The first major severe weather episode occurred on the afternoon and evening of the 16th as a moist and unstable atmosphere was in place across the Billings Forecast Area.
Low-level moisture combined with a southwest flow aloft and strong jet stream provided the necessary ingredients for thunderstorm development. A tornado watch was issued for the afternoon and evening hours. Numerous severe thunderstorms producing large hail developed by mid afternoon and continued into the evening hours. One particular thunderstorm produced a tornado near Bridger on the west side of the Pryor Mountains.

Flash Flood in FALLON, MONTANA
From 16-JUN-10 22:40:00 to 17-JUN-10 03:00:00 (MST-7)
Location: OLLIE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A very heavy thunderstorm produced about five inches of rain during the late evening hours on the 16th. This resulted in flash flooding on Beaver and Spring Creeks.

Hail in STILLWATER, MONTANA
From 16-JUN-10 13:36:00 to 16-JUN-10 13:36:00 (MST-7)
Location: COLUMBUS
Magnitude: 1.75 
Reported by: COOP Observer

Hail in STILLWATER, MONTANA
From 16-JUN-10 13:40:00 to 16-JUN-10 13:40:00 (MST-7)
Location: PRYOR
Magnitude: 1.75 
Reported by: Trained Spotter

Golf ball size hail lasted for about 12 minutes.

Hail in STILLWATER, MONTANA
From 16-JUN-10 14:40:00 to 16-JUN-10 14:40:00 (MST-7)
Location: WHEAT BASIN
Magnitude: 1.00 
Reported by: Trained Spotter

Hail in STILLWATER, MONTANA
From 16-JUN-10 14:23:00 to 16-JUN-10 14:23:00 (MST-7)
Location: COLUMBUS
Magnitude: 1.50 
Reported by: Trained Spotter

Ping pong ball size hail was reported along with 30 mph winds.

Hail in STILLWATER, MONTANA
From 16-JUN-10 14:35:00 to 16-JUN-10 14:35:00 (MST-7)
Location: COLUMBUS
Magnitude: 1.00 
Reported by: Trained Spotter

Hail in YELLOWSTONE, MONTANA
From 16-JUN-10 16:10:00 to 16-JUN-10 16:10:00 (MST-7)
Location: LOCKWOOD
Magnitude: 1.50 
Reported by: Trained Spotter

Hail in YELLOWSTONE, MONTANA
From 16-JUN-10 16:10:00 to 16-JUN-10 16:10:00 (MST-7)
Location: SHEPHERD
Magnitude: 1.00 
Reported by: Public

Hail damage to a vehicle and estimated winds of 75-80 mph was reported.

Thunderstorm Wind in YELLOWSTONE, MONTANA
From 16-JUN-10 16:19:00 to 16-JUN-10 16:19:00 (MST-7)
Location: WORDEN
Magnitude: 73.00 MG
Reported by: Public

A wind gust of 84 mph was reported in Worden.

Hail in YELLOWSTONE, MONTANA
From 16-JUN-10 16:21:00 to 16-JUN-10 16:21:00 (MST-7)
Location: (BIL)LOGAN ARPT BILL
Magnitude: 1.75 
Reported by: Trained Spotter

Winds were estimated at 50 mph.

Hail in POWDER RIVER, MONTANA
From 16-JUN-10 16:27:00 to 16-JUN-10 16:27:00 (MST-7)
Location: EPSIE
Magnitude: 1.00 
Reported by: Trained Spotter

Funnel Cloud in ROSEBUD, MONTANA
From 16-JUN-10 17:10:00 to 16-JUN-10 17:10:00 (MST-7)
Location: JOPPA
Reported by: Trained Spotter

Rotation was spotted in the cloud.

Thunderstorm Wind in CARBON, MONTANA
From 16-JUN-10 15:29:00 to 16-JUN-10 15:29:00 (MST-7)
Location: WARREN
Magnitude: 50.00 EG
Property damage: 2.00K
Reported by: Trained Spotter

Downed tree limbs greater than 3 inches in diameter and siding off houses was reported in Warren.

Hail in FALLON, MONTANA
From 16-JUN-10 19:10:00 to 16-JUN-10 19:10:00 (MST-7)
Location: OLLIE
Magnitude: 1.00 
Reported by: Trained Spotter

Hail lasted for ten minutes.

Hail in FALLON, MONTANA
From 16-JUN-10 19:20:00 to 16-JUN-10 19:20:00 (MST-7)
Location: OLLIE
Magnitude: 1.00 
Reported by: Trained Spotter

Hail in FALLON, MONTANA
From 16-JUN-10 20:10:00 to 16-JUN-10 20:10:00 (MST-7)
Location: OLLIE
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Flood in YELLOWSTONE, MONTANA
From 16-JUN-10 19:40:00 to 17-JUN-10 07:00:00 (MST-7)
Location: NEWTON GROVE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Four inches of rain fell between 6pm and 7pm MDT about six miles south of Melstone. Alkali Creek ran out of its banks and washed out fences.

Tornado in CARBON, MONTANA
From 16-JUN-10 16:00:00 to 16-JUN-10 16:05:00 (MST-7)
Location: WARREN
Tornado F-scale: EF2
Property damage: 12.00K
Crop damage: 0.00K
Reported by: Public

The Bowler Flats tornado was on the ground for approximately one mile and lasted for five minutes. The tornado destroyed four transmission structures, damaged a transmission pole, shredded two wooden power poles and damaged some fencing.
Otherwise, it remained over open areas. The EF-2 damage was based on power and transmission poles being shredded with winds estimated from 111-135 mph.

Hail in YELLOWSTONE, MONTANA
From 16-JUN-10 15:51:00 to 16-JUN-10 15:51:00 (MST-7)
Location: (BIL)LOGAN ARPT BILL
Magnitude: 0.88 
Reported by: Trained Spotter

Funnel Cloud in CUSTER, MONTANA
From 16-JUN-10 17:20:00 to 16-JUN-10 17:20:00 (MST-7)
Location: MIZPAH
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter