750
FXUS65 KRIW 300047
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
647 PM MDT Sun Jun 29 2025

.KEY MESSAGES...

- Mostly dry and warm Monday and Tuesday with shower and
  thunderstorm coverage increasing Wednesday, continuing
  through the end of the week.

- Hottest days this week are Tuesday and Wednesday, with
  widespread highs in the 90s.

&&

.UPDATE...
Issued at 645 PM MDT Sun Jun 29 2025

Most of the showers and storms have diminished or moved out of
the area this evening. A few still linger over southern
Sweetwater County, where gusts 30 to 40 mph continue from the
outflows. The other location is southeast Natrona County, with
the final storms making their way out of the county in the next
hour. The final showers in Sweetwater should be gone shortly
after midnight.

Northeast surface winds move in from the east this evening and
through the overnight hours. Some gusty winds up to about 30
mph could occur with its passage from Natrona County and into
Sweetwater County. Any gusty winds decrease by around sunrise.

&&

.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 /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 347 PM MDT Sun Jun 29 2025

VFR conditions will prevail at terminals through the period.
Convection will remain much more limited today, with the best
chances at KCPR and KRKS. Gusty outflow winds are possible with
this activity through around 02Z. Convection will end after
sunset leaving mostly clear skies through Monday morning.
Several terminals will continue to see a breeze overnight as a
cold front pushes south. Monday afternoon will be dry with
mostly calm winds.

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

&&

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

&&

$$

UPDATE...Wittmann
DISCUSSION...Hattings
AVIATION...Myers