An expansive surface low pressure area and plentiful moisture shifted into eastern Montana and directed multiple and persistent severe thunderstorms from south to north through the region from mid-afternoon through then late night hours of the 20th.  One of these stronger storms produced a brief weak tornado in Valley County.

Hail in PRAIRIE, MONTANA
From 20-MAY-20 18:18:00 to 20-MAY-20 18:18:00 (MST-7)
Location: MC CLOUD
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported quarter size hail.

Thunderstorm Wind in GARFIELD, MONTANA
From 20-MAY-20 19:25:00 to 20-MAY-20 19:25:00 (MST-7)
Location: JORDAN AIRPORT (KJDN)
Magnitude: 54.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

The Jordan airport ASOS site (KJDN) recorded a 62 mph wind gust.  Time estimated by radar.

Thunderstorm Wind in MCCONE, MONTANA
From 20-MAY-20 19:08:00 to 20-MAY-20 19:08:00 (MST-7)
Location: BROCKWAY
Magnitude: 96.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

NWS employees conducted a damage survey in the Brockway area.  Damage to buildings and sheared power poles indicated wind speeds of 105 to 110 mph. Other power poles both east and west of this area were also damaged.

Thunderstorm Wind in MCCONE, MONTANA
From 20-MAY-20 19:25:00 to 20-MAY-20 19:25:00 (MST-7)
Location: CIRCLE MCCONE CO ARP
Magnitude: 64.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

The Circle Town County airport mesonet site (K4U6) at 1.7 E Circle, recorded a 74 mph wind gust.

Thunderstorm Wind in MCCONE, MONTANA
From 20-MAY-20 19:37:00 to 20-MAY-20 19:37:00 (MST-7)
Location: WELDON
Magnitude: 57.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

The mesonet site 4 WSW Weldon (D0807), recorded a 66 mph wind gust.

Thunderstorm Wind in PRAIRIE, MONTANA
From 20-MAY-20 18:58:00 to 20-MAY-20 18:58:00 (MST-7)
Location: MC CLOUD
Magnitude: 56.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: RAWS

At the Big Sheep Mountain RAWS site (LCFM8), a 65 mph wind gust was measured.

Thunderstorm Wind in MCCONE, MONTANA
From 20-MAY-20 19:18:00 to 20-MAY-20 19:18:00 (MST-7)
Location: CIRCLE
Magnitude: 61.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Social Media

Public reported, via Facebook, a grain bin was blown over.  Event time was estimated by radar.

Thunderstorm Wind in GARFIELD, MONTANA
From 20-MAY-20 19:30:00 to 20-MAY-20 19:30:00 (MST-7)
Location: VAN NORMAN
Magnitude: 58.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Public measured a 67 mph wind gust.

Thunderstorm Wind in MCCONE, MONTANA
From 20-MAY-20 19:35:00 to 20-MAY-20 19:35:00 (MST-7)
Location: WELDON
Magnitude: 70.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Public measured 80 mph winds on a home weather station, resulting in damage to some farm outbuildings.

Thunderstorm Wind in WIBAUX, MONTANA
From 20-MAY-20 19:38:00 to 20-MAY-20 19:38:00 (MST-7)
Location: BEAVER HILL DOT
Magnitude: 54.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

At the Beaver Hill I-94 DOT site (MTBVR), a wind gust of 62 mph was measured.

Thunderstorm Wind in GARFIELD, MONTANA
From 20-MAY-20 19:45:00 to 20-MAY-20 19:45:00 (MST-7)
Location: VAN NORMAN
Magnitude: 61.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Public reported several power poles were blown down near the Flowing Wells Rest Area.

Thunderstorm Wind in GARFIELD, MONTANA
From 20-MAY-20 19:51:00 to 20-MAY-20 19:51:00 (MST-7)
Location: SOUTH SAWMILL RAWS
Magnitude: 56.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: RAWS

The South Sawmill Creek RAWS site (SSMM8) recorded a 64 mph wind gust.

Thunderstorm Wind in MCCONE, MONTANA
From 20-MAY-20 19:57:00 to 20-MAY-20 19:57:00 (MST-7)
Location: WELDON
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Public reported wind gusts up to 60 mph with many power poles blown over in the surrounding areas.

Thunderstorm Wind in MCCONE, MONTANA
From 20-MAY-20 20:01:00 to 20-MAY-20 20:01:00 (MST-7)
Location: FT PECK LAKE HANDAR
Magnitude: 70.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter estimated wind gusts up to 80 mph.

Thunderstorm Wind in MCCONE, MONTANA
From 20-MAY-20 20:04:00 to 20-MAY-20 20:04:00 (MST-7)
Location: FT PECK LAKE HANDAR
Magnitude: 61.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported several large tree branches blown down in the area around the Fort Peck Dam and spillway.

Thunderstorm Wind in VALLEY, MONTANA
From 20-MAY-20 20:05:00 to 20-MAY-20 20:05:00 (MST-7)
Location: FT PECK
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: NWS Employee

NWS employee reported wind gusts of at least 60 mph in the town of Fort Peck.

Thunderstorm Wind in MCCONE, MONTANA
From 20-MAY-20 20:05:00 to 20-MAY-20 20:05:00 (MST-7)
Location: FT PECK LAKE HANDAR
Magnitude: 58.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

At the handar mesonet site 2.4 E Fort Peck (GGWFP), a 64 mph wind gust was recorded.  Time estimated by radar.

Hail in VALLEY, MONTANA
From 20-MAY-20 20:02:00 to 20-MAY-20 20:05:00 (MST-7)
Location: GLASGOW
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

CoCoRaHS observer reported quarter size hail which lasted for three minutes.

Thunderstorm Wind in VALLEY, MONTANA
From 20-MAY-20 20:05:00 to 20-MAY-20 20:05:00 (MST-7)
Location: NASHUA
Magnitude: 61.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Social Media

Public reported, via Facebook, a tree was blown down, knocking a fence over.  Time estimated by radar.

Thunderstorm Wind in RICHLAND, MONTANA
From 20-MAY-20 20:07:00 to 20-MAY-20 20:07:00 (MST-7)
Location: ENID
Magnitude: 56.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

The Badger Creek mesonet site (F2498) recorded a 65 mph wind gust. Time estimated by radar.

Thunderstorm Wind in VALLEY, MONTANA
From 20-MAY-20 20:11:00 to 20-MAY-20 20:11:00 (MST-7)
Location: NASHUA
Magnitude: 61.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Public reported, via Facebook, that several trees were blown down.

Thunderstorm Wind in VALLEY, MONTANA
From 20-MAY-20 20:14:00 to 20-MAY-20 20:14:00 (MST-7)
Location: KING COULEE RAWS
Magnitude: 50.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: RAWS

King Coulee RAWS site (KIGM8) recorded a 58 mph wind gust.  Time estimated by radar.

Hail in VALLEY, MONTANA
From 20-MAY-20 20:15:00 to 20-MAY-20 20:15:00 (MST-7)
Location: GLASGOW
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Official NWS Observations

Employees at the NWS forecast office in Glasgow observed quarter size hail.

Funnel Cloud in VALLEY, MONTANA
From 20-MAY-20 20:16:00 to 20-MAY-20 20:16:00 (MST-7)
Location: NASHUA
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported a funnel cloud located just east of the town of Whatley.

Tornado in VALLEY, MONTANA
From 20-MAY-20 20:17:00 to 20-MAY-20 20:22:00 (MST-7)
Location: NASHUA
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

NWS employees conducted a storm survey, which showed evidence of a brief tornado near the town of Whatley, traveling north across US Highway 2.  Damage included: the doors blown in and part of the roof blown off of a metal barn with metal roofing scattered around for 100 yards, a cottonwood tree was snapped, the metal roof of a house was peeled back, a carport roof was completely ripped off, and an aluminum boat was blown 100 feet.  Peak winds speeds were estimated at 80 mph.  Tornado was rated an EF-0.

