425
FXUS65 KRIW 270445
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1045 PM MDT Thu Jun 26 2025

.KEY MESSAGES...

- Warm temperatures, low RH, and gusty winds have lead to a Red
  Flag Warning being issued for portions of Natrona County
  Friday afternoon through the evening.

- Elevated to near critical fire weather conditions are expected
  to be widespread Friday into Saturday.

- Small chances for daily showers and thunderstorms will be
  possible through the weekend with the highest likelihood being
  over northern WY.

&&

.UPDATE...
Issued at 1244 PM MDT Thu Jun 26 2025

The forecast continues to remain mostly unchanged with fire weather
conditions becoming the next concern through the weekend.
Temperatures will continue to gradually warm through the start of
next week. Highs today will range from the middle to upper 70s
west of the Divide and middle to upper 80s east of the Divide.
Temperatures are expected to remain above normal through the
rest of June with highs in the low 80s to low 90s. Through the
start of next week a few weak shortwaves will move over the
region, which will bring increased winds and slight chances for
showers and thunderstorms. Precipitation chances overall remain
low and will likely be fairly limited. Better chances for more
widespread showers and thunderstorms do not look to arrive until
next week.

As mentioned earlier the main concern over the next few days will be
fire weather conditions. A Fire Weather Watch for portions of
Natrona County has been upgraded to a Red Flag Warning. This will go
into effect Friday afternoon through Friday evening. While this is
the only location with a fire related highlight, other areas are
going to see elevated to near critical conditions Friday and
Saturday. Winds will increase both Friday and Saturday with fairly
widespread wind gusts of 20 to 30 mph. RH values will be bone dry
across much of central and southern WY with values ranging from 10
to 15%. These fire weather conditions look to improve slightly by
Sunday with weaker, but still breezy winds and moister RH
values.

Looking forward to the end of June and the start of July, the
CPC outlook is suggesting above normal temperatures prevailing
over the region. Precipitation chances are slightly above normal
as well, likely in the form of afternoon convective showers and
thunderstorms. However, there are some signals that moisture
may eventually be cut off to the region. This would lead to
drier conditions and possibly a transition from the convective
season to the heart of fire weather season.

&&

.DISCUSSION...
Issued at 249 AM MDT Thu Jun 26 2025

June is typically the most active month for severe weather
(hail, tornadoes) etc in western and central Wyoming and the
past month is no exception. Eventually, we begin to transition
into a drier time when fire weather concerns become the main
concern and while we are not completely there yet, we have
begun the slow transition.

Flat ridging will dominate the weather through around Saturday. This
typically means flow will be mainly from the west and southwest, and
will bring warmer temperatures. We will see a period of above normal
temperature through the weekend. Areas in our warmer locations, like
Greybull and Worland, will see highs climb back close to the 90s
today with 80s widespread across most of the lower elevations. We
could still see a few thunderstorms today, mainly across the
northern mountains and adjacent foothills as a shortwave brushes by
to the north. The atmosphere is much drier today though. This is the
first day in a while that precipitable water values are below
the 50th percentile. This means coverage will be isolated (at
most a 1 out of 5 chance). However, it also means dewpoint
depressions will be large so any thunderstorm or shower that
forms could have strong wind gusts of 40-50 mph. As for fire
weather concerns, humidity will be low, falling below 15 percent
in many lower elevation locations (especially across central and
southern portions). Wind should remain on the light to moderate
side, so critical fire weather is not expected.

Concerns do increase on Friday though. Another shortwave will move
by to the north. Again, isolated storms (a 1 out of 6 chance)
will be possible in the northwest but this is the main concern.
The pressure gradient will be a bit tighter. In addition, a jet
streak moving across Montana will put Wyoming in the right
front quadrant of the jet, enhancing downward momentum of 20 to
30 knot 700 millibar winds. Increased southwest flow will also
bring a hot day, with fairly widespread highs in the low to mid
90s. Humidity will be very low as well, falling into the single
digits at this time. Additionally, fuels have turned critical
in a few locations. One of these locations is Natrona County,
and this is also one of our windier locations. With this, we
have hoisted a Fire Weather Watch for Friday afternoon and
evening. Other locations could have elevated to critical fire
weather, but less wind or fuels not being critical should
prevent more widespread watches.

On Saturday, we have a few more questions. We thought about going
two days on the Watch, but have held off for now. For one, the
best jet forcing moves a bit further north, reducing downward
momentum. The result is wind should be a bit lighter. In
addition, most guidance shows a bit more moisture moving in,
raising dewpoints anywhere from 5 to 10 degrees, making things
more borderline. The increased moisture and with what forcing we
have from the right rear quadrant of the jet, thunderstorm
chances may increase a bit, but the chance is still only around
1 out of 4.

A somewhat stronger wave and associated weak cold front will swing
through the area on Sunday, taking the edge off of the heat. It will
also increase chances for showers and storms in eastern portions of
the area, where surface easterly flow may provide convective
initiation, mainly in Johnson and Natrona Counties. Ridging then
builds northward for early next week, resulting in above normal
temperatures again. Most convection these days should be in the
mountains and adjacent foothills, but any spot generally only
has a 1 in 4 chance of a shower or thunderstorm. Another wave
may bring increased showers and storms for Wednesday, but timing
this far out is uncertain.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1035 PM MDT Thu Jun 26 2025

VFR conditions throughout the period for all TAF sites remaining dry
throughout. Light winds and scattered mid to upper level clouds
overnight. Winds will start to increase after 15Z-17Z then pick
up with gusts up to 25 kt at all locations after 18Z-19Z due to
the stronger mixing with peak heating of the afternoon. Winds
will diminish after 01Z-02Z towards sunset becoming around
8-12 kt through the end of the period and overnight into
Saturday morning. Mid to upper level clouds remain scattered to
broken throughout the day Friday remaining above the 10-12kft
mark. No other weather elements are expected at this time.

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 1244 PM MDT Thu Jun 26 2025

Elevated to near critical fire weather conditions will be
prevalent across much of central and southern WY on Friday and
Saturday. Temperatures are forecast to remain above normal into
the weekend. Low RH will range from 10 to 20% across much of
this area with winds gusting 20 to 30 mph at times. A Red Flag
Warning has been issued for zone 280 as a result of these
conditions and dried fuels.

&&

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

&&

$$

UPDATE...Dziewaltowski
DISCUSSION...Hattings
AVIATION...LaVoie/Lowe
FIRE WEATHER...Dziewaltowski