A strong cold front and upper level disturbance moved across the  central and eastern counties in the Billings County Warning Area during the late afternoon and evening hours of the 13th. Several thunderstorms developed across Northern Stillwater and Sweet Grass Counties before evolving into Supercell thunderstorms over Northern Yellowstone County. These thunderstorms then merged into a squall line across Eastern Yellowstone County and Treasure County before moving across Rosebud, Custer and Fallon Counties. Very large hail and damaging winds accompanied these thunderstorms with widespread damage reported across these areas.

Hail in BIG HORN, MONTANA
From 13-MAY-07 17:57:00 to 13-MAY-07 17:57:00 (MST-7)
Location: HARDIN
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in BIG HORN, MONTANA
From 13-MAY-07 18:00:00 to 13-MAY-07 18:00:00 (MST-7)
Location: HARDIN
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in BIG HORN, MONTANA
From 13-MAY-07 18:10:00 to 13-MAY-07 18:10:00 (MST-7)
Location: HARDIN
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in ROSEBUD, MONTANA
From 13-MAY-07 18:50:00 to 13-MAY-07 18:50:00 (MST-7)
Location: VANANDA
Magnitude: 1.25 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Flash Flood in ROSEBUD, MONTANA
From 13-MAY-07 20:40:00 to 13-MAY-07 20:40:00 (MST-7)
Location: FORSYTH
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Spotter in Broadus heard report over police scanner of flash flooding on Interstate 94 between Miles City and Forsyth.

Thunderstorm Wind in FALLON, MONTANA
From 13-MAY-07 21:00:00 to 13-MAY-07 21:00:00 (MST-7)
Location: WILLARD
Magnitude: 61.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Buildings moved approximately 500 yards from original location...trees
down...shingles off patio roof and power out.

Thunderstorm Wind in FALLON, MONTANA
From 13-MAY-07 22:00:00 to 13-MAY-07 22:00:00 (MST-7)
Location: BAKER
Magnitude: 61.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Fallon County Sheriff reported trees and power lines down along with
heavy rain.

Hail in YELLOWSTONE, MONTANA
From 13-MAY-07 16:20:00 to 13-MAY-07 16:20:00 (MST-7)
Location: RIMROCK
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in YELLOWSTONE, MONTANA
From 13-MAY-07 17:04:00 to 13-MAY-07 17:04:00 (MST-7)
Location: BALLANTINE
Magnitude: 1.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in YELLOWSTONE, MONTANA
From 13-MAY-07 17:10:00 to 13-MAY-07 17:10:00 (MST-7)
Location: WORDEN
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in YELLOWSTONE, MONTANA
From 13-MAY-07 17:21:00 to 13-MAY-07 17:21:00 (MST-7)
Location: BALLANTINE
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in PARK, MONTANA
From 13-MAY-07 14:15:00 to 13-MAY-07 14:15:00 (MST-7)
Location: (LVM)LIVINGSTON ARPT
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in SWEET GRASS, MONTANA
From 13-MAY-07 14:54:00 to 13-MAY-07 14:54:00 (MST-7)
Location: BIG TIMBER
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in SWEET GRASS, MONTANA
From 13-MAY-07 15:00:00 to 13-MAY-07 15:00:00 (MST-7)
Location: BIG TIMBER
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in ROSEBUD, MONTANA
From 13-MAY-07 18:31:00 to 13-MAY-07 18:31:00 (MST-7)
Location: HATHAWAY
Magnitude: 1.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Hail in STILLWATER, MONTANA
From 13-MAY-07 16:55:00 to 13-MAY-07 16:55:00 (MST-7)
Location: PARK CITY
Magnitude: 1.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in YELLOWSTONE, MONTANA
From 13-MAY-07 17:23:00 to 13-MAY-07 17:23:00 (MST-7)
Location: BILLINGS
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in CUSTER, MONTANA
From 13-MAY-07 18:36:00 to 13-MAY-07 18:36:00 (MST-7)
Location: MILES CITY
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in FALLON, MONTANA
From 13-MAY-07 20:37:00 to 13-MAY-07 20:37:00 (MST-7)
Location: BAKER
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm Wind in ROSEBUD, MONTANA
From 13-MAY-07 19:32:00 to 13-MAY-07 19:32:00 (MST-7)
Location: COLSTRIP
Magnitude: 61.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Public reported estimated winds of 70-80 mph.

