246
FXUS65 KRIW 161728
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1128 AM MDT Sun Aug 16 2026

.KEY MESSAGES...

- Somewhat drier air moving into the area will bring less
  coverage of showers and thunderstorms today through Monday.

- Increased moisture should bring another more active day on
  Tuesday with more numerous showers and thunderstorms.

- Drier air returns Wednesday into Friday with only isolated
  thunderstorms expected. Above normal temperatures return
  Friday into the weekend with highs in the 90s East of the
  Continental Divide.

&&

.UPDATE...
Issued at 1125 AM MDT Sun Aug 16 2026

A mostly clear sky at the moment, with only a few clouds over
western Wyoming. The first signs of cumulus are developing over the
higher terrain and should increase over the next few hours. Isolated
showers and thunderstorms are possible today, though will be much
more limited than yesterday due to the drier air in place. Most of
this convection should be across western areas, though some should
make it into central Wyoming as well. Gusty outflows to 40 mph would
be the mostly likely hazard, though an isolated stronger gust could
occur.

&&

.DISCUSSION...
Issued at 157 AM MDT Sun Aug 16 2026

I have stated a few times before how much I hate forecasting the
monsoon. The models do not handle it well, especially in weakly
forced situations. An example is tonight where continue to have some
showers and embedded thunder in western Wyoming and stretching into
southern Idaho. No guidance had this last night, and nighttime is
where it really struggles. In this case, as has been the case
much of the previous several weeks, having as much vision of it
as Helen Keller or Stevie Wonder. So, although my confidence in
the trend of the coverage of the monsoon is fairly high,
placement and timing of any convection, especially at night, is
very low.

The general trend of the showers is down, but some will linger all
night. Most guidance does show drier is moving into the area,
especially across eastern and southern Wyoming. Precipitable water
values drop another 20 percent or so, and dew points should average
5 to 10 degrees less than yesterday. This means a lesser coverage of
showers and storms (generally no more than a 1 in 3 chance at any
point, and less then 1 in 5 at most places), and also less of a
chance of heavy rain that could lead to local flooding. For
now, we confined most POPs to the northwestern half of the
state, and I have higher confidence during the day since there
has been better model performance during this time frame. And,
with more sunshine, temperatures should be somewhat warmer. As
for tonight, most convection should end after sunset. However,
my confidence in dry overnight period is low given the terrible
performance of the models over the past few weeks with the
monsoon during the nighttime hours. I just don`t have the
confidence to pinpoint an area at this time.

Monday at this point looks fairly similar to Sunday, with mainly
isolated convection and largely across northern and western Wyoming
with less activity to the south and east. Temperatures should run
fairly similar to Sunday. Some guidance is giving a surge of
moisture at night and possible increase in activity but guidance is
split. This, plus the models weakness in nighttime monsoon
convection, confidence is low. With precipitable waters around 125
to 150 percent of normal on Tuesday, this also looks like a
more active day with temperatures close to seasonal averages.

There has been a bit of a change for Wednesday, and there is decent
model agreement on this. It is that most show drier air moving in
from the southwest and lessening the chance of showers and
thunderstorms, with the best chance across eastern Wyoming. The
drier pattern looks to hold at least into Friday with near normal
precipitable water across the area and high pressure building
northward out of the desert southwest. The forecast for Friday
is probably the wettest it would be. Monsoonal moisture may
increase again for next weekend, but timing this far out is
uncertain. And with the ridge building northward again,
temperatures will be on the rise again. Highs will begin to
rise again on Thursday. By Friday and into next weekend, highs
in the 90s look fairly commonplace East of the Divide and in the
80s West of the Divide.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1126 AM MDT Sun Aug 16 2026

VFR conditions are generally expected through the period. The main
aviation concern continues to be convection chances this afternoon
and evening. This could bring brief heavy rain and MVFR conditions
to terminals through sunset before chances decrease. The more
widespread impact is likely to be outflow winds gusting 30 to 40
knots. Lighter winds and decreasing clouds are expected overnight
with VFR conditions then prevailing through the end of the period.

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...Hattings
AVIATION...Myers