091
FXUS65 KRIW 290906
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
306 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, on has improved
somewhat and one is about the same. The one 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 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 dew
points. 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 but
not a ton. There will also be an approaching jet streak to enhance
lift somewhat. For now, kept storm chances largely from the Bighorn
Range and eastward. The main risk from any thunderstorm would be
gusty wind 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 through around
Wednesday, with cooler temperatures later next week as cloud
cover increases from the increased cloud cover and possible
showers.


&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 946 PM MDT Sat Jun 28 2025

VFR conditions prevail through the TAF period. Winds will be
diurnally driven, increasing a bit for Sunday afternoon. A cold
front pushes in from the east late in the period, with winds from
the east-northeast behind it. There is about a 20% chance for a
shower/thunderstorm at KCPR Sunday afternoon, starting about 20z.

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...Wittmann