June 21, 2011 - Severe Winds and Tornadoes

Severe Winds (Bow Echo) and 2 Tornadoes

Once again...severe weather struck parts of south-central and southeast Wisconsin on June 21st, 2011.

It was only a year ago that an EF2 tornado tore through the community of Eagle in Waukesha County.  For a complete story of the severe weather on June 21st, 2010- click HERE.

Fast forward now to June 21, 2011 - once again the weather picture consisted of tornadoes and damaging, downburst, straight-line winds that uprooted or damaged thousands of trees and damaged or destroyed structures and vehicles. The severe weather was associated with a warm front which pushed north through much of southern Wisconsin.

Quick Facts:

Fatalities - none reported.

Injuries - 1 person injured by airborne tree debris near border of Delafield and Pewaukee

# tornadoes - 2 documented with both affecting the counties of Fond du Lac and Green Lake

# Thunderstorm Wind events - 1 major squall line (bow echo) with general gusts of 60 to 80 mph that affected the counties of Walworth, Jefferson, Waukesha, and Washington.  Local gusts to around 100 mph in western Waukesha County.  Several homes and vehicles damaged, several barns and sheds damaged or destroyed, thousands of trees damaged and a good number uprooted.  One semi-trailor on I-94 blown over in Waukesha County.

Thunderstorm Wind Damage Event

While many locations in southern Wisconsin had thunderstorms at some point during the day, most of the strongest storms occurred in the southeast area during the early to mid-afternoon hours as a piece of atmospheric energy moved north into a warm and very juicy environment. A complex of thunderstorms, known as a squall line with powerful downburst winds, rapidly developed over northern Illinois and quickly moved through southeastern Wisconsin in the form of a bow echo.

Doppler radar measured winds of up to around 100 mph at the peak intensity of these storms!  In fact, for a brief moment Doppler radar measured a wind speed of 126 mph about 350 feet above the ground near Dousman as the bow echo accelerated northeast.  Below, and to the left, is a loop of radar velocity from 2:18 pm to 4:27 pm. Click on the far left image for the radar loop (4 MB animation). The individual images to the right are high resolution snapshots of the bow echo as it moved from northern Walworth county, across the NWS MKX radar and into southern Dodge county. Note, green/blue colors are winds moving toward the radar and red/brown colors are winds moving away from the radar.

The squall line bow echo resulted in numerous reports of damage, mainly in the form of damaged or uprooted trees. Some homes and vehicles were damaged by tree debris, and a barn was destroyed in southern Washington County.  Many  wind reports of 60 to 80 mph were also received.  Below is a graphic illustrating the severe weather events reported to the National Weather Service office in Sullivan. The shaded area indicates the broad region that the wind damage reports were in. Not all locations within this area reported damage.  Click on the image for a larger version.

Within the large purple-colored area in the above map was a smaller region of intense microburst activity - mainly western Waukesha County.  Below is map showing the region affected by the strongest winds; indicated by the red cross-hatched area.  The map was generated by Bill Stolte, Emergency Management Director for Waukesha County.  Bill also shared 3 pictures of wind damage in western Waukesha County.  Click on each image for larger version.

Below are some photos of damage from the straight-line winds that crossed Waukesha and Washington Counties. Click on each image for larger version.

Photo - Thomas Thomson      

Below are additional pictures of wind damage from around the Dousman area south to CTH CI in western Waukesha County.  The pictures were taken by NWS employees at 2 pm Thursday, June 23rd.  A swath of significant tree damage (hundreds of trees uprooted or broken branches) extended from around Beaver Dam Lake at CTH CI northeast over CTH ZC to the area where School Section Lake Rd and STH 67 intersect. Much of the tree debris had been cleared from CTH ZC, as you can see in the pictures taken of the road.  CTH ZC was closed to traffic for a number of hours.  This was one of several smaller, severe microbursts embedded within the larger squall line-bow echo.  Click on each image for larger version.

The house below, located north of Golden Lake in extreme western Waukesha County, wasn't damaged by the squall line-bow echo winds since the winds were weaker near the Jefferson-Waukesha County line.  However, had the strongest winds occurred near this home, it's safe to say it would have been blown off its wood supports prior to being lowered and connected to the foundation.

The squall line-bow echo winds damaged trees, destroyed a barn, and pulled down a power-pole about 3 miles south of Slinger in southern Washington County.  Additionally, the tree debris damaged a vehicle.  Below are some pictures taken on Slinger Road.  The pictures were taken by Rob Schmid, Washington County Emergency Management Director. Click on each image for larger version.

As the squall line-bow echo moved through the Richfield area in southern Washington County, Patti Domacker snapped a picture of the shelf cloud that was on the front side of the storms.  Squall lines typically have the best developed shelf clouds.  In her picture below a localized microburst was pushing through resulting in a rounded appearance of the shelf cloud.  Patti also noticed some rotation in the clouds.  However, this rotation was not persistent - it was temporary as the microburst pushed forward.  Tornadoes are uncommon on the front sides of squall lines-bow echoes.  Click on image for larger version.

Tornado Events in Green Lake County and Fond du Lac County

Around the same time that severe winds were occurring across the southeast, some storms over the counties of Columbia, Dodge, Marquette, Green Lake, and Fond du Lac developed rotation within their updraft towers. Ultimately, two tornadoes spun up with both affecting the county border area of Green Lake and Fond du Lac County.

Our office received a public report of a tornado about 3 miles southeast of the city of Ripon, but we were unable to verify that report given that there was no associated damage. 

A National Weather Service storm survey team confirmed that two F1 tornadoes occurred in Green Lake and Fond Du Lac Counties. Below on the left is a graphic illustrating the tornado paths. The image on the right is a base reflectivity loop indicating the movement of the thunderstorm responsible for the two tornadoes.  Included is one Storm Relative Motion image which reveals the mesocyclone "velocity couplet."  Click on the images for larger versions.

First, More Southerly Tornado

The more southern tornado was very unique in that the ground damage pattern suggested three different tornadic vorticies developed with one taking over as the previous one dissipated.  However, collectively, the three vorticies were one tornado that affected both Fond du Lac and Green Lake County.

Tornado #1 specifics:

Start - 3.6 WSW Alto at 321 pm       End - 4.5 ENE Markesan at 330 pm

EF1 (100 mph), Path Length (5 miles), Max Path Width=150 yds 

Below are pictures of damage inflicted by the first, more southerly, tornado:

Second, More Northerly Tornado

The second, more northerly, tornado initially moved northeast toward the county line and turned north while it was over Searle Rd (the county-line road that separates Green Lake County and Fond du Lac County). Thereafter it curved back toward the northwest.

Tornado #2 specifics:

Start - 6.2 SE Green Lake at 336 pm      End - 4 SE Green Lake at 340 pm

EF1 (90 mph), Path Length(3 miles-curved), Max Path Width=100 yds 

Below are pictures of damage inflicted by the second, more northerly,tornado:

Below is a picture of a rotating wall cloud at the bottom of the supercell thunderstorm that spun up the two tornadoes in the counties of Green Lake and Fond du Lac.  In the picture the storm is near Fairwater - and we estimate it was taken about 2-3 minutes prior to the start of the second tornado. Note the curved appearance of the wall cloud which indicates rotation.  The person taking the picture was on the county line west-northwest from the thunderstorm. Click on image for larger version.

Photo Courtesy of  Dominic Wunderlin

Besides the two tornadoes, there were at least 3 verified funnel cloud reports.  Gary Podall, Green Lake Emergency Management Director, reported two funnel clouds south of the city of Berlin in Green Lake County.  A severe weather spotter in Madison took a picture of a funnel cloud on the south side of Madison.  His picture is below. Click on image for larger version.

Flash Flood Event in Milwaukee Area

Winds were not the only threat for the day. Heavy rains hit many parts of southern Wisconsin, with the Milwaukee area being hit the hardest. A Flash Flood Warning was necessary for the evening hours, with many reports of road closures due to flooding and even vehicles stalling. Below are a few sites that reported over 3 inches of rain that led to the flooding.

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1000 PM     HEAVY RAIN       ELM GROVE               43.05N 88.09W
06/21/2011  M3.33 INCH       WAUKESHA           WI   MESONET

            3.33 INCHES OF RAINFALL FROM MIDNIGHT THROUGH 10 PM THIS
            EVENING...FROM MMSD RAIN GAUGE.

1000 PM     HEAVY RAIN       7 WSW MILWAUKEE         42.99N 88.04W
06/21/2011  M3.45 INCH       MILWAUKEE          WI   MESONET

            3.45 INCHES OF RAINFALL FROM MIDNIGHT THROUGH 10 PM THIS
            EVENING...FROM MMSD RAIN GAUGE.

1000 PM     HEAVY RAIN       1 W MILWAUKEE           43.03N 87.94W
06/21/2011  M3.40 INCH       MILWAUKEE          WI   MESONET

            3.40 INCHES OF RAINFALL FROM MIDNIGHT THROUGH 10 PM THIS
            EVENING...FROM MMSD RAIN GAUGE.

1000 PM     HEAVY RAIN       3 NW MILWAUKEE          43.06N 87.96W
06/21/2011  M3.56 INCH       MILWAUKEE          WI   MESONET

            3.56 INCHES OF RAIN FROM MIDNIGHT THROUGH 10 PM THIS
            EVENING...FROM MMSD RAIN GAUGE.