Special Weather Statement, NWS Riverton, WY

Area Forecast Discussion
National Weather Service Riverton WY
751 PM MDT Tue Jul 7 2026

.KEY MESSAGES...

- Showers and storms have primarily ended across the forecast
  area this evening. Any additional showers and storms will be
  very isolated through the night.

- Wednesday will see another round of afternoon and evening
  showers and thunderstorms with near seasonable temperatures.
  Strong storms are possible over Johnson County late Wednesday
  afternoon. Showers will again linger Wednesday night into
  Thursday morning over some areas.

- Isolated showers and thunderstorms are possible again Thursday
  afternoon over central WY, and perhaps Friday afternoon across
  western WY. Temperatures begin to climb on Friday to 5-10
  degrees above normal.

- Very warm to hot temperatures are expected this weekend along
  with dry conditions. Record-breaking temperatures are possible
  Saturday, Sunday, and Monday, with mid 90s in the western
  valleys, and 100 to 105 degrees in the basins east of the
  divide.

&&

.UPDATE...
Issued at 1245 PM MDT Tue Jul 7 2026

As I wrote in a couple of discussions last week about this same
time of day, another shortwave trough is moving from the
northeast Great Basin through WY. Moisture is ample with
surface dewpoints ranging from the low 40s to the mid 50s and
precipitable water values around two-thirds to three-quarters of
an inch. Based on the RIW 18Z sounding (still in flight), as
temperatures reach around 90F, CAPE around 1000 J/kg will allow
isolated to scattered showers and thunderstorms to develop and
continue through the afternoon and into the evening. As of 1210
PM, convection has already initiated in the Upper Green River
Basin and near Cokeville and Flaming Gorge, moving ENE today.
The area from southwest WY toward central WY and into Johnson
County will have the higher probabilities of thunderstorms
today, with gusty outflow winds of 40-50 mph the primary threat,
especially in areas where the dewpoint depressions are larger.
Brief heavy rain even from higher cloud bases and small(ish)
hail will also occur with frequent lightning. SPC maintains a
slight risk of severe storms for northeast WY, so storms that
develop around Johnson County from 5 to 8 PM have a higher
chance of producing severe convective weather. CAMs and
mesoscale models continue to show areas of showers through
midnight across much of western and central WY too.

The general instability and increased boundary layer moisture
continues into Wednesday for more isolated showers and
thunderstorms during the afternoon. Gusty outflow winds will be
the primary threat, with stronger storms expected yet again over
Johnson County.

&&

.DISCUSSION...
Issued at 328 AM MDT Tue Jul 7 2026

A few showers and thunderstorms continue to linger across the state
early this morning. As of writing this around 0100 MDT, a couple
flashes of lightning have been detected over portions of western WY.
However, convective activity is gradually waning with clusters of
lightning continuing to decrease. Precipitation chances will remain
mostly across western and northern WY through the predawn hours.
Showers and storms will continue to trek east through the morning
with the bulk dissipating by sunrise.

A shortwave will be the main instigator for the "active" weather
today and Wednesday. The shortwave currently is making its way
across Montana while ushering in above normal moisture to the
region. This can be seen with PWATs being nearly 100-150% above
normal across much of the area. Dewpoints also reflect this with
portions of the Bighorn Basin and Johnson County likely to see
values in the 50s this afternoon. As for temperatures, they will be
similar to Monday with highs in the upper 80s to lower 90s east
of the Divide and low to mid 80s west of the Divide. Scattered
showers and thunderstorms will once again be possible later this
afternoon and evening. Coverage today will shift farther south
with northwestern WY likely having lesser chances of seeing a
shower or storm compared to elsewhere. Precipitation chances
across the forecast area aside from northwestern WY look to
range from 20-40% with the best chances being over central and
portions of southern WY.

