Riverton, Wyoming 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

658
FXUS65 KRIW 260717
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
117 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 /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 953 PM MDT Mon May 25 2026

SOUTHERLY FLOW WILL CONTINUE TO BRING IN MOISTURE TO THE AREA OVER
THE NEXT 24 HOURS. THIS WILL KEEP ISOLATED SHOWERS IN THE AREA
TONIGHT AND RESULT IN SCATTERED SHOWERS AND STORMS TUESDAY AFTERNOON
INTO TUESDAY EVENING. CONDITIONS WILL PREDOMINANTLY REMAIN VFR
THROUGH THE TAF PERIOD, BUT MAY DROP TO MVFR/IFR IN THE STRONGEST
SHOWERS AND STORMS TUESDAY AFTERNOON INTO TUESDAY EVENING. AN AREA
OF RAIN, AND POSSIBLY A STORM, WILL MOVE INTO SOUTHWEST WYOMING
EARLY TUESDAY MORNING AND PUSH NORTH THROUGH TUESDAY MORNING. RAIN
IS POSSIBLE (15-25%) AT KBPI, KPNA, AND KJAC WITH THIS AREA OF RAIN
TUESDAY MORNING. WIDESPREAD CLOUD COVER TUESDAY MORNING MAY KEEP
CONVECTION FROM DEVELOPING UNTIL MID-AFTERNOON TUESDAY, WHICH WOULD
ALLOW FOR CONVECTION TO SURVIVE WELL INTO TUESDAY EVENING. TERMINALS
WITH THE BEST CHANCE FOR RAIN AND THUNDERSTORMS HAVE PROB30 GROUPS
AT THIS TIME, BUT PREVAILING GROUPS MAY BE NECESSARY WITH THE NEXT
COUPLE OF TAF ISSUANCES.

WIND WILL LIGHT TONIGHT, WELL BELOW 10 KNOTS, BUT WILL INCREASE
TUESDAY MORNING INTO TUESDAY AFTERNOON. WIND WILL BE FROM THE SOUTH
AND WILL AVERAGE 10-15 KNOTS, WITH GUSTS OF 15-25 KNOTS AT MOST
TERMINALS TUESDAY AFTERNOON. TYPICAL STRONGER GUSTS CAN BE EXPECTED
WITH CONVECTIVE ACTIVITY.

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...Rowe