Special Weather Statement, NWS Riverton, WY

Area Forecast Discussion
National Weather Service Riverton WY
1049 PM MDT Mon Aug 7 2023

.DISCUSSION...(This afternoon through Sunday)
Issued at 1159 AM MDT Mon Aug 7 2023

Another cooler than average afternoon in store to start the new
work week under mainly cloudy skies and some scattered rain
showers ongoing for areas along and near the Winds and through the
Bighorns. A subtle short wave is propagating down the main
longwave trough extending in from the Gulf of Alaska. Being more
progressive and not as strong upper level diffluence, expect less
precipiation activity late this afternoon and evening to include a
handful of isolated thunderstorms mainly for eastern zones to the
I-25 corridor. With decent MLCAPE over 500 J/kg for this corridor
off the Bighorns, an isolated marginal severe storm is possible.
Being high based, damaging winds will be the main threat but some
small hail could be present early in the initial stages of
development.

Overnight, expect the main trough to close in on the Wyoming state
line sparking some widely scattered rain showers early Tuesday
morning before sunrise lasting throughout much of the day. Light
in nature, flooding concerns are not prevalent at this time with
PWATs less than half an inch expected. Even cooler temperatures
Tuesday with the aforementioned trough. Rain showers and isolated
thunderstorm will push east of the CWA by early evening to sunset
timeframe with improving skies into the overnight hours into mid
week.

Upper level ridging will now begin to build northward into the
upper Rockies to include the CWA Wednesday onward through the end
of the week into the weekend. Warmer temperatures can be had as
the trend pushes back to average temperatures for this time of
year seeing more widespread 80s by Friday. Precipitation chances
will be limited to northern counties Wednesday before the ridge
builds that far north but nothing significant is to be noted for
the slimmer rain chances. Mainly dry Thursday onward with only a
limited chance for a storm for the higher terrain more in line
with the late summer regime. Longer term models are in line with
the CPC outlooks of back to near average temperatures and dryer
conditions for mid month to the later days of August.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday)
Issued at 1044 PM MDT Mon Aug 7 2023

A few showers may linger through 08/09Z across northern WY, but then
diminish for a few hours.  A low pressure system will move from
central into eastern Idaho early Tuesday morning, bringing an area
of showers to west-central WY before sunrise.  Models are showing an
area of heavy showers moving from west-central WY toward north-
central WY during the day.  KJAC, KBPI, KPNA may see brief MVFR
conditions under heavy showers during the morning hours as a result.
Isolated thunderstorms are possible during the morning as well
across western WY with gusty outflow winds and brief heavy rain.
Showers and thunderstorms should then spread eastward through the
day, with gusty west winds across southern into central WY during
the afternoon and early evening. Again, general VFR conditions may
become MVFR under and around stronger storms. Gusty NW winds are
likely during the late afternoon and early evening behind the
storminess as the low pressure system moves into eastern WY. Showers
will linger across central WY through 09/06Z, with clearing across
western WY.  The higher terrain will generally be obscured at times
through the day due to the storm system.  High pressure then builds
in Tuesday night into Wednesday, with gusty west winds across
southern WY.

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

&&

.FIRE WEATHER...
Issued at 1159 AM MDT Mon Aug 7 2023

No fire weather concerns for today or Tuesday with the continued
precipitation chances and cooler than average temperatures. More
widespread rain Tuesday with more limited chances for northern
counties come Wednesday. Relative humidity values will remain
above the 35-45 percent range with relatively light winds less
than 10-20 mph. Dryer conditions and a warming trend for Thursday
onward into the weekend with a better chance for any fire weather
risk.

&&

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

&&

DISCUSSION...Lowe
AVIATION...McDonald
FIRE WEATHER...Lowe

Hazardous Weather Outlook
National Weather Service Riverton WY
546 PM MDT Mon Aug 7 2023

WYZ001>020-022>030-081300-
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-
546 PM MDT Mon Aug 7 2023

This Hazardous Weather Outlook is for Western and Central Wyoming.

.DAY ONE...Rest of Today and Tonight.

Scattered thunderstorm persist until around sunset over northwest
Wyoming, the Bighorn Basin, and adjacent areas. Locally heavy
rain and pea-sized hail are the primary hazards. A second round
of thunderstorms arrives in southwest Wyoming late tonight.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

Tuesday...Scattered thunderstorms continue with locally heavy
rain and gusty wind the main hazards.

Thursday...Another round of thunderstorms is possible across
northern Wyoming, generally during the afternoon and early evening.

.SPOTTER INFORMATION STATEMENT...

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

Special Weather Statement
National Weather Service Riverton WY
221 AM MDT Tue Aug 8 2023

WYZ023-024-080845-
Star Valley-Salt River and Wyoming Ranges-
221 AM MDT Tue Aug 8 2023

...A strong thunderstorm will impact portions of west central
Sublette and west central Lincoln Counties through 245 AM MDT...

At 220 AM MDT, Doppler radar was tracking a strong thunderstorm near
Smoot, which is also 9 miles southwest of Afton, moving east at 45
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.

This strong thunderstorm will be near...
  Smoot and Salt River Pass around 225 AM MDT.
  Mount Wagner around 235 AM MDT.

Other locations in the path of this storm include Mount Coffin,
Corral Creek Guard Station, Wyoming Peak and Middle Piney Lake.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 4270 11105 4283 11047 4250 11042 4250 11105
TIME...MOT...LOC 0820Z 261DEG 41KT 4260 11101

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

Dziewaltowski