387
FXUS65 KRIW 070153
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
753 PM MDT Sun Jul 6 2025

.KEY MESSAGES...

- Warmer temperatures Monday through Wednesday with an
  increasing chance for elevated fire weather conditions due to
  gusty southwest wind and low relative humidity.

- Very hot conditions with widespread 90s and some locations
  getting close to the triple digit mark Tuesday and Wednesday.
  The lowest elevations of the Bighorn and Wind River Basins
  have a 30-50 percent chance of 100 degree highs Wednesday.

- A 20-40 percent chance of thunderstorms returns Thursday
  afternoon and evening, especially along and east of the
  Continental Divide.

&&

.UPDATE...
Issued at 1216 PM MDT Sun Jul 6 2025

No major updates to the forecast with the afternoon update. Hi-res
models continue to depict virga or weak storms forming across
Sweetwater, Natrona, and Johnson Counties for the latter half of the
afternoon through the evening. Any of these could produce a 50 to 55
mph outflow gust; these gusts would be more likely in Sweetwater
County, (generally along and south of I-80) where drier air is in
place. Showers/storms linger longest around Johnson County, and
should be done around midnight. Some models do keep reflectivity in
a little longer.

&&

.DISCUSSION...
Issued at 120 AM MDT Sun Jul 6 2025

Isolated showers have gradually ended over eastern portions of the
CWA this morning. Mostly clear skies are in place elsewhere away
from this activity. There is a low chance (20%) for low clouds to
develop around Casper between 10Z-14Z. One of the aspects against
this will be sfc winds turning to the west-southwest after sunrise.
The passage of Saturday`s shortwave will mark the end of the latest
active weather pattern, as drier air moves into the region. Flat
ridging will be in place today, with the front from Saturday night
washing out through the day and keeping daytime temperatures similar
to Saturday. Conditions will be mostly dry across the area
today, with Casper being an exception once again. A shower
and/or thunderstorm looks possible between 22Z-01Z over southern
Natrona County, including the Casper area and Casper Mountain.
Wind gusts up to 55 mph and small hail would be the likely
threats. Isolated virga showers will also be possible over
southern portions of Sweetwater County, with wind gusts up to 55
mph also possible.

Otherwise, the focus will shift to fire weather for the first
half of this week, as an upper level ridge builds over the
region from a strengthening high center over the Four Corners.
Winds look to remain light through Wednesday with mostly dry
conditions. A weak, shallow back door cold front will push
through Natrona County and the Wind River and Bighorn Basins
after sunset Monday evening, turning winds easterly in its wake.
The front will stall and wash out by sunrise Tuesday morning.
The warming trend will continue Tuesday, with 90 degree
temperatures returning for areas east of the Divide as well as
across portions of Sweetwater County. Several locations east of
the Divide could reach 100 degrees Wednesday, including
Greybull, Worland, Thermopolis, Casper and Riverton. The GFS
extended MOS guidance is forecasting 100 degrees at Riverton and
Greybull.

The next chance for precipitation looks to occur Thursday, as a
trough digs southward from Canada over MT. The previously discussed
remnant low will speed up and reach the Cowboy State Thursday
morning and eventually get absorbed by the incoming trough. This
could result in isolated showers early Thursday morning. This trough
would lower temperatures a bit and cause the high to retreat further
south. Moisture return looks to be confined over northern portions
at this time, with Johnson County having the best chances for
precipitation. Additionally, strong northwest winds could hit
northern Johnson County, including Buffalo, in the wake of the cold
front associated with the trough. No strong wind signatures are
evident yet, but gusts of 50 to 60 mph could occur as this would be
common with these kinds of fronts. There could also be a
significant reduction in temperatures Friday morning as a result
of this front.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 519 PM MDT Sun Jul 6 2025

Daytime cumulus along with weak convection near KCPR and KRKS
will fade between 02Z-04Z/Monday, with VFR conditions through
the night. Some lower clouds may develop at KCPR around sunrise,
but should stay above MVFR limits. Skies will be mostly clear
Monday, with no showers expected at terminals. Winds east of the
Continental Divide will be light from the north, while winds
west of the Divide blow from the west and have occasional gusts
near 15kts Monday afternoon.

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

&&

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

&&

$$

UPDATE...Wittmann
DISCUSSION...LaVoie
AVIATION...Straub