649
FXUS65 KRIW 261848
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1248 PM MDT Thu Jun 26 2025

.KEY MESSAGES...

- A warm and pleasant day across the Cowboy State today with
  plenty of sunshine.

- 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 mid to upper 70s west of
the Divide and mid 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 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 /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1105 AM MDT Thu Jun 26 2025

VFR flight conditions prevail the entire TAF period at all terminals
with afternoon CU development and increasing mid-level clouds.
Westerly winds increase between 19-22Z at all west of the Divide
terminals and KCPR with gusts around 20kts. Gusty winds diminish
around sunset. Winds less than 10kts are forecast at all other
terminals.

Isolated showers and thunderstorms are possible across western and
northern Wyoming between 21Z-04Z. Confidence is highest (30%) in a
shower and/or thunderstorm at KCOD and this is reflected as a PROB30
group. Confidence is too low (20%) in a shower and/or thunderstorm
at KJAC and KWRL so there is no mention is TAF at this time. A
thunderstorm could produce gusty outflows around 30kts.

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...Gerhardt
FIRE WEATHER...Dziewaltowski