Hail in YELLOWSTONE, MONTANA
From 13-MAY-07 17:42:00 to 13-MAY-07 17:42:00 (MST-7)
Location: BILLINGS
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in YELLOWSTONE, MONTANA
From 13-MAY-07 17:50:00 to 13-MAY-07 17:50:00 (MST-7)
Location: CUSTER
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in SWEET GRASS, MONTANA
From 13-MAY-07 15:10:00 to 13-MAY-07 15:10:00 (MST-7)
Location: GREYCLIFF
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Hail in SWEET GRASS, MONTANA
From 13-MAY-07 15:50:00 to 13-MAY-07 15:50:00 (MST-7)
Location: GREYCLIFF
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in SWEET GRASS, MONTANA
From 13-MAY-07 16:05:00 to 13-MAY-07 16:05:00 (MST-7)
Location: GREYCLIFF
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in STILLWATER, MONTANA
From 13-MAY-07 16:10:00 to 13-MAY-07 16:10:00 (MST-7)
Location: REED PT
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm Wind in CUSTER, MONTANA
From 13-MAY-07 20:35:00 to 13-MAY-07 20:35:00 (MST-7)
Location: MILES CITY
Magnitude: 65.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

Numerous power outages were reported across the area.

Hail in PARK, MONTANA
From 13-MAY-07 14:12:00 to 13-MAY-07 14:12:00 (MST-7)
Location: (LVM)LIVINGSTON ARPT
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Pea to quarter size hail covered the ground.

Thunderstorm Wind in YELLOWSTONE, MONTANA
From 13-MAY-07 17:10:00 to 13-MAY-07 17:10:00 (MST-7)
Location: WORDEN
Magnitude: 61.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Numerous tree branches were knocked down.

Thunderstorm Wind in STILLWATER, MONTANA
From 13-MAY-07 16:05:00 to 13-MAY-07 16:05:00 (MST-7)
Location: RAPELJE
Magnitude: 66.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Numerous tree branches were knocked down.

Thunderstorm Wind in YELLOWSTONE, MONTANA
From 13-MAY-07 17:21:00 to 13-MAY-07 17:21:00 (MST-7)
Location: BALLANTINE
Magnitude: 61.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A few power outages were reported.

Thunderstorm Wind in YELLOWSTONE, MONTANA
From 13-MAY-07 17:23:00 to 13-MAY-07 17:23:00 (MST-7)
Location: POMPEYS PILLAR
Magnitude: 61.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A few power outages were reported.

Hail in MUSSELSHELL, MONTANA
From 13-MAY-07 17:55:00 to 13-MAY-07 17:55:00 (MST-7)
Location: DELPHIA
Magnitude: 1.50 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Several large limbs were broken off twelve foot diameter Cottonwood trees. Portions of a tin roof were blown off a few buildings.

Thunderstorm Wind in ROSEBUD, MONTANA
From 13-MAY-07 18:12:00 to 13-MAY-07 18:12:00 (MST-7)
Location: FORSYTH
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Winds were sustained from the west at 40 mph.

Hail in YELLOWSTONE, MONTANA
From 13-MAY-07 17:18:00 to 13-MAY-07 17:18:00 (MST-7)
Location: SHEPHERD
Magnitude: 1.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Quarter to golfball size hail was reported.

Thunderstorm Wind in YELLOWSTONE, MONTANA
From 13-MAY-07 17:15:00 to 13-MAY-07 17:15:00 (MST-7)
Location: WORDEN
Magnitude: 61.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Poplar trees two to three feet in diameter were snapped in half a couple of feet off the ground. Shingles were ripped off a home.

Hail in YELLOWSTONE, MONTANA
From 13-MAY-07 17:15:00 to 13-MAY-07 17:15:00 (MST-7)
Location: WORDEN
Magnitude: 1.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Poplar trees two to three feet in diameter were snapped in half a couple of feet above the ground. Shingles were also ripped off a home.

Thunderstorm Wind in FALLON, MONTANA
From 13-MAY-07 21:14:00 to 13-MAY-07 21:14:00 (MST-7)
Location: BAKER
Magnitude: 61.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A wind tower was knocked over along with several reports of tree damage.

Hail in SWEET GRASS, MONTANA
From 13-MAY-07 14:56:00 to 13-MAY-07 14:56:00 (MST-7)
Location: BIG TIMBER
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Soft hail with heavy rain and light winds were reported.

Hail in SWEET GRASS, MONTANA
From 13-MAY-07 15:12:00 to 13-MAY-07 15:12:00 (MST-7)
Location: BIG TIMBER ARPT
Magnitude: 1.25 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm Wind in STILLWATER, MONTANA
From 13-MAY-07 16:30:00 to 13-MAY-07 16:30:00 (MST-7)
Location: RAPELJE
Magnitude: 66.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Numerous windows were broken out in Rapelje from the hail and winds.

Thunderstorm Wind in YELLOWSTONE, MONTANA
From 13-MAY-07 17:19:00 to 13-MAY-07 17:19:00 (MST-7)
Location: POMPEYS PILLAR
Magnitude: 63.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A few shingles along with some tin were ripped off a building.

Thunderstorm Wind in FALLON, MONTANA
From 13-MAY-07 20:56:00 to 13-MAY-07 20:56:00 (MST-7)
Location: BAKER
Magnitude: 56.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

No damage was reported.

Flash Flood in ROSEBUD, MONTANA
From 13-MAY-07 22:39:00 to 13-MAY-07 22:39:00 (MST-7)
Location: FORSYTH
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

A foot of water was reported at Exit 93 on Interstate 94. Traffic was  rerouted.

Thunderstorm Wind in FALLON, MONTANA
From 13-MAY-07 21:00:00 to 13-MAY-07 21:00:00 (MST-7)
Location: WILLARD
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

No damage was reported.

Hail in STILLWATER, MONTANA
From 13-MAY-07 16:30:00 to 13-MAY-07 16:30:00 (MST-7)
Location: RAPELJE
Magnitude: 1.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Numerous windows were broken out in Rapelje from the hail and winds.

Thunderstorm Wind in YELLOWSTONE, MONTANA
From 13-MAY-07 17:55:00 to 13-MAY-07 17:55:00 (MST-7)
Location: POMPEYS PILLAR
Magnitude: 61.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Several large limbs were broken off of twelve foot diameter Cottonwood trees. Portions of tin roof were lost on a few buildings.

Thunderstorm Wind in TREASURE, MONTANA
From 13-MAY-07 18:12:00 to 13-MAY-07 18:12:00 (MST-7)
Location: HYSHAM
Magnitude: 50.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

No damage was reported.

Thunderstorm Wind in YELLOWSTONE, MONTANA
From 13-MAY-07 18:00:00 to 13-MAY-07 18:00:00 (MST-7)
Location: BILLINGS
Magnitude: 56.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Many tree branches were knocked down.

Thunderstorm Wind in ROSEBUD, MONTANA
From 13-MAY-07 18:43:00 to 13-MAY-07 18:43:00 (MST-7)
Location: COLSTRIP
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

No damage was reported.

Thunderstorm Wind in ROSEBUD, MONTANA
From 13-MAY-07 19:00:00 to 13-MAY-07 19:00:00 (MST-7)
Location: FORSYTH
Magnitude: 61.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A shed was blown into a house. In addition, fully mature trees were blown down.

Thunderstorm Wind in ROSEBUD, MONTANA
From 13-MAY-07 18:48:00 to 13-MAY-07 18:48:00 (MST-7)
Location: FORSYTH
Magnitude: 61.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Shingles were blown off houses along with numerous tree branches down.

