A strong upper low moved across Wyoming during the late afternoon and early evening hours of the 5th. This resulted in warm, southerly winds across portions of South Central and Southeast Montana. In addition,  plenty of afternoon heating resulted in an unstable atmosphere ahead of a cold front that moved across the area during the early evening hours. Thunderstorms developed across Northern Wyoming and Southern Montana during the late afternoon hours and moved northeast across Southeast Montana during the evening. These thunderstorms produced primary large hail.

Hail in BIG HORN, MONTANA
From 05-SEP-15 17:45:00 to 05-SEP-15 17:45:00 (MST-7)
Location: ABERDEEN
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in ROSEBUD, MONTANA
From 05-SEP-15 18:21:00 to 05-SEP-15 18:21:00 (MST-7)
Location: BIRNEY
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in BIG HORN, MONTANA
From 05-SEP-15 18:25:00 to 05-SEP-15 18:25:00 (MST-7)
Location: CROW AGENCY
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Hail in BIG HORN, MONTANA
From 05-SEP-15 18:25:00 to 05-SEP-15 18:25:00 (MST-7)
Location: KIRBY
Magnitude: 1.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in POWDER RIVER, MONTANA
From 05-SEP-15 18:40:00 to 05-SEP-15 18:40:00 (MST-7)
Location: OTTER
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm Wind in ROSEBUD, MONTANA
From 05-SEP-15 19:05:00 to 05-SEP-15 19:05:00 (MST-7)
Location: ASHLAND
Magnitude: 52.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in POWDER RIVER, MONTANA
From 05-SEP-15 19:24:00 to 05-SEP-15 19:24:00 (MST-7)
Location: EPSIE
Magnitude: 1.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

Hail in POWDER RIVER, MONTANA
From 05-SEP-15 19:25:00 to 05-SEP-15 19:25:00 (MST-7)
Location: SONNETTE
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

Hail in POWDER RIVER, MONTANA
From 05-SEP-15 19:28:00 to 05-SEP-15 19:28:00 (MST-7)
Location: BROADUS
Magnitude: 1.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in POWDER RIVER, MONTANA
From 05-SEP-15 19:30:00 to 05-SEP-15 19:30:00 (MST-7)
Location: SONNETTE
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in POWDER RIVER, MONTANA
From 05-SEP-15 19:30:00 to 05-SEP-15 19:30:00 (MST-7)
Location: BROADUS
Magnitude: 2.50 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

There were numerous reports of hail 1.5-2.0 in diameter in Broadus.

Hail in POWDER RIVER, MONTANA
From 05-SEP-15 19:37:00 to 05-SEP-15 19:37:00 (MST-7)
Location: BROADUS
Magnitude: 2.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in POWDER RIVER, MONTANA
From 05-SEP-15 19:40:00 to 05-SEP-15 19:40:00 (MST-7)
Location: COALWOOD
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

Hail in FALLON, MONTANA
From 05-SEP-15 20:08:00 to 05-SEP-15 20:08:00 (MST-7)
Location: WILLARD
Magnitude: 1.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Hail in FALLON, MONTANA
From 05-SEP-15 20:40:00 to 05-SEP-15 20:40:00 (MST-7)
Location: OLLIE
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter