Severe Thunderstorm Warning 45, NWS Riverton, WY

Area Forecast Discussion
National Weather Service Riverton WY
1229 PM MDT Fri Jul 4 2025

.KEY MESSAGES...

- Scattered showers and thunderstorms today; a few strong to
  severe storms possible in the afternoon.

- Chances for showers and thunderstorms continue into Saturday
  with a greater chance for severe storms developing especially
  across northern and eastern WY. Hail and strong winds are the
  main hazards.

- Drier and warmer weather returns for Sunday, bringing
  increased chances for fire weather conditions.

&&

.UPDATE...
Issued at 1227 PM MDT Fri Jul 4 2025

The overall message for today remains the same: scattered showers
and thunderstorms this afternoon and evening, with strong winds
being the main hazard. Hi-res models continue to show widespread
thunderstorms moving across the area this afternoon, generally
ending between 6pm and 1am. There could be an additional cluster of
showers over central Wyoming through about sunrise, though not all
models have this feature. The main hazard with any storms will be
gusty outflows, the strongest of which could be around 60 mph.

&&

.DISCUSSION...
Issued at 227 AM MDT Fri Jul 4 2025

Its the United States' birthday today and turns 249, also known as
Independence Day or the 4th of July. The weather across the
Cowboy State is looking quite unsettled with chances for natural
fireworks occurring in the form of lightning and thunder.
Temperatures today will be on the cooler side but still around
seasonable values. Highs range from the low to mid 70s west of
the Divide and low 80s east of the Divide.

Two shortwaves will move across the region today, both are expected
to influence and aid in the development of showers and
thunderstorms. PWATs will remain above normal across the area
but the main concern as a result of this will be brief heavy
downpours. Moisture has had issues mixing down to the surface
which has limited any flooding concerns. So while flash flooding
is not likely it cannot be entirely ruled out. CAMs continue to
show a couple rounds of showers and thunderstorms today. The
first moves into western WY by the mid morning then gradually
spreads into central and northern WY. The next round follows
shortly behind, developing by the early afternoon with coverage
being more widespread. There are some signs of a third push
developing in the late afternoon, lingering into the evening.
Another concern today will be the chance for a few isolated
strong to even severe storms developing. Instability is fairly
limited but a brief period of clearing should allow for CAPE to
increase, ranging from 700-1200 J/kg. Low to mid level lapse
rates will be fairly steep and favorable for some of these
storms to become severe. Other components such as bulk shear
will be present with values around 40 knots over parts of the
area. The main hazards as a result of these components will be
strong gusty winds mixing down to the surface as these storms
move across the state. CAMs are showing potentially widespread
outflows of 40 to 50 mph with isolated gusts possibly nearing 60
mph. Small hail will be possible if storms are able to organize
and enough instability develops. The best chances for hail
looks to be across western WY where some models show CAPE values
ranging from 1000 to 1500 J/kg. The potential for strong to
severe storms is also represented by the SPCs outlooks which has
placed much of WY in a Marginal risk for strong wind gusts and
small hail. Overall, today is not looking to be a washout but as
mentioned earlier it will be unsettled with chances for showers
and some strong to severe thunderstorm throughout the day.

The weekend is looking less active, but will still have some chances
for showers and thunderstorms. Coverage of these showers and
thunderstorms will be less widespread Saturday, with the best
chances being across central and northern WY. There is the potential
for some severe storms to develop Saturday as a result of the second
shortwave moving across Montana. The SPCs day 2 outlook highlights
this potential with parts of the state being placed in a Slight
risk. The areas of concern look to be across northern and eastern
WY, specifically the Bighorn Basin along with Johnson and Natrona
Counties. These areas will see instability develop during the day
and will be combined with favorable dynamics from the nearby
shortwave. The main hazards will be large hail and strong gusty
winds along with an isolated tornado or two.

The unsettled weather pattern finally looks to quiet down for
Sunday. Temperatures will be seasonable but begin to gradually warm
as ridging looks to start building in over the western CONUS. A
period of hot and dry conditions is beginning to look more likely
for the upcoming week. A big factor will be the strength of the
ridging and how long it can prevail over the region. There is still
time for things to change but as of right now the July heat and
dryness looks to be right around the corner. This may lead to some
elevated fire weather conditions so it will need to be monitored as
we head into the start of next week.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1118 AM MDT Fri Jul 4 2025

Shower and thunderstorms are starting to develop along most
higher elevation mountain ranges currently, and these are
expected to move quickly to the northeast through the afternoon.
Confidence in showers and thunderstorms remains high for today,
so have added TSRA to all TAF sites for some time this
afternoon, trying to focus tempo groups on the best period for
thunder. Any thunderstorms that do form may be accompanied by
brief gusty winds, so have also added some variable gusts into
TEMPO groups. Calmer conditions expected overnight tonight for
all sites. Another round of thunderstorms is expected tomorrow,
but these would be limited more east of the Divide after 18Z/05.

&&

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

&&

UPDATE...Wittmann
DISCUSSION...Dziewaltowski
AVIATION...Straub

Hazardous Weather Outlook
National Weather Service Riverton WY
240 AM MDT Fri Jul 4 2025

WYZ001>020-022>030-051245-
Yellowstone National Park-Absaroka Mountains-Cody Foothills-
North Bighorn Basin-Southwest Bighorn Basin-Southeast Bighorn Basin-
Owl Creek and Bridger Mountains-Bighorn Mountains West-
Bighorn Mountains Southeast-Northeast Johnson County-
Southeast Johnson County-Teton and Gros Ventre Mountains-
Jackson Hole-Wind River Mountains West-Wind River Mountains East-
Upper Wind River Basin-Wind River Basin-Lander Foothills-
Green Mountains and Rattlesnake Range-
Natrona County Lower Elevations-Casper Mountain-Star Valley-
Salt River and Wyoming Ranges-Upper Green River Basin Foothills-
Upper Green River Basin-South Lincoln County-
Rock Springs and Green River-Flaming Gorge-East Sweetwater County-
240 AM MDT Fri Jul 4 2025

This Hazardous Weather Outlook is for Western and Central Wyoming.

.DAY ONE...Today and tonight.

Multiple rounds of showers and thunderstorms will move through the
state today. The first round is expected to begin developing by the
late morning with the next following shortly behind during the early
afternoon. A later round develops by the late afternoon lingering
into the late evening hours. A few isolated strong to severe storms
cannot be ruled out. These stronger storms may be capable of
producing small hail, heavy downpours, and strong gusty winds.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

Saturday...Thunderstorms develop once again in the afternoon with
coverage being more limited in nature. Convection chances look to
remain mainly across central and northern WY. Some strong to severe
storms will be possible, especially across the eastern Bighorn Basin
into Johnson and Natrona Counties. These strong to severe storms will
be capable of producing large hail, strong gusty winds, and an
isolated tornado or two.

Sunday through Thursday...Drier and warmer weather is expected to
develop and prevail across the region. This will likely lead to
increased chances for elevated fire weather conditions for much of
the state.

.SPOTTER INFORMATION STATEMENT...

Weather spotters are encouraged to report significant weather
conditions according to Standard Operating Procedures.

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