A cluster of thunderstorms developed over eastern North Dakota and northwestern Minnesota the evening of Wednesday July 20th. The outflow from the storms coalesced into a couple main bow echoes that quickly sped across northeast and central Minnesota and then over western Lake Superior during the early morning hours of Thursday July 21st. It produced widespread straight-line wind gusts of 60 to 80 mph across northeast Minnesota, especially closer to the Duluth area by the time it reached Lake Superior. One of the hardest hit areas was Duluth, with a couple wind gust reports around 100 mph, including from the Algoma Guardian, a ship that was moving through the Duluth ship canal when the winds struck. The derecho raced across Lake Superior, doing damage to parts of the south side of the Lake along northwest Wisconsin, including to the Apostle Islands.

Marine Thunderstorm Wind in LS W OF IN SAXON HBR WI TO GRAND PORTAGE MN BYD 5NM, LAKE SUPERIOR
From 21-JUL-16 03:01:00 to 21-JUL-16 03:01:00 (CST-6)
Location: SILVER BAY HARBOR
Magnitude: 63.00 EG
Reported by: Mariner

The measurement was from the American Integrity, a 1000' long freighter.

Marine Thunderstorm Wind in LS W OF IN SAXON HBR WI TO GRAND PORTAGE MN BYD 5NM, LAKE SUPERIOR
From 21-JUL-16 02:56:00 to 21-JUL-16 02:56:00 (CST-6)
Location: DULUTH
Magnitude: 47.00 MG
Reported by: Mariner

The wind gust measurement was from a tugboat, the Spartan.

Marine Thunderstorm Wind in SAND IS TO BAYFIELD WI, LAKE SUPERIOR
From 21-JUL-16 03:31:00 to 21-JUL-16 03:31:00 (CST-6)
Location: BASS ISLAND RAWS STATION APOW3
Magnitude: 61.00 EG
Reported by: Newspaper

Numerous trees were blown down on Oak Island.

Marine Thunderstorm Wind in PT WING TO SAND IS WI, LAKE SUPERIOR
From 21-JUL-16 03:20:00 to 21-JUL-16 03:20:00 (CST-6)
Location: SAND ISLAND
Magnitude: 61.00 EG
Reported by: Newspaper

Numerous trees were blown down on Sand Island.

Marine Thunderstorm Wind in DULUTH MN TO PT WING WI, LAKE SUPERIOR
From 21-JUL-16 02:39:00 to 21-JUL-16 02:39:00 (CST-6)
Location: SKY HARBOR AIRPORT
Magnitude: 50.00 MG
Reported by: Mesonet

Marine Thunderstorm Wind in SAND IS TO BAYFIELD WI, LAKE SUPERIOR
From 21-JUL-16 03:38:00 to 21-JUL-16 03:38:00 (CST-6)
Location: BASS ISLAND RAWS STATION APOW3
Magnitude: 61.00 EG
Reported by: Newspaper

Numerous trees were down on Stockton Island.

Marine Thunderstorm Wind in DULUTH MN TO PT WING WI, LAKE SUPERIOR
From 21-JUL-16 02:53:00 to 21-JUL-16 02:53:00 (CST-6)
Location: SKY HARBOR AIRPORT
Magnitude: 51.00 MG
Reported by: AWOS

This measurement was from the AWOS at Sky Harbor Airport.

Marine Thunderstorm Wind in LS W OF IN SAXON HBR WI TO GRAND PORTAGE MN BYD 5NM, LAKE SUPERIOR
From 21-JUL-16 03:40:00 to 21-JUL-16 03:40:00 (CST-6)
Location: SAND ISLAND
Magnitude: 61.00 EG
Reported by: Newspaper

Numerous trees were blown down on Michigan Island.

Marine Thunderstorm Wind in SAND IS TO BAYFIELD WI, LAKE SUPERIOR
From 21-JUL-16 03:38:00 to 21-JUL-16 03:38:00 (CST-6)
Location: DEVILS ISLAND LIGHTHOUSE STATION DISW3
Magnitude: 61.00 EG
Reported by: Newspaper

Numerous trees were blown down on Cat Island.

Marine Thunderstorm Wind in DULUTH MN TO PT WING WI, LAKE SUPERIOR
From 21-JUL-16 02:50:00 to 21-JUL-16 02:50:00 (CST-6)
Location: BRULE POINT
Magnitude: 61.00 EG
Reported by: Trained Spotter

Multiple large spruce and poplar trees were blown down.