Tracking a Couple of Storm Systems Across the Country

Showers, along with a few strong to severe thunderstorms, are expected from the Great Lakes, New England and southward into the Ohio and Tennessee Valleys. In the wake of this system, a stronger storm is expected to track from the Pacific Northwest, Plains and through the Eastern U.S. this weekend. Strong winds, showers and a larger drop in temperatures are expected this weekend into Monday. Read More >

Overview

On the evening of September 21, 2005 a series of supercells produced four tornadoes, widespread wind damage, large hail, and flash-flooding in east central Minnesota. 3 inch hail was reported in Rice Lake (Barron County) Wisconsin while 2.5 inch hail was reported in Andover (Anoka County) Minnesota. Wind gusts of 78 miles per hour were reported in Crystal, Minnesota (Hennepin County) and it is possible that wind gusts reached 100 miles per hour in some areas of Andover. Although four tornadoes occurred, damage was mainly caused by downbursts. For example, most of the tree damage in Maple Grove, Brooklyn Center, Brooklyn Park, and north Minneapolis was due to the rear flank downdraft. There was one fatality in Minneapolis in which a large tree branch fell on the victim.

Tornado
Photos
Radar
Storm Reports
Environment

Tornadoes:

Tornado #1- 3 miles S of Atwater
Kandiyohi County

Date	21 September 2005
Time (Local)	6:22 PM CDT
F Rating	F-0
Est. Peak Winds	<73 mph
Path Length	0.1 mile
Max Width	20 yards
Injuries/Deaths	None

Tornado #2- Brooklyn Park
Hennepin County

Date	21 September 2005
Time (Local)	7:07 PM CDT
F Rating	F-0
Est. Peak Winds	<73 mph
Path Length	0.3 mile
Max Width	30 yards
Injuries/Deaths	None
Summary: This tornado touched down in the northeast corner of Brooklyn Park, but the vast majority of the major damage in northern Hennepin County was caused by the rear flank downdraft.

Tornado #3- Andover
Anoka County

Date	21 September 2005
Time (Local)	7:16 PM CDT
F Rating	F-0
Est. Peak Winds	<73 mph
Path Length	0.3 mile
Max Width	25 yards
Injuries/Deaths	None
Summary: The vast majority of the major damage in Andover was caused by the rear flank downdraft. Houses, large trees, and garages were damaged, and a canoe was thrown 2 blocks.

Tornado #4- Coon Rapids, Blaine
Anoka County

Date	21 September 2005
Time (Local)	7:17 PM - 7:21 PM CDT
F Rating	F-2
Est. Peak Winds	113-157 mph
Path Length	2 miles
Max Width	50 yards
Injuries/Deaths	1 injured
Summary: This tornado first touched down in east central Coon Rapids and continued into Blaine. The worst damage was just south of Madison Elementary School. A rear flank downdraft was also responsible for causing damage in parts of Coon Rapids and Blaine. A large portion of a roof was removed and blown onto University Avenue and 100 trees were damaged at Bunker Hills Golf Course. Also, 10 homes were severely damaged while 20 other homes were significantly damaged.

In 2005, the Fujita (F) Scale was used to classify tornadoes into the following categories:

F0 Weak <73 mph	F1 Moderate 73-112 mph	F2 Significant 113-157 mph	F3 Severe 158-206 mph	F4 Extreme 207-260 mph	F5 Catastrophic 261-318 mph

Photos:


Rear flank downdraft damage along 138th Ave in Andover	F-2 tornado damage on 104th Court in Blaine	F-0 tornado damage along 142nd Ave in Andover	Fallen tree on house in Shoreview of Ramsey County

Radar:


Reflectivity at 6:58 PM	Reflectivity (left) and storm relative velocity (right) at 7:08 PM	Reflectivity at 7:16 PM	Reflectivity at 7:24 PM

Storm Reports

Reports of tornadoes, wind gusts, hail, and flash-floods on September 21, 2005

Environment

High values of effective helicity and effective bulk shear, as well as 850 and 700 mb troughs and a strong low-level jet created a favorable environment for severe weather. Also, high precipitable water values, high surface dewpoints, and southerly moisture transport led to flash-flood conditions in Brooklyn Park.


Downdraft CAPE at 6 PM	0-3 km effective helicity at 7 PM	Effective bulk shear at 7 PM


Precipitable water at 8 PM	Significant Tornado Parameter at 7 PM	850 mb analysis map at 7 PM showing deep trough over MN and southerly flow into MN


	300 mb map analysis at 7 PM showing strong winds over MN

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Tracking a Couple of Storm Systems Across the Country

Summary of September 21, 2005 Severe Weather in East Central Minnesota