Severe Storms 7/20/10

The active severe weather pattern continues in North Central Wisconsin.  A little less than a week after the outbreak of storms that caused flash flooding, wind damage and a couple confirmed tornadoes, potent thunderstorms once again rolled through the region, particularly along and south of Highway 29.

Let's start off with what sparked this latest batch of storms.  Unlike the week before where a well defined warm & cold front made their passes across the Badger State, the boundary that sparked the severe weather on Tuesday was a wind shift front, accompanied by a disturbance (small scale low pressure) riding along the front.  Prior to the arrival of the boundary in Central Wisconsin, winds were generally out of the south to southwest at 5-10 mph.  Once this front plowed on by, the winds were calm for a while and then turned over to the northwest.  Temperatures really didn't drop off much in the wake of this front (so can't really say it was a cold front) and the dew point values actually stayed pretty consistent before and after the storms rumbled on across.  The end result was a couple isolated storms that bubbled up in western Wisconsin and tracked into Taylor County around 3pm.  At this point, the storms produced damaging winds in Gilman and Medford, along with hail ranging in size from penny to half dollar size (.75 to 1.5").  As the clock rolled closer to 4pm, these two intense storms continued to the southeast, hitting Wausau and surrounding areas on the north side of town with torrential downpours, damaging winds that blew down many trees in the Riverview area of Wausau, along with flash flooding on Bridge St & Grand Ave, and not to be forgotten hail from 1/4" to as big as 1.0" in diameter.

The damaging wind aspect of the storms that hit on the north end of Wausau continued to make an impact farther southeast into western Shawano County, with additional damage taking place in Birnamwood and Wittenberg.  From damaged rooftops to numerous large trees being toppled, the storms left their mark. Update at 8pm Wednesday, the National Weather Service (NWS) in Green Bay had determined that straight line winds where the cause for damage in Wittenberg along with other parts of western Shawano & eastern Marathon County. 

I did have the opportunity to travel out to Birnamwood and Wittenberg on Wednesday morning and from my best estimates, it appears this storm may have produced straight line winds or a microburst of wind.  In other words, a strong downward force of wind that blew down many of the trees just south of the Highway 29 and Highway 45 interchange down to County Road Q which is where the high school is in town.  Many of the trees I saw were either lying on the ground with the tree tops pointed to the southeast or northeast, which would support the downburst of wind coming from one direction, that being from the west.  I wasn't able to find a defined area where there was a circular pattern of damage, which in my view means there wouldn't have been a tornado.  That aside, the result was plenty of damage, but from what I saw the building damage was not widespread, but scattered in variety.

Back in Wausau, straight line winds were the likely cause of more downed trees and power lines in the Riverview section of town.  In this case from roughly N. 6th St on the western side and Highway 52 on the south end with Evergreen Rd being the cutoff on the north end.  Once again in this case, there was some damage to a few buildings, but no homes or apartments that were totally destroyed by the trees slamming down.

 To check out the official word on the impact of the storms, here's the link to the NWS Green Bay along with the preliminary storm surveys in East Central Marathon & Western Shawano County and straight line wind damage in Northern Marathon County.

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