Overview
A line of thunderstorms developed the evening of September 19th across the eastern Dakotas and moved into western Minnesota before midnight of September 20th. Severe thunderstorms developed into west central and parts of central Minnesota producing large hail, downbursts and six tornadoes. This line of thunderstorms slowly weakened as it moved into far eastern Minnesota, with general, non-severe thunderstorms as the line progressed into West Central Wisconsin after 3 am CDT. |
Tornado, Downburst, and Indeterminate Damage Points |
Tornadoes:
Tornado #1
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Tornado #2
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Tornado #3
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Tornado #4
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Tornado #5
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Tornado #6
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Tornado #7
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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 & Video:
Photos of Damage
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Corn Damage 4 Miles West of Elrosa, MN | Damage 4.5 Miles West of Elrosa, MN | Damage to the Northeast of Camp Lake, MN | Trees Uprooted 5.5 Miles West of Sunburg, MN |
Radar:
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Radar reflectivity (left) and storm relative velocity (right) loop of tornadic storm across West Central Minnesota from 12:02 am CDT through 1:13 am CDT. |
Storm Reports
Click link to see storm reports for September 20, 2017: http://www.spc.noaa.gov/exper/archive/event.php?date=20170919
Environment
A strong and potent upper level disturbance in combination with a cold front acted as the forcing mechanisms for thunderstorm development. The environment in Western Minnesota during the early morning hours of September 20, 2017 was favorable for severe thunderstorm and tornado development as it was unstable with nearly 1000 J/kg of mixed layer CAPE and had plenty of wind shear with about 60 kt of 0-6 km shear.
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Figure 1: Surface Observations at 1 AM CDT | Figure 2: 850 mb Analysis at 1 AM CDT | Figure 3: 500 mb Analysis at 1 AM CDT |
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Figure 4: Mixed Layer Cape and Mixed Layer CIN at 1 AM CDT | Figure 5: Effective Bulk Shear at 1 AM CDT | Figure 6: MPX Sounding at 1 AM CDT |
Additional environmental data.
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