Deep moisture and a passing shortwave combined to produce to slow moving strong to severe thunderstorms across Natrona County. The most notable storm occurred in northern Natrona County to the south of Midwest.
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Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS RIW wrote it up.
Deep moisture and a passing shortwave combined to produce to slow moving strong to severe thunderstorms across Natrona County. The most notable storm occurred in northern Natrona County to the south of Midwest. A thunderstorm dropped large amounts of hail up to quarter size along Highway 259, leaving up to a foot of hail on the road that made travel very difficult for several hours. The combination of hail and very heavy rain brought local flooding to that area as well, resulting in some dirt and gravel roads washing out. To the southwest of Casper, there was a brief touchdown of a rope tornado, but no damage was reported. Heavy rain also caused minor flooding in northwestern Natrona County later in the evening.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Riverton, WY wrote its last area forecast discussion before the first event at Jun 29, 11:16 AM MST, 44 minutes earlier.
Area Forecast Discussion National Weather Service Riverton WY 1216 PM MDT Thu Jun 29 2023 .DISCUSSION...(This afternoon through Thursday) Issued at 1215 PM MDT Thu Jun 29 2023 The positively tilted upper-level trough is slowly moving to the ESE and is now over western WY. Lowering heights and slightly increased instability has initiated thunderstorms over some mountains areas. Increasing surface heating this afternoon will give rise to scattered showers and thunderstorms across the forecast area, with emphasis on the mountains and eastern foothills. Certainly expect the storms to move over the lower elevations in the afternoon and evening, through storm movement will be varied and difficult due to less shear through the column. Moisture is still abundant with the morning RIW sounding PWAT at 130%. Slightly better instability and shear though is expected from eastern Sweetwater County into Natrona County as the trough axis moves ESE during the afternoon and evening. Wouldn't be surprised to see some stronger storms from southern Johnson County into Natrona County due to higher dewpoints and CAPE of 500-1000 J/kg. The trough axis should increase northerly flow east of the divide this afternoon to set up a boundary with drier southerly flow in northern Colorado. Some models are indicating moderate precip rates from southern into central WY this evening. Interestingly, the Tetons appear to have the lowest chances of storms this afternoon. The convective activity should persist across central WY past sunset with some areas possibly getting more than a half inch of rain with some small hail. With the 500mb low stagnating over central WY overnight, showers could continue through the night over central WY, particularly Natrona County and southern Johnson County. With the trough axis still in eastern WY on Friday and a good 700mb circulation setting up over east-central WY, showers and isolated thunderstorms will increase over the Bighorns and Johnson and Natrona Counties during the morning hours. North-northwest winds should increase during the afternoon on the backside of the trough as temperatures remain on the cool side blow normal to finish out the month. Isolated storms are possible YNP to the Absarokas and Wind Rivers, be the likelihood is decreasing with successive model runs. Friday looks to be a very nice day across much of western Wyoming. Saturday will see a positively tilted ridge axis stretch from the Great Basin to eastern Montana to being bringing in warmer air and more westerly flow. A weak shortwave trough in the westerly flow from the PacNW toward central MT should help isolated showers and thunderstorms develop across northwest and northern WY Saturday afternoon. The shortwave has the chance of moving more SE during the evening into NE WY though, which would bring storms into central WY Saturday evening with gusty NW winds. Temperatures will rise about 5-8 degrees across the forecast area compared to Friday, while RH values drop below 20% across southern WY. The zonal flow increases on Sunday with 700mb temps warming another 2-3degC to lift afternoon max temps to near normal - upper 70s to upper 80s in the lower elevations. Isolated showers and thunderstorms are still possible across northern and western WY. Both the GFS and ECMWF have another weather shortwave trough from Idaho into western WY interacting with a southward moving trough from Alberta into Montana Monday afternoon. The result is likely scattered showers and thunderstorms across most of the forecast area. The northern wave then moves into WY east of the divide early Tuesday on the Fourth of July to being a very good chance of showers and isolated thunderstorms to locations along and east of the divide. Obviously this should cool temperatures in this area, while western and southwest WY stay more in the drier warmer air with only isolated showers and thunderstorms. Wednesday will then see a stationary front set up along the divide, for isolated showers east of the divide and warm dry gusty west winds west of the divide. Thursday looks much the same as Wednesday though the boundary could move eastward as zonal mid-level flow brings in pockets of shortwave energy and moisture. Still a very active pattern through the end of next week! && .AVIATION...(For the 18Z TAFS through 18Z Friday afternoon) Issued at 1121 AM MDT Thu Jun 29 2023 VFR conditions prevail through the TAF period. Showers and thunderstorms expected this afternoon and evening, with chances for each TAF location. MVFR conditions are briefly possible with any showers or storms. Gusty winds will be the main impacts with any showers/storms. KCPR and KRKS are the most likely locations to receive more prolonged rain, rather than just VCTS conditions. Stronger storms will also be favored in the KCPR area. Most rain activity will decrease this evening, however models are showing continued shower chances over central locations, potentially impacting KCPR/KLND/KRIW into the night. Winds become lighter overnight, with decreasing clouds outside those locations with continued rain shower chances. Rain chances again Friday afternoon, but chances are lower for much of the area. 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 1140 AM MDT Thu Jun 29 2023 An upper-level low pressure system is moving from WNW to ESE over Wyoming today. Isolated showers and thunderstorms late in the morning will become more numerous in the afternoon and evening, especially over the mountains along and east of the divide, as well as the lower elevations from Sweetwater County into central WY. Some storms in Natrona County could be stronger. Breezy and gusty north winds will develop this afternoon, especially east of the divide. While western WY will see showers diminish by sunset, central WY will see rain showers continue through the night, particularly from Johnson County and the Bighorns into Natrona County. Temperatures remain below normal this afternoon and will persist into Friday. Friday morning will see continued showers over central and eastern WY, with isolated showers and thunderstorms developing in the afternoon, though very slim chances the further west. Breezy north winds will again be over the area Friday afternoon. Saturday and Sunday will see a pattern change with increasing west winds, drier and warmer flow, but thunderstorms are possible again across northwest and northern WY Saturday afternoon. Near normal temperatures with gusty west winds and isolated storms expected on Sunday. && .RIW WATCHES/WARNINGS/ADVISORIES...NONE. && DISCUSSION...McDonald AVIATION...Wittmann FIRE WEATHER...McDonald
Hazardous Weather Outlook National Weather Service Riverton WY 430 AM MDT Thu Jun 29 2023 WYZ001>020-022>030-301430- 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- 430 AM MDT Thu Jun 29 2023 This Hazardous Weather Outlook is for Western and Central Wyoming. .DAY ONE...Today and tonight. Widespread showers and thunderstorms expected across the state today. Main threat remains hail and heavy downpours. Storms will gradually dissipate after sunset. .DAYS TWO THROUGH SEVEN...Friday through Wednesday. Showers and thunderstorms return to the forecast Monday and continue into the middle of next week. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time.
Special Weather Statement
National Weather Service Riverton WY
1257 PM MDT Thu Jun 29 2023
WYZ020-291930-
Natrona County Lower Elevations-
1257 PM MDT Thu Jun 29 2023
...A strong thunderstorm will impact portions of northeastern Natrona
County through 130 PM MDT...
At 1257 PM MDT, Doppler radar was tracking a strong thunderstorm over
Edgerton, which is also 30 miles southeast of Kaycee, moving
northeast at 5 mph.
HAZARD...Winds in excess of 30 mph and penny 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...
Edgerton around 115 PM MDT.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
Conditions are favorable for the development of weak, brief funnel
clouds. This type of funnel cloud is harmless, but on rare occasions
they can briefly touch down, producing wind gusts over 50 mph. If a
funnel cloud is spotted move indoors and report your sighting to the
National Weather Service.
&&
LAT...LON 4322 10626 4334 10639 4350 10627 4350 10626
4341 10607 4332 10607
TIME...MOT...LOC 1857Z 235DEG 6KT 4337 10624
MAX HAIL SIZE...0.75 IN
MAX WIND GUST...30 MPH
WittmannThe Riverton/Lander radar (KRIW), 179 km away, was scanning. The volume nearest the first event began at 18:57 UTC.
2 flash flood, 1 hail, 1 funnel cloud. Local standard time, as filed.
Video was posted to Facebook by a spotter of several inches of hail up to quarter size covering Highway 259 to the south of Midwest.
Social media picture of a funnel cloud was shared. Location estimated based on storm location and direction of picture. No reports of damage and no evidence of touchdown was found.
Rain and hail flowed to the west of Highway 257 and washed out dirt roads in Brown Draw.
A trained spotter reported that Badwater Creek was out of it's banks. One resident reported water coming inside their barn.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2023Every state in 2023This day in weather historyWarnings in Wyoming, June 2023
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 1113376, 1138376, 1113379, 1113380.