713
FXUS65 KRIW 170800
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
200 AM MDT Fri Jul 17 2026

.KEY MESSAGES...

- The axis of thunderstorms pushes a bit further west today,
  with a higher chance in the western mountains and a bit less
  in southern Wyoming. Local flooding is still possible with any
  shower or thunderstorm though.

- The threat of drenching thunderstorms remains mainly across
  the western half of the area on Saturday, then spreading
  across much of the area on Sunday.

- The chance of showers and thunderstorms continues each day
  through much of the week, again with the chance of local
  flooding each afternoon and evening.

&&

.DISCUSSION...
Issued at 157 AM MDT Fri Jul 17 2026

Have you ever been stopped at a train crossing watching a really
long freight train go by? One of those really long ones that tend to
always show up when you are running late for something. Well, I am
comparing that long freight train to the monsoonal pattern that we
look to be locked in for at least another week. There will be day to
day fluctuations, but there will be at least some chance of showers
and thunderstorms each day, and possibly the chance of flooding.

We will have one of those fluctuations today, as the ridge builds
back to the west somewhat. This will lead to somewhat higher
heights and warmer temperatures. The biggest impact though will be
that precipitable waters will drop about 15 to 25 percent roughly
west of a Buffalo to Riverton to Rock Springs line. This means that
the chance of storms and the chance of flooding should be somewhat
reduced today in this area. However, this will not be the case for
the Bighorn Basin as well as the western mountains. So, the main
area of showers and storms will be here, with tapering chances
further south and east. And with the continued chance of flooding,
we will issue another flood watch for the Absarokas and much of the
Bighorn Basin given the saturated soils. We thought about on for the
western mountains but rainfall hasn`t been as heavy here and we will
hold off for now. However, much like yesterday, and shower or storm
could have heavy rain given the abnormally moist atmosphere. Like
yesterday, most storms will be over shortly after sunset, but a few
may linger until after midnight.

The moisture axis will shift a bit further to the east on Saturday,
and as a result so will the chance of showers and thunderstorms.
Precipitable waters climb back to levels similar to Thursday, so the
chance of storms should be similar as well. Again, the Big Horn
Basin looks to be area under the gun again as well as the Absarokas
as the low level easterly upslope flow continues. Far eastern areas,
like Kaycee and Casper, who have been wondering where their rain is,
will have another dry day on this day. This will also be a warmer
day, and some locations in the eastern Bighorn Basin might make a
run at 100 degrees if they can get enough sunshine.

It still looks like the transition day will be on Sunday. On this
day, some drier air will begin to move into western Wyoming, drying
things out somewhat. The main focus then moves to East of the
Divide, including locations like Casper that have remained hot and
dry through much of the week. Precipitable water values will again
average around 175 percent of normal, and again, sounding like a
broken record, the threat of heavy rain and localized flooding. With
more clouds shifting eastward, temperatures should begin to cool
down as well on this day, although they will remain well above
normal.

There is a wrinkle for Monday, as there is no some split in the
guidance. Some ensemble members, as well as the deterministic
European model run, now builds the ridge over the state, shutting
off most of the convection. Others keep things quite active though.
For now, the compromise was to dry out northern Wyoming and have the
highest POPs across southern Wyoming. There is still plenty of
moisture in the atmosphere so it would not take much for a few
storms to fire.

Following Monday, there is greater model agreement in bringing the
deep monsoonal moisture back over the area, especially East of the
Divide. Precipitable water values look exceptionally high on some
model runs. This is still 5 or more days out, so take this with a
grain of salt. For example, at Riverton, our mean precipitable water
value is 0.63 inches. On Wednesday, some ensemble members and the
deterministic GFS is showing precipitable waters of over 1.3 inches.
This is over 200 percent of normal. It is also close to the record
high precipitable water value of 1.46 inches that was set back in
2003. Again, it is a long way out but there is the potential for
some very heavy rain from any thunderstorm that could develop for
the middle of the week. The abnormally high precipitable water
values look to stick around through at least Thursday. So, the
monsoonal fright train will continue to transport moisture into the
area, along with the chance of drenching thunderstorms, for the next
several days.


&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1030 PM MDT Thu Jul 16 2026

Showers and storms have primarily ended across the area. SCT-BKN
mid to high level clouds will continue through 15Z. Another
round of showers and thunderstorms returns again Friday
afternoon. Similar to today, these storms will be scattered in
nature, so pinpointing impacts on area airports will depend on
daytime heating and initial development. Best chances for
thunderstorms again remains over the Absaroka and Wind River
Mountains, with KCOD and KJAC likely being impacted by 21Z.
Additional terminals, KBPI/KPNA, KRIW/KLND and KWRL, look to be
impacted by 23Z. KCPR is expected to remain dry again, and
chances at KRKS currently look lower and to the west of the
terminal, so have left out any mention of precip there for the
time being. However, these two terminals could be impacted by
outflow boundaries. Convection is expected to be ending across
the area after sunset again Friday evening, with showers
remaining possible near KCOD through 04Z.

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 from noon MDT today through this evening for
WYZ002>005-007.

&&

$$

DISCUSSION...Hattings
AVIATION...LaVoie/Straub