PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE DES MOINES IA
458 PM CDT MON JUL 11 2011

…PRELIMINARY DAMAGE SURVEY RESULTS FOR STORY…MARSHALL AND TAMA
COUNTIES…

THIS STORM SURVEY INVESTIGATION IS STILL ONGOING AND SUBJECT TO
FURTHER COORDINATION WITH LOCAL EMERGENCY MANAGEMENT AGENCIES.

…WIDESPREAD AND EXTREME STRAIGHT LINE WIND EVENT…

THE FOLLOWING IS A PRELIMINARY ASSESSMENT FOR THE DAMAGE THAT OCCURRED OVER STORY…MARSHALL AND TAMA COUNTIES…OR FROM CENTRAL
INTO EAST CENTRAL IOWA…EARLY IN THE MORNING ON MONDAY…JULY 11…2011.

* EVENT DATE: 07/11/2011.

* ESTIMATED START TIME: APPROXIMATELY 320 AM CDT.

* EVENT TYPE: DERECHO. NO TORNADOES WERE INDICATED DURING THIS EVENT. THIS PARTICULAR DERECHO BEGAN IN CENTRAL IOWA AND TRAVELED ACROSS CENTRAL AND EASTERN IOWA…AS WELL AS ACROSS ILLINOIS…LAKE MICHIGAN…MICHIGAN…AND ENDED IN ONTARIO CANADA. THIS DERECHO TRAVELED FROM CENTRAL IOWA TO DETROIT MICHIGAN…OR A DISTANCE OF APPROXIMATELY 550 MILES…OVER THE TIME SPAN OF NINE HOURS. A DERECHO IS A LONG LIVED… WIDESPREAD…DAMAGING WIND STORM WHICH IS ASSOCIATED WITH RAPIDLY MOVING SHOWERS AND THUNDERSTORMS. DERECHOES ARE OFTEN CURVED OR BOWED IN THEIR SHAPE. WINDS IN DERECHOES CAN EXCEED 100 MPH. THE WINDS ASSOCIATED WITH DERECHOES ARE NOT CONSTANT AND MAY VARY CONSIDERABLY ALONG THEIR PATHS.

* EVENT LOCATION: BEGAN JUST WEST OF INTERSTATE 35 IN SOUTHERN STORY AND NORTHERN POLK COUNTIES. CONTINUED EASTWARD INTO MARSHALL AND TAMA COUNTIES.

* PEAK WIND: THE HIGHEST WINDS WERE AT LEAST 80 TO 105 MPH.

* PATH WIDTH: THE PATH WIDTH OF THE STRONGEST…HIGH-END WINDS WAS IN TAMA COUNTY AND WAS 5 MILES WIDE. IN ADDITION…THERE WAS A 10 MILE WIDE PATH OF WIND SPEEDS OF 70 TO 80 MPH. THERE WAS ALSO A 15 TO 20 MILE WIDE PATH OF WIND SPEEDS OF 60 MPH OR GREATER. IT SHOULD BE NOTED THAT THE DAMAGE SWATHS FROM THESE WINDS WERE NEARLY CONTINUOUS…AND EXTENDED FROM SOUTHERN STORY AND NORTHERN POLK COUNTIES…ACROSS MARSHALL AND TAMA COUNTIES.

* PATH LENGTH: THE DAMAGE SWATHS FROM THESE WINDS WERE NEARLY CONTINUOUS…AND EXTENDED FROM SOUTHERN STORY AND NORTHERN POLK COUNTIES…ACROSS MARSHALL AND TAMA COUNTIES.

* INJURIES: NONE HAVE BEEN REPORTED TO THE NATIONAL WEATHER SERVICE IN DES MOINES THUS FAR.

* FATALITIES: NONE HAVE BEEN REPORTED TO THE NATIONAL WEATHER SERVICE IN DES MOINES THUS FAR.

* DISCUSSION/DAMAGE: THIS WIND EVENT HAS BEEN THE MOST WIDESPREAD AND DAMAGING ONE TO AFFECT CENTRAL AND EAST CENTRAL IOWA SINCE 1998. AGAIN…NO TORNADOES WERE INDICATED. THE DAMAGE WAS DUE TO STRAIGHT LINE WINDS FROM A DERECHO. HAVING SAID THAT…THE STRONGEST WINDS DURING THIS EVENT WERE SIMILAR TO THOSE FOUND IN AN EF1 TORNADO. THE WIND DAMAGE FROM THIS EVENT WAS MORE WIDESPREAD THAN THE DAMAGE A TORNADO HOWEVER. EXAMPLES OF THE NOTABLE WIND SPEEDS FOLLOW AND HAVE BEEN ESTIMATED FROM OBSERVED DAMAGE. NEAR HUXLEY…96 MPH. MAXWELL…94 MPH. NEAR MARSHALLTOWN…70 TO 90 MPH. JUST EAST OF GARWIN…105 MPH. BETWEEN GARWIN AND UNION GROVE STATE PARK…85 TO 97 MPH. JUST SOUTH OF TRAER…100 MPH. JUST SOUTH AND SOUTHWEST OF DYSART…105 TO 110 MPH. SOUTH OF DYSART…80 TO 100 MPH.