655
FXUS65 KRIW 232155
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
355 PM MDT Sun Aug 23 2026

.KEY MESSAGES...

- Monsoonal moisture continues this afternoon and evening but
  not as widely scattered as Saturday with localized flooding
  possible in the strongest storms.

- Strong to severe storms possible (30-40%) looking more like
  the evening time frame after 6PM with a line of storms from
  Idaho capable of producing damaging winds up to 60 mph.

- Monsoonal moisture will linger much of the week, with a chance
  of showers and thunderstorms each day. Temperatures will be
  closer to seasonable for this time of year nearing the end of
  August.

&&

.UPDATE...
Issued at 1200 PM MDT Sun Aug 23 2026

Much more ample sunshine across the CWA for the noon update as
compared to yesterday. As such, temperatures will be a couple
degree warmer this afternoon as Saturday afternoon as well.
With better mixing, there will be a stronger breeze to go along
with it as well gusting up to 25-30 mph at times outside of any
storm activity and outflow winds. Nothing on radar currently but
HiRes data is still pinpointing development by 2-3PM off
leeside of the Absarokas and pushing in from the south off the
Uintas for Sweetwater County. Much of this activity will be
isolated in nature compared to yesterday`s showers but expect
lightning and a brief outflow over 40 mph with its eastward
progression through the evening. With this, PoPs have been
adjusted and especially after the CRON wiped out the night
shift`s work to account for this heading into the evening hours.

This is where it will get a bit more interesting at least for
Wyoming standards. A line of storm activity looks to form from
southern Montana and across eastern Idaho by 6-7PM before
pushing east into western Wyoming shortly there after along and
ahead of the cold front. This will track through the CWA by
Monday morning. SPC continues with the Marginal Severe Risk,
with an introduced Slight to the southwest portions of the
state to include hatched wind. This looks to be overdone, even
though damaging winds are possible up to 60 mph from the
outflows ahead of the front. The instability with DCAPE values
less than 500 J/kg just don`t look to impressive as it nears
radiational cooling towards sunset. There might be an hour or so
before darkness, but the FROPA will be later further south for
the CWA with its positive tilt and progressive eastward push.
Stronger winds than that don`t look great in the least but
something to keep an eye on between 6-10PM west of the Divide.
Beyond that as it makes its way to the east after midnight, the
juice of the storms will be lost with mainly shower activity in
its wake. The cold front will push the warmer moist air south
and southeast.

Beyond that, status quo, as the monsoonal pattern continues but
to a bit lesser extent. Temperatures behind this aforementioned
cold front will bring afternoon highs closer to seasonable for
this time of year ending the month of August with 80s east of
the Divide even into next weekend.

&&

.DISCUSSION...
Issued at 226 AM MDT Sun Aug 23 2026

It was a typical monsoon day yesterday, with some areas, mainly in
southwest and in Johnson and Natrona Counties getting a LOT of rain,
causing some local flooding. Other areas saw nothing. And we
continue to have some showers and embedded thunder around late
tonight, although intensity is significantly less. And these will
continue through the night, gradually becoming weaker and less
numerous.

We will have another round of showers and storms today. There are
some differences. For one, precipitable water values are less today
by about 20 percent in most locations. This should bring less
coverage and somewhat lesser rainfall rates. The other difference is
that there will be more steering flow today,  generally about 10 to
15 knots at 700 millibars and 25 to 35 knots at 500 millibars. So
storms should have more movement. This should decrease the chance of
flooding somewhat. We still have an excessive rainfall outlook
across most ares West of the Divide though, so the threat is
still there. There is also the risk of strong to severe
thunderstorms. Most of the area is under a marginal risk of
severe weather today. There could be some small hail, but this
not the main risk. The main risk looks to be strong wind gusts.
Roughly north and west of a Buffalo to Riverton to Lyman line
has a Conditional 1 outlook for wind, or possible convective
wind gusts to 75 mph. Soundings do show some inverted V
profiles, especially across northwestern Wyoming where the
surface will be drier, with low and mid level lapse rates close
to 9 C/Km. This could lead to some strong downburst winds later
today. Again, the best chance would be across the northwest but
most areas will have a chance. And, like previous nights, most
convection should end after sunset but a few showers and storms
will likely linger through the night. As for temperatures, they
should be a few degrees warmer than yesterday with more sunshine
expected.

The rest of the week looks like more of the same as the annoying
monsoonal moisture will hang around the area through at least
Thursday and possibly into Friday as well. The models continue to
have different ideas on which day will be more active with no real
well defined shortwaves with changes from day to day. Precipitable
water generally average about 125 to 150 percent of normal through
the period though. So, at this point we went with a generic solution
of mainly diurnal showers and storms each afternoon. Temperatures
should remain fairly similar through the period, not very hot but
averaging around 4 to 8 degrees above normal on average, with the
possibility of a cooler day if there is more cloud cover than
expected. Drier air may then work in for next weekend and bring a
return to drier weather but uncertainty remains high on the exact
timing. So, all in all, it continues to look like more of the same
as the summer of the monsoon lives on in western and central
Wyoming.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 355 PM MDT Sun Aug 23 2026

Most showers and thunderstorms end through about 03z. Lingering
chances continue overnight for southwestern Wyoming, including KBPI,
KPNA, and KRKS and should be done by sunrise, if not sooner. Outside
any convection, winds lessen overnight, following typical diurnal
trends. Isolated showers and thunderstorms are again possible Monday
afternoon.

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.

&&

$$

UPDATE...Lowe
DISCUSSION...Hattings
AVIATION...Wittmann