589
FXUS65 KRIW 260853
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
253 AM MDT Thu Jun 26 2025

.KEY MESSAGES...

- Warmer and drier today with only isolated thunderstorms in
  northern Wyoming. Elevated fire weather is likely in central
  and southern Wyoming.

- Elevated to critical fire weather is likely for much of the
  area on Friday afternoon.

- Above normal temperatures are expected to continue through
  much into early next week.

&&

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

Here in western and central Wyoming, June is typically our most
active month for severe weather (hail, tornadoes) etc. And the past
month is no exception. And 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 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 dew point depressions will be
large so any thunderstorm or shower that forms could have a strong
wind gusts. As for fire weather concerns, humidity will be low,
falling below 15 percent in many lower elevation locations. Wind
should remain on the light to moderate side though, 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 today, falling into the single digits at this time. And
we also have something else, 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. We held off for now though. 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 dew points
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 bring convective
initiation, mainly in Johnson and Natrona Counties. Ridging then
builds northward for early next week, bring above normal
temperatures. 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 FRIDAY/...
Issued at 945 PM MDT Wed Jun 25 2025

VFR conditions expected throughout the entire period for all TAF
sites with only a few mid and upper level clouds expected. Any
shower activity will be north of KCOD and not expected to affect any
locations. Otherwise, light winds overnight through about 15Z-19Z
before increasing some to around 10kts for all, and some breezy
gusts up to around 18kts west of the Divide as well as KCOD/KCPR.
These winds decrease towards sunset after 00Z/01Z due to radiational
cooling remaining light into the Thursday overnight hours. 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 icing and turbulence forecasts.

&&

.FIRE WEATHER...
Issued at 249 AM MDT Thu Jun 26 2025

Elevated fire weather is possible this afternoon with humidity
falling below 15 percent across much of the southern half of the
area. Wind should remain light to moderate though. On Friday,
stronger wind combined with low humidity will lead the
likelihood of elevated to critical fire weather across much of
the area.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch from Friday afternoon through Friday
evening for WYZ280.

&&

$$

DISCUSSION...Hattings
AVIATION...Lowe
FIRE WEATHER...