Dangerous, prolonged heat is ongoing in the Mid-South to Mid-Mississippi Valley and heat expands into the Northeast for a brief period today. Widely scattered instances of flash flooding due to heavy rains are forecast from northeast Kansas to much of Indiana. Scattered strong to severe thunderstorms are possible across parts of New England, northern Mid-Atlantic, and North Dakota. 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)]. |
Tornadoes:
Tornadoes - Southern Metro
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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 |
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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
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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.
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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)
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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)
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Figure 7: 2 AM Supercell Composite Parameter | Figure 9: 2 AM Effective Storm Relative Helicity |
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