724
FXUS65 KRIW 290928
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
328 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 /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 948 PM MDT Thu Aug 28 2025

VFR conditions are expected for all TAF sites most of the night.
A few showers may occur in vicinity of KCOD, but conditions are
expected to remain VFR. Fog is again possible around KLND and
KRIW tonight. We have elected to go with vicinity for now as it
is not a certainty. The most likely time would be from 11Z
through 16Z Friday.Largely VFR conditions are expected on
Friday. Isolated convection is possible again in the northern
TAF sites (mainly in vicinity of KWRL and KCOD) but the chance
is much less than today, mainly less than 1 out of 3 at any spot
so we have elevated to go with PROB30 groups for now rather
than prevailing.


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...Hattings