The other aspect regarding the convection possible this afternoon
and evening, will be the potential for a few strong to severe storms
developing. The Storm Prediction Center has highlighted much of the
state with a marginal risk (1 out of 5). The only exception to this
is portions of northwestern and western WY, specifically much of YNP
and the Tetons/Jackson Hole where the marginal risk has been
excluded. There is a very small sliver of slight risk (2 out of 5)
for a portion of Johnson County mainly due to large hail threat. The
setup is a wide swath of above normal moisture across the area.
Morning cloud cover is expected to gradually clear by the early
afternoon with daytime heating helping produce CAPE values around
500 J/kg over much of the state. Some CAMs are highlighting portions
of Johnson County and central WY with swaths of CAPE nearing 1000
J/kg. So if this were to occur, there could be more juice for any
storms that develop. Steep low to mid level lapse rates are forecast
over much of the state as well. The other factor will be favorable
dynamics as a result of the nearby short wave. Low to mid level wind
shear values currently look to range from 25 to 35 knots. Overall,
the main threat today will be strong gusty winds with CAMs
highlighting favorable downdraft CAPE values. Storms could
produce strong gusty outflow winds of 50 mph or more at times.
There does remain a threat for hail with the most favorable
locations being central and northern WY, specifically Johnson
County. Otherwise, frequent lightning and brief moderate
rainfall may be possible with any storms. Showers and
thunderstorms may linger into the late evening hours Tuesday and
possibly into the early morning hours Wednesday.

Wednesday has trended towards another day with possible afternoon
showers and thunderstorms. This once again is the result of
lingering moisture and the exiting shortwave. Currently, much of the
state looks to have similar chances for precipitation as Tuesday.
However, chances for strong to severe storms looks to diminish and
shift farther east. The SPC currently has far eastern portions of
Johnson and Natrona Counties in a marginal risk with the main
concerns being strong gusty winds and hail. Aside from these
locations, the remainder of the state will see similar hazards as
the previous days with frequent lightning, gusty winds, and small
hail possible.

No, there does not seem to have been a technical glitch in the long
term forecast models, it really is looking to be that hot this
weekend. Some long term models have done a good job of indicating
this heat as early as last week. Barring some miraculous shift in
the weather pattern, we are likely to see a period of dangerously
hot, record breaking temperatures this weekend. This heat will be
the result of an anomalously potent high pressure ridge that builds
across the western/central CONUS. Temperatures start to turn up
Friday with current highs getting into the middle to upper 90s
east of the Divide and upper 80s to lower 90s west of the
Divide. The warmest temperatures look to arrive for the weekend.
Guidance is showing western valleys such as Star Valley and
Jackson Hole possibly seeing highs around 95F Saturday.
Locations east of the Divide to no surprise are warmer, with
central basins seeing highs nearing the century mark. Northern
locations, such as portions of the Bighorn Basin may see highs
nearing 105F. Sunday looks even warmer with locations west of
the Divide seeing 20-40% of highs nearing 100F. East of the
Divide central basins have 20-50% for highs around 105F.
Portions of the Bighorn Basin may see highs near 110F with
chances sitting around 10-30%. These percentages are to show the
potential range for high temperatures. So if there is a 20-50%
for highs near 105F, its likely the highs will at least be
greater than 100F. There is increasing likelihood that numerous
daily high temperature records and even all-time high
temperature records may be met or broken. Climate data at KLND
goes back to 1891 and the current all time high temperature is
102F set back in 1935 on July 27th. Currently, the NBM has a
forecast high of 104F for Sunday, so that should give an idea of
how historic this period of heat may be. Yes, this degree of
heat can be dangerous for those who are at risk or do not use
caution. So be sure to stay up to date on the forecast and be
prepared, especially if planning outdoor activities!

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 506 PM MDT Tue Jul 7 2026

Convection continues into Tuesday evening before coverage and
intensity begin to subside between 02Z-05Z/Wednesday. Gusty wind 25-
40kts remains the primary hazard. However, better surface moisture
could still allow for brief, less than 30-minute, MVFR to IFR
visibility over the north-half of the state, while a dry sub-cloud
base over the south favors gusty outflow wind 30-45kts. Moisture in
the northern Great Basin persists in streaming northeast across the
forecast area much of tonight. As a result, light showers linger
overnight, especially across the southern-third of Wyoming. By
15Z/Wednesday, cloud cover clears the region and allows for better
daytime heating heading into the afternoon. This sets the stage for
another round of afternoon convection, although coverage should be
less than that of Tuesday. Confidence is highest for Wednesday
afternoon storms in the vicinity of KRKS and near the northern
terminals of KCOD and KWRL where PROB30 groups have been included.
Otherwise, all terminals to be VFR through the period with the
possible exception of the aforementioned short-term MVFR.

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...McDonald
DISCUSSION...Dziewaltowski
AVIATION...CNJ/Rowe

Preliminary Local Storm Report
National Weather Service Riverton WY
726 PM MDT Tue Jul 7 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0626 PM     Tstm Wnd Gst     14 N Bar Nunn           43.12N 106.34W
07/07/2026  M64 MPH          Natrona            WY   Mesonet

            Mesonet station KTMH I-25 Twenty Mile Hill
            (DOT).

