August 9, 2009 Severe Thunderstorms - Wind Damage

Severe thunderstorms crossed southern Wisconsin on Sunday August 9.  The first storm to move into the state had tracked across Iowa leaving a path of wind damage.  Once into Wisconsin around 130 PM, the storm briefly weakened over Lafayette and Green counties, then picked up strength once again over Rock and Walworth counties into Racine and southern Milwaukee counties. This storm caused extensive wind damage across Walworth and Racine counties between 3 and 4 pm where trees and power lines were reported down across both counties.

The second round of storms moved into Iowa and Lafayette counties by around 3pm, bringing wind gusts and damage from Iowa and Lafayette counties all the way across to Milwaukee and Racine counties.

The map below shows the swath of wind damage across southern Wisconsin.  Triangle markers indicate measured or estimated wind gusts, some including damage reports.  Wind speeds are shown in mph.  Green circles are reports of wind damage, mostly to trees and powerlines.

The second storm produced an impressive shelf cloud as it tracked across the state.  This picture was taken by an NWS employee just west of Gratiot in Lafayette County.

 
...A SUMMARY OF THE SEVERE WEATHER FROM SUNDAY AUGUST 9...

DURING SUNDAY AFTERNOON AND EVENING AUGUST 9TH...THREE ROUNDS OF
ROUNDS OF THUNDERSTORMS SWEPT ACROSS SOUTHERN WISCONSIN. THE FIRST
TWO ROUNDS CAUSED SOME SIGNIFICANT WIND DAMAGE TO DIFFERENT PARTS OF
THE MILWAUKEE/SULLIVAN COUNTY WARNING AREA. MORE SPECIFICALLY...
THREE SIGNIFICANT WIND DAMAGE SWATHS OCCURRED. NONE OF THE DAMAGE
APPEARS TO BE RELATED TO TORNADIC ACTIVITY...BUT RATHER SIGNIFICANT
STRAIGHT-LINE WINDS.

.SWATH ONE.../NORTHEAST WALWORTH CO. TO NORTHERN RACINE CO./...
330 PM TO 415 PM


A SEVERE THUNDERSTORM MOVED EAST-NORTHEAST FROM NORTHEAST WALWORTH
COUNTY AND EVENTUALLY PASSED THROUGH FAR SOUTHEASTERN WAUKESHA
COUNTY...MOST OF RACINE COUNTY...AND SOUTHERN MILWAUKEE COUNTY. WIND
DAMAGE WAS REPORTED ACROSS ALL OF THOSE AREAS...BUT THE MOST
SIGNIFICANT WIND DAMAGE OCCURRED IN RACINE COUNTY.

WIDESPREAD TREE DAMAGE WAS NOTED ALL ACROSS RACINE COUNTY...IN
PARTICULAR FROM WATERFORD AND WIND LAKE THROUGH THE CITY OF RACINE.
A SPOTTER NEAR WIND LAKE ESTIMATED WIND GUSTS WERE AROUND 70 MPH. A
SCHOOL MESONET SITE AT 21ST CENTURY PREP SCHOOL MESURED A 61 MPH
WIND GUST IN THE CITY OF RACINE. THE MILWAUKEE /MKE/ TERMINAL
DOPPLER RADAR ABOUT 3 MILES NNE OF NORTH CAPE MEASURED WIND
VELOCITIES AROUND 95 MPH A FEW HUNDRED FEET ABOVE THE GROUND IN
NORTHERN RACINE COUNTY AT THE HEIGHT OF THE STORM.

.SWATH TWO.../SOUTHEAST IOWA CO. TO SOUTHERN DANE CO./...
345 PM TO 430 PM


A MORE INTENSE THUNDERSTORM EMBEDDED WITHIN A LINE OF STORMS MOVED
FROM SOUTHEAST IOWA COUNTY AND NORTHEAST LAFAYETTE COUNTY
EAST-NORHTEAST INTO SOUTHERN DANE COUNTY AND NORTHERN GREEN COUNTY.

THE MOST SIGNIFICANT DAMAGE WAS IN A PATH FROM NEAR THE IOWA AND
LAFAYETTE COUNTY BORDER NORTH OF YELLOWSTONE LAKE STATE PARK
EAST-NORTHEAST TO THE BELLEVILLE AREA. NUMEROUS TREES WERE REPORTED
DOWN IN THIS NARROW CORRIDOR...PARTICULARLY IN WALDWICK AND
HOLLANDALE IN SOUTHEAST IOWA COUNTY...AND IN PERRY TOWNSHIP IN
SOUTHWEST DANE COUNTY. BASED ON EYEWITNESS ACCOUNTS...THE DAMAGE WAS
LIKELY DUE TO A WET MICROBURST.

.SWATH THREE.../ROCK CO. TO SOUTHERN WALWORTH CO./...
430 PM TO 515 PM


DAMAGE IN THIS SWATH WAS A LITTLE MORE SPORADIC THAN THE OTHER TWO.
TREES AND POWER LINES WERE REPORTED DOWN IN A GENERAL LINE FROM
ORFORDVILLE AND FOOTVILLE NORTHEAST THROUGH THE NORTHERN SIDE OF
JANESVILLE AND INTO THE MILTON TOWNSHIP. ONE REPORT WAS OF HEALTHY
TREES SNAPPED OFF ABOUT 10 FEET ABOVE GROUND LEVEL. WE RECEIVED A
MEASURED 78 MPH WIND GUST REPORT FROM THE JANESVILLE AREA WITH THIS
STORM.

ANOTHER HURRICANE-FORCE WIND GUST WAS MEASURED IN WALWORTH COUNTY
NEAR DELAVAN /74 MPH/. A TV-METEOROLOGIST VISITING LAKE GENEVA
ESTIMATED A 60 MPH WIND GUST IN THAT CITY. REPORTS OF TREE DAMAGE
WERE MORE SPORADIC IN WALWORTH COUNTY THAN IN ROCK COUNTY.
 

 

Along with Sunday's severe weather, several rounds of rain fell across southern Wisconsin over the weekend.  The rain was much needed for many parts of the state where lawns and crops suffered through less than an inch of rain through all of July. Several locations received more than 3 inches of rain over the weekend.  One of the harder hit areas was extreme southern Wisconsin where the storms on Sunday produced up to 2 inches of rain in a short period of time.  Another hard hit area was west-central Wisconsin where more than 6 inches of rain fell in some parts of Jackson County.

Here's a plot of preliminary rainfall totals for the month of July (very dry month) to compare to rainfall totals for August 7th-9th.


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