762
FXUS65 KRIW 240430
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1030 PM MDT Sun Aug 23 2026

.KEY MESSAGES...

- Scattered showers and thunderstorms will continue this
  evening. Locally heavy rain, small hail and wind gusts up to
  50 mph will be the main threats.

- A separate area of storms looks to push in from northern UT
  between 8PM and 10PM and with a 20-30% chance of being strong
  to severe. Damaging winds up to 60 mph, lightning and locally
  heavy rain will be possible as these storms move over
  southwestern and southern portions of the state through
  midnight.

- 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
degrees warmer this afternoon than 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 thereafter 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 too 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 /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1028 PM MDT Sun Aug 23 2026

Showers and thunderstorms have weakened and will continue to
dissipate across much of the area to start of the period. VFR
conditions are expected to prevail over nearly all terminals through
the period. Winds remain light through much of the overnight into
the morning hours Monday. Winds begin to increase to 10-15 knots
ahead of the next round of convection during the early afternoon
hours on Monday. Showers and thunderstorms are forecast to begin
developing Monday afternoon and into the evening. All terminals look
to have chances for a shower or storm mainly from 19Z Monday to 04Z
Tuesday. The main concerns with any of the stronger storms will be
strong gusty outflow winds of 30 to 40 knots, frequent lightning,
and brief periods of heavy rain. MVFR to IFR conditions cannot be
ruled out especially if any storms move directly overhead a
terminal. Showers and thunderstorms should come to a gradual end by
03-04Z Tuesday. However, a few lingering showers cannot be ruled out
to the end of the TAF period but at this time there still remains
low confidence in the location and timing for these showers.
Mountains may be obscured at times to start the TAF period but
conditions should improve during the day Monday. Obscuration is
likely to return in association with developing showers and
thunderstorms Monday afternoon and evening.

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...Dziewaltowski