219
FXUS65 KRIW 250852
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
252 AM MDT Fri Jul 25 2025

.KEY MESSAGES...

- Turning much drier today with hot temperatures and elevated
  fire weather.

- Critical fire weather is possible Saturday afternoon from Rock
  Springs through Casper.

- Elevated to possibly critical fire weather continues through
  Monday, when chances of showers and thunderstorms increase.

&&

.DISCUSSION...
Issued at 246 AM MDT Fri Jul 25 2025

Today is the day when we transition our concerns from thunderstorms
to fire weather concerns. There are still a few light showers out
there this morning, mainly firing along the boundary of the drier
and more moist air as the drier air pushes in from the south and
west. For example, at 2 am, Thermopolis has a dew point of 35,
Worland`s is 45 and at Greybull, it is 52. Drier air will
continue to push in tonight as ridging builds into the area.

As for tomorrow, it will be a typical late July day with hot
temperatures, but nothing extreme. Highs will be largely in the 90s
East of the Divide, with 80s West of the Divide. It will be a dry
atmosphere though, with precipitable water values anywhere from
40 to 70 percent of normal and this continues through the
weekend. This will keep any convection limited, largely in far
northern Wyoming and near the mountains where there will be a
bit more lingering moisture. But even here, the chance is at
most 1 out of 5 in any particular location. Dew point
depressions will be very large though, over 60 degrees in many
locations, so any thunderstorm or even shower could produce a
strong wind gust. However, the main concern is fire weather.
Humidity will be very low, falling in the single digits for much
of central and southern Wyoming. However, wind is expected to
remain light to moderate. So, we have classified the fire
weather today as elevated, not critical, so no highlights.

This changes tomorrow though. A weak shortwave will cross the area,
and this will be just enough to mix 20 to 25 knot winds at 700
millibars to the surface, mainly across areas prone to southwest
flow. This covers the area from Sweetwater County through Natrona
County. Reaching humidity values is a slam dunk (greater than a 9 in
10 chance). Wind will be a bit more questionable. However, with the
chance greater than 1 out of 2, we have hoisted Fire Weather Watches
across the above area from noon through 8 pm. The decision to
upgrade to a warning can be made by the day shift or the midnight
shift Friday night. Any convection on this day would be very
isolated, (less than a 1 in 10 chance) and restricted to the
northern mountains. Temperatures will remain hot with temperatures
similar to the high temperatures today. As for Sunday, highlights
may need to be extended for some areas, but this looks more
restricted, with Sweetwater County, mainly eastern portions, the
main area of concern. Any convection on this day would again be
largely restricted to the northern mountains.

Monday may be a transition day as a cold front approaches from
Montana. There is a spread as to how far south the front can reach
though. A majority of the ensemble members show it remaining north,
so this again looks like a dry and warm to hot day. Monsoonal
moisture may then push into the area for the middle of the week and
bring an increased chance of showers and storms starting Tuesday and
continuing through at least Thursday. Details regarding which day
will be the most active is still uncertain this far out though. The
increased cloud cover will also cool temperatures to below normal
levels, especially East of the Continental Divide.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 948 PM MDT Thu Jul 24 2025

Lingering showers and storms will end by the start of the TAF
period. An area of showers exiting Sweetwater County could hold
together and reach KCPR by 06Z/07Z, but only have a 20%
confidence. VFR conditions prevail overnight and through the
day Friday. Drier air Friday will limit shower/storm chances.
The best chances (15% to 30%) will occur over northwest Wyoming.
Currently only have KCOD with a PROB30 group for afternoon
storms. FEW-SCT FL150-200 will continue across the area through
the evening Friday.

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 246 AM MDT Fri Jul 25 2025

Fire weather will be elevated across most of the area with
humidity falling to under 15 percent across much of the area.
However, wind should remain below critical levels. On Saturday.
an approaching weak weather system will increase wind somewhat
from Rock Springs through Casper and increase the possibility
of critical fire weather during the afternoon and evening.
Continued elevated to critical fire weather remains likely
through Monday across much of the area.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch from Saturday afternoon through Saturday
evening for WYZ277-279-280-289.

&&

$$

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