451
FXUS65 KRIW 110442
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1042 PM MDT Sun May 10 2026

.KEY MESSAGES...

- Mostly clear skies and tranquil weather conditions continue
  through tonight. Lows will be 5-10 degrees warmer than last
  night.

- There is a 10% to 15% chance of virga and/or light rain and a
  few rumbles of thunder Monday afternoon and evening across
  northern Wyoming. Across the Bighorn Basin, gusty outflows of
  45 to 55 mph will be the primary threat, even with no rain.

- A combination of very warm temperatures, very low humidity
  (less than 15 percent), and gusty winds will bring elevated to
  near critical fire weather Monday afternoon through much of
  the work week.

- Well above normal temperatures in the 80s, and potentially in
  the low 90s, are expected much of this week. Record high
  temperatures are possible each day Monday through Thursday.

&&

.UPDATE...
Issued at 1148 AM MDT Sun May 10 2026

A tranquil afternoon continues this afternoon with only a few cirrus
clouds passing over. This pleasant weather is all thanks to
subsidence from high pressure across the area. Today`s high
temperatures (widespread 70s) are forecast to be the "coolest" highs
through at least Thursday. There is still high confidence in
widespread highs in the 80s beginning Monday with increasing wind.
The elevated to near critical fire weather conditions remain each
afternoon through Thursday.

The forecast largely remains on track for Monday afternoon and
evening as a weak shortwave traverses over the region. It looks as
if there will be some accompanying mid-level moisture across
northern Wyoming with the passing shortwave. Because of this, light
rain chances (10% to 15%), and some thunder, have been added to the
forecast beginning around 3PM MDT Monday across northwest Wyoming.
As the shortwave progresses eastward, these chances also shift east
across the Bighorn Basin and into Johnson County. Confidence in
anything actually making it to the ground is relatively low, with
virga being the most likely scenario because of the dry low levels.
For the Bighorn Basin, gusty 45 mph to 55 mph, and potentially
closer to 60 mph, downdrafts and outflows are possible even in the
absence of any liquid making it to the ground. This is largely due
to dew point depressions in the 45 mph to 55 mph range. Outside of
these low rain/virga chances, Monday will still be a windy day as
the shortwave passes over.

&&

.DISCUSSION...
Issued at 144 AM MDT Sun May 10 2026

Many meteorologists are shift workers, and are often more tired than
many people. And what do you drink when you need energy? For most
people, that is coffee (myself excluded, I never developed a taste
for coffee and usually only drink water on shift). And one of the
things people put in coffee reminds me of weather this weekend. And
that is half and half.

The active half was yesterday, with showers and thunderstorms, and
even a brief landspout tornado. Temperatures were also below normal
as well. The shortwave that caused this has now moved away from the
area, and ridging will build across the area today, bring a very
nice spring day to end the weekend. Temperatures should average 5 to
10 degrees above normal, comfortably warm for most. There
should be plenty of sunshine as well with only some passing high
clouds and some cumulus near the mountain ranges. In addition, wind
should remain light to moderate, although some locally breezy
conditions are possible. If you can, get out and enjoy it.

We then turn to something we have seen much of this calendar year,
even dating back to last fall. This relates to a song I heard this
evening while listening to 80s music. The song was "The Heat Is On"
by the late, great Glenn Frey (cue sax solo). Of course, I am
referring to another period of likely record high temperatures.
The 700 millibar temperatures will be on the rise, from an
average of 7 celsius today to 10 to 12 celsius on Monday to as
high as 15 celsius on Wednesday. As a result, temperatures will
average 15 to as much as 20 degrees above normal through the
period. Assisting in the warming on Monday will be a weak
shortwave moving through the flow. There is little moisture with
it, with only only a less than 1 in 5 chance of a mountain
shower or thunderstorm Monday afternoon. The main impact will be
mix the atmosphere and mix some 30 to 40 knot 700 millibar
winds to the surface, aiding in downsloping and further raising
temperatures. Many locations will be into the 80s, some
locations well into the 80s. Chances of reaching 90 are small
this day though, less than 1 out of 4 any only in warmest spots
like Basin and Worland. The main concern on this day will be
elevated to near critical fire weather, as humidity will fall
into the teens for most locations, even the single digits. No
fire weather highlights will be issued at this time since fuels
aren`t critical, but burning is not advised on this day.

The ridge axis then builds over the area on Tuesday. With less
mixing and wind, temperatures should cool somewhat East of the
Divide, but still remain well above normal. The heat will likely
peak on Wednesday, as the wind increases somewhat and 700 millibar
temperatures peak. This will likely be when high temperatures will
peak. At this time, there is a greater than 2 out of 3 chance of a
high temperatures over 90 across the warmer locations like from
Thermopolis to Greybull in the Bighorn Basin. This would be around 2
and a half weeks before the average first 90 degree high, but not
the earliest at most locations here. Chances are lower elsewhere
East of the Divide, generally 1 in 4 to 1 out of 3. However, it
would tie or set the earliest appearance of 90 degree temperatures
in locations like Riverton, Casper and Lander. At the same
time, some moisture returning to the west ahead of an upper
level low approaching the west coast may bring a few showers and
storms to the west, but most locations will not see one.

There will likely be one more day of warm weather on Thursday before
cooler air returns as the Pacific low approaches. Confidence is very
low on what will happen with this system as some deterministic and
ensemble members bring a secondary piece of energy over Wyoming
Friday with a decent amount of QPF, while others keep the
precipitation largely over Montana. At this point, there continues
to be a lot of uncertainty, stay tuned.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1038 PM MDT Sun May 10 2026

High cirrus will begin to thicken across northern and central WY
later tonight into Monday morning, as thicker wave cloud action
increases. These will remain above 25000, but will signal some
higher turbulence in the vicinity. All sites will see increasing
winds during the afternoon, with most sites reaching gusts
around 30kts. Winds will relax at all sites around sunset.

There is still a low chance (~20%) of a brief shower at or near
KCOD during the late afternoon after 20Z, but any showers will
be high based above 8000 feet, and will remain small enough to
only impact for 15 to 20 minutes.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC
for the latest information on icing and turbulence forecasts.

&&

.FIRE WEATHER...
Issued at 144 AM MDT Sun May 10 2026

It will be much warmer today with humidity falling into the
teens, but wind should remain light to moderate. On Monday, a
weak weather system will approach and bring gusty to strong
wind. With humidity falling below 15 percent and temperatures
well above normal, elevated to near critical fire weather is
likely for many areas Monday afternoon.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

UPDATE...Gerhardt
DISCUSSION...Hattings
AVIATION...Straub
FIRE WEATHER...Hattings