743  
AWCN12 CWTO 231507  
WEATHER SUMMARY FOR NORTHERN ONTARIO  
ISSUED BY ENVIRONMENT CANADA TORONTO  
AT 10:14 AM EDT SATURDAY 15 AUGUST 2009.  
 
SUMMARY OF THE TORNADO OUTBREAK OVER ONTARIO ON AUGUST 20.  
-------------------------------------------------------------  
==WEATHER EVENT DISCUSSION==  
 
A TRIPLE BARRELLED SEVERE WEATHER OUTBREAK STRUCK ONTARIO  
THURSDAY.  
 
SHORTLY AFTER NOON A SUPERCELL STORM DEVELOPED JUST SOUTH  
OF LAKE HURON. THIS CELL TRACKED NORTHEASTWARD FOR A REMARKABLE 200  
KM PRODUCING THE DURHAM AND THORNBURY TORNADOES. THE STORM  
CELL FINALLY WEAKENED OVER GEORGIAN BAY TOWARD EVENING.  
 
AT THE SAME TIME A SQUALL LINE DEVELOPED OVER LOWER MICHIGAN THEN  
TRACKED ACROSS SOUTHERN ONTARIO DURING THE AFTERNOON AND EVENING  
HOURS. THIS FEATURE PRODUCED STRAIGHT LINE WIND DAMAGE TO SEVERAL  
LOCALES FROM WINDSOR TO WELL NORTHEAST OF TORONTO AS WELL AS THE  
DESTRUCTIVE VAUGHAN AND NEWMARKET TORNADOES.  
 
FINALLY IN THE EARLY EVENING AN ISOLATED SUPERCELL STORM DEVELOPED  
NORTHEAST OF GEORGIAN BAY AND TRACKED NORTHEASTWARD TO PRODUCE A  
POSSIBLE TORNADO OVER THE AREA BETWEEN ARNSTEIN AND NORTH BAY AS  
WELL AS A WATERSPOUT OVER LAKE NIPISSING.  
 
THERE WAS ONE FATALITY WITH THE TORNADO IN THE SOUTH END OF DURHAM.  
SEVERAL OF THE TORNADOES WERE RATED AS F2 DAMAGE ON THE FUJITA  
SCALE. F2 DAMAGE IS EQUIVALENT TO WIND STRENGTH OF 180 TO 250 KM/H.  
 
THE FOLLOWING IS A LIST OF TORNADOES AND ASSOCIATED DAMAGE ASSESSED  
BY FOUR SEPARATE ENVIRONMENT CANADA STORM DAMAGE TEAMS.  
 
-------------------------------------------------------------  
DATE  
TORNADO LOCATION/PATH DAMAGE OVERVIEW  
 
TORNADO 1 5 KM SW OF DURHAM TO MARKDALE F2 TORNADO DAMAGE  
(CONFIRMED) (ROUGHLY 20 KM) (SIGNIFICANT HOUSE  
+ TRAILER DAMAGE,  
TREES DOWN)  
 
TORNADO 2 FROM SOUTH OF THORNBURY TO THE F2 TORNADO DAMAGE  
(CONFIRMED) SOUTHEAST OF THORNBURY (PATH (DETAILS UNCERTAIN  
LENGTH UNKNOWN) AT THIS TIME)  
 
TORNADO 3 WOODBRIDGE/VAUGHAN F2 TORNADO DAMAGE  
(CONFIRMED) (SEVERAL KM LONG (HUNDREDS OF HOMES  
+ 50 METRES WIDE) DAMAGED, TREES DOWN,  
CARS FLIPPED)  
 
TORNADO 4 NEWMARKET AREA F1 TORNADO DAMAGE  
(CONFIRMED) (HOCKEY ARENA ALMOST  
DEMOLISHED)  
 
TORNADO 5 ARNSTEIN TO RESTOULE TO NORTH WATERSPOUT/TORNADO  
(PROBABLE) BAY (PATH LENGTH UNKNOWN AT SIGHTINGS (DAMAGE DETAILS  
THIS TIME) UNCERTAIN AT THIS TIME)  
 
TORNADO 6 MILTON F1 DAMAGE  
(POSSIBLE) (SOME ROOF DAMAGE)  
 
ENVIRONMENT CANADA CONTINUES TO EVALUATE THE DAMAGE FROM THE STORMS.  
AN INVESTIGATION IS BEING CONDUCTED ON REPORTED DAMAGE IN THE  
GRAVENHURST AREA TODAY.  
 
END/OSPC  
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