171
FXUS65 KRIW 270421
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1021 PM MDT Sun Jul 26 2026

.KEY MESSAGES...

- Isolated to widely scattered showers and thunderstorms become
  decrease in coverage this evening. The best chance for the
  showers and storms remains over the north-half of the state
  where a few storms could be strong (wind gusts around 50 mph).

- Smoke will begin to filter into the state this week from
  wildfires to the west and southwest.

- Moisture from the southwest continues to stream northward into
  Wyoming through at least Wednesday, allowing for little
  change in the cadence of afternoon and evening showers and
  thunderstorms. Temperatures remain above normal.

&&

.UPDATE...
Issued at 1222 PM MDT Sun Jul 26 2026

Moisture continues to spread northward across Wyoming as it
rotates around high pressure anchored over the southern Rockies.
There is little, if any, change in this pattern over the next
several days. A shortwave within this southwest flow aloft will
track across southern Montana Sunday afternoon and evening.
Scattered showers and thunderstorms erupt across mainly northern
Wyoming by 2 PM Sunday and progress east through the afternoon.
Many locations will see a downturn in convective coverage by 7
PM Sunday, while locations over north-central Wyoming see the
convection linger until 9-10 PM Sunday. Latest 18Z KRIW sounding
shows 0.81" of precipitable water, well-above average, but much
of it is concentrated above 550mb. Therefore, as we saw
Saturday, brief downpours are possible with the thunderstorms.
However, again given high-based convection and a dry sub-cloud
layer, the primary hazard will be gusty outflow wind 40 to 50
mph. SPC has our northern-tier of counties highlighted within a
marginal risk for severe wind gusts. A secondary shortwave works
its way north from Utah Sunday evening and overnight leading to
intermittent light showers across the far south and eventually
western portions of the forecast area through sunrise Monday.
Increased mid/high-level cloud cover associated with this wave
should help drop Monday highs a few degrees, while possibly
delaying the onset of scattered showers and thunderstorms until
closer to mid-afternoon Monday.

&&

.DISCUSSION...
Issued at 249 AM MDT Sun Jul 26 2026

The overall pattern across the western US remains relatively
unchanged today, with the H5 ridge centered over the Four
Corners, and WY along the northern periphery of the ridge. Above
normal temperatures remain in place across the state under the
ridge, with record to near-record highs again expected today.
The Heat Advisory remains in place for the lower elevations of
central and northern WY for the continued heat and the very warm
overnight temperatures. Monsoon moisture continues to wrap
around the northern edge of the ridge into NW WY, which will
bring another round of showers and thunderstorms. Storms again
will initially form on the higher elevations of the western
mountains and move to the northeast. Storms will have good
forward motion again, so this will minimize the overall flooding
threat. Strong Inverted-V profile indicates main thunderstorm
threat will be gusty winds, possibly gusting above 50 mph,
especially across northern WY where the T-Td spread will be
greatest.

Longer term models show nearly no change in this pattern the
entire week, with the H5 ridge holding fast across the Southern
Rockies. This will keep the heat in place, with the daytime
thunderstorms each afternoon for NW WY. An embedded shortwave
races around the northern edge of the ridge on Wednesday, which
could bring an enhancement of the thunderstorms for more of the
state.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1015 PM MDT Sun Jul 26 2026

Chances for light, weak showers will continue over southern
portions of the forecast area to start the TAF period, as a
moist, southwest flow brings another moisture surge northward
through the rest of the night. These showers will spread
northward over the western mountains between 10Z and 13Z. Gusty
outflow wind around 35kt will be possible through the rest of
the morning with these showers. This moisture then serves as
the fuel for another round of diurnal convection beginning
around mid- afternoon Monday. Many terminals see wind less than
10kt, outside of convection, until late Monday afternoon when
convective outflows occur.

The showers over the western mountains will spread east into the
central basins and other points east of the Divide late in the
morning into early afternoon. Additional thunderstorms look to
develop over the Upper Green River Basin and southern portions
after 21Z and move toward the northeast into the evening. Will
keep the current PROB30 groups that are already in place, as
widespread convection is still expected during the afternoon.
This may change depending on how the morning showers impact the
afternoon convection.

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

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 9 PM MDT this evening for WYZ003>006-010-
011-017-018-020.

&&

$$

UPDATE...CNJ
DISCUSSION...Straub
AVIATION...LaVoie/CNJ