7/15/97 Chase by Don Lloyd

From: Don Lloyd (dlloyd@INC.NET):

I did not see July 15th as a chase day in the morning. The models were consistent in keeping storms confined to the northern half of the state until near sunset due to strong capping inversion in the south. The area south of Green Bay seemed too removed from the upper level energy anyway. Nevertheless, I had the day off so I kept watch on the surface maps and satellite images, as well as the sky. Anvil debris was visible to the north all day as two waves of storms crossed the state. A yellow box was issued for the north half of the state but the ETA progged at least marginal helicities if storms propagated to the south. Around 4pm, they seemed to be doing just that. Northwest of Fond du Lac, towers were punching up and breaking through the cap surrounded by crisp turkey towers. Storms to the north had already produced Doppler indicated mesos with an unconfirmed tornado near Tigerton. This line propagated almost due south. At 4:30, Jennie and I drove up US41 to intercept. As the anvil pushed south, mammatus proliferated beneath the canopy in a matter of minutes, growing large and pendulous just as quickly indicating a very strong updraft(s). North of Oshkosh, the structure became increasing visible and impressive, especially for Wisconsin, since the structure is often cluttered or obscured by low-level garbage. And what structure it was. A massive wall rose skyward to the anvil, tiered by at least four well defined low and middle level inflow bands and and a prominent inflow jet, wrapping around a mid-level meso (observational deduction only) over the north end of Lake Winnebago--it was best the structured HP supercell I've seen this year. The shelf cloud at first appeared like a long set of jagged teeth beneath the wall but quickly gusted outward as the storm went outflow dominant. The shelf cloud and outflow blasted around the right side of the meso so quickly we were nearly overrun by it, and even travelling south on US41 at 65mph, we barely stayed ahead of it. The storm bowed towards and through the city of Oshkosh, raising clouds of dust and downing numerous trees and utility poles. The eastern flank of the storm weakened while it intensified over western Fond du Lac County as the system began backbuilding from Marquette across Green Lake County. A few funnels were reported but at this point I considered a tornado very unlikely given the amount of outflow. The lightning was spectacular at times, especially in the wake of the storm, but the best sight of the day had come earlier in the form of a finely sculptured HP supercell as it moved across Outagamie and Winnebago counties. Sadly, there was one fatality in Oshkosh when a tree was blown down onto a minivan. The area was under a severe thunderstorm warning at the time. Photos will be posted on my web page by Friday night. Chase distance: 115 miles *********** Don and Jennie Lloyd (dlloyd@inc.net) (KB9OXW) Fond du Lac, Wisconsin

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