As can be seen in the enhanced GOES-16 satellite imagery (Fig. Research suggests that thunderstorm (supercell) updraft speeds of 100 mph would be required to support the 4.5" hail stone that fell just north of Appleton! Two rounds of severe storms rapidly moved across the forecast area during the early to mid-morning hours. Rotating updrafts generate vertical pressure perturbations that can further strengthen an updraft. The storms that dropped the largest hail on September 7th were supercell thunderstorms characterized by a persistent cyclonically rotating updraft. Other factors that can also contribute to enhancing the updraft in a thunderstorm, include whether or not the updraft is rotating. Large CAPE in the HGZ favors very strong updrafts that can support/suspend large hail stones. Figure 3A indicates that the largest CAPE values (~ 600 J/kg) in the HGZ was located right over Wisconsin. This region is referred to as the Hail Growth Zone (HGZ) and refers to the layer in the atmosphere where temperatures range from -10 C and -30 C. Forecasters can examine the amount of available CAPE in the region where hail typically grows within a thunderstorm updraft. A RAP analysis estimated sounding near Oshkosh, WI (valid at 10 am CDT), indicated MUCAPE values were likely greater than 2000 J/kg (Fig. The white rectangle denotes the area where the HREF ensemble forecast mean deep layer wind shear was greater than 60 knots AND where mean MUCAPE (Most Unstable CAPE) was forecast to range from 1500 to 2000 J/kg. This was the case early Tuesday morning September 7 (Fig. Severe thunderstorms typically develop in areas where strong vertical wind shear ( related to storm updraft maintenance/persistence) and sufficient buoyancy ( related to the updraft strength/intensity) coincide.
In the mid-levels of the atmosphere (Fig.1), a seasonably strong 500 mb trough was deepening over Wisconsin that was accompanied by winds of 70-75 knots and temperatures of -14 to -18 degrees C. The previous latest date for hail of 4 inches or greater was August 14, 2000. The 4.5 inch diameter hailstone north of Appleton on Septemwould be the largest hail stone to fall so late in the season (since 1950)!
4.5 inch diameter - Oakdale (Monroe County) - June 1, 2000ĥ NNE Appleton (Outagamie County) - September 7, 2021 5.5 inch diameter - Port Edwards (Wood County) - June 7, 2007ģ. 5.7 inch diameter - Wausau (Marathon County) - May 22, 1921Ģ. Here is a list of some of the largest hail stones ever recorded in Wisconsin:ġ. Severe hail ranging from 1 to 4+ inches in diameter damaged some vehicles and roofs of homes from New London and Hortonville, east across the I-41 corridor near Appleton, to southern Brown County ( see map below for location of hail and wind reports). The largest measured hail stone reported was at least 4.5 inches in diameter (preliminary) that fell about 5 miles NNE of Appleton! This was the third largest hailstone ever recorded in Wisconsin (see below)! A second and more intense squall line (and a few supercells) developed rapidly, shortly after the first, producing swaths of large hail across east-central Wisconsin and the I-41 corridor between about 8 am and 11 am CDT. These storms knocked trees and powerlines down across the northern portion of Door County between 6:00 and 6:30 am CDT. The first squall line developed shortly after midnight on September 7 and impacted areas north of Green Bay and the Fox Valley. SeptemAn Early Morning Late Season Large Hail Event in Northeast Wisconsinĭuring the early to mid-morning hours of September 7, 2021, two separate squall lines developed over parts of northcentral and northeast Wisconsin. The storms impacted the morning rush hour as they raced east at speeds of 50-60 mph.
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