National Weather Service United States Department of Commerce

*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: