The combination of a stalled frontal boundary, jet streak dynamics, and an upper level disturbance sweeping across Wyoming created the conditions necessary to produce severe thunderstorms in central Wyoming. A moisture-laden atmosphere also set the stage for flash flooding. Johnson County took the brunt of the heavy rainfall and flash flooding on Wednesday evening, June 3. Both the city of Buffalo and Interstate 90 were severely impacted by flood waters. Roads were closed, homes damaged or destroyed, and at least a few public buildings damaged. To the south and west, there were multiple reports of large hail in Fremont and Natrona counties.

Hail in NATRONA, WYOMING
From 03-JUN-15 16:29:00 to 03-JUN-15 16:29:00 (MST-7)
Location: BUCKNUM
Magnitude: 1.50 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Ping pong ball sized hail was observed by a trained spotter near the intersection of US Highway 20/26 and Bucknum Road west of Casper.

Hail in FREMONT, WYOMING
From 03-JUN-15 17:51:00 to 03-JUN-15 17:55:00 (MST-7)
Location: SHOSHONI
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Hail as large as one inch in diameter fell in Shoshoni.

Hail in NATRONA, WYOMING
From 03-JUN-15 16:54:00 to 03-JUN-15 17:03:00 (MST-7)
Location: MIDWEST
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail of various sizes fell in Midwest, with the largest stones being one inch in diameter. Most of the stones were penny and nickel sized.

Flash Flood in JOHNSON, WYOMING
From 03-JUN-15 19:15:00 to 04-JUN-15 07:00:00 (MST-7)
Location: BUFFALO
Flood cause: Heavy Rain
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Department of Highways

Strong thunderstorms produced heavy rain across eastern Johnson and western Campbell counties near Interstate 90. The heaviest rain, estimated at three inches, fed Dead Horse Creek, a small tributary of the Powder River. Dead Horse Creek overflowed and eventually inundated a stretch of Interstate 90 around mileposts 90 and 91, which resulted in the closure of the road from late Wednesday evening, June 3, until the morning of June 4.

Flash Flood in JOHNSON, WYOMING
From 03-JUN-15 20:00:00 to 04-JUN-15 09:00:00 (MST-7)
Location: BUFFALO ARPT
Flood cause: Heavy Rain
Property damage: 1.50M
Crop damage: 0.00K
Reported by: Emergency Manager

The last in a series of thunderstorms on Wednesday, June 3, brought very heavy rain to Buffalo and the surrounding area. The ASOS at Johnson County Airport measured 0.98 inches of rain in less than 25 minutes as the storm moved north and then stalled over Buffalo. The ASOS recorded a grand total of 1.26 inches in less than one hour. Saturated soils were unable to absorb the rain which quickly ran through the streets of Buffalo and filled area creeks. Five Buffalo homes were declared destroyed, and the senior center and BLM office sustained flood damage. Some reports indicated water four feet deep in low-lying areas. The water was running fast enough to lift and carry the top layer of pavement on a couple of Buffalo streets. A few county roads and some private bridges were washed out due to culvert failures as a result of the raging flood waters.

Hail in JOHNSON, WYOMING
From 03-JUN-15 14:45:00 to 03-JUN-15 14:45:00 (MST-7)
Location: BUFFALO
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

One in a series of strong thunderstorms dropped penny sized hail near Buffalo.

Flash Flood in JOHNSON, WYOMING
From 03-JUN-15 23:00:00 to 04-JUN-15 02:00:00 (MST-7)
Location: LINCH
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: River/Stream Gage

Small tributaries feeding Salt Creek in southeast Johnson County were out of their banks as a result of an estimated three inches of rainfall on already saturated soils. Additional water upstream near Midwest, where 1.07 inches of rain fell in 30 minutes late Wednesday, June 3, moved downstream and exacerbated the rural flooding. The extreme run-off eventually caused rises of over one foot per hour on the much wider Powder River at Sussex.