Meteorologically speaking, this was a very active severe weather day for south central Montana. A very moist and unstable atmosphere was in place across portions of the Billings Forecast area during the afternoon and evening of the 20th (Father's Day). A moist, southeast surface flow, strong wind shear aloft, and ample afternoon heating provided the necessary ingredients for severe weather. Numerous thunderstorms, some of which became rapidly severe producing tornadoes and large hail, developed across South Central Montana.

Hail in MUSSELSHELL, MONTANA
From 20-JUN-10 15:30:00 to 20-JUN-10 15:30:00 (MST-7)
Location: MUSSELSHELL
Magnitude: 1.00 
Reported by: Trained Spotter

Hail in YELLOWSTONE, MONTANA
From 20-JUN-10 15:30:00 to 20-JUN-10 15:30:00 (MST-7)
Location: (BIL)LOGAN ARPT BILL
Magnitude: 1.50 
Reported by: COOP Observer

Hail in MUSSELSHELL, MONTANA
From 20-JUN-10 15:10:00 to 20-JUN-10 15:10:00 (MST-7)
Location: MELSTONE
Magnitude: 1.25 
Reported by: Insurance Company

Hail in YELLOWSTONE, MONTANA
From 20-JUN-10 14:57:00 to 20-JUN-10 14:57:00 (MST-7)
Location: RIMROCK
Magnitude: 1.75 
Reported by: COOP Observer

Hail in YELLOWSTONE, MONTANA
From 20-JUN-10 15:20:00 to 20-JUN-10 15:20:00 (MST-7)
Location: BILLINGS HGTS
Magnitude: 1.75 
Reported by: COOP Observer

Hail in YELLOWSTONE, MONTANA
From 20-JUN-10 15:38:00 to 20-JUN-10 15:38:00 (MST-7)
Location: (BIL)LOGAN ARPT BILL
Magnitude: 1.75 
Reported by: COOP Observer

Hail in YELLOWSTONE, MONTANA
From 20-JUN-10 15:50:00 to 20-JUN-10 15:50:00 (MST-7)
Location: BILLINGS
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Hail in BIG HORN, MONTANA
From 20-JUN-10 16:04:00 to 20-JUN-10 16:04:00 (MST-7)
Location: DECKER
Magnitude: 2.75 
Reported by: COOP Observer

Hail in BIG HORN, MONTANA
From 20-JUN-10 13:20:00 to 20-JUN-10 13:20:00 (MST-7)
Location: HARDIN
Magnitude: 1.50 
Reported by: COOP Observer

Hail in YELLOWSTONE, MONTANA
From 20-JUN-10 15:22:00 to 20-JUN-10 15:22:00 (MST-7)
Location: (BIL)LOGAN ARPT BILL
Magnitude: 1.75 
Reported by: COOP Observer

Hail in POWDER RIVER, MONTANA
From 20-JUN-10 15:25:00 to 20-JUN-10 15:25:00 (MST-7)
Location: BROADUS
Magnitude: 1.00 
Reported by: COOP Observer

Thunderstorm Wind in POWDER RIVER, MONTANA
From 20-JUN-10 16:10:00 to 20-JUN-10 16:10:00 (MST-7)
Location: BROADUS
Magnitude: 52.00 EG
Reported by: COOP Observer

An estimated wind gust of 60 mph was reported 14 miles east of Broadus.

Hail in MUSSELSHELL, MONTANA
From 20-JUN-10 16:12:00 to 20-JUN-10 16:12:00 (MST-7)
Location: ELSO
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Hail in BIG HORN, MONTANA
From 20-JUN-10 16:25:00 to 20-JUN-10 16:25:00 (MST-7)
Location: DECKER
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Hail in CARTER, MONTANA
From 20-JUN-10 16:45:00 to 20-JUN-10 16:45:00 (MST-7)
Location: RIDGEWAY
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

Hail in BIG HORN, MONTANA
From 20-JUN-10 13:25:00 to 20-JUN-10 13:25:00 (MST-7)
Location: HARDIN
Magnitude: 1.00 
Reported by: COOP Observer

Hail in POWDER RIVER, MONTANA
From 20-JUN-10 14:38:00 to 20-JUN-10 14:38:00 (MST-7)
Location: (4BQ)BROADUS ARPT
Magnitude: 1.00 
Reported by: CoCoRaHS

Hail in POWDER RIVER, MONTANA
From 20-JUN-10 16:50:00 to 20-JUN-10 16:50:00 (MST-7)
Location: BROADUS
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Hail in CARTER, MONTANA
From 20-JUN-10 16:51:00 to 20-JUN-10 16:51:00 (MST-7)
Location: ALBION
Magnitude: 2.00 
Reported by: COOP Observer

