Severe Thunderstorm Warning 7, NWS Riverton, WY

Area Forecast Discussion
National Weather Service Riverton WY
1145 AM MDT Fri May 26 2023

.DISCUSSION...(This afternoon through Thursday)
Issued at 1141 AM MDT Fri May 26 2023

Another day of showers and thunderstorms is expected today as the
West Coast low and blocking high to our east remain in place.
This continues to bring a southwesterly divergent flow aloft,
aided at the surface by southeasterly moisture advection.
Currently, convection is ongoing this morning across western
Wyoming, as well as some isolated weak showers across central
Wyoming. The western convection is expected to continue to push
northeastward, with additional storms initiating east of the
Divide by early afternoon. With dewpoints in the 40s and 50s, as
well as mostly clear skies for diurnal heating, central and
northern Wyoming will be most favored for stronger storms today.
Given the increased moisture, steep lapse rates, and slightly
better shear today, storms have the potential to be a little
stronger than yesterday, which did produce some large hail. MLCAPE
values over 1000 J/kg are expected east of the Divide, with
values over 1500 J/kg farther east across Natrona and Johnson
Counties. Strong winds and large hail will again be possible with
this activity. Convection will wane after sunset across northern
Wyoming, with mostly dry conditions expected overnight.

Not much change is expected through the weekend as the main pattern
players persist. Saturday will see additional widespread showers
and thunderstorms, though a slightly eastward trough shift will
likely limit the strongest activity to Johnson and Natrona
counties. On Sunday convection currently looks a little less
widespread. Otherwise, temperatures will continue to peak around
normal west of the Divide, and about five degrees above normal
east.

By early next week, guidance is starting to favor the longstanding
trough dropping farther south, with a low positioned across southern
California. While the southwest flow would continue over Wyoming,
upper divergence would shift farther away from the area, likely
decreasing precipitation coverage. Overall, though, the active
pattern is likely to continue through at least midweek, with
generally above normal temperatures persisting.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1043 AM MDT Fri May 26 2023

VFR conditions expected throughout the TAF period for all
locations. Light and varying wind to start the period with mid
level ceilings as scattered rain showers and isolated
thunderstorms develop and approach from the south to north through
the afternoon and evening hours. Gusty winds up to 20-30 kts
possible with some of the storms but isolated in nature,
confidence low on exact locations of storms and outflows carrying
VCTS through about the 01-02Z time frame. After that point couple
with radiational cooling after sunset, winds will become light
once again with scattered mid clouds expected through the end of
the period.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on icing and turbulence forecasts.

&&

.FIRE WEATHER...
Issued at 1141 AM MDT Fri May 26 2023

The active pattern continues this afternoon as showers and
thunderstorms spread across most of the area. The strongest storms
are expected across central, northern, and eastern portions of the
forecast area, especially Johnson and Natrona counties. With any
storm, large hail and strong outflow winds are possible. Otherwise,
temperatures will peak above normal this afternoon for most
locations, with a gusty south wind developing over Sweetwater
County. Much of the same is forecast for Saturday and Sunday, with
continued thunderstorm chances in the afternoons. Minimum humidity
values will generally remain above 20 percent through the weekend.
Warmer than normal temperatures and rain chances will continue next
week.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

DISCUSSION...Myers
AVIATION...Lowe
FIRE WEATHER...Myers

Hazardous Weather Outlook
National Weather Service Riverton WY
302 AM MDT Fri May 26 2023

WYZ001>020-022>030-271315-
Yellowstone National Park-Absaroka Mountains-Cody Foothills-
North Big Horn Basin-Southwest Big Horn Basin-
Southeast Big Horn 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-
302 AM MDT Fri May 26 2023

This Hazardous Weather Outlook is for Western and Central Wyoming.

.DAY ONE...Today and Tonight.

Another chance of showers and thunderstorms, especially in the
afternoon and evening. Strong to severe thunderstorms are possible
this afternoon, especially along and north of a Casper to Thermopolis
to Cody line. The best chance will be in Johnson County.

Mountain snowmelt continues to keep water levels elevated on western
Wyoming creeks and rivers.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

Saturday through Wednesday...More chances of mainly afternoon and
evening showers and thunderstorms. Mountain snowmelt continues.

.SPOTTER INFORMATION STATEMENT...

Weather spotters are encouraged to report significant weather
conditions according to standard operating procedures.

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Special Weather Statement
National Weather Service Riverton WY
130 PM MDT Fri May 26 2023

WYZ014-015-018-026-262030-
Wind River Mountains West-Upper Green River Basin-Wind River
Mountains East-Lander Foothills-
130 PM MDT Fri May 26 2023

...A strong thunderstorm will impact portions of southeastern
Sublette and south central Fremont Counties through 230 PM MDT...

At 129 PM MDT, Doppler radar was tracking a strong thunderstorm 9
miles west of South Pass Rest Area, or 27 miles northeast of Farson,
moving north at 25 mph.

HAZARD...Winds in excess of 40 mph and half inch hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

Locations impacted include...
  Christina Lake, Louis Lake, Upper Silas Lake, Fiddlers Lake,
  Worthen Meadows Reservoir, Frye Lake, Sinks Canyon State Park and
  Lander.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 4233 10919 4297 10915 4274 10848 4264 10859
      4265 10860 4263 10861 4237 10890 4237 10895
      4232 10895 4228 10900
TIME...MOT...LOC 1929Z 200DEG 29KT 4239 10908

MAX HAIL SIZE...0.50 IN
MAX WIND GUST...40 MPH

Lowe

Special Weather Statement
National Weather Service Riverton WY
134 PM MDT Fri May 26 2023

WYZ002>004-262030-
North Big Horn Basin-Cody Foothills-Absaroka Mountains-
134 PM MDT Fri May 26 2023

...A strong thunderstorm will impact portions of southeastern Park
County through 230 PM MDT...

At 133 PM MDT, Doppler radar was tracking a strong thunderstorm 15
miles north of Washakie Needles, or 18 miles southwest of Meeteetse,
moving north at 30 mph.

HAZARD...Winds in excess of 40 mph and nickel size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

This storm will remain over mainly rural areas of southeastern Park
County, including the following locations... Sunshine Reservoir.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 4389 10906 4389 10920 4397 10931 4448 10932
      4429 10855
TIME...MOT...LOC 1933Z 193DEG 28KT 4397 10915

MAX HAIL SIZE...0.88 IN
MAX WIND GUST...40 MPH

Lowe