Tornadoes to Torrents The Southern Ontario Severe Weather Event of Aug 19, 2005

Social Aspects of the Event “Two” F2 Tornadoes…15 Minutes Apart Extensive Flooding in the Greater Toronto Area… >6 “ Rain in 90 min Insured Losses >$400 Million in Toronto Alone….Most Expensive in Ontario History No Serious Injuries or Loss of Life

The Journey Across Southern Ontario “Tornadoes to Torrents” Define Two Part Event Synoptic Set Up The Tornadoes Flooding Rains Interesting Lightning Features Conclusions/Summary

Supercell Track Fergus Tornadoes Flash Flooding

Environment Canada

Lake Superior Geo Bay Lake Huron Lake Ontario Lake Erie Lake Nipigon

Supercell Track Fergus Tornadoes Flash Flooding

CENTER NORMAN OK 0755 AM CDT FRI AUG VALID Z Z SPC AC DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION...LWR GRT LKS... TSTMS EXPECTED TO FORM IN RESPONSE TO MODEST DIURNAL HEATING AND LOW LEVEL CONVERGENCE INVOF WARM FRONT CROSSING ERN OH/WRN PA AND WRN NY. COMBINATION OF INCREASING BOUNDARY LAYER MOISTURE /DEWPOINTS IN THE UPR 60S TO LOW 70S/ AND 40+ KT DEEP WNW SHEAR SHOULD SUPPORT A FEW DISCRETE SUPERCELLS. COUPLED WITH ENLARGED LOW LEVEL HODOGRAPHS INVOF WARM FRONT AND LOW LCLS ASSOCIATED WITH HIGH REGIONAL PWS...SETUP MAY ALSO SUPPORT A FEW TORNADOES. WIND PROFILES LIKELY WILL FAVOR STORM MOTION ACROSS THE BOUNDARY INTO THE COOLER AIR. HOWEVER...PRESENT AND EXPECTED AFTERNOON SURFACE CONDITIONS SUGGEST THAT A SUFFICIENTLY WIDE CORRIDOR FAVORABLE FOR SURFACE OR NEAR SURFACE-BASED SUPERCELLS WILL EXIST TO SUPPORT AN ENHANCED POTENTIAL FOR TORNADOES. THE CONVECTION SHOULD CONSOLIDATE INTO ONE OR TWO CLUSTERS THAT CONTINUE E AND WEAKEN BY EARLY EVENING.

MDT

...LOWER GREAT LAKES/UPPER OH VALLEY... CLOUDS ARE BEGINNING TO THIN ACROSS OH WHERE STRONG HEATING IS NOW OCCURRING WITH SURFACE TEMPERATURES WARMING INTO THE 80S. THIS CLEARING IS EXPECTED TO SPREAD EWD INTO WRN PARTS OF NY AND PA DURING THE AFTERNOON. SURFACE DEW POINTS NEAR 70F COUPLED WITH WARMING TEMPERATURES WILL CONTRIBUTE TO DIURNAL DESTABILIZATION WITH MLCAPE INCREASING TO AROUND 1500 J/KG THIS AFTERNOON. DYNAMIC FORCING ASSOCIATED WITH THE LAKE HURON UPPER LOW AND ASSOCIATED MID LEVEL JET STREAK ACROSS LOWER MI/SWRN ONTARIO MAY BE STRONGEST OVER CANADA...HOWEVER WEAK CONVERGENCE ALONG THE COLD FRONT AND BETTER DEFINED CONVERGENCE NEAR THE WARM FRONT MAY BE SUFFICIENT FOR WIDELY SCATTERED THUNDERSTORMS TO DEVELOP THIS AFTERNOON AND EVENING. MODEL GUIDANCE PROVIDES A VARIETY OF SOLUTIONS WITH 12Z ETA GENERATING LITTLE CONVECTION ACROSS THE REGION...WHEREAS 15Z RUC AND 09Z SREF GUIDANCE ETAKF AND RSM MEMBERS INDICATE GREATER LIKELIHOOD FOR THUNDERSTORM DEVELOPMENT. SUFFICIENT INSTABILITY AND VEERING WIND PROFILES IN THE LOWEST 1-2 KM SUGGEST POTENTIAL FOR ROTATING UPDRAFTS WITH ANY PERSISTENT STORMS THAT CAN DEVELOP...WITH CONDITIONAL THREAT FOR A FEW SEVERE STORMS INCLUDING A FEW TORNADOES. SPC AC DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1146 AM CDT FRI AUG VALID Z Z

MDT

WWCN11 CWTO SEVERE WEATHER BULLET INISSUED BY ENVIRONMENT CANADA AT 12:50 PM EDT FRIDAY 19 AUGUST WATCHES/WARNINGS IN EFFECT FOR SOUTHERN ONTARIO... TORNADO WATCH FOR: =NEW= GODERICH - BLUEWATER - SOUTHERN HURON COUNTY =NEW= WINGHAM - BLYTH - NORTHERN HURON COUNTY =NEW= KITCHENER - CAMBRIDGE - REGION OF WATERLOO =NEW= GUELPH - ERIN - SOUTHERN WELLINGTON COUNTY =NEW= DUFFERIN - INNISFIL =NEW= GREY - BRUCE =NEW= BARRIE - COLLINGWOOD - HILLSDALE = NEW= MIDLAND - COLDWATER - ORR LAKE...RISK OF A TORNADO AHEAD OF A COLD FRONT THIS AFTERNOON.. THIS IS AN ALERT TO THE POTENTIAL DEVELOPMENT OF TORNADOES AND SEVERE THUNDERSTORMS WITH LARGE HAIL AND DAMAGING WINDS. MONITOR WEATHER CONDITIONS..LISTEN FOR UPDATED STATEMENTS. IF THREATENING WEATHER APPROACHES..TAKE IMMEDIATE SAFETY PRECAUTIONS.SEVERE THUNDERSTORM WATCH FOR: Upgraded from Sev Tstorm Watch

==DISCUSSION== A FRONTAL SYSTEM CROSSING THE ABOVE REGIONS WILL COLLIDE WITH AN INCREASINGLY MOIST AND UNSTABLE AIRMASS TO PRODUCE FAVOURABLE CONDITIONS FOR SEVERE THUNDERSTORMS AND POSSIBLY TORNADOES THIS AFTERNOON INTO EARLY THIS EVENING. RADAR IS CURRENTLY SHOWING TWO LINES OF STRONG THUNDERSTORMS.. THE FIRST FROM SOUTH OF OWEN SOUND TO EXETER AND A