558
FXUS65 KRIW 311016
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
416 AM MDT Fri Jul 31 2026

.KEY MESSAGES...

- One more day of isolated showers and thunderstorms today, with
  temperatures a few degrees warmer than yesterday.

- Very hot temperatures return this weekend, many lower
  elevation sites having highs over 100. Some all time record
  high August temperatures may be set, especially on Sunday.

- Elevated to critical fire weather is likely this weekend into
  early next week, with Sunday and Monday looking like the days
  of most concern.

- A cold front will bring some relief from the hot temperatures
  early next week, mainly across northern and central Wyoming.

&&

.DISCUSSION...
Issued at 158 AM MDT Fri Jul 31 2026

We have finally reached the end of July. And, like many of the past
months in the past year, it has been a very warm one. Several of our
climate sites are having their warmest July on record and many
others are in the top 5. And this looks to continue into the
weekend. And then, we may finally get some relief from the record
warmth we have been experiencing.

It is generally more of the same today. It will be another very warm
to hot day today, with temperatures a few degrees warmer than
yesterday. Precipitable water values also drop another 10 to 20
percent today, finally getting back to near climatological averages.
However, there is still just enough low and mid level moisture for
some isolated showers and storms. As for where, the models continue
to be on the struggle bus when it comes to where they will form. So,
for now I have just gone with a broad area of slight POPS across
most of the area, similar to the Storm Prediction Center outlook.
The chance at most spots is less than 1 out of 5 though and most
areas will not see one. The main threat from any storm would be
strong wind gusts given the large dew point depressions. And this
should be another show where most showers and storms should end
by sunset with all showers done by midnight.

The ridge builds northward over Wyoming over the weekend. This will
have two impacts. One, with the warming aloft and much drier air,
the chance of convection will be almost zero. It will also warm
quite a bit, with 700 millibar temperatures climbing as high as 20
to 21 degrees celsius. This should push high temperatures in
locations below 7000 feet into the 90s, with areas below 5000 feet
likely seeing highs into the triple digits. The peak of the heat
still looks to be on Sunday. The reason for this will be a
southwesterly, downsloping breeze that will develop ahead of an cold
front dropping into Montana. This should add a few degrees to the
temperatures in the lower elevations, with most locations below 5500
feet having at least a 3 in 5 chance of high temperatures of 100 or
higher. The center of the heat looks to be in central Wyoming,
where the Big Horn Basin from Basin to Thermopolis as well as the
Wind River Basin below 5000 feet have a 1 in 2 chance of high
temperatures of 105 or higher. This is the day we could see some all
time record high temperatures for August. For some locations, this
could be the third time this calendar year (they also occurred in
March and July, as well as December of last year). As for
highlights, we elected to go with heat advisories rather than
excessive heat warnings. Why? For one, the really hot temperatures
should only last two days, not four like back in July. In addition,
the nights are now getting longer so we have a longer period to cool
off at night. And relative humidity will be very low, as low as 5
percent. And this lowers the heat index. However, this will lead to
another possible hazard.

And that hazard is elevated to critical fire weather. Elevated fire
weather is likely on Saturday with the low humidity. However, wind
is not expected to be strong and should remain below critical
levels. It will be a different story on Sunday as the cold front
approaches and tightens the pressure gradient. It is a bit lighter
than yesterday, but still has a greater than 1 in 2 chance of gusts
over 25 mph over portions of the area. We will hold off for now
since there is still time, but future shifts may have to issue Fire
Weather Watches starting on Sunday afternoon.

The aforementioned cold front drops through the area Sunday night
and Monday, although it will be a slow passage. Temperatures will
cool East of the Divide on Monday anywhere from 10 to 20 degrees,
making for a nice, refreshing change from the recent hot weather.
Southern Wyoming will likely see one more hot day before the front
sips through Monday night. There is very little moisture with it
though, so the chance of any showers is basically zero. And with the
poor humidity recovery and gusty wind around the front, there will
likely be another day of elevated to critical fire weather, so any
highlights may end up being multi-day warnings.

Tuesday may should end up being the coolest and most comfortable
day, possibly a taste of September. Many areas have at least a 1 in
2 chance of high temperatures under 85 degrees, with the warmest
temperatures in southern Wyoming, where the front will likely wash
out. The GFS MOS has a high temperature of 65 in Cody on Tuesday.
This looks way too cool given the early August sun angle though.
Following this, we should see a gradual warming trend, although
record warm temperatures look unlikely the rest of next week.
It also looks rather dry, with any deeper moisture likely
remaining south of Wyoming. So, any chances of precipitation
look slim for much of next week.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 412 AM MDT Fri Jul 31 2026

Largely VFR conditions should prevail through 12Z Saturday. The
main concern will be for possibly convection, mainly between 20Z
today to around 03Z Saturday. With the models continued poor
performance on placement of showers and thunderstorms, we have
decided to include PROB30 groups at all TAF sites (for a 15 to
25 percent chance) of afternoon showers and storms. We left out
KRKS since the chance is around 10 percent. Wind should
generally remain under 12 knots except in and near any shower or
thunderstorm where wind gusts to 40 knots will be possible. All
convection should end by 05Z with mainly dry conditions after
that.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from noon Saturday to 10 PM MDT Sunday for
WYZ003>006-010-011-013-016>020-023-025>030.

&&

$$

DISCUSSION...Hattings
AVIATION...Hattings