973
FXUS65 KRIW 300839
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
239 AM MDT Sun Aug 30 2026

.KEY MESSAGES...

- Fewer showers and thunderstorms around today then yesterday.
  The most numerous will be in southern Wyoming where locally
  heavy rain and flooding remains a possibility.

- Monday looks drier for most, with deeper moisture and
  increasing chance of showers and storms late in the day and at
  night, especially in southern and western Wyoming.

- Monsoonal moisture remains over the area through the week.
  There will be some drier days, but which days will be drier
  remains somewhat uncertain, especially Wednesday and beyond.

&&

.DISCUSSION...
Issued at 236 AM MDT Sun Aug 30 2026

Another night is upon us and, once again, it is more monsoonal
activity with some showers and isolated storms scattered through the
area, although as I write this around 1 am most are west and south
of Wyoming. These will continue through the night as well as this
morning. And the main story for the next seven days will be, once
again, the ebbs and flows of the monsoon, although we also have
something else to talk about.

For the next 24 hours we have two concerns. The first concerns the
convection. Overall, things looks somewhat less active today. Most
guidance does show drier air spreading across much of the area from
west to east starting this morning, but especially so this
afternoon and evening as a cold front and trough move through the
area. It could end up being below normal for the
first time in a while across most of the area. There will still be
one area of concern though, and that is largely south of a Casper to
Evanston line. Moisture will linger here and so will the chance of
heavy rain. Precipitable water remains around 150 percent of normal
here. especially in southern Sweetwater County which has a slight
risk of heavy rainfall, with a marginal chance further north. The
main mitigating factor again is that there are decent low to mid
level winds so the storms will be moving, so any threat of local
flooding would be from training convection. Further north, the main
threat from storms would shift to strong wind gusts, as we have
larger dew point depressions, higher cloud bases, steep lapse rates
as well as inverted V soundings. This should also be an earlier
show, as most guidance shows the dry air making all the way to the
southern border, and this should bring a dry period from late
tonight to Monday morning. And, with the threat of heavier rain
ending further north, we will likely cancel the flood watch sometime
this morning.

The other concern is the coolest temperatures so far this season.
There will be cooler air moving in behind the front, with lows
falling into the 30s for many. The question is the concern for a
frost or freeze. Temperatures have trended a bit warmer this
morning. The only lower elevation locations with a greater than 2
out of 5 chance of lows below 32 degrees is the northern Jackson
valley and around Bondurant. As for 28 degrees of below, the chance
is less than 1 out of 4 everywhere. So, we will not issue a freeze
watch at this time. If we still issued frost advisories, I would
have considered one though. Just about all locations will have the
coolest night they have seen in a while.

Monday should start dry. However, the monsoonal moisture will begin
pushing northward again, and once again increase the chance of
showers and thunderstorms, especially in southern and western
Wyoming. It may take a while to arrive though, with the deepest
arriving after sunset. This may limit heavy rain potential somewhat
with the lack of instability, despite precipitable water values once
again rising to over 150 percent at times, especially in southern
Wyoming. And with southwest flow returning, warmer temperatures will
returning to somewhat above normal levels.

The rest of the forecast period is again dependent on the movement
of the monsoonal moisture. At this point, Tuesday looks to be more
active with above normal precipitable waters and a shortwave moving
through the area. Wednesday or Thursday could then be less active
as drier air moves in from the west with another uptick in
convection for Friday and into the weekend. However, the models
have been terrible in predicting these ups and downs in the
monsoonal moisture so may confidence in timing the surges of
moisture is low at best. With the southwest flow continuing,
temperatures will remain above normal. With the center of the
ridge possibly retrograding back to the west toward next
weekend, it could get quite warm again with highs in the 90s
possible for the upcoming holiday weekend. So, it continues to
more of the same with the monsoon continuing to dominate the
weather conversation.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 945 PM MDT Sat Aug 29 2026

Conditions remain dry for most locations to start the forecast,
with the exception being a line of showers and embedded
thunderstorms moving over far western portions. These showers
will move eastward through 12Z, with a greater focus shifting
southward over the Upper Green River Basin and KBPI/KPNA.
Minimal impacts are expected (apart from lightning) with
marginal VFR conditions. Showers will become widespread across
western portions of the state after sunrise. The area of showers
over the Green River Basin and the other developing over
northwestern portions as a trough and associated cold front
begin to move over the area. Showers and storms will not be as
widespread through the afternoon, mainly impacting KBPI, KPNA,
KCOD, and KRKS, as drier air quickly filters into the area
behind the cold front and any convection ending by 00Z. With
any of this activity, brief heavy rain and low clouds may lead
to occasional MVFR conditions. The more widespread impact
continues to be strong outflow wind gusts of 30 to 40 knots
Sunday afternoon. Low clouds will lead to frequent mountain
obscuration through the period, especially across western
Wyoming through 18Z Sunday. Confidence is low for fog in the
western valleys Sunday night with skies clearing Sunday
afternoon. This could change if showers move over the valley
later tonight.

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...
Flood Watch until noon MDT today for WYZ001-002-012>014-023-
024.

&&

$$

DISCUSSION...Hattings
AVIATION...LaVoie/Myers