&&

Preliminary Local Storm Report
National Weather Service Riverton WY
727 PM MDT Tue Jul 7 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0634 PM     Tstm Wnd Gst     14 SE Kaycee            43.54N 106.48W
07/07/2026  M61 MPH          Johnson            WY   Mesonet

            Mesonet station WY63 I-25 Tisdale Divide
            (DOT).

&&

Special Weather Statement
National Weather Service Riverton WY
735 PM MDT Tue Jul 7 2026

WYZ003-004-080200-
North Bighorn Basin-Cody Foothills-
735 PM MDT Tue Jul 7 2026

...A STRONG THUNDERSTORM WILL IMPACT NORTHEASTERN PARK COUNTY THROUGH
800 PM MDT...

At 734 PM MDT, Doppler radar was tracking a strong thunderstorm near
Clark, which is 19 miles west of Powell, moving east at 35 mph.

HAZARD...Wind gusts of 50 to 55 mph and pea size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could blow around unsecured objects. Minor hail
         damage to vegetation is possible.

This storm will remain over mainly rural areas of northeastern Park
County, including the following locations... Clark Elementary School
and Powell Municipal Airport.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 4470 10930 4493 10925 4490 10879 4461 10884
TIME...MOT...LOC 0134Z 274DEG 29KT 4482 10915

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...55 MPH

TL

Special Weather Statement
National Weather Service Riverton WY
758 PM MDT Tue Jul 7 2026

WYZ003-004-080230-
North Bighorn Basin-Cody Foothills-
758 PM MDT Tue Jul 7 2026

...STRONG THUNDERSTORMS WILL IMPACT NORTHEASTERN PARK COUNTY THROUGH
830 PM MDT...

At 758 PM MDT, Doppler radar was tracking strong thunderstorms along
a line extending from near Clark to 9 miles southeast of Dead Indian
Pass. Movement was east at 25 mph.

HAZARD...Wind gusts up to 50 mph and pea size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could blow around unsecured objects. Minor hail
         damage to vegetation is possible.

Strong thunderstorms will be near...
  Elk Basin around 815 PM MDT.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 4500 10859 4452 10884 4460 10926 4460 10923
      4461 10924 4461 10922 4462 10922 4464 10925
      4463 10927 4464 10929 4465 10926 4468 10928
      4501 10911
TIME...MOT...LOC 0158Z 268DEG 21KT 4496 10907 4465 10923

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...50 MPH

TL

Special Weather Statement
National Weather Service Riverton WY
829 PM MDT Tue Jul 7 2026

WYZ003-004-080300-
North Bighorn Basin-Cody Foothills-
829 PM MDT Tue Jul 7 2026

...STRONG THUNDERSTORMS WILL IMPACT NORTHWESTERN BIG HORN AND
NORTHEASTERN PARK COUNTIES THROUGH 900 PM MDT...

At 828 PM MDT, Doppler radar was tracking strong thunderstorms along
a line extending from near Elk Basin to 6 miles southwest of Ralston.
Movement was east at 20 mph.

HAZARD...Wind gusts up to 50 mph.

SOURCE...Radar indicated.

IMPACT...Gusty winds could blow around unsecured objects.

Strong thunderstorms will be near...
  Powell and Ralston around 835 PM MDT.
  Frannie around 845 PM MDT.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 4452 10869 4460 10904 4500 10878 4500 10846
TIME...MOT...LOC 0228Z 272DEG 19KT 4494 10880 4467 10897

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...50 MPH

TL

Special Weather Statement
National Weather Service Riverton WY
910 PM MDT Tue Jul 7 2026

WYZ004-080345-
North Bighorn Basin-
910 PM MDT Tue Jul 7 2026

...A STRONG THUNDERSTORM WILL IMPACT WEST CENTRAL BIG HORN COUNTY
THROUGH 945 PM MDT...

At 910 PM MDT, Doppler radar was tracking a strong thunderstorm 8
miles south of Lovell, moving east at 30 mph.

HAZARD...Wind gusts up to 50 mph and half inch hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could blow around unsecured objects. Minor hail
         damage to vegetation is possible.

This storm will remain over mainly rural areas of west central Big
Horn County, including the following locations... Greybull South Big
Horn County Airport and Bighorn Canyon National Recreation Area.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 4481 10842 4476 10797 4449 10805 4459 10850
TIME...MOT...LOC 0310Z 278DEG 26KT 4471 10834

MAX HAIL SIZE...0.50 IN
MAX WIND GUST...50 MPH

TL