Casper, Wyoming 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

844
FXUS65 KRIW 261828
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1228 PM MDT Sat Jul 26 2025

.KEY MESSAGES...

- Elevated to critical fire weather today, with isolated
  afternoon showers and thunderstorms.

- Hot and dry weather continues through Monday.

- A transition to a cooler and wetter pattern begins Tuesday and
  continues through at least Thursday.

&&

.UPDATE...
Issued at 1226 PM MDT Sat Jul 26 2025

Red Flag Warnings continue through 8pm MDT today due to a
combination of low RHs and gusty winds. No major changes to the
forecast today regarding these weather elements. Have updated the
low precipitation chances with latest model guidance. Still
expecting mostly virga, with an occasional light shower. Could
see a little lightning over northern Wyoming if a stronger cell
forms. Main hazard with any convection today continues to be
gusty outflow winds. The latest HRRR runs would suggest 30 to 40
mph gusts are most likely, but with the dry air in place, there
is potential for stronger gusts.

For fire weather tomorrow, winds do not look quite as strong during
the afternoon. The one place where 25+ mph wind gusts may occur
would be over eastern Sweetwater County (eastern fire zone 279).
Given the limited extent and lack of confidence in wind, will hold
off on extending any fire highlights for tomorrow. Overnight shift
can take one more look at winds for tomorrow. At the very
least, widespread elevated fire weather conditions will be in
place Sunday, with afternoon RHs in the single digits across
much of the area, with breezy winds 15 to 25 mph.

&&

.DISCUSSION...
Issued at 252 AM MDT Sat Jul 26 2025

Climatologically, we are in the hottest time of the year. And the
next few days are no exception. Ridging will control the weather
over the Cowboy state and bring hot temperatures to much of the
area. Not record breaking heat, but highs in the 90s will be fairly
widespread in the lower elevations East of the Divide with 80s in
the lower elevations to the west. However, temperatures are not the
main concern of the forecast, fire weather is.

All in all, today looks to be main day of concern. A weak shortwave
will move across the state today, helping to enhance mixing any with
700 millibar winds anywhere from 20 to 30 knots expected to mix to
the surface, critical fire weather looks likely. This will be mainly
in the southwestern Wind Corridor from Rock Springs through Casper
where the chance of 3 hours of wind gusts past 25 mph is greater
than 3 out of 5. So, we upgraded the Fire Weather Watches to
warnings. We also gave thought to adding Zone 283, which could see
gusty wind this afternoon. The chance here is only 1 out of 3
though, so we decided not to. Elsewhere, elevated fire weather is
likely given that humidity will be very low, with most areas under
15 percent and many areas under 10 percent. There is another concern
though. The shortwave could produce isolated showers and
thunderstorms this afternoon. Given the lack of moisture, these
would all be high based and the chance at any point is less than
1 out of 5. These are also impossible to pinpoint. So, we left
continuity alone. Many of these would not have any rain, only
virga. However, given the high bases of the convection and very
large dew point depressions, (over 60 degrees in many
locations), any thunderstorm, shower or even enhanced cumulus
cloud could produce strong wind gusts if it collapses.

The next question is, what about fire weather for tomorrow. It looks
more borderline. For one, there will be no shortwave to mix the
atmosphere and 700 millibar winds are 5 to 10 knots lighter. This is
especially the case in Natrona and Fremont Counties. For now, we
kept the warning for today but we may end up extending it out
through Sunday. This would be mainly for Sweetwater County though.
We will let the day shift or Saturday`s night shift take another
look at it before issuing. And with no shortwave, the chance of
convection will be near zero for most locations. The only place
would be the northern mountains but even here the chance is less
than 1 out of 6.

Monday at this point looks like another hot and dry day, with the
same chance of isolated storms across the far north. Wind looks
lighter on this day though, so the chance of critical fire weather
looks low (less than a 1 out of 4 chance) despite humidity remaining
low. This changes on Tuesday though. A cold front will slide toward
the area from the north. At the same time, a surge on monsoonal
moisture moves in from the south and east. The result will be a much
more moist atmosphere. Precipitable waters will jump from 30 percent
below normal to 150 percent above normal for areas East of the
Divide on Tuesday and most areas on Wednesday. And the result will
be more cloud cover, cooler temperatures, and an increased chance of
showers and thunderstorms through at least Thursday. At this point,
Wednesday looks to be the day of the most widespread showers and
storms. Pinpointing areas of the heaviest precipitation, especially
with convection, is very difficult this far out though. However,
confidence is high (around a 4 in 5 chance) that will will
transition into a wetter pattern starting on Tuesday.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1119 AM MDT Sat Jul 26 2025

High clouds continue to overspread the region, also bringing
smoke from fires to the south. This wave will bring a few virga
showers to the far western WY this afternoon, with the best
chances at KCOD/KWRL between 21Z and 00Z. Added a brief VCSH for
KJAC, as confidence is high there will be some shower activity
nearby, but airport impacts would be lower. Any showers
statewide would produce briefly gusty winds, but cigs and vis
remain well above MVFR criteria. Any showers will be dissipating
or moving northeast by 00Z, with clearing skies and light winds
overnight. Hazy conditions return for the day tomorrow.

&&

.FIRE WEATHER...
Issued at 252 AM MDT Sat Jul 26 2025

A combination of humidity falling into the single digits and a
gusty afternoon breeze will bring critical fire weather to
southern Lincoln, Sweetwater, southeastern Fremont and Natrona
Counties this afternoon. Elevated fire weather is likely for
other locations. Elevated to possible critical fire weather
continues on Sunday with some easing of conditions on Monday and
especially the middle of next week.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 8 PM MDT this evening for WYZ277-279-
280-289.

&&

$$

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