Heavy Rain in ROOSEVELT, MONTANA
From 20-MAY-20 19:45:00 to 20-MAY-20 20:30:00 (MST-7)
Location: VOLT
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported heavy rain from a thunderstorm, measuring 2.00 inches in 45 minutes, as well as 50 mph wind gusts.

Thunderstorm Wind in VALLEY, MONTANA
From 20-MAY-20 20:35:00 to 20-MAY-20 20:35:00 (MST-7)
Location: LARSLAN
Magnitude: 63.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Social Media

Public reported, via Facebook, thunderstorm wind damage, including a roof blown off a farm building and a fence blown over south of Fuhrman Road.  Time estimated from radar.  Wind speed measured from a home weather station.

Thunderstorm Wind in VALLEY, MONTANA
From 20-MAY-20 20:38:00 to 20-MAY-20 20:38:00 (MST-7)
Location: BAYLOR
Magnitude: 61.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Public reported, via Facebook, thunderstorm wind damage, including power lines down, a sliding door ripped off a large farm shop building, several large tree branches down, and a 500 gallon propane tank knocked over.  Time estimated by radar.

Thunderstorm Wind in VALLEY, MONTANA
From 20-MAY-20 20:40:00 to 20-MAY-20 20:40:00 (MST-7)
Location: BAYLOR
Magnitude: 54.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Cooperative observer measured 62 mph wind gusts from a home weather station.

Thunderstorm Wind in VALLEY, MONTANA
From 20-MAY-20 20:41:00 to 20-MAY-20 20:41:00 (MST-7)
Location: LARSLAN
Magnitude: 61.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Social Media

Public reported, via Facebook, a farm building was destroyed by severe thunderstorm wind gusts.  Winds speed estimated.  Time estimated by radar.

Lightning in VALLEY, MONTANA
From 20-MAY-20 20:45:00 to 20-MAY-20 20:45:00 (MST-7)
Location: GLASGOW
Property damage: 0.10K
Crop damage: 0.00K
Reported by: Public

Public reported damage from a lightning strike to their home, including the top few bricks knocked off the chimney, and in the living room, ash was blown in from the chimney and the fireplace guard doors were flexed.

Thunderstorm Wind in VALLEY, MONTANA
From 20-MAY-20 20:48:00 to 20-MAY-20 20:48:00 (MST-7)
Location: BAYLOR
Magnitude: 55.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter measured 63 mph wind gusts.  Time estimated from radar.

Heavy Rain in GARFIELD, MONTANA
From 20-MAY-20 20:50:00 to 20-MAY-20 20:50:00 (MST-7)
Location: VAN NORMAN
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Public measured a storm total rainfall amount of 3.23 inches.

Thunderstorm Wind in DANIELS, MONTANA
From 20-MAY-20 20:51:00 to 20-MAY-20 20:51:00 (MST-7)
Location: FLAXVILLE
Magnitude: 61.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Social Media

Public reported, via Facebook, a 3-sided farm shed destroyed.  Wind speed estimated.  Time estimated from radar.

Thunderstorm Wind in VALLEY, MONTANA
From 20-MAY-20 21:01:00 to 20-MAY-20 21:01:00 (MST-7)
Location: GLENTANA
Magnitude: 52.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

At the mesonet site located 10 NNE Glentana (FW2113), a 60 mph wind gust was recorded.

Thunderstorm Wind in VALLEY, MONTANA
From 20-MAY-20 21:01:00 to 20-MAY-20 21:01:00 (MST-7)
Location: BLUFF CREEK RAWS
Magnitude: 52.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: RAWS

At the Bluff Creek RAWS site (BLUM8), a 60 mph wind gust was recorded.  Time estimated from radar.

Heavy Rain in VALLEY, MONTANA
From 20-MAY-20 22:00:00 to 20-MAY-20 22:00:00 (MST-7)
Location: FT PECK
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

CoCoRaHS observer measured a storm total rainfall amount of 2.05 inches.

