485
FXUS65 KRIW 291115
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
515 AM MDT Fri Aug 29 2025

.KEY MESSAGES...

- Another comfortable day with isolated to widely scattered
  shower and thunderstorm chances (up to 70%) along and east of
  the Divide and across southern Wyoming today. Isolated periods
  of heavy downpours are possible across Johnson County.

- Isolated to widely scattered shower and thunderstorms chances
  (up to 70%) again on Saturday. The greatest chances (60%-70%)
  are across Johnson and Natrona Counties.

- A warmer and drier trend looks more favorable Sunday through
  at least Wednesday of next week.

&&

.DISCUSSION...
Issued at 224 AM MDT Fri Aug 29 2025

An upper-level ridge extending from New Mexico to the Pacific
Northwest and an upper-level low over eastern Montana, both evident
on 08Z water vapor imagery, will be the main players for our weather
today and Saturday. There is consensus that the upper-level ridge
will continue to build west of Wyoming today as the low expands into
into the Dakotas. This leaves Wyoming in deep west to northwest
flow. Two separate areas of increased support aloft, vorticity
maxima, will be present today. One area will be across southern
Wyoming and the other is associated with the upper-low for areas
along and east of the Divide. Thus, these will be the areas of
interest today for scattered showers and isolated thunderstorms.

The greater deep moisture will be associated with the upper-level
low so areas along and east of the Divide have a greater chance (40%-
70%) at seeing more rain shower activity through the day. Brief
periods of heavy downpours are possible across the aforementioned
area, however, the chances of widespread rain amounts over 0.10" are
overall less than 30%. The exception is east of the northern Bighorn
Mountains (Johnson County), where moisture is greatest (mean PWATs
around 1.0") and northerly low-level flow favors upsloping. There is
a 60%-80% chance of at least 0.25" today and tonight for the
aforementioned area. Across southern Wyoming, shower and thunderstorm
chances (15%-30%) are much lower compared to the northern half of
the state and will likely be more isolated in nature and diurnally
driven. Dewpoint depressions across southern Wyoming peak around 40
degrees F, so isolated 40 mph gusts cannot be ruled out during the
afternoon. Temperatures across the area are forecast to be slightly
below to near normal (70s).

A somewhat similar pattern is forecast again on Saturday, with the
only difference being that the upper-level ridge builds and shifts
east into Wyoming. This ultimately will keep shower and thunderstorm
chances widely scattered along and east of the Divide. Temperatures
on Saturday are forecast to be similar to today with more sunshine.

Ensemble guidance remains in consensus that the upper-ridge will be
over Wyoming with high pressure at the surface Sunday through much
of next week. With limited moisture, dry weather and near to
slightly above normal temperatures look to return, despite weak
disturbances aloft each day. The day that could be the exception is
Wednesday. There are indications that on Wednesday there could be a
slight uptick in available moisture along a frontal boundary for
areas along and east of the Divide. However, it is unlikely that we
will see any substantial precipitation with this system at this time.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 448 AM MDT Fri Aug 29 2025

Fog looks to be developing near KJAC to begin the period this
morning. Expect VLIFR/LIFR conditions through 16Z/17Z if it does
reach the terminal. Fog is again possible around KLND and
KRIW but has yet to develop. Will leave VCFG in the forecast for
now. Otherwise, VFR conditions are expected through the rest of
the TAF period. Isolated showers will occur across Sweetwater
County after 18Z, but are not expected in the vicinity of KRKS
until 00Z. Showers and isolated thunderstorms will also impact
KBYG by 21Z. Isolated showers will be possible across areas east
of the Divide after 00Z, possibly impacting KCOD through 03Z.
Showers will be possible at KWRL and KCPR by 05Z and 09Z,
respectively.

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...
None.

&&

$$

DISCUSSION...Gerhardt
AVIATION...LaVoie/Hattings