973
FXUS65 KRIW 190758
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
158 AM MDT Sun Jul 19 2026

.KEY MESSAGES...

- There will be a lull in the number of showers and
  thunderstorms for the next two days, reducing the chance of
  local flooding.

- Very moist conditions return by Tuesday with an increased
  chance of thunderstorms and possible flooding. Wednesday at
  this point looks to be most impactful day for heavy rain.

- Temperatures remain above normal through Monday, with 100
  degree highs in the warmer spots. Somewhat cooler temperatures
  move in for midweek with the increase in cloud cover.

&&

.DISCUSSION...
Issued at 155 AM MDT Sun Jul 19 2026

Like last night, we continue to have some annoying little showers
lingering, although nothing heavy at this time. The monsoonal
pattern looks like it will continue for several days, but there will
be ups and downs with it through the next week. And that is the main
challenge with the forecast today, as it has been for past few days.

We should be entering a less active period for the next 36 to 48
hours or so. Most guidance shows the monsoonal plume pushing to the
east and south today, dropping precipitable water values by around
20 to 30 percent across the area. They will still be above normal,
but only 130 to 150 percent versus 175 to 200 percent yesterday. The
result will be fewer showers and storms and less chance for
flooding, although the chance is not zero. As for where the
thunderstorms will be, the best chance is across the south where the
deeper moisture will be, and the far north where a weak short will
be passing through. However, since the models have been nothing
short of hot garbage with the placement and timing of the storms the
past few days, I have gone with around a 15 percent chance across
most areas except for the far west, where the chance is less than 1
out of 10. The other story will be the continued very warm
temperatures, even warmer than yesterday. The warmer spots in the
Bighorn Basin, like Worland and Greybull, have around a 1 in 2
chance of reaching 100 degrees. Highs in the 90s will be fairly
widespread below 6300 feet as well.

Activity also looks fairly sparse on Monday as well. The Weather
Prediction Center has removed all of our area from the Excessive
Rainfall Outlook on this day. Moisture does increase with
precipitable waters rising again but now it looks to be more at
night than during the day when instability would be limited so the
threat of flooding would be reduced. Coverage looks to be largely
across southwestern Wyoming with mainly dry conditions further north
and east. Most areas will probably not see a shower or thunderstorm
on this day, although most areas should have at least a 1 in 10
chance. Again, no confidence in locations of daytime convection
except in the favored mountain areas like the Absarokas. And it will
be another hot day, high temperatures look similar to Sunday, with
warmer areas of the Bighorn Basin having around a 1 in 2 chance of
high temperatures of 100 or higher.

The monsoonal moisture really makes it`s return on Tuesday, as we
see values again climb to an average of 175 to 200 percent of normal
once again. And the expected result will be a return to a bigger
coverage of showers and thunderstorms, with most guidance showing
the southwestern portions of the area the favored location. This is
roughly the area that has a marginal chance of Excessive Rainfall as
well. And like previous nights, most coverage will during the day,
but more showers and even a few thunderstorms should linger through
the night. In addition, with the increased cloud cover from the
increased moisture should allow for cooler temperatures across the
area.

The main event still looks to be on Wednesday. The models have been
fairly consistent in bringing some very deep moisture into western
and central Wyoming on this day. The mean precipitable water at our
office continues to be around 1.50 inches, which would be the
highest in station history (the all time high is 1.41 inches) and
around 250 percent of normal. At the same time, a shortwave will be
approaching the area, bringing some additional lift in the afternoon
and evening. As for the excessive rainfall outlook, it was upgraded
to a slight risk. We don`t see that much around here on Day 4. If we
have a day with a more widespread flooding risk, this would be the
day for it. We will have to watch it closely.

Starting Thursday, the core of the monsoonal moisture should shift
east of the area, with precipitable waters falling back more toward
175 percent of normal. This is still plenty for another good
coverage of showers and thunderstorms though. Moisture remains above
average through next weekend as well, before drier air may begin to
move in for the start of next week, possibly shutting off the
monsoon. However, we have several days to get through so be alert
for heavy rain and possibly flooding and make sure to turn around,
don`t drown if you encounter flooding.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 950 PM MDT Sat Jul 18 2026

Most, if not all, showers and thunderstorms will end by the start of
the TAF period. Conditions will then be VFR through at least Sunday
morning. Convection will be more scattered and much weaker Sunday
afternoon. Chances for showers and storms will only reach about 10%
for most terminals, with up to 30% for KCOD Sunday afternoon. VIS
may drop to MVFR if one of the stronger storms moves directly over
KCOD. Wind will be below 10 knots for most terminals through the TAF
period. Stronger gusts are possible with outflows or downdrafts
Sunday 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.

&&

$$

DISCUSSION...Hattings
AVIATION...Rowe