Hail in ROSEBUD, MONTANA
From 13-MAY-07 18:43:00 to 13-MAY-07 18:43:00 (MST-7)
Location: COLSTRIP
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm Wind in CARTER, MONTANA
From 13-MAY-07 21:00:00 to 13-MAY-07 21:00:00 (MST-7)
Location: EKALAKA
Magnitude: 52.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

A few power outages were reported.

Thunderstorm Wind in FALLON, MONTANA
From 13-MAY-07 21:04:00 to 13-MAY-07 21:04:00 (MST-7)
Location: BAKER
Magnitude: 65.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

Numerous tree branches were reported down.

Thunderstorm Wind in ROSEBUD, MONTANA
From 13-MAY-07 21:00:00 to 13-MAY-07 21:00:00 (MST-7)
Location: FORSYTH
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

No damage was reported.

Hail in YELLOWSTONE, MONTANA
From 13-MAY-07 16:41:00 to 13-MAY-07 16:41:00 (MST-7)
Location: RIMROCK
Magnitude: 1.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Numerous quarter size and a few golfball size hail stones were reported.

Hail in YELLOWSTONE, MONTANA
From 13-MAY-07 16:36:00 to 13-MAY-07 16:36:00 (MST-7)
Location: COMANCHE
Magnitude: 1.25 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Anywhere from pea size to quarter size hail was reported.

Thunderstorm Wind in FALLON, MONTANA
From 13-MAY-07 21:12:00 to 13-MAY-07 21:12:00 (MST-7)
Location: BAKER
Magnitude: 61.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trees knocked down along with numerous power outtages.

Thunderstorm Wind in GOLDEN VALLEY, MONTANA
From 13-MAY-07 16:00:00 to 13-MAY-07 16:00:00 (MST-7)
Location: RYEGATE
Magnitude: 61.00 EG
Crop damage: 0.00K
Reported by: Emergency Manager

A mobile home was destroyed.

Hail in YELLOWSTONE, MONTANA
From 13-MAY-07 16:45:00 to 13-MAY-07 16:45:00 (MST-7)
Location: LAUREL
Magnitude: 1.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Winds were gusting around 30 to 40 mph.

Hail in YELLOWSTONE, MONTANA
From 13-MAY-07 17:11:00 to 13-MAY-07 17:11:00 (MST-7)
Location: SHEPHERD
Magnitude: 1.25 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm Wind in CUSTER, MONTANA
From 13-MAY-07 20:00:00 to 13-MAY-07 20:00:00 (MST-7)
Location: (MLS)WILEY FLD MILES
Magnitude: 56.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

A few tree limbs were blown down.

Thunderstorm Wind in ROSEBUD, MONTANA
From 13-MAY-07 19:12:00 to 13-MAY-07 19:12:00 (MST-7)
Location: ANGELA
Magnitude: 56.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A few power outages were reported.

Thunderstorm Wind in CUSTER, MONTANA
From 13-MAY-07 20:00:00 to 13-MAY-07 20:00:00 (MST-7)
Location: (MLS)WILEY FLD MILES
Magnitude: 66.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

Numerous trees were blown down. Several power outages were also reported.

Hail in SWEET GRASS, MONTANA
From 13-MAY-07 15:09:00 to 13-MAY-07 15:09:00 (MST-7)
Location: BIG TIMBER
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in YELLOWSTONE, MONTANA
From 13-MAY-07 16:59:00 to 13-MAY-07 16:59:00 (MST-7)
Location: BALLANTINE
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in YELLOWSTONE, MONTANA
From 13-MAY-07 17:15:00 to 13-MAY-07 17:15:00 (MST-7)
Location: WORDEN
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Amateur Radio

Hail in ROSEBUD, MONTANA
From 13-MAY-07 18:20:00 to 13-MAY-07 18:20:00 (MST-7)
Location: ROSEBUD
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in SWEET GRASS, MONTANA
From 13-MAY-07 15:07:00 to 13-MAY-07 15:07:00 (MST-7)
Location: GREYCLIFF
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter