603
FXUS65 KRIW 241108
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
508 AM MDT Sun Aug 24 2025

.KEY MESSAGES...

- Coverage of showers and thunderstorms increases today as
  monsoonal moisture increases from the south.

- Storm coverage increases for the next few days, with Wednesday
  or Thursday looking like the days of greatest coverage.

- Local flooding may be possible with some of these storms, with
  the best chance of this on Wednesday and Thursday.

&&

.DISCUSSION...
Issued at 225 AM MDT Sun Aug 24 2025

The weather is mainly quiet across the area covered by the humble
Riverton weather abode. We only have a few virga showers at this
time. This will not last though as precipitation chances will be on
the upswing as we head into the next week.

Monsoonal moisture will be on the increase from the south today.
However, the models trend to rush it in by around a day. In
addition, it usually comes in aloft at first in the mid and high
levels. So, although there will be an increased coverage of storms,
with the best chance across the southern Wyoming (as much as a 2 in
5 chance later this afternoon), we kept QPF under a tenth of an inch
for most part. If there is a spot that could get more, it looks to
be far southwestern Wyoming where the moisture will deepen the
fastest. Chances generally taper East of the Divide, where the
chance is 1 out of 5 at most with most areas seeing nothing.
Temperatures should run close to normal and fairly close to
yesterday`s highs. Storms should decrease tonight, but some showers
may linger through the night.

Coverage of showers and storms, and the chance of rain, possibly
excessive then really increases starting Monday as the moisture
layer begins to deepen. Reasoning on the timing remains fairly
similar to yesterday`s forecast remains the same. For Monday and
Tuesday, the most numerous storms look to be largely West of the
Continental Divide, with precipitable water values rising as high as
150 to 175 percent above climatological normals. In areas East of
the Divide, values remain near to below normal on Monday before
increasing on Tuesday as moisture begins spread eastward. The most
numerous showers and storms still look to be on Wednesday and
Thursday as the core of the moisture moves over the area. At this
point, which day is the wettest is still in question as there is
still some spread. Most guidance agrees on Wednesday bring wet, with
some areas seeing precipitable water values climbing as high as 200
percent of normal, possibly increasing the chance of localized
flooding. There is more spread on Thursday as some guidance,
especially the GFS, is showing drier air pushing in as flow turns
more westerly as opposed to southerly, dropping precipitable water
values back to near normal levels. This has not been consistent
though and I am not buying it yet. Most guidance then shows a drying
trend starting Friday and into next weekend as ridging slowly builds
across the northern Rockies.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 508 AM MDT Sun Aug 24 2025

VFR conditions prevail through the period. Increasing moisture from
the southwest brings increasing middle and upper level clouds, as
well as shower and thunderstorm chances. These chances will
primarily be be around KBPI, KPNA, and KRKS today, with lesser
chances elsewhere. Currently, chances look to be best at KRKS, where
a PROB30 group is included. Smoke will also be around again today,
coming from various wildfires around the area.

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 Monday for WYZ014-025-026.

&&

$$

DISCUSSION...Hattings
AVIATION...Wittmann