Severe Thunderstorm Warning 101, NWS Riverton, WY

Area Forecast Discussion
National Weather Service Riverton WY
540 PM MDT Sun Aug 6 2023

.DISCUSSION...(This evening through Sunday)
Issued at 1230 PM MDT Sun Aug 6 2023

Weak zonal upper level flow mostly across the state with a subtle
shortwave to the northwest into Montana. This will propagate
through the CWA this afternoon and into Monday that will spark off
scattered rain showers and isolated thunderstorms, mainly east of
the Divide. Development early in the afternoon before spreading
east to northeastward with time into the late evening hours before
weakening and pushing into eastern portions of the state. The
main concerns will be frequent lightning and some gusty winds up
to 30-40 mph possible as DCAPE values having enough juice of
200-300 J/kg to show some stronger outflows. Development of storms
are not of high confidence of location, just dependent on which
boundaries it occurs and where these will be. Regardless, a
marginal risk for southern counties but any severe weather looks
to be further south and southeast for Colorado. The higher
dewpoints and higher MLCAPE values will be had there and not as
high across the state line into Wyoming.

Similar conditions Monday through Wednesday but a little less
coverage with each passing day as models are indicating the upper
level ridge to build slowly back in from the south as convergence
aloft increases. By Thursday and Friday, expect mainly dry
conditions with only a stray higher elevation storm possible at
that point under a weak upper level no flow pattern. The mild
temperatures early in the period 10-20 degrees below average for
this time of year will slowly start a warming trend throughout
the work week back to around average by weeks end and into next
week as the aforementioned ridge builds in from the south.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 540 PM MDT Sun Aug 6 2023

Showers and thunderstorms stretch along a line from Lovell, to near
Riverton, to Pinedale late Sunday afternoon. IFR/MVFR conditions,
gusty wind to 45kts, and hail are all possible with the strongest
storms through 01Z/Monday, mainly in the Wind River Basin. CAMS show
this convection spawning additional showers and storms and heading
toward KCPR between 02Z-04Z/Monday. Showers and a few storms are
likely to persist until around 06Z/Monday additional clearing
arrives after 08Z. Other than the convection, terminals should
remain VFR through the forecast period. Those locations that receive
heavy rain Sunday afternoon and clear out early Monday morning could
see patchy fog around sunrise. Another round of convection is
anticipated Monday afternoon, although coverage should be less than
that of Sunday.

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 1230 PM MDT Sun Aug 6 2023

Temperatures will continue to be less than average for this time
of year with relative humidity values remaining above the 30-40
percent range, lowest along the I-80 corridor and into the Bighorn
Basin. Otherwise, expect scattered rain showers and a few isolated
thunderstorms this afternoon and evening east of the Divide
lasting through sunset dissipating before midnight. Expect
similar conditions Monday and Tuesday, a bit less in precipitation
coverage with time each day. Winds will remain relatively light
outside of any thunderstorm outflows, 10-20 mph from the south to
west with no higher winds expected.

&&

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

&&

DISCUSSION...Lowe
AVIATION...CNJ
FIRE WEATHER...Lowe

Hazardous Weather Outlook
National Weather Service Riverton WY
418 AM MDT Sun Aug 6 2023

WYZ001>020-022>030-071430-
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-
418 AM MDT Sun Aug 6 2023

This Hazardous Weather Outlook is for Western and Central Wyoming.

.DAY ONE...Today and tonight.

Scattered to numerous showers and thunderstorm over the area,
especially for northern Wyoming this afternoon. Locally heavy rain
may bring localized flooding.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

Monday and Tuesday...Scattered showers and thunderstorms, more
numerous over the northern mountains, persist with locally heavy rain
the primary hazard.

.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
430 PM MDT Sun Aug 6 2023

WYZ015>017-062315-
Wind River Basin-Upper Wind River Basin-Wind River Mountains East-
430 PM MDT Sun Aug 6 2023

...A strong thunderstorm will impact portions of central Fremont
County through 515 PM MDT...

At 430 PM MDT, Doppler radar was tracking a strong thunderstorm over
Crowheart, which is also 25 miles southeast of Dubois, moving
southeast at 20 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 strong thunderstorm will be near...
  Crowheart around 435 PM MDT.

Other locations in the path of this storm include Bull Lake and
Diversion Dam Rest Area.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 4328 10938 4342 10924 4335 10882 4305 10911
TIME...MOT...LOC 2230Z 305DEG 15KT 4331 10923

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

VandenBoogart

Special Weather Statement
National Weather Service Riverton WY
436 PM MDT Sun Aug 6 2023

WYZ005-007-062315-
Owl Creek and Bridger Mountains-Southwest Big Horn Basin-
436 PM MDT Sun Aug 6 2023

...A strong thunderstorm will impact portions of southeastern Hot
Springs County through 515 PM MDT...

At 436 PM MDT, Doppler radar was tracking a strong thunderstorm 11
miles southeast of Hamilton Dome, which is also 11 miles west of
Thermopolis, moving east 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.

Locations impacted include...
  Thermopolis and Hot Springs State Park.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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 4373 10795 4373 10791 4346 10802 4357 10857
      4374 10852 4374 10795
TIME...MOT...LOC 2236Z 282DEG 25KT 4364 10844

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

VandenBoogart

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