Heavy Rain in VALLEY, MONTANA
From 20-MAY-20 22:59:00 to 20-MAY-20 22:59:00 (MST-7)
Location: HINSDALE
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Public measured a storm total rainfall amount of 2.86 inches.

Thunderstorm Wind in GARFIELD, MONTANA
From 20-MAY-20 18:49:00 to 20-MAY-20 18:49:00 (MST-7)
Location: SAND SPGS
Magnitude: 50.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

At the Lufborough Hill MT-200 DOT site (MTLUF), a 58 mph wind gust was measured.

Thunderstorm Wind in MCCONE, MONTANA
From 20-MAY-20 19:00:00 to 20-MAY-20 19:00:00 (MST-7)
Location: BROCKWAY
Magnitude: 61.00 EG
Property damage: 187.00K
Crop damage: 0.00K
Reported by: Utility Company

Utility company reported more than 100 power poles and 16 distribution towers down along MT-Highway 200.  Started about 2 miles west of Brockway, then northeastward toward the town of Circle.

Thunderstorm Wind in MCCONE, MONTANA
From 20-MAY-20 19:08:00 to 20-MAY-20 19:08:00 (MST-7)
Location: BROCKWAY
Magnitude: 61.00 EG
Property damage: 350.00K
Crop damage: 0.00K
Reported by: Public

Public reported wind damage just west of Brockway and just south of US Highway 200. Former emergency manager's roof was blown half off, and part of his garage was collapsed. Event time is estimated.  House was totaled by insurance.

Thunderstorm Wind in VALLEY, MONTANA
From 20-MAY-20 22:30:00 to 20-MAY-20 22:30:00 (MST-7)
Location: OPHEIM
Magnitude: 60.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Public measured a 69 mph wind gust.

Heavy Rain in VALLEY, MONTANA
From 20-MAY-20 23:30:00 to 20-MAY-20 23:30:00 (MST-7)
Location: BLUFF CREEK RAWS
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Public measured a storm total rainfall amount of 3.42 inches near the Frenchman Dam.

Thunderstorm Wind in PRAIRIE, MONTANA
From 20-MAY-20 18:50:00 to 20-MAY-20 18:50:00 (MST-7)
Location: MC CLOUD
Magnitude: 61.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported a well house blown over, roofing peeled off an additional building, and broken tree limbs up to 8 inches in diameter.

Thunderstorm Wind in MCCONE, MONTANA
From 20-MAY-20 19:28:00 to 20-MAY-20 19:28:00 (MST-7)
Location: WELDON
Magnitude: 53.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Social Media

Public reported, via social media, a 61 mph wind gust measured on a hand held wind sensor.

Thunderstorm Wind in MCCONE, MONTANA
From 20-MAY-20 19:31:00 to 20-MAY-20 19:31:00 (MST-7)
Location: WELDON
Magnitude: 61.00 EG
Property damage: 100.00K
Crop damage: 0.00K
Reported by: Law Enforcement

At the Nelson Creek Recreation Area, law enforcement officials reported three unoccupied camping trailers were rolled and destroyed.

Thunderstorm Wind in MCCONE, MONTANA
From 20-MAY-20 19:35:00 to 20-MAY-20 19:35:00 (MST-7)
Location: WELDON
Magnitude: 78.00 EG
Property damage: 100.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

NWS employees conducted a damage survey of a collapsed barn, estimating winds speeds of 85 to 90 mph.

Thunderstorm Wind in VALLEY, MONTANA
From 20-MAY-20 20:35:00 to 20-MAY-20 20:35:00 (MST-7)
Location: LARSLAN
Magnitude: 63.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Social Media

Public reported, via Facebook, 72 mph wind gusts measured from a home weather station.  Time estimated by radar.

Heavy Rain in VALLEY, MONTANA
From 20-MAY-20 22:00:00 to 20-MAY-20 22:00:00 (MST-7)
Location: GLASGOW
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Public reported a storm total rainfall amount of 2.3 inches.