994
FXUS65 KRIW 271831
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1231 PM MDT Sun Jul 27 2025

.KEY MESSAGES...

- Warm temperatures and elevated to critical fire weather
  across the area today.

- The warm and dry weather continues tomorrow (Monday) but with
  less wind.

- A pattern change begins Tuesday and lasts through the end of
  the week, with cooler temperatures and an increased chance of
  showers and thunderstorms.

&&

.UPDATE...
Issued at 1230 PM MDT Sun Jul 27 2025

No major changes to today`s forecast. The main focus is on the
elevated to critical fire weather over central and southern portions
of Wyoming. RH recovery overnight will be poor across many areas,
with maximum overnight RHs 20 to 35 percent. Most places remain dry
this afternoon, though an isolated (15%-20%) shower or storm could
pop-up over far northern Yellowstone or the Absaroka Range,
especially for the northern range. Over the northern Bighorn Range,
the chances are 10 to 15 percent. Tomorrow will likely see the peak
heating for the week, before a system pushes in mid-week, bringing
cooler and wetter conditions.

&&

.DISCUSSION...
Issued at 321 AM MDT Sun Jul 27 2025

On this last Sunday morning of July, the reasoning of the
forecast remains similar to yesterday. Ridging will remain over
the area today and bring another hot and, in some locations,
breezy day. The question is about potential fire weather. Just
about all areas will have at least elevated fire weather, given
the very low humidity with many locations having single digit
humidity this afternoon. The main question is about wind once
again. Wind does not look quite as strong as yesterday since
there will be no shortwave moving through, limiting mixing more.
The 700 millibar winds are also around 5 to 10 knots less than
yesterday. However, some locations still look critical. For
guidance, we used the NBM ensemble of probability of wind gusts
past 25 mph. For the most part, we used a chance of 3 out of 5
or higher this afternoon. And this gave southern Lincoln County,
Sweetwater County and the Green and Rattlesnake Ranges. So, Red
Flag Warnings were hoisted here from 12 pm to 8 pm. We thought
about Natrona County, but wind looks lighter here and anything
would be isolated. The Wind River Range has some but on the west
side for the most part, which does not have critical fuels yet.
And portions of the Salt and Wyoming Range. However, these are
in the highest elevations and a lot are above the timber line.
Fremont County had a thought to, especially eastern portions,
but again, here we thought it would be isolated. As for
convection, with higher heights and a lack of moisture, chances
would be very small. The main location would be the far northern
mountains but even here the chance is less than 1 out of 5.
Temperatures look similar, with widespread 90s East of the
Divide and 80s in the lower elevations West of the Divide.

Monday looks like another hot and mainly dry day. There will be the
first indications of a change in the pattern though. For one,
somewhat more humid air will return East of the Divide. Critical
humidity is still likely for most (below 15 percent) but most places
will see at least in the double digits. The increasing moisture may
also touch of a few thunderstorms, especially in Johnson County
where humidity will recover faster. But again, coverage remains less
than 1 out of 5. Temperatures will remain hot in most locations,
similar to today`s highs. Wind will also be down a few ticks, so
fewer places may have fire weather highlights (far southwestern
Wyoming has the best chance).

Tuesday is when the pattern really begins to change. Monsoonal
moisture will begin to surge back into the area and increase the
chance of showers and storms. The return has slowed a bit this
morning, however areas East of the Divide still have anywhere from
120 to 150 percent of normal of precipitable water values. Things
could set interesting this day as we have both a marginal risk of
excessive rainfall and severe thunderstorms on this day. For
Tuesday, this would be mainly East of the Divide, as areas to the
west should have one more mainly dry. Wednesday and Thursday are
the days when the deeper moisture moves across most of the area and
brings the best chances of more widespread showers and storms.
Wednesday may be the most active day, with the highest precipitable
waters and best low level easterly flow that will bring in deeper
moisture and initiate upslope flow along the eastern peaks.
Placement of the storms is impossible to pinpoint at this time, but
things look rather active through Thursday. By the end of the week,
drier area may try to push in, cutting the coverage of the showers
and storms. Temperatures will fall to below normal levels by Tuesday
and remain there through Thursday with the increased cloud cover
before recovering to near normal levels for next weekend.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1217 PM MDT Sun Jul 27 2025

Mostly clear skies continue today, with variable haze from smoke
still in the region. Winds will continue from the southwest,
with main gusts limited to KCPR and KRKS. Light and variable
winds return overnight, before light south winds return for
Monday.

&&

.FIRE WEATHER...
Issued at 321 AM MDT Sun Jul 27 2025

A combination of humidity falling into the single digits and a
gusty southwesterly breeze will bring critical fire weather to
southern Wyoming again this afternoon. Elsewhere, wind should
remain below critical threshold but humidity will remain very
low, in the single digits as well. The most likely locations for
near critical fire weather East of the Continental Divide will
be Fremont and Natrona Counties.

&&

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

&&

$$

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