures remain hot critical RHs spread with values of 6 to
15 occurring across the area. Gusty winds will increase this
afternoon, with frequent gusts reaching 20 mph, with higher
gusts in the higher elevations. Red Flag Warnings continue to
look marginal due to gusty winds above 25 mph being isolated over
critical zones. Gusts of 25 to 35 mph will occur over zones 140
and 286 through the afternoon. Isolated virga showers will
remain possible this afternoon, with zone 279 having the best
chances. Gusts of 55 to 60 mph could occur with the showers.

&&

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

&&

$$

DISCUSSION...LaVoie
AVIATION...Hattings
FIRE WEATHER...LaVoie