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Heavy Rainfall and Flash Flood Threats Shift From Southern Plains to Lower Mississippi Valley; Elevated to Critical Fire Concerns Out West

Heavy to excessive rainfall with flash flood concerns will shift from the southern Plains into the Lower Mississippi Valley. Elevated to Critical Fire weather threats will linger through the weekend across the Great Basin and central Rockies. Finally, Major to Record river flooding will continue in portions of the Midwest and across parts of North and South Carolina this weekend. Read More >

*Updated to extend path into Sun Prairie due to video received from the Sun Prairie Police Department.*

Location: 1 SE Maple Bluff to 1 E Sun Prairie

Date: 10/7/17

Rating: EF-0

Estimated Peak Wind Speed: 80 mph

Path Length: 9.9 miles

Peak Path Width: 100 yards

Start Time: 4:59 PM CDT

End Time: 5:15 PM CDT

Fatalities: 0

Injuries: 0


Tornadoes in Wisconsin in October aren't common, but not unprecedented.  Late Saturday (October 7, 2017) afternoon, a line of showers developed along a frontal boundary pushing northeast through southern Wisconsin.  See the surface weather analysis map below (click to enlarge)

These showers weren't big/tall enough to produce lightning, but there was enough shear (changing wind directions and wind speeds) and instability, coupled with a very moist atmosphere, to cause many of the showers to rotate.  The shower that moved through the east side of Madison was strong enough to produce a tornado along East Washington Ave, tracking northeast to Sun Prairie.

Madison to Sun Prairie Tornado Path

Below are a series of radar images (4 panel) that begin at around 4:58 pm and end around 5:12 pm in the Sun Prairie area.  The top left quadrant is reflectivity, top right is velocity, bottom left is reflectivity and bottom right is Correlation Coefficient (CC).  CC is is a dual-pol product that allows us to see if debris is being lofted into the storm from a tornado.  You'll see at around 5:02 there is a good CC signature of the debris (mostly leaves).  

Tornado genesis around 4:58 PM (click to enlarge):

At 5:02 PM:

At 5:06 PM:

At 5:11 PM:

We have received reports of several trees down, some trees on homes, and damage to a few businesses. 

The pictures below are from John Marion and provided to us by Milwaukee SKYWARN:





Pictures below are from our NWS Storm Survey





Below are pictures of thunderstorm wind damage in Pardeeville from storm spotter David Casper: