A deep low pressure system moving through northwest Ontario pushed a warm front across the Upper Great Lakes region on the morning of the 19th.  This warm front produced strong to severe thunderstorms over western Lake Superior.

Marine Thunderstorm Wind in SAXON HARBOR WI TO UPPER ENTRANCE OF PORTAGE CANAL MI 5NM OFFSHORE TO US/CANADIAN BORDER INC ISLE ROYAL NP, LAKE SUPERIOR
From 19-AUG-11 04:10:00 to 19-AUG-11 04:20:00 (EST-5)
Location: UPPER ENTRANCE PORTAGE CANAL
Magnitude: 35.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Wind gust measured at the Portage Canal GLOS Station.

Marine Thunderstorm Wind in ONTONAGON TO UPPER ENTRANCE OF PORTAGE CANAL MI, LAKE SUPERIOR
From 19-AUG-11 04:10:00 to 19-AUG-11 04:20:00 (EST-5)
Location: KEWEENAW UPR ENT LT
Magnitude: 35.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Wind gust measured at the Portage Canal GLOS Station.

Marine Thunderstorm Wind in UPPER ENTRANCE OF PORTAGE CANAL TO EAGLE RIVER MI, LAKE SUPERIOR
From 19-AUG-11 04:10:00 to 19-AUG-11 04:20:00 (EST-5)
Location: MCCLAIN STATE PARK
Magnitude: 35.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Wind gust measured at the Portage Canal GLOS Station.

Marine Thunderstorm Wind in UPPER ENTRANCE OF PORTAGE CANAL TO MANITOU ISLAND MI 5NM OFFSHORE TO US/CANADIAN BORDER, LAKE SUPERIOR
From 19-AUG-11 04:10:00 to 19-AUG-11 04:20:00 (EST-5)
Location: UPPER ENTRANCE PORTAGE CANAL
Magnitude: 35.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Wind gust measured at the Portage Canal GLOS Station.

Marine Thunderstorm Wind in BLACK RIVER TO ONTONAGON MI, LAKE SUPERIOR
From 19-AUG-11 06:47:00 to 19-AUG-11 06:50:00 (EST-5)
Location: UNION BAY BEACH
Magnitude: 60.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Park/Forest Service

The spotter at the headquarters of Porcupine Mountains State Park reported severe downdrafts, trees falling and dime-sized hail.

Marine Thunderstorm Wind in BLACK RIVER TO ONTONAGON MI, LAKE SUPERIOR
From 19-AUG-11 07:05:00 to 19-AUG-11 07:08:00 (EST-5)
Location: ONTONAGON LIGHT
Magnitude: 60.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

Numerous trees uprooted and power poles snapped from confirmed weak tornado in the village of Ontonagon.

Marine Thunderstorm Wind in ONTONAGON TO UPPER ENTRANCE OF PORTAGE CANAL MI, LAKE SUPERIOR
From 19-AUG-11 07:05:00 to 19-AUG-11 07:08:00 (EST-5)
Location: ONTONAGON LIGHT
Magnitude: 60.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

Numerous trees uprooted and power poles snapped from confirmed weak tornado in the village of Ontonagon.

Marine Thunderstorm Wind in POINT ISABELLE TO LOWER ENTRANCE OF PORTAGE CANAL MI, LAKE SUPERIOR
From 19-AUG-11 08:10:00 to 19-AUG-11 08:15:00 (EST-5)
Location: KEWEENAW LOWER ENTRANCE LIGHT
Magnitude: 36.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Buoy

Wind gust measured at buoy 45025 near the Lower Entrance of Portage Canal.

Marine Thunderstorm Wind in PORTAGE LAKE TO HURON IS MI TO LOWER ENTRANCE OF PORTAGE CANAL TO HURON IS INC KEWEENAW AND HURON BAYS, LAKE SUPERIOR
From 19-AUG-11 08:10:00 to 19-AUG-11 08:15:00 (EST-5)
Location: KEWEENAW LOWER ENTRANCE LIGHT
Magnitude: 36.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Buoy

Wind gust measured at buoy 45025 near the Lower Entrance of Portage Canal.