887
FXUS65 KRIW 201106
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
506 AM MDT Wed Aug 20 2025

.KEY MESSAGES...

- Wednesday will see near record high temperatures as high
  pressure continues, with some locations east of the
  Continental Divide hitting 100 degrees.

- Northwest Wyoming will have a slight chance (10-20%) of
  showers in the morning, with isolated showers and
  thunderstorms in the afternoon. Any convection that wanders
  east into the Bighorn Basin could be capable of generating
  erratic outflow wind gusts of 40 to 50 mph.

- A cool front early Thursday morning returns daytime high
  temperatures to more seasonable levels Thursday and Friday,
  with increasing chances of showers and thunderstorms. Far
  west-central Wyoming may remain very warm and dry with gusty
  west winds in the afternoon.

- There are early indications that a potential surge of moisture
  from the southwest could reach the forecast area early next
  week.

&&

.DISCUSSION...
Issued at 130 AM MDT Wed Aug 20 2025

WV imagery continues to show the weak confluent upper level flow
across the CWA. Mainly clear on IR and nothing on radar to speak
of through much of Wednesday morning to early afternoon. Record
high temperatures to be had once again east of the Divide
especially for Wednesday afternoon under mainly clear skies and
relatively weak winds throughout the entire day. Some weak rain
showers and an isolated thunderstorm are possible (10-15%)
across northwestern portions of the state for Yellowstone and
Absarokas with more of an alignment with the Hi-Res models.
These should mostly push out of northeastern portions of Idaho
by 1-2PM and spread east and northeast through the afternoon
hours. The main hazard of note will be frequent lightning and
ignitions of more fires. Gusty outflow winds should be at bay as
forecast sounding show weak DCAPE values not seeing anything to
mix down more than 20-25 mph as the best possibility. Otherwise,
this activity will weaken after 6PM towards sunset and move out
of the CWA with a quiet overnight into Thursday morning.

Thursday will see a breakdown of the upper level high near the
Four Corner Region weakening due to decreased convergence aloft.
This will allow a shortwave to push off the GOA low and skirt to
the north of the CWA through MOntana. With the bulk of the
energy north, there will still be an uptick in storm activity
increasing through the weekend but remaining isolated to widely
scattered throughout. Some induced ridging will keep activity a
bit more isolated for Saturday afternoon.

The main upper level ridge will break down and weaken even
moreso come late Sunday and into early next week. This will
allows for a series of shortwaves to push through the upper
Rockies from the L/W trough off the west coast with increasing
divergence aloft and upper level moisture of monsoonal
advection. There is still quite a bit of disagreement to be had
with model consistency this far out in time, but the EC that
handles the longer solutions more consistently keep the ridge
more in place to block much of the activity to the west. In
other words, stay tuned for updates in the coming days as it
will change on a daily basis from one model run to the next.

In all, heat and mostly dry today before a more active and
"cooler" pattern (more seasonable) pushes in to end the work
week through the weekend and into next week.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 506 AM MDT Wed Aug 20 2025

VFR conditions prevail through the TAF period. Smoke from wildfires
will continue to be around KCOD and KWRL through the period.
Showers/storms or virga are possible (10%-25% chances) over
northwest Wyoming this afternoon and evening. There are 10% to 15%
chances at KJAC and 15% chances at KCOD between 17z and 03z. Another
day of hot temperatures keeps highs near or above 90 degrees for all
sites; cooler temperatures starting Thursday.

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...
Air Quality Alert until 1 PM MDT this afternoon for WYZ003>008.

&&

$$

DISCUSSION...Lowe
AVIATION...Wittmann