Riverton, Wyoming 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

834
FXUS65 KRIW 071825
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1225 PM MDT Thu Aug 7 2025

.KEY MESSAGES...

- Critical fire weather remains likely across central and
  southern Wyoming through Friday.

- Isolated showers and thunderstorms with strong wind gusts are
  possible this afternoon and Friday afternoon, mainly across
  northern Wyoming.

- Below freezing temperatures and frost is possible (20 to 40
  percent) in the western valleys Friday night.

&&

.UPDATE...
Issued at 1219 PM MDT Thu Aug 7 2025

Today is the peak of fire weather conditions, with gusty southwest
winds ahead of a cold front, hot temperatures, and low relative
humidities (RH). RH recovery overnight was poor, with many areas
only recovering into the 20 percents. The cold front then begins to
move in from the north this evening, entering the northern Bighorn
Basin between 01z and 04z (7pm to 10pm MDT). Behind it, much cooler,
but still dry, air. Highs Friday are 10 to almost 20 degrees cooler
across the area, with the higher of that range east of the Divide.
Latest hi-res models do have some showers or storms with the front,
though there is not much moisture to work with, so chances remain
low (40 percent or less) and limited to northern Wyoming, namely
Yellowstone, the Absaroka Range, the northern Bighorn Range, and the
northern Bighorn Basin. Elsewhere, clouds and possibly virga are
most likely overnight and into tomorrow morning as the front moves
through.

&&

.DISCUSSION...
Issued at 307 AM MDT Thu Aug 7 2025

The main concern today remains fire weather. And concerns look to
amp up a few notches today as a cold front approaches the area.
This will turn flow southwest across much of the area,
especially central and southern Wyoming. This will likely bring
the warmest day of the week, with highs well into the 90s East
of the Divide. A few spots may briefly touch 100. It will also
bring a gusty wind as the pressure gradient tightens across the
area. Like previous days, I have used the NBM ensemble for wind
gusts to determine potential warning areas, with areas with a
greater than 3 out of 5 chance for 3 hours of wind gusts past 25
mph. This is definitely the case in Fremont and Natrona
Counties, so the watches were upgraded. We also added the Owl
Creek Range and the southern Big Horn Range to the Red Flag
Warnings. Of all the days, this one to me looks to most
concerning with the combination of the low humidity (single
digits in some cases), gusty wind, and hot temperatures.
Elevated fire weather is likely elsewhere. We thought about a
few other locations for critical fire weather but either the
wind was too borderline (lower elevations of Big Horn and
Washakie Counties) or humidity was a bit too high (locations
further west). And, we have to worry about a few showers and
thunderstorms. This would be mainly across the northern
mountains and the northern Big Horn Basin. The only concern
would be wind gusts given the dry low levels. Dew point
depressions are very large though (up to 60 degrees) so any
storm, shower, or even enhanced cumulus cloud could have a wind
gust past 50 mph. A few showers may linger past midnight, but
coverage will be sparse (at most 1 out of 5) in most locations.

The cold front will drop southward across Wyoming on Thursday night
and Friday. This will bring some relief from the hot temperatures,
lowering highs from 10 to 20 degrees East of the Continental Divide.
However, the air mass will remain dry behind the cold front.
Northern Wyoming, as far south as the Owl Creek and Big Horn Range,
should see humidity rise enough for critical fire weather to end.
Further south, low humidity will persist, along with a gusty wind,
although this time from the northwest. This will bring another day
of critical fire weather to the other locations through Friday. And,
with slightly more moisture, there will be another chance of showers
and thunderstorms across northern Wyoming. However, with the
atmosphere remaining fairly dry the chance is again small, only 1
out of 5.

And we have one more concern for Friday night. With the dry airmass
over the area, low temperatures Friday night will be chilliest we
have seen in a while. We do have the potential for some frost in the
western valleys. A hard freeze (28 degrees) looks unlikely at this
point (chances are generally less than 1 out of 5). However, some
areas, like the Jackson and Star Valleys as well as the Green River
Basin have some areas with greater than a 1 in 2 chance of below
freezing temperatures. So, don`t be surprised if some areas wake up
to frost Saturday morning.

Fire concerns should really ease on Saturday as the pressure
gradient slackens and wind decreases. The only area of concern would
Sweetwater and southern Lincoln Counties, but even here the wind
is borderline. Temperatures will remain rather comfortable
though, averaging 5 to 10 degrees below normal.

The weather looks relatively uneventful for Sunday and Monday with
mainly dry conditions and near normal temperatures. Fire weather
could become a concern again toward the middle of next week though
as another trough and cold front approach the area from the north
and west.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1155 AM MDT Thu Aug 7 2025

Hot dry and windy across western and central this afternoon and
early evening yields VFR conditions at all TAF sites through at
least 08/06Z tonight. West-southwest wind gusts of 22-30 kts
will develop this afternoon as the surface pressure gradient
tightens in advance of a cold front. Mostly clear skies late
this morning will become partly cloudy this afternoon across
northwest and northern WY, then move southeast overnight. As the
front move south into the Bighorn Basin, marginal MVFR ceilings
are possible starting around 08/09Z then moving to KWRL and
KCPR. Light showers are possible in the surrounding mountains,
but the chances are too low to include in the terminal
forecasts. Far northern WY may see some thunderstorms as
well late this afternoon and early evening, but the best chances
are in southern MT and across the NW tip of YNP. The stronger
winds are expected to decrease by sunset, though a couple of
site may see breezy conditions overnight, especially where the
cool front keeps winds elevated.

As the initial wave move southeast Friday morning, clouds are
expected to drape across the state from SW WY toward east-
central WY with lingering lower(ish) clouds east of the
continental divide. Post-frontal west-northwest winds will
increase by 08/18Z across western and southern WY and push off
the Absarokas and Wind Rivers to create a boundary east of the
divide, where winds on the NE side will be from the north.
Weaker northerly flow will then develop late Friday evening.
Some showers and very isolated thunderstorms may develop over
the Bighorns Friday afternoon and move eastward.

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

&&

.FIRE WEATHER...
Issued at 307 AM MDT Thu Aug 7 2025

A combination of a gusty wind, relative humidity falling below
15 percent and dry fuels will bring critical fire weather to
much of central and southern Wyoming through Friday as a mainly
dry cold front moves through Wyoming. Elsewhere, elevated fire
weather is likely each afternoon. Fire weather concerns should
ease Saturday and Sunday as the wind decreases.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 8 PM MDT this evening for WYZ285-287.

Red Flag Warning until 8 PM MDT Friday for WYZ277>280-283-288-
289-300-414-416.

&&

$$

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