7/20/2010 DISC: WI

[Tim Marquis]

Interesting event unfolded in North central Wisconsin yesterday. A shortwave embedded in the zonal flow crossed into western wisconsin during the afternoon. At the surface, there was confluent/convergence zone across the central part of the state. During the day, western Wisconsin remained relatively clear, allowing enough heating to get around 1300 j/kg of cape. SPC initially had the entire area out of the Day 1 outlook but throughout the day the area got upgraded to a see text at the morning update, and then a slight during the afternoon. Right as storms initiated along this convergent zone, SPC put out a severe thunderstorm watch. These storms then tracked SE and produced widespread hail and wind damage with one cell developing rotation around the Wittenberg, WI that prompted the NWS to issue a tornado warning on it. Was there anyone out on this cell? If so I encourage you to start a thread for reports and post pictures.

The rotation died out and the storms continued to track SE towards lake Michigan with lots of hail reports following in their path especially around the Appleton, WI area. Very marginal event that formed well off the warm front.

 

[Paul Townsend]

I was on the storm but have no pics or video of the storm. That area is hilly and forested and just plain lousy to do any storm observing, at least from the south. The storm was HP and I never saw a base, but only varying shades of black, grey, and green. Since it is hilly and forested, the roads are relatively sparse and definitely not gridded, so there was no way I was going to poke my head up there right in front of the beast to see if I could see something through the notch. I got white out with rocking gusts just to the southeast of Wittenberg, which I assume was the RFD. Got hailed on for a while as I travelled east from Tigerton. Stopped, then turned south toward Clintonville and got hailed on again. Used RadarScope on my iPad to head south and west from Clintonville to intercept the final supercell. Passed through the Wolf River valley between New London and Northport on WI 54 just a little bit before they got 60+ winds and trees on the road making it nearly impassable. Went down to Weyauwega to hop on US 10 and flew back east to catch the beast just west of Appleton. Started getting into hail at county CB. As I moved east on county BB and toward home suddenly I saw hail on the ground....then more....and as I got near home there was hail covering the ground and hail fog. The largest stones had a diameter of 1.5". Unreal sight. Leaf and plant debris everywhere.

 

[MattKaskavitch]

I spoke with the WCM at NWS-GRB today and the supercell near Wittenberg you are referencing produced widespread damage just as it became tornado warned in Shawano county. It was found that a massive downburst produced winds near 90 mph that caused the damage in this area, not a tornado. Still, a very impressive damage swath.

This supercell also produced at least two downbursts in the previous 60 minutes before the damage in Wittenberg in portions of Marathon County, though much more isolated and likely in the 60-70 mph range.

 

[Doug Raflik]

I dont think the storms were HP at all. I got on the first cell (the one that went tornado warned) right after the tor warning expired. The updraft area was gusting out, but reorginized near Seymor, WI.

The storm weakened after this and I could see an updraft base on the otherside of some serious precip just to the NW of Appleton. I tried to beat the precip but wasnt able to do it. Traffic on 41 came to a standstill due to the heavy rain and hail. I have never seen rain THAT heavy. Even with wipers on full speed, I couldnt see the hood of the car. The precip passed and I was able to get to the south west side of the storm where I could see the base, but due to Appleton, and the lake, was unable to follow.

Doug