Powell, Wyoming 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

900
FXUS65 KRIW 261020
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
420 AM MDT Tue May 26 2026

.KEY MESSAGES...

- A warm day today with a scattering of showers and
  thunderstorms, the most numerous in western Wyoming (around a
  1 in 2 chance) and Johnson and Natrona Counties (a 1 in 3
  chance). A few storms could be strong, especially in
  northwestern Wyoming.

- Remaining warm Wednesday and Thursday with most showers and
  storms restricted to northern Wyoming.

- An approaching weather system may bring more numerous showers
  and storms for Friday or the weekend, but details remain
  uncertain.

&&

.DISCUSSION...
Issued at 111 AM MDT Tue May 26 2026

Back when I was a little kid and dinosaurs roamed the earth (it was
the 1970s) I had a favorite toy, like many little girls and boys
did. And may favorite toy when I was 3 and 4 years old relates to
the one of the main driving factors with the weather the next
several days. The weather feature I am speaking of is an upper level
low that is moving onshore in the Pacific northwest. And that toy I
am speaking of is the Sit And Spin. Models have finally started to
come into better agreement that the upper level low will, move close
to the Great Basin and, sit and spin for a few days.

And the main impact from this, in conjunction with a strong,
blocking ridge over the Plains States, will keep southerly flow over
the area for the next several days. This will keep temperatures
above normal for several days, generally between 5 to 15 degrees
above normal. It will also keep rotating a few shortwaves over
the area, keeping varying chances and placements of largely
diurnal showers and thunderstorms.

And today may be one of the more active days across the area. Radar
shows an area of rain and embedded thunder across Utah and northern
Colorado slowly moving northward as the shortwave moves north. This
will bring the chance of showers and storms today. Model guidance is
zeroing in on two locations. One is western Wyoming, Where
upper level forcing will be greater with a weak jet streak
moving through, this is where the most numerous showers and storms
will be. One question is will there be any stronger storms? The
Storm Prediction Center has a Marginal Risk of severe
thunderstorms across northern Yellowstone. Soundings are showing
a decent amount of shear as well. The limiting factor may be
cloud cover, especially further south where surface instability
could be limited. The highest values (CAPE up to 700 J/Kg and
lifted indices of minus 2) are across northwestern Wyoming. So,
if any stronger storms develop it would likely be here. Chances
here range from a 1 in 3 chance to a 4 in 5 chance with the
highest chance in the northern mountains. The main threat would
be strong wind gusts given the very steep lapse rates, but some
small hail may also be possible. The other areas of concern is
East of the Big Horn Range in Johnson and Natrona Counties. Low
level south-southeast flow will likely bring some upslope flow
to initiate showers and storms. And in this area, the highest
instability parameters are further north, although shear is
less. Chances here range from 1 in 4 to 1 out of 2, with the
highest POPs close to the Bighorn Range. With some cloud cover
to start, this could be a later show as well, with storms
extending into the evening. Elsewhere, we can`t rule out a
shower or storm, but with less instability and more cloud cover,
the chance is only 1 out of 5 or less. The shortwave will also
bring a gusty breeze in some locations, although high wind is
not expected.

Less activity is now expected for Wednesday and Thursday, Most
guidance is showing much drier air moving in from the south, with
precipitable water values falling below climatological normals
for much of the southern half of the state. On Wednesday, most
convection would occur either in or near the northern mountains
where some weak upslope and high level heat source convection is
possible. A few showers and storms (about a 1 out of 3
coverage) are also possible across Johnson and Natrona County,
with the western boundary close to the 0.5 inch precipitable
water line. Thursday looks even drier as the atmosphere dries
out even more. And storms on these days would be in the same
locations, but only around a 1 out of 5 chance.

It continues to look like Friday or Saturday when we get the plunger
out to break up the blockage as another trough finally kicks the
low to the east and it opens up into a wave. There are still
differing solutions on how far east it can get. A closer pass
would obviously bring a better chance of showers and storms, but
there is still a fair amount of uncertainty right now. Stay
tuned.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 412 AM MDT Tue May 26 2026

Moisture and a shortwave moving north will bring moisture into
the area, with the highest chance of showers across western
Wyoming and in Johnson and Natrona Counties. The best chance
will be across the western terminals, with the best chance in
vicinity of KJAC, where there is around a 30 to 40 percent
chance of an afternoon shower or thunderstorm and 40 percent
chance of a vicinity shower. KBPI and KPNA also have a 30
percent chance of a shower or thunderstorm. East of the Divide,
a surge of deeper moisture will bring around a 30 percent of a
shower or thunderstorm in vicinity of KCPR and in vicinity of
KCOD. A shower or thunderstorm can`t be ruled out at the other
terminals, but the chance is less than 20 percent. Other than
the light morning showers in the west, most convection should be
later, generally between 21Z Tuesday and 03Z Wednesday, with
all showers ending by 06Z Wednesday.

Wind will increase at most terminals today as well, with gusts
over 15 knots possible at all terminals in the afternoon. Any
shower or thunderstorm could bring gusts greater than 35 knots,
wind should decrease after sunset as convection subsides and the
atmosphere decouples.
&&

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

&&

$$

DISCUSSION...Hattings
AVIATION...Hattings