540
FXUS65 KRIW 120825
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
225 AM MDT Tue May 12 2026

.KEY MESSAGES...

- Still warm but not quite as hot today with less wind than
  yesterday.

- Record heat is likely on Wednesday afternoon. An approaching
  weather system will bring strong winds as well as some showers
  and thunderstorms, with very strong wind gusts possible with
  any shower or storm.

- Warm temperatures, low humidity and gusty wind will bring
  elevated to near critical fire weather each afternoon from
  Wednesday through Friday.

&&

.DISCUSSION...
Issued at 215 AM MDT Tue May 12 2026

Recently I was discussing underrated films of the past, most
specifically in the 90s. And one of the movies that was brought up
will be the story across the area over the next couple of days, but
especially on Wednesday. If you guessed the 1995 police / crime
action / drama "Heat", you would be correct.

We had several record high temperatures set across western Wyoming
on Monday afternoon. Expect another day of well above normal high
temperatures today. However, with the passage a cold front (if you
can call it that, more like a not quite as hot front.) Temperatures
will be down around 5 to 10 degrees compared to yesterday East of
the Divide. However, West of the Divide it will be another very warm
day with most lower elevations well into the 80s, leading to another
very warm day, possibly with more record highs. As for any showers,
we can`t rule out a stray shower near the mountains, but with the
chance less than 1 out of 7 we left the forecast dry for now. Also,
with the ridge axis building over the area, wind should be lighter
than today, leading to some decrease of fire weather concerns.

Wednesday looks to be the warmest day, and more active in regards to
impacts. There are three main concerns. We will start with the heat.
On this day, 700 millibar temperatures climbing as high as 15
celsius. This is combined with increased southwest wind head of an
advancing cold front. This will lead to downsloping flow leading to
compression warming to bring the warmest day East of the Divide.
Locations in Big Horn Basin from Thermopolis through Lovell have a
greater than 3 out of 4 chance of seeing their first 90 degree high
temperatures of the year, with a 1 in 4 chance of temperatures as
high as 95. As for earliest 90 degree high temperatures, these
locations have already passed these dates. Places like Riverton,
Lander and Casper have around a 2 in 5 chance of seeing a high
temperatures of 90 as well. And here it would be the earliest 90
degree high temperatures in history (currents are May 14th in
downtown Riverton, May 20th in Lander, May 26th in Casper and May
28th at the Riverton airport). Numerous high temperatures records
are expected to fall regardless.

The second concern is fire weather. All fuels in western and central
Wyoming have been deemed not critical, so no Red Flag Warnings will
be issued. However, with a greater than 4 out of 5 chance of
relative humidity falling below 15 percent across most of the
eastern two thirds of the area and a greater than 3 out of 4 chance
of wind gusts of 25 mph or greater in the afternoon, elevated to
near critical fire weather is a near certainty. Burning is not
advised on Wednesday, especially in the afternoon.

And finally, we turn to convection. The cold front will approach the
western portions of the state in the afternoon, in association with
an 80 knot jet streak to provide some upper level forcing.
Instability parameters look good as well with as much as 700 J/Kg of
CAPE and lifted indices as low as minus 3. The one thing missing is
low level moisture, although there is a decent amount of mid
level moisture. This looks like a very good set up for downburst
winds. We have very steep lapse rates of greater than 9 degrees
celsius per kilometer. Sounding have a well defined inverted V
signature with LCL levels anywhere from 6000 to 9000 feet off
the surface. And guidance gives very large dew point depressions
approaching 60 degrees fahrenheit. The Storm Prediction Center
has noted this as well and has hoisted a marginal risk across
far western Wyoming. This looks like an ideal "Little Green
Blob" day as well with any shower or even a cumulus cloud
possibly producing wind gusts over 50 mph. Most convection looks
diurnal, ending by midnight.

Thursday and Friday look similar with flat ridging across Wyoming.
Temperatures will continue to be above normal, but not record
breaking, averaging 10 to 15 degrees above normal. Fire weather will
continue to be a concern as relative humidity remains very low and
wind remains rather gusty. And there is the chance of high winds on
Thursday. This is mainly in the Cody Foothills with a shortwave
moving across Montana along with an associated jet streak. Model
guidance also shows 50 to 55 knots of westerly wind at 700
millibars. There is a greater than 1 out of 2 chance of wind gusts
55 mph or greater. However, right now this is mainly in locations
near the Absarokas where there is little impact. We still have time
to decide on any potential highlights though. Gusty wind continues
on Friday but with the jet moving away the threat of high wind
should end. With low humidity continuing as well, elevated fire
weather will continue through Friday.

We could see a bit of a pattern change on Saturday and especially
Sunday as a trough and cold front digs into the northern Rockies.
This is especially so on Sunday as some model guidance shows 700
millibar temperatures falling as low as minus 6. If any moisture can
work in this likely means mountain snow and possibly even in some of
the lower elevations. There is poor agreement on any placement of
potential precipitation though. However, there is a decent chance of
a cooler pattern arriving this weekend and possibly lasting into
early next week.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 956 PM MDT Mon May 11 2026

Prevailing VFR conditions continue through the TAF period, with
mostly clear skies by Tuesday morning. A few rain showers over
northern portions of the area linger for an hour or two to begin the
period. Gusty downdrafts remain a threat with these showers. A cold
front will continue passing through central portions of the area
early in the period, but should stall along the Continental Divide
early Tuesday morning.

Wind is northwest to northeast behind the front and will remain a
bit breezy for most of tonight. Wind will increase again Tuesday
afternoon, but will be much lighter than this past afternoon. The
front will finally reach KRKS by 05Z Wednesday with wind shifting
from the west to the east. Shortly thereafter this front will
dissipate heading into Tuesday night.

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 215 AM MDT Tue May 12 2026

Although relative humidity will remain under 15 percent in some
locations today, somewhat cooler temperatures and less wind
should ease fire concerns somewhat. On Wednesday, a combination
of record warm temperatures, a gusty to strong southwest wind
and humidity under 15 percent will bring elevated to near
critical fire weather to much of the area. Dry showers and
thunderstorms are also possible in the afternoon, especially
across western Wyoming with wind gusts past 50 mph possible with
any shower or thunderstorm. Although temperatures will cool
somewhat Thursday and Friday, a continued gusty to strong wind
and low humidity will keep elevated fire weather in place across
much of the area.

&&

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

&&

$$

DISCUSSION...Hattings
AVIATION...Rowe
FIRE WEATHER...Hattings