Nocturnal tornado and wind damage, July 17-18, 2015

Radar loop and wind gusts between 9 p.m. and 10 a.m. across region
Courtesy: Greg Carbin, NWS Storm Prediction Center

Severe thunderstorms developed in eastern South Dakota during the afternoon of Friday, July 17, and pushed eastward in Minnesota through the evening, crossing the Twin Cities shortly after midnight on July 18. The National Weather Service confirmed a nocturnal EF-1 tornado, near Watertown in Carver County. In addition to the tornado, straight-line winds and strong winds well after the storms passed, combined to knocked down numerous trees and limbs, causing an estimated 225,000 Xcel Energy customers to lose power.

The images and information below were provided by the National Weather Service.

NWS description of radar techniques and indicators used to detect Watertown, Minn., tornado
Courtesy: NWS, Chanhassen Forecast Office

Tornado damage near Watertown, Minn.
Courtesy: NWS, Chanhassen Forecast Office (via Twitter)

...UPDATE TO NWS DAMAGE SURVEY FOR 07/17/2015 TORNADO EVENT...

...EF-1 TORNADO OCCURRED WEST OF WATERTOWN IN CARVER COUNTY
MINNESOTA...

BASED ON LOCAL MEDIA HELICOPTER FOOTAGE...THE BEGINNING POINT HAS
BEEN PUSHED WEST 3/4 MILE TO WEEKS AVENUE. ALSO...THE ENDING POINT
WAS PUSHED NORTH SLIGHTLY TO ACCOUNT FOR STRONGER WINDS ON THE SOUTH
SIDE OF THE TORNADO AT TIME OF DISSIPATION. DAMAGE THERE WAS
PRIMARILY TO THE SOUTH OF THE CENTER OF THE TRACK BECAUSE STRAIGHT
LINE WINDS OFFSET THE NORTHERN SIDE OF THE TORNADO/S INFLUENCE. THIS
WAS ALSO THE CASE AT THE BEGINNING POINT WHEN THE TORNADO WAS FAIRLY
WEAK.

A LINE OF SEVERE THUNDERSTORMS TRACKED EAST ACROSS MOST OF CENTRAL
MINNESOTA DURING THE LATE EVENING OF JULY 17TH. A TORNADO
DEVELOPED ON THE LEADING EDGE OF THIS LINE AND IMPACTED PORTIONS
OF NORTHERN CARVER COUNTY. NWS DUAL POL RADAR OBSERVED TORNADIC
DEBRIS...AND A DAMAGE SURVEY CONFIRMED A 5.2 MILE LONG TORNADO.

RATING: EF-1
ESTIMATED PEAK WIND: 105 MPH
PATH LENGTH /STATUTE/: 5.2 MILES
PATH WIDTH /MAXIMUM/: 500 YARDS
FATALITIES: 0
INJURIES: 0

START DATE: JULY 17 2015
START TIME: 1156 PM CDT
START LOCATION: WEEKS AVENUE JUST SOUTH OF 32ND STREET... 3NNW
HOLLYWOOD
START LAT/LON: 44.9450/-93.9889

END DATE: JULY 18 2015
END TIME: 1202 AM CDT
END LOCATION: NORTH OF ROSE AVENUE AND COUNTY 122... 2WSW WATERTOWN
END LAT/LON: 44.9550/-93.8848

SURVEY SUMMARY: TORNADO SPUN UP 3 MILES NORTH NORTHWEST OF HOLLYWOOD
AND CONTINUED GENERALLY EAST NORTHEAST TO 2 MILES WEST SOUTHWEST OF
WATERTOWN. THE MOST DAMAGE OCCURRED AS THE TORNADO CROSSED VEGA
AVENUE WHERE NUMEROUS TREES WERE SNAPPED AND SOME MINOR STRUCTURAL
DAMAGE WAS FOUND. THERE...A HOME WEATHER STATION RECORDED A 99 MPH
WIND BEFORE IT BLEW OFF THE HOUSE. THE WEATHER STATION REPORT...IN
ADDITION TO THE DEGREE OF TREE DAMAGE...SUPPORTS AN ESTIMATED
MAXIMUM WIND SPEED OF 105 MPH.

Last modified: July 20, 2015