388
FXUS65 KRIW 281016
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
416 AM MDT Sat Jun 28 2025

.KEY MESSAGES...

- More gusty wind and low humidity will bring another day of
  elevated to critical fire weather today.

- Isolated thunderstorms are possible (from Sweetwater County to
  Natrona County) this afternoon as well as Sunday afternoon.

- Much of next week will feature above normal temperatures and a
  possible increase of convection, especially Wednesday and
  beyond.

&&

.DISCUSSION...
Issued at 248 AM MDT Sat Jun 28 2025

Compared to yesterday, we have some things that are similar and some
things that are not. As for similarities, we will continue to have
above normal temperatures, with most locations having high
temperatures from 5 to as much as 12 degrees above normal. There
will also continue to be a gusty breeze in many locations, although
a little less than yesterday in northern portions of the area. And,
we will continue to have low humidity across a good portion of
the forecast area, although a bit higher than yesterday. And
that leads to the question of the day. Do we need another Red
Flag Warning for Natrona County? Humidity will still be
critical, dropping down to close to 10 percent at times. Wind
will also be gusty, but is borderline, with most areas having
around 1 in 2 chance of gusts past 25 mph. But we do have a
difference. That is an approaching shortwave and weak cold
front that has a bit more moisture than the wave of yesterday.
Most of the moisture is of the mid level variety, with
soundings in most locations showing a very substantial inverted
V signature. This includes at Casper, with dewpoint depressions
approaching 60 degrees. As a result, any storms or even showers
that form could cause dry microbursts with wind gusts around 60
mph. And with the possibility of lightning, this was the factor
that tipped the balance to issuing the Red Flag Warning for
this afternoon and evening. Much of northern Wyoming could have
a shower or thunderstorm as well, but the chance of one at any
particular location is only 1 out of 5. This also looks like a
later show, with a few storms lingering in Johnson County after
midnight before everything ends between 1 and 4 am.

Fire concerns should be less tomorrow across most of the northern
two-thirds of the area, with somewhat cooler temperatures and
higher humidity moving in as flow turns north to northwesterly.
Elevated to critical fire weather will continue across southern
Wyoming though, with gusty wind continuing and humidity again
falling below 15 percent. Another shortwave will bring a chance
of a few showers and thunderstorms. There is more model
disagreement in placement this day though. For the most part, we
kept a 1 in 4 chance across portions of Johnson and Natrona
Counties while keeping the rest of the area largely dry.

Ridging then gradually builds over the area through the middle of
the week, bringing a return to above normal temperatures but
nothing out of the ordinary for late June / early July. Monday
looks like a mainly dry and nice day with lighter wind and any
isolated convection (1 out of 6 chance) limited to in and near
the mountains. Coverage of storms may increase Tuesday and
especially Wednesday as deeper moisture moves in from the south,
with precipitable water values rising to as much as 150 percent
above normal by Wednesday afternoon and a weak shortwave
bringing some additional destabilization of the atmosphere. The
end of the week looks to be the same with above normal
temperatures and a scattering of showers and thunderstorms, with
an average of a 1 in 4 to 1 in 3 chance each afternoon and
evening. As per usual this time of year, the best chance will be
in and near the mountains.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 400 AM MDT Sat Jun 28 2025

VFR conditions continue through the TAF period. Lee-enhanced
clouds, SCT-BKN FL200-250, along the east slopes of the
Absaroka Mountains into the Bighorn Basin will decouple and
disperse by 18Z. All sites except KWRL will see gusty winds
again Saturday, with frequent gusts of 20 to 25 kt in the
afternoon. During the afternoon, isolated/scattered virga
showers and thunderstorms are expected to develop from roughly
KRKS to KCPR around 21Z, then progress east through the
evening. Have continued with PROB30 in the forecast for those 2
sites for this possibility. This activity has the potential to
produce locally gusty winds as they pass, with gusts of 40 to 50
kt possible due to large dewpoint spreads. Showers will be
weakening and moving east by 03Z, with lighter winds through the
rest of forecast period.

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 248 AM MDT Sat Jun 28 2025

Another day of low humidity (as low as 10 percent) and gusty wind
(gusts as high as 30 mph) will bring elevated to critical fire
weather to approximately the southern two-thirds of the area,
with a Red Flag Warning in effect for the lower elevations of
Natrona County. Fire weather concerns should ease for central
Wyoming on Sunday, but continue across southern Wyoming as
humidity remains below 15 percent and a gusty wind continues.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from noon today to 9 PM MDT this evening for
WYZ280.

&&

$$

DISCUSSION...Hattings
AVIATION...LaVoie/Straub
FIRE WEATHER...Hattings