Heavy Rainfall and Severe Thunderstorm Threats; Heat Risk Expands; Monitoring the Tropics

Flash flooding risks continue for portions of the Four Corners and Great Basin through today. Severe thunderstorms are outlooked from the eastern Great Lakes, southern New England into the mid-Atlantic through Tuesday. Heat risk increases and expands across the center of the nation and across the Ohio Valley and mid-Atlantic this week. Continue to closely monitor tropical development in the Gulf. Read More >

Overview

A line of severe thunderstorms moved across southern Minnesota during the early morning hours of September 17th. The bulk of the storm reports and damage occurred between 2-4 AM CDT. A damage survey conducted on Friday found 4 EF-0 QLCS tornadoes occurred (3 within the southern Twin Cities metro). Received reports of numerous areas with straight-line wind damage [downed tree branches, uprooted trees, and structural damage (significant damage did occur to Hudson, WI's library)].

Tornado
Photos
Radar
Environment

Tornadoes:

Tornadoes - Southern Metro
SCOTT & DAKOTA COUNTY

Date	September 17, 2021
Time (Local)	3:00 AM - 3:08 AM
EF Rating	EF-0
Est. Peak Winds	85 MPH
Path Length	0.8 to 2.1 miles
Max Width	Unavailable
Injuries/Deaths	0/0
Summary: A tornado touched down near Highway 13 and Connelly Pkwy and moved east for 2.1 miles. Most damage was due to trees falling on houses and vehicles. Roof damage occurred at Savage Public Works and a light standard was bent at a baseball field. Another tornado touched down near Cedar Ave and 145th St W in Apple Valley. Most damage was due to trees falling on houses and vehicles. Third tornado touched down near Highway 13 and Cliff Rd in northeast Burnsville. Again, most damage with this tornado was due to trees falling on houses and vehicles.

Track Map

Downloadable KMZ File

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

Savage Bent Light Pole

(Photo FOX 9)

Savage Tree Damage

(Photo FOX 9)

Burnsville Tree Damage

(Photo Brandon Spratt)

Damage to Hudson Library

Hudson, WI

(Photo KARE 11)

Radar

Line of storms at 2:46 AM

(Radar Reflectivity)

Savage tornado at 3:02 AM

(Storm Relative Motion - SRM)

Burnsville & Apple Valley tornadoes at 3:08 AM

(Storm Relative Motion - SRM)

Environment

During early Friday morning, a line of thunderstorms ahead of a cold front moved east across southern Minnesota. Environmental parameters indicated that the remnant atmosphere from the previous evening still was slightly favorable for severe storms.


Figure 1: 8 PM SPC Day 1 Outlook	Figure 2: 3 AM Surface Analysis	Figure 3: 1 AM Mesoscale Discussion SPC

Additional severe weather parameters. (From SPC)


Figure 4: 2 AM SBCAPE & CIN	Figure 5: 2 AM 500 MB Short Wave	Figure 6: 2 AM Effective Bulk Shear

Additional severe weather parameters. (From SPC)


Figure 7: 2 AM Supercell Composite Parameter	Figure 9: 2 AM Effective Storm Relative Helicity

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Heavy Rainfall and Severe Thunderstorm Threats; Heat Risk Expands; Monitoring the Tropics

Summary of September 17, 2021 Preliminary Survey Results