July 11, 2011 Severe Weather - Bow Echo Summary (updated 935 pm 7/14)

Quick Facts:

What - thunderstorm wind damage due to a squall line (bow echo) with gusts of 60 to 80 mph. Tree, structural, vehicle, and corn crop damage.

Where - South-central and Southeast Wisconsin, south of a Dodgeville to Madison to Milwaukee line.

When - about 610 am to 830 am CDT Monday, July 11, 2011.

Fatalities - none reported.

Injuries - none reported.

No tornadoes - atmosphere didn't support vertical rotation.


During the early morning hours of July 11, 2011, a powerful squall line moved west to east across southern Wisconsin between 6 am and 830 am CDT.  Basically, the two bottom rows of counties in Wisconsin were affected.

During its lifespan the squall line took the shape of an archer's bow--known as a "bow echo" in the meteorological world.

It generated widespread, downburst, straight-line wind gusts on the order of 60 to perhaps 80 mph that resulted in uprooted trees, broken tree limbs that brought down power lines, and damaged buildings and corn crops.  Some vehicles were damaged when broken tree branches fell on them.  The maximum wind gusts were generally out of the west-southwest to northwest direction, depending on the location along the bow echo. 

Below is an animated radar loop showing the progression of the bow echo.  Click on the image for a larger version:

radar loop

Below is a plot of the time that maximum wind gusts occurred, give or take about 5 minutes.  These times corresponded to the front and middle of the band of moderate to heavy rains as indicated by the red colors in the radar loop above.  The time lag of the maximum windn gusts over the counties of Jefferson, Waukesha, and Milwaukee was due to the later arrival of strong winds associated with the "comma head" of the bow echo lagging behind the accelerating portion of the bow echo.  Storms in the "comma head" brought strong wind gusts down to the ground.  Click on the image for a larger version.

max gust times

Here are radar images from 7:13am CDT.  The first image shows base reflectivity.  The bright yellow, red, and purple shades in this image indicate the areas of heaviest rainfall.  The wider area where these colors are seen, over northwestern Rock, northeastern Green, and southern Dane counties is the "comma head" structure.  In the second image, we show the storm-relative motion within the storm.  Arrows have been drawn on the image to show the directions of motion; basically, red shades are moving away from the radar (shown as KMKX at the right side of the image) and green shades are moving toward the radar.  The image shows the strong inflow winds behind the leading edge of the storm, as well as the circulation associated with the "comma head" part of the storm system.

[base reflectivity image]   [storm relative velocity image]

Localized intense damage was created by small scale microbursts with "runaway vortex rolls" which were documented by Dr. Ted Fujita back in the 1970s.  These localized, linear, swaths of intense damage may give a person the perception that a tornado occurred.  However, this was not the case for July 11, 2011.  Our WSR-88D Doppler radar system did not show any signs of classic low-to-mid-level rotations, called mesocyclones, that would support the idea of tornadoes.  Below is an image produced by Dr. Ted Fujita showing what "runaway vortex rolls" look like. Click on the image to see a larger version.

vortex rolls

Below are some pictures of damage in Green County, taken by Tana McKeon of the Green County Emergency Management team.  The pictures are from the city of Monroe, which was hit hard by the winds.  Tanna mentioned that thousands of acres of corn were damaged in Green County, but some of the corn should recover.  Click on the images for larger versions.

green county 1  green county 2  green county 3

green couinty 4  green county 5  green county 6

From Roger Wildermuth, fire fighter in Rock County, we obtained the two pictures below.  Note what a lightning bolt did to the road asphalt!  They had to put that road fire out!

road fire  Rock Co. tree damage

John Ennis, Walworth County Emergency Management Director, submitted the following damage pictures from his county:

Darien barn  Elkhorn barn  Salt Shed

Below we have a couple damage pictures from the Eagle Spring Lake area in southwestern Waukesha County, submitted by Peter Jensen.  Two power lines are on the ground in the picture on the right.

branches down  power line down

In Rock County, Brent Cook and Steve Stageman, of the MidWest Severe Storm Tracking/Response Center (MidWest SSTRC) took the following pictures of tree, structural, and corn crop damage.  Some of the corn should recover with time.  They said the clean-up crews were moving fast!

