Strong afternoon heating along the high terrain combined with increased forcing from a short-wave trough resulted in the development of severe thunderstorms. A moist environment along with steep low to midlevel lapse rates and ample vertical shear supported supercells and bow structures that resulted in damaging winds and hail.
Significant crop damage occurred in Park County due to the combination of wind and hail.
The following is a Loss Assessment Report from the USDA:
Crop;              Destroyed Acres;           Damaged Acres;      Dollar Loss
Alfalfa,             2,400,                         1,000,                 $1,764,000.00
Barley,             3,000,                            700,                 $2,268,000.00
Mixed Forage,   3,500,                          5,200,                 $1,177,500.00
Wheat,            2,000,                          1,000,                 $1,720,000.00
In addition, three farm structures were damaged totaling $5,500.00.

Hail in YELLOWSTONE, MONTANA
From 01-AUG-13 19:28:00 to 01-AUG-13 19:28:00 (MST-7)
Location: BILLINGS
Magnitude: 1.50 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in YELLOWSTONE, MONTANA
From 01-AUG-13 19:28:00 to 01-AUG-13 19:28:00 (MST-7)
Location: (BIL)LOGAN ARPT BILL
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Official NWS Observations

Thunderstorm Wind in YELLOWSTONE, MONTANA
From 01-AUG-13 19:29:00 to 01-AUG-13 19:29:00 (MST-7)
Location: (BIL)LOGAN ARPT BILL
Magnitude: 51.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

Hail in YELLOWSTONE, MONTANA
From 01-AUG-13 19:30:00 to 01-AUG-13 19:30:00 (MST-7)
Location: BILLINGS
Magnitude: 1.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: NWS Employee

Thunderstorm Wind in YELLOWSTONE, MONTANA
From 01-AUG-13 19:44:00 to 01-AUG-13 19:44:00 (MST-7)
Location: HUNTLEY
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A thunderstorm wind gust of 60 mph was estimated just south of Shepherd.

Hail in YELLOWSTONE, MONTANA
From 01-AUG-13 19:50:00 to 01-AUG-13 19:50:00 (MST-7)
Location: WORDEN
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in PARK, MONTANA
From 01-AUG-13 14:05:00 to 01-AUG-13 14:05:00 (MST-7)
Location: LIVINGSTON
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Thunderstorm Wind in PARK, MONTANA
From 01-AUG-13 16:55:00 to 01-AUG-13 16:55:00 (MST-7)
Location: WILSALL
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Tree limbs were broken.

Thunderstorm Wind in YELLOWSTONE, MONTANA
From 01-AUG-13 19:50:00 to 01-AUG-13 19:50:00 (MST-7)
Location: WORDEN
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A thunderstorm wind gust of 60 mph was estimated just west of Worden.

Hail in BIG HORN, MONTANA
From 01-AUG-13 20:24:00 to 01-AUG-13 20:24:00 (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 01-AUG-13 20:28:00 to 01-AUG-13 20:28:00 (MST-7)
Location: HARDIN
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in SWEET GRASS, MONTANA
From 01-AUG-13 17:55:00 to 01-AUG-13 17:55:00 (MST-7)
Location: BIG TIMBER
Magnitude: 1.50 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in STILLWATER, MONTANA
From 01-AUG-13 18:41:00 to 01-AUG-13 18:41:00 (MST-7)
Location: RAPELJE
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Hail in SWEET GRASS, MONTANA
From 01-AUG-13 17:56:00 to 01-AUG-13 17:56:00 (MST-7)
Location: BIG TIMBER
Magnitude: 1.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in SWEET GRASS, MONTANA
From 01-AUG-13 17:58:00 to 01-AUG-13 17:58:00 (MST-7)
Location: BIG TIMBER
Magnitude: 1.50 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm Wind in YELLOWSTONE, MONTANA
From 01-AUG-13 19:22:00 to 01-AUG-13 19:22:00 (MST-7)
Location: ACTON
Magnitude: 78.00 EG
Crop damage: 0.00K
Reported by: NWS Storm Survey

A severe thunderstorm produced a damaging microburst in the Acton area. The winds were estimated to be 90 mph with the worst damage in an area about 250 yards wide and a mile long. Structural damage consisted of a dozen mobile homes experiencing damage, two of which experienced significant damage with roof tops ripped off of them. In addition, three garages were destroyed and numerous other structures damaged.

Hail in SWEET GRASS, MONTANA
From 01-AUG-13 17:58:00 to 01-AUG-13 17:58:00 (MST-7)
Location: BIG TIMBER
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Hail in SWEET GRASS, MONTANA
From 01-AUG-13 18:00:00 to 01-AUG-13 18:00:00 (MST-7)
Location: BIG TIMBER
Magnitude: 1.50 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in SWEET GRASS, MONTANA
From 01-AUG-13 18:05:00 to 01-AUG-13 18:05:00 (MST-7)
Location: BIG TIMBER
Magnitude: 1.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Amateur Radio

The winds were estimated at 60 mph. The hail and wind combination broke skylights and windows.

Hail in YELLOWSTONE, MONTANA
From 01-AUG-13 19:13:00 to 01-AUG-13 19:13:00 (MST-7)
Location: RIMROCK
Magnitude: 1.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Funnel Cloud in YELLOWSTONE, MONTANA
From 01-AUG-13 19:13:00 to 01-AUG-13 19:13:00 (MST-7)
Location: ACTON
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Hail in YELLOWSTONE, MONTANA
From 01-AUG-13 19:20:00 to 01-AUG-13 19:20:00 (MST-7)
Location: RIMROCK
Magnitude: 1.50 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: NWS Employee

Hail in YELLOWSTONE, MONTANA
From 01-AUG-13 19:22:00 to 01-AUG-13 19:22:00 (MST-7)
Location: ACTON
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Hail in YELLOWSTONE, MONTANA
From 01-AUG-13 19:25:00 to 01-AUG-13 19:25:00 (MST-7)
Location: BILLINGS HGTS
Magnitude: 1.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: NWS Employee

Thunderstorm Wind in YELLOWSTONE, MONTANA
From 01-AUG-13 19:25:00 to 01-AUG-13 19:25:00 (MST-7)
Location: BILLINGS HGTS
Magnitude: 56.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: NWS Employee

A thunderstorm wind gust was estimated at 65 mph.

Thunderstorm Wind in YELLOWSTONE, MONTANA
From 01-AUG-13 19:55:00 to 01-AUG-13 19:55:00 (MST-7)
Location: WORDEN
Magnitude: 61.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Numerous tree limbs were broken.

Thunderstorm Wind in YELLOWSTONE, MONTANA
From 01-AUG-13 19:44:00 to 01-AUG-13 19:44:00 (MST-7)
Location: SHEPHERD
Magnitude: 56.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A 12 inch diameter tree was uprooted. In addition, numerous tree limbs were broken.

Flash Flood in ROSEBUD, MONTANA
From 02-AUG-13 05:15:00 to 02-AUG-13 05:45:00 (MST-7)
Location: ASHLAND
Flood cause: Heavy Rain / Burn Area
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Very heavy rains from several thunderstorms during the late evening hours of the 1st into the early morning hours of the 2nd resulted in flash flooding across portions of the Ash Creek Burn Scar area around Highway 212 near mile marker 55. Rainfall was estimated to be around an inch in about a 30 min time period. In addition, a significant amount of small hail fell as well. Power outages also occurred as a result of the series of thunderstorms. Water around 4 inches deep flowed across the road bringing a significant amount of large pieces of burned wood, trash and silt.

Thunderstorm Wind in YELLOWSTONE, MONTANA
From 01-AUG-13 19:43:00 to 01-AUG-13 19:43:00 (MST-7)
Location: SHEPHERD
Magnitude: 70.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A garage was destroyed.