Heavy Rainfall in the Southwest and Southeast This Weekend; Monitoring Tropical Cyclone Formation Which Could Impact the Southeast U.S.

Heavy rainfall from monsoon thunderstorms may bring isolated flash and urban flooding to the Desert Southwest. A near-stationary front will bring numerous showers and thunderstorms to much of the Mid-Atlantic and Southeast. Tropical wave (AL94) is likely to become a depression. Significant uncertainty remains in the track and intensity, but chances for impacts to the Southeast are increasing. Read More >

Overview

During the early morning hours of July 12th, a line of severe storms tracked from central Minnesota into western Wisconsin. This line of storms created widespread damaging straight line winds across Anoka and northern Washington Counties in eastern Minnesota, with the damaging winds continuing into northwest St. Croix and southwestern Polk counties in western Wisconsin. Within this broad swath of damaging winds, there were four tornadoes. In East Bethel, Columbus, Wyoming, southern Forest Lake, and Hugo, two tornadoes occurred, both with concentrated paths of more significant damage. Two more tornadoes occurred elsewhere: one touched down southeast of Chisago City and the other hit Warner Nature Center and surrounding areas, southwest of Marine on St. Croix.

Tornado
Photos
Radar
Storm Reports
Environment

Tornadoes:

Tornado #1 - East Bethel, Columbus, Linwood Township, Wyoming
Anoka, Chisago Counties

Date	12 July 2017
Time (Local)	2:20 AM - 2:34 AM CDT
EF Rating	EF-0
Est. Peak Winds	80-85 mph
Path Length	12.6 miles
Max Width	440 yards
Injuries/Deaths	None
Summary: This tornado started in East Bethel, on 225th Ave NE and just east of Hwy 65. It moved across the northern part of Carlos Avery Wildlife Management Area, then Columbus, and dissipated in Wyoming, just before reaching Washington County. It mostly broke or toppled hundreds of trees, but it did take some siding off a house and dented a garage door. After the tornado dissipated, strong downburst winds spread out across a 2.5 mile wide swath that took down hundreds of trees around Forest Lake. Other downbursts hit the Coon Lake area of East Bethel.

Tornado #2 - Columbus, Forest Lake, Hugo
Anoka, Washington Counties

Date	12 July 2017
Time (Local)	2:27 AM - 2:38 AM CDT
EF Rating	EF-1
Est. Peak Winds	90 mph
Path Length	10.7 miles
Max Width	400 yards
Injuries/Deaths	None
Summary: This tornado started in the southern part of Carlos Avery Wildlife Management Area, just east of Lexington Ave and Constance Blvd. It moved across Columbus and clipped the southwest part of Forest Lake before moving into Hugo, where it dissipated. It mostly broke or toppled hundreds of trees, but it did destroy an attached garage and hit other structures.

Tornado #1 Track Map

The green dots represent some of the locations of downburst damage.

Tornado #2 Track Map

The green dots represent some of the locations of downburst damage

Tornado #3 - Lindstrom
Chisago County

Date	12 July 2017
Time (Local)	2:39 AM - 2:40 AM CDT
EF Rating	EF-0
Est. Peak Winds	65-85 mph
Path Length	0.6 mile
Max Width	200 yards
Injuries/Deaths	None
Summary: This brief tornado hit three properties and then dissipated. It destroyed a barn and broke or uprooted dozens of trees.

Tornado #4 - May Township, near Marine on St. Croix
Washington County

Date	12 July 2017
Time (Local)	2:41 AM - 2:44 AM CDT
EF Rating	EF-0
Est. Peak Winds	65-85 mph
Path Length	3.0 miles
Max Width	250 yards
Injuries/Deaths	None
Summary: This tornado uprooted and broke over 1000 trees at the Warner Nature Center in May Township, several miles southwest of Marine on St. Croix. After the tornado dissipated, strong downburst winds broke or toppled hundreds of trees south of Marine on St. Croix.

Tornado #3 Track Map

The green dot represents location of some of the downburst damage

Tornado #4 Track Map

The green dot represents location of some of the downburst damage

The Enhanced Fujita (EF) Scale classifies tornadoes into the following categories:

EF0 Weak 65-85 mph	EF1 Moderate 86-110 mph	EF2 Significant 111-135 mph	EF3 Severe 136-165 mph	EF4 Extreme 166-200 mph	EF5 Catastrophic 200+ mph

Photos


A garage collapsed just south of Columbus.	Tree damage was common along the path.	Minor roof damage to this home. A window was also broken, but was quickly replaced.	Destroyed barn in southern Chisago County

Radar:

Radar reflectivity (left) and storm relative velocity (right) loop of tornadic storm across far eastern Anoka and northwestern Washington counties from 227 AM through 237 AM.

Storm Reports

Click link to see storm reports for July 9, 2017: http://www.spc.noaa.gov/exper/archive/event.php?date=20170711

Environment

The overall low level environment was not supportive of tornadoes given a sizable stable layer as shown in the special balloon launch a couple hours before the tornado formed. However, if that stable layer mixed out locally as was suspected, then the storm was able to work with a lot of instability and low level shear.

Special Chanhassen (MPX) sounding at 1 AM

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Heavy Rainfall in the Southwest and Southeast This Weekend; Monitoring Tropical Cyclone Formation Which Could Impact the Southeast U.S.

Summary of July 11-12, 2017 Severe Weather Event