Hail in CARTER, MONTANA
From 20-JUN-10 17:02:00 to 20-JUN-10 17:02:00 (MST-7)
Location: RIDGEWAY
Magnitude: 1.00 
Reported by: COOP Observer

Hail in CARTER, MONTANA
From 20-JUN-10 17:20:00 to 20-JUN-10 17:20:00 (MST-7)
Location: RIDGEWAY
Magnitude: 1.75 
Reported by: COOP Observer

Hail in CARTER, MONTANA
From 20-JUN-10 17:35:00 to 20-JUN-10 17:35:00 (MST-7)
Location: PINIELE
Magnitude: 1.75 
Reported by: Law Enforcement

Sheriff reported golf ball size hail was breaking windows.

Hail in YELLOWSTONE, MONTANA
From 20-JUN-10 14:53:00 to 20-JUN-10 14:53:00 (MST-7)
Location: HESPER
Magnitude: 2.75 
Reported by: COOP Observer

Tornado in YELLOWSTONE, MONTANA
From 20-JUN-10 15:24:00 to 20-JUN-10 15:36:00 (MST-7)
Location: BILLINGS
Tornado F-scale: EF2
Property damage: 30.00M
Crop damage: 0.00K
Reported by: Public

Based on the observed damage, the tornado was classified as an EF-2 on the Enhanced Fujita Scale. Wind speeds within an EF-2 tornado range from 111-135 mph, and the associated damage observed at the Billings MetraPark and nearby businesses was consistent with this classification. The damage path was 120 yards wide with a length of about a half mile and on the ground an estimated 12 minutes.
The damage assessment and eyewitness accounts indicate that the tornado developed near the intersection of Lake Elmo Drive and Main Street in the Billings Heights at approximately 4:24 pm, with significant EF-2 damage to several nearby businesses. Damage included rooftops being blown off of three structures, windows blown out, power poles downed, business signs and billboards blown down along with several trees uprooted. The tornado appeared to weaken slightly as it progressed southeast across Alkali Creek. Limbs were broken off numerous trees in the vicinity of the creek. The tornadic circulation then appeared to have strengthened once again as it moved south over the Rimrock Auto Arena at Metrapark. EF-2 damage was again observed to the arena with much of the roof blown off along with other damage to the exterior of the building. Debris from the arena impacted other nearby businesses creating additional damage, mainly in the form of broken windows. Debris from the arena was reported landing as far away as a mile from the tornado touchdown. The tornado then dissipated over the arena around 4:36 pm.
The associated thunderstorm then moved northeast away from Billings. Numerous sightings of funnel clouds were reported as this storm moved east-northeast of Billings, however no additional tornado touchdowns were reported.

Flash Flood in YELLOWSTONE, MONTANA
From 20-JUN-10 17:05:00 to 20-JUN-10 21:00:00 (MST-7)
Location: (BIL)LOGAN ARPT BILL
Flood cause: Heavy Rain
Property damage: 2.70M
Crop damage: 0.00K
Reported by: Public

Flood waters from a thunderstorm turned downtown streets into rivers, parking lots into lakes and basements into swamps. So much rain fell so fast on Billings that storm drains wide enough to hold a small car were filled for hours. Streets turned into rushing rivers, basements filled with muddy water and some residents went swimming with shovels and sticks to clear clogged storm drains. More than an inch of water seeped into the Billings Clinic hospital corridors and the basement near the buildings north entrances. Mud and water flooded the atrium area of Billings Clinic. In the hospital's north parking lot, storm water rose above the tires of passenger cars. Flooding was also reported in the underground parking garage of the hospital. Flash flooding was also reported on Alkali Creek as the creek flooded in several places. There were numerous calls of flooding in the basements of residential homes and businesses and water being over roads in some places. In addition, manhole covers were blown off by the pressure of water flooding the city's storm sewer system. The heavy rain caused a significant amount of water damage throughout the main part of the city.

Flash Flood in CARTER, MONTANA
From 20-JUN-10 20:00:00 to 21-JUN-10 01:00:00 (MST-7)
Location: RIDGEWAY
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Carter County sheriff reported flooding over Hammond Road and along Mile Marker 30 on Highway 323. The Department of Emergency Services and the sheriff reported that 1-4 inches of rain fell over Central Carter County and that Box Elder Creek was running high.
In addition, a county official reported 2.5 inches of rain had fallen in one hour which resulted in flash flooding on Cabin Creek.