Nearly stationary thunderstorms developed across portions of southeast Wyoming leading to flash flooding in the Central Laramie Range west of Wheatland as well as in eastern Laramie County with flooded and washed out roads.
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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 CYS wrote it up.
Nearly stationary thunderstorms developed across portions of southeast Wyoming leading to flash flooding in the Central Laramie Range west of Wheatland as well as in eastern Laramie County with flooded and washed out roads.
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 Cheyenne, WY wrote its last area forecast discussion before the first event at Jun 11, 2:21 PM MST, 1 hour 9 minutes earlier.
Area Forecast Discussion National Weather Service Cheyenne WY 321 PM MDT Sun Jun 11 2023 .SHORT TERM...(This evening through Monday) Issued at 321 PM MDT Sun Jun 11 2023 Key Impact Messages: 1) Marginal Risk for excessive rainfall across much SE Wyoming. Scattered showers and thunderstorms are expected this afternoon which will continue through the evening. Periods of heavy rainfall and small will be possible. 2) A Slight Risk for excessive rainfall is highlighted across the SE corner of Wyoming tomorrow. Scattered to widespread showers and thunderstorms are expected which could bring heavy rainfall and instances of flash flooding. 3) Cooler temperatures expected across the region on Monday. Weather Details: A few thunderstorms have began to develop across the south Laramie Range. THis activity should continue to push to the NE and expand in coverage. HI-RES models have been consistent in a cluster of thunderstorms impacting areas across the I-25 corridor from Chugwater south to Cheyenne and portions of the southwestern Nebraska Panhandle. Heavy downpours and small hail will be the main concern with these storms before they diminish over the evening. Discussion: A strong area of low pressure across the upper midwest and an advancing closed low moving across central Colorado will place much of our area in a persistent moist, upslope flow Monday and lingering into Tuesday morning where PWAT values are set to remain at around an inch. Prolonged periods of heavy rainfall are becoming increasingly likely across the North River Platte Valley, SE Wyoming and the south Laramie Range. With the arrival of larger scale lift, wind shear parameters and upper level divergence increase tomorrow allowing for more robust convection to develop that have the potential to produce 1-2"/hr rainfall rates and train over the same areas for a few hours. A Slight Risk for excessive rainfall has been extended into portions of SE Wyoming for tomorrow. HI-RES models show widespread areas of rain with several strong thunderstorm cores impacting SE Wyoming for a large part of Monday and potentially into Tuesday morning. Need to see better agreement amongst HI-RES models from run to run to see if a Flash Flood Watch needs to be issued. .LONG TERM...(Monday night through Sunday) Issued at 321 PM MDT Sun Jun 11 2023 The long term forecast remains consistent, showing a pattern change with more movement in the upper atmosphere compared to the last few weeks. Although the pattern changes, daily storm chances are still expected through at least Friday as the CWA stays sandwiched between a weak ridge to the south and a trough to the north. Cannot rule out any severe storms during this time, especially towards the end of the work week. Starting on Tuesday, conditions start to dry out as flow becomes more westerly. Storms will still be possible as a strong vort max passes just south of the CWA, but coverage looks fairly isolated to scattered. Severe storms look limited due to instability and very weak shear. Storms will likely be pulsey in nature as cloud layer winds range from 5 to 10 kts. Flooding concerns on Tuesday will be decreased as PW values drop substantially. Wednesday looks similar to Tuesday in regards to westerly winds as well as a shortwave tracking just south of the CWA. This shortwave has a bit more moisture with it so coverage of storms will likely be more scattered. Instability looks better with about 1200 J/kg of MUCAPE. Severe potential will still be limited by weak shear. Heading into the end of the week, flow becomes more northwesterly with a trough passing to the north. Storms during this time look more likely with more widespread coverage. Severe storms cannot be ruled out during this time, especially Friday. Instability and shear look the best on Friday compared to any other day of the week, so will continue to monitor this. The weekend may feature the first summer-like and dry days in what feels like forever. Weak ridging will help dry conditions out and increase 700 mb temperatures. High temperatures will range from the mid 70s to upper 80s with mostly sunny skies! && .AVIATION...(For the 18Z TAFS through 18Z Monday afternoon) Issued at 1104 AM MDT Sun Jun 11 2023 A tricky aviation forecast continues to occur for the next 24 hours as slow-moving -SHRA and -TSRA will combine with upslope flow east of the Laramie Range into the NE Panhandle for the forecast period. Expect multiple fluctuations between MVFR and IFR where -SHRA and VCTS are present, with the remaining terminals seeing VFR. Low-end VFR will occur this evening after 0Z through 6Z for terminals, but increasing confidence of MVFR to IFR conditions due to low CIGs for the NE Panhandle terminals is anticipated between 6Z to 12Z. Brief wind gusts to 25 knots is anticipated in locations that have VCTS and -TSRA through the forecast period, otherwise expect winds of 12 knots or lower. && .FIRE WEATHER... Issued at 132 PM MDT Sun Jun 11 2023 The continuation of showers and thunderstorms today through Tuesday, and ongoing green- up will preclude fire weather concerns. Temperatures will be cooler today and tomorrow before gradually warming up by mid-week. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && SHORT TERM...AW LONG TERM...SF AVIATION...BW FIRE WEATHER...AW
Hazardous Weather Outlook National Weather Service Cheyenne WY 148 PM MDT Sun Jun 11 2023 NEZ002-003-019>021-054-055-095-096-WYZ101>119-122000- Dawes County-Box Butte County-Scotts Bluff County-Banner County- Morrill County-Kimball County-Cheyenne County- Northern Sioux County-Southern Sioux County- Converse County Lower Elevations-Niobrara County- North Laramie Range-Ferris/Seminoe/Shirley Mountains- Shirley Basin-Central Laramie Range and Southwest Platte County- East Platte County-Goshen County-Central Carbon County- North Snowy Range Foothills-Southwest Carbon County- Sierra Madre Range-Upper North Platte River Basin-Snowy Range- Laramie Valley-South Laramie Range-South Laramie Range Foothills- Central Laramie County-East Laramie County- 148 PM MDT Sun Jun 11 2023 This hazardous weather outlook is for portions of panhandle Nebraska...east central Wyoming...south central Wyoming and southeast Wyoming. .DAY ONE...THIS AFTERNOON AND TONIGHT Showers will increase in coverage later this morning with scattered thunderstorms this afternoon and early evening. Brief gusty winds, small hail and locally heavy rain are possible. .DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY Daily chances for showers and thunderstorms will continue through much of the week. Heavy rainfall will be possible Monday with an elevated risk for localized flash flooding in the Mullen Burn Scar. .Spotter information statement... Spotter activation will not be required.
The Cheyenne radar (KCYS), 94 km away, was scanning. The volume nearest the first event began at 22:32 UTC.
2 flash flood. Local standard time, as filed.
Received a video of flash flooding outside of a residence at Cross C Ranch that was estimated 5 feet deep swiftly carrying away a horse trailer. Also received a report from local emergency manager of a partial road washout on Tunnel Road.
Received a video on Facebook of flooded fields with water running over Carpenter Road just north of Road 208. Water over roadway appeared to be a least a foot deep.
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: 1094121, 1094120.