Official Statement on June 11, 2010 Sioux Falls storm damage

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1150 AM CDT FRI JUN 11 2010

...STRAIGHT LINE WINDS TO AROUND 100 MPH CAUSE DAMAGE TO SOUTHWEST
SIOUX FALL NEIGHBORHOOD EARLY FRIDAY MORNING...

A LINE OF SEVERE THUNDERSTORMS...PACKING HIGH WINDS AND TORRENTIAL
RAIN...SWEPT ACROSS SOUTHEAST SOUTH DAKOTA AND ADJOINING AREAS OF
NORTHEAST NEBRASKA...SOUTHWEST MINNESOTA AND NORTHWEST IOWA EARLY
FRIDAY MORNING JUNE 11 2010. NUMEROUS REPORTS OF WIND DAMAGE AND
FLOODING HAVE BEEN RECEIVED...INCLUDING STRUCTURAL DAMAGE TO SEVERAL
HOMES IN SOUTHWEST SIOUX FALLS.

A NATIONAL WEATHER SERVICE ON SITE SURVEY HAS DETERMINED THE SIOUX
FALLS DAMAGE TO BE THE RESULT OF STRAIGHT LINE WINDS...CAUSED BY A
WET MICROBURST. A WET MICROBURST OCCURS WHEN THUNDERSTORM WINDS
ALOFT DESCEND RAPIDLY DOWNWARD...SPLASHING TO THE GROUND AT A VERY
HIGH RATE OF SPEED. IN THIS CASE THE STRONG WINDS WERE ACCOMPANIED
BY HEAVY RAIN CREATING THE WET MICROBURST CONDITION.

WIND SPEEDS IN THE AFFECTED SIOUX FALLS NEIGHBORHOOD WERE ESTIMATED
TO RANGE FROM 85 MPH TO AROUND 100 MPH. WHILE STRAIGHT LINE IN
NATURE...THESE WINDS SPEEDS ARE EQUIVALENT TO THOSE TYPICAL OF AN
EF1 TORNADO ON THE ENHANCED FUJITA (EF) SCALE.

THE STRONG WINDS HIT THE NEIGHBORHOOD AT APPROXIMATELY 240 A.M.
FRIDAY MORNING. THE SURVEY TEAM FOUND EVIDENCE OF WIND DAMAGE
EXTENDING EAST OF THE NEIGHBORHOOD ABOUT 1 MILE.

AT ABOUT THE SAME TIME...A SECOND WET MICROBURST...WITH SOMEWHAT
LESS WIND...PRODUCED SCATTERED DAMAGE IN THE VICINITY OF ELMWOOD
GOLF COURSE...EASTWARD TO MINNESOTA AVENUE.

DAMAGE FROM STRAIGHT LINE MICROBURSTS CAN OFTEN BE MORE WIDESPREAD
AND JUST AS DESTRUCTIVE AS THAT OF A TORNADO.

TREES THROUGHOUT SIOUX FALLS SUSTAINED VARYING AMOUNTS OF
DAMAGE...AS THE LINE OF SEVERE STORMS MOVED THROUGH THE CITY SHORTLY
BEFORE 3 A.M. FRIDAY MORNING.

RADAR IMAGERY...DAMAGE PICTURES AND ADDITIONAL INFORMATION ON THE
STORMS FROM FRIDAY MORNING WILL BE POSTED TO THE NWS SIOUX FALLS
MAIN WEB PAGE AT WWW.WEATHER.GOV/SIOUXFALLS...UNDER THE TOP NEWS OF
THE DAY HEADLINE.

GREG HARMON - METEOROLOGIST IN CHARGE
NWS SIOUX FALLS