MidWestTrees  MidWest roof  MidWest house

MidWest corn down  MidWest Tree Close  MidWest corn field

The graphic below shows the locations and types of reports received during the event.  The numbers plotted on the map indicate a wind gust report with the number indicating the speed in MPH.  "W" indicates a report of wind damage.  Click on this image to be taken to an interactive version, where you may mouse over the plotted reports to see more specific information about the report.  Following the graphic is a text listing of all the reports.

Image of storm reports from 7/11/11

NWUS53 KMKX 112209
LSRMKX

PRELIMINARY LOCAL STORM REPORT...SUMMARY

NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI
509 PM CDT MON JUL 11 2011

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...

..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0405 AM     TSTM WND GST     BERLIN                  43.97N 88.95W

07/11/2011  M63.00 MPH       GREEN LAKE         WI   EMERGENCY MNGR


0530 AM     TSTM WND GST     PORT WASHINGTON LAKESHO 43.39N 87.87W

07/11/2011  M44.00 MPH       OZAUKEE            WI   C-MAN STATION

            38 KNOT WIND GUST AT PWAW3 MARINE WEATHER STATION.

0540 AM     MARINE TSTM WIND 17 E PORT WASHINGTON    43.38N 87.53W

07/11/2011  U60.00 MPH       LMZ669             WI   SHIP

0609 AM     TSTM WND GST     10 S JANESVILLE         42.54N 89.02W

07/11/2011  E55.00 MPH       ROCK               WI   911 CALL CENTER

            SEMI OVERTURNED ON I-90 AT MILE MARKER 178 WINDS

0625 AM     TSTM WND DMG     DARLINGTON              42.68N 90.12W

07/11/2011                   LAFAYETTE          WI   LAW ENFORCEMENT

            REPORTS OF TREES AND POWERLINES DOWN IN VARIOUS LOCATIONS
            IN LAFAYETTE COUNTY.

0630 AM     TSTM WND GST     DARLINGTON              42.68N 90.12W

07/11/2011  M54.00 MPH       LAFAYETTE          WI   MESONET

            DRLNG

0656 AM     TSTM WND GST     MONROE AIRPORT          42.62N 89.59W

07/11/2011  M62.00 MPH       GREEN              WI   AWOS

            DIALED VOICE. SUSTAINED 40 KNOTS GUST TO 54 KNOTS. STILL
            38 KNOTS GUSTING TO 51 KNOTS AT 706 AM.

0658 AM     TSTM WND GST     2 S BRODHEAD            42.59N 89.38W

07/11/2011  M62.00 MPH       GREEN              WI   TRAINED SPOTTER

0709 AM     TSTM WND DMG     9 WNW BELOIT            42.57N 89.18W

07/11/2011                   ROCK               WI   TRAINED SPOTTER

            SCREEN HOUSE TORN APART BENDING 1 INCH SQUARE STEEL
            TUBES. WIND MEASURED AT 30 MPH. MEASURED RAINFALL 0.48
            INCHES.

0719 AM     TSTM WND GST     JANESVILLE AIRPORT      42.62N 89.04W

07/11/2011  M56.00 MPH       ROCK               WI   AWOS

            AT 1210Z 38G45 KNOTS VIA METAR. HOWEVER...DIALED INTO
            VOICE AT 1219Z AND WAS GUSTING TO 49 KNOTS.

0720 AM     TSTM WND GST     BELOIT                  42.52N 89.02W

07/11/2011  E65.00 MPH       ROCK               WI   AMATEUR RADIO

0725 AM     TSTM WND DMG     EVANSVILLE              42.78N 89.30W

07/11/2011                   ROCK               WI   TRAINED SPOTTER

            POWER LINES DOWN. ESTIMATED WIND GUST OF 55 MPH.

0735 AM     TSTM WND DMG     4 S JANESVILLE          42.63N 89.02W

07/11/2011                   ROCK               WI   TRAINED SPOTTER

            POWER LINES BLOCKING ALL FOUR LANES OF HWY 51 NEAR THE
            AIRPORT. FOUR INCH DIAMETER BRANCHES AND EIGHT INCH
            DIAMETER TREE DOWN. ESTIMATED WIND GUST OF 55 MPH.

0750 AM     TSTM WND DMG     1 S FORT ATKINSON       42.91N 88.84W

07/11/2011                   JEFFERSON          WI   NWS EMPLOYEE

            1 FT DIAMETER HEALTHY TREE BRANCH FOUND ON GARAGE
            ROOF...TIME ESTIMATED FROM RADAR

0750 AM     TSTM WND DMG     SALEM                   42.55N 88.11W

07/11/2011                   KENOSHA            WI   LAW ENFORCEMENT

            ABOUT A DOZEN TREES DOWN ACROSS THE WESTERN HALF OF
            KENOSHA COUNTY.

0752 AM     TSTM WND GST     BURLINGTON AIRPORT      42.69N 88.30W

07/11/2011  M47.00 MPH       WALWORTH           WI   AWOS

            VOICE DIAL GUST TO 41 KNOTS. KBUU

0802 AM     TSTM WND DMG     1 SW PALMYRA            42.87N 88.60W

07/11/2011                   JEFFERSON          WI   NWS EMPLOYEE

            30 FT MAPLE UPROOTED...ABOUT 3 FOOT DIAMETER...TIME
            ESTIMATED FROM RADAR

0802 AM     TSTM WND GST     S WHITEWATER            42.83N 88.74W

07/11/2011  M58.00 MPH       WALWORTH           WI   AMATEUR RADIO

0802 AM     TSTM WND DMG     1 SW PALMYRA            42.87N 88.60W

07/11/2011                   JEFFERSON          WI   NWS EMPLOYEE

            MULTIPLE 6-12 FT LONG BRANCHES COVERING ROAD...TREE
            BRANCH DOWN ON DAY CARE CENTER CORNER OF CTY RD H AND
            BLUE SPRING LAKE DR...TIME ESTIMATED FROM RADAR

0803 AM     NON-TSTM WND DMG PALMYRA                 42.88N 88.59W

07/11/2011                   JEFFERSON          WI   NWS EMPLOYEE

            ROOF TORN OFF FROM HANGER AT THE AIRPORT AND MANY LARGE
            TREE LIMBS DOWN THROUGH OUT THE CITY

0807 AM     TSTM WND GST     KENOSHA AIRPORT         42.60N 87.93W

07/11/2011  M51.00 MPH       KENOSHA            WI   ASOS

            KENW PEAK WIND 44 KNOTS.

0812 AM     TSTM WND GST     KENOSHA                 42.58N 87.82W

07/11/2011  E60.00 MPH       KENOSHA            WI   TRAINED SPOTTER

0812 AM     TSTM WND GST     KENOSHA                 42.58N 87.82W

07/11/2011  M61.00 MPH       KENOSHA            WI   TRAINED SPOTTER

            NUMEROUS SMALL BRANCHES DOWN 2 INCHES OR LESS IN
            DIAMETER.

0812 AM     TSTM WND GST     NWS SULLIVAN/MILWAUKEE  42.97N 88.55W

07/11/2011  M54.00 MPH       JEFFERSON          WI   OFFICIAL NWS OBS

            SUSTAINED 42 MPH GUSTING 54 MPH.

0812 AM     TSTM WND GST     3 SE EAGLE              42.85N 88.43W

07/11/2011  M55.00 MPH       WAUKESHA           WI   TRAINED SPOTTER

            SMALL BRANCHES DOWN.

0814 AM     TSTM WND GST     RACINE BATTEN AIRPORT   42.76N 87.81W

07/11/2011  M45.00 MPH       RACINE             WI   ASOS

            KRAC PEAK WIND 39 KNOTS.

0815 AM     TSTM WND DMG     2 ESE EDGERTON          42.83N 89.04W

07/11/2011                   ROCK               WI   PUBLIC

            MANY 4-5 FIVE INCH TREE LIMBS DOWN THROUGH THE AREA

0830 AM     TSTM WND DMG     1 N WAUKESHA            43.03N 88.24W

07/11/2011                   WAUKESHA           WI   911 CALL CENTER

            NUMEROUS 12 TO 18 INCH DIAMETER TREES DOWN ACROSS THE
            NORTHERN HALF OF THE CITY

0830 AM     TSTM WND GST     EVANSVILLE              42.78N 89.30W

07/11/2011  M48.00 MPH       ROCK               WI   TRAINED SPOTTER

            POWER LINES DOWN ON WATER STREET...TREES BLOCKING RURAL
            ROADS WEST OF CITY SOME LOCAL STREET FLOODING...MEASURED
            1.57 INCHES OF RAIN IN 25 MINUTES.

0830 AM     TSTM WND GST     MILWAUKEE LAKESHORE     43.05N 87.88W

07/11/2011  M43.00 MPH       MILWAUKEE          WI   C-MAN STATION

            37 KNOT WIND GUST AT MLWW3 MARINE WEATHER STATION.



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