882
FXUS65 KRIW 290951
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
351 AM MDT Sun Jun 29 2025

.KEY MESSAGES...

- Elevated fire weather continues in the southern Wyoming today,
  with a few thunderstorms mainly in Johnson and Natrona
  Counties.

- Mainly dry and warm for Monday and most of Tuesday.

- Coverage of showers and thunderstorms increases Wednesday and
  likely continues through the end of the week.

&&

.DISCUSSION...
Issued at 303 AM MDT Sun Jun 29 2025

As of 2 am, the last of the showers have ended and things are quiet
right now. Like yesterday, we have two concerns; one has
improved somewhat and one is about the same. The one concern that
has improved at bit is fire weather. We will not have any Red
Flag Warnings today. Flow has turned to the north or northeast
east of the Divide due to a weak frontal boundary and that has
brought somewhat cooler temperatures and higher humidity. As a
result, critical fire weather is not expected here, although
local elevated fire weather is still possible. Elevated to
critical fire weather will continue in southern Wyoming, but
fuels are not critical here.

The concern that is the same is the chance of convection. We do have
an area of Marginal risk largely along and east of Interstate
25. The best chance will be in eastern portions of the area,
close to the frontal boundary and in the area with somewhat
higher dewpoints. Instability parameters are decent, especially
in the Marginal risk area with over 1000 J/kg of CAPE and
lifted indices as low as minus 3. Lapse rates are decent as
well, with some shear (close to 40 kt). There will also be an
approaching jet streak to enhance lift somewhat. For now, have
kept storm chances largely from the Bighorn Range eastward. The
main risk from any thunderstorm would be gusty wind and/or
small hail, although there could be a few storms that have
marginally severe hail. This looks like an earlier show, with
most storms over shortly after sunset. Coverage does not look
very big though, at most 1 out of 3 at any particular location.
Otherwise, expect a seasonable day across the area.

Most areas should have a nice summer day to end the month of June on
Monday with lots of sunshine, warm but not hot temperatures and,
thankfully, lighter wind. I can`t completely rule out a shower or
thunderstorm, but the chance is less than 1 out of 10 so we kept the
forecast dry for now. The chance of thunderstorms increases again on
Tuesday as moisture begins to move in from the south, but this would
initially be of the mid level variety. Storms on this day would
likely stay near the mountains with only around a 1 in 6 chance
at any location. Moisture return has slowed somewhat in the
latest model runs for Wednesday, so we did trim PoPs somewhat.
A shortwave and much deeper moisture moving in now makes
Thursday a more likely time for the arrival of more widespread
showers and storms. This could especially be the case on
Thursday and Friday, as some guidance shows some precipitable
water values possibly climbing as high as 200 percent of normal
(for example, around 1.2 inches at our office, normal is closer
to 0.60 inches). A lot will depend of the progress of an upper
level low now off the California coast and move eventually open
up and move northeastward. These are notoriously fickle and hard
to time and track, especially this far out. However, we have
the potential for an active period of showers and storms later
next week. As for temperatures, look for above normal temps through
around Wednesday, with cooler temperatures later next week as
cloud cover increases from the increased moisture and possible
showers/thunderstorms.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 346 AM MDT Sun Jun 29 2025

MVFR ceilings have developed near KCPR this morning, but should
disperse/improve by 15Z/16Z. Otherwise, SKC skies will be in
place across much of the forecast area through the TAF period.
Winds will be diurnally driven, increasing a bit during the
afternoon. A cold front pushes in from the north late in the
afternoon and through the evening, with winds from the east-
northeast behind it. Virga showers will be possible (15%
chance) over portions of Johnson and Natrona counties in the
afternoon, with better chances (30%) around the WY/UT/CO border.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on icing and turbulence forecasts.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Hattings
AVIATION...LaVoie/Wittmann