237
FXUS65 KRIW 220744
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
144 AM MDT Wed Jul 22 2026

.KEY MESSAGES...

- The monsoon peaks today with numerous showers and
  thunderstorms expected, with the possibility of local
  flooding. The best timing at this time is mainly afternoon in
  the west, and the afternoon and evening East of the Divide.

- The chance of thunderstorms and heavy rain continues Thursday,
  although coverage should be less, especially in western
  Wyoming.

- Hot temperatures return for Friday and the weekend. Friday
  looks mainly dry, with a better chance of showers and storms
  returning for the weekend.

&&

.DISCUSSION...
Issued at 140 AM MDT Wed Jul 22 2026

The monsoon is now completely over us. Not everyone saw rain today,
but a lot of locations, especially West of the Divide, has some, and
a good amount in some locations. See still have some showers and
embedded thunder tonight but the general trend for the night is
down. However, showers will continue for much of the night.

The main event with the monsoon still looks to be today. The
headliners in the monsoonal movie remain the same. The leading actor
is obviously the monsoonal moisture. The guidance for the expected
precipitable water has dropped just a bit today, but it is still
very high. It now maxes out at around 1.50 inches, down from 1.61
yesterday. However, it has been running a bit hot by about 15 to 20
percent. So, in reality, the maximum, would be closer to 1.25 to
1.35. However, this is still more than 200 percent of normal. The
supporting actor (or actress) is a shortwave moving in from the west
that will move into Wyoming this afternoon and evening. This will
help give everything a little more lift of the synoptic variety and
help enhance rainfall rates even more. We continue to have most of
the area under a slight risk of excessive rainfall. With this, we
will continue the flood watch as is for now. As for general timing,
western Wyoming would see a vast majority of the activity through
sunset. East of the Divide, it would be a later show, starting in
the afternoon and then continuing well into the evening before
coverage lessens after midnight. Watch for flooded roads, and always
remember: Turn around, don`t drown!

There will be one more day of concern across the area on Thursday.
Precipitable waters remain rather high on this day as well. However,
they do drop about 20 percent East of the Divide and around 30
percent West of the Divide. However, values are still between 150
and 200 percent of normal, so some flooding is still possible,
although not as likely as today. The Excessive Rainfall Outlook has
not really changed, with a vast majority of the area still in a
Marginal risk. One change is that the far southwestern portion of
our area is now out of it. We still expect the majority of the
activity to be in areas East of the Divide. As for the flood
watch, we will leave it alone for now, but it may need to be
extended, especially for areas East of the Divide. Most activity
should end shortly after sunset, but a few showers again may
linger after midnight.

The break finally comes in on Friday as some much drier air pushes
across most of the area. Precipitable water values finally fall
under one inch across much of the area, although still somewhat
above normal. The chance of convection is not zero on this day,
although less than 1 out of 4 for all areas. However, it will come
with a side effect. One benefit of the deeper cloud cover is
temperatures have cooled somewhat. However, we still have ridging
over us and with 700 millibar temperatures climbing back toward the
plus 20 celsius mark, it will get rather hot again. Most locations
below 6200 feet will again see highs into the 90s an d the warmer
spots in the Bighorn Basin have at least a 1 in 2 chance of highs
of 100 or greater.

A bit more monsoonal moisture will move over the area for the
weekend, but at this point values look more like 150 percent of
normal versus the 200 to 250 percent of normal we may see today.
Nevertheless, it will increase the chance of diurnal convection on
both days. And temperatures look to remain very warm as well, more
than likely similar to Friday, with widespread 90s in the lower
elevations with triple digit highs in the warmer spots. Models are
split for early next week though, with some showing drier conditions
and others keeping the diurnal convection trend continuing. However,
above normal temperatures are likely to continue.
&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1145 PM MDT Tue Jul 21 2026

There is lower than usual confidence in the 22/0600Z TAFs
tonight into Wednesday, as abundant atmospheric moisture
combined with a passing weather system will make showers and
thunderstorms numerous. Overall, the next 24 hours will be a
period where pilots should expect quickly changing conditions, a
lot of mid-level cloud cover, and occasional very heavy rain
and visibility reduction. Lightning looks most likely in the
typical noon to sunset timeframe, but this will be a 24 hour
period where isolated lightning is possible overnight and in
the post-sunrise morning hours. Small hail will be possible in
the strongest cells, but occasional strong downdrafts,
lightning, and localized flooding are the bigger threats with
storms through early Thursday morning.

Weather models show various timings for when storms are most
likely at TAF sites, so an attempt was made at finding a rough
consensus. However, wind direction will be fickle, and largely
determined by where individual showers and clusters of storms
sit relative to terminals (with storm outflow blowing winds away
from nearby rain shafts).

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Flood Watch through late tonight for WYZ001>020-022>030.

&&

$$

DISCUSSION...Hattings
AVIATION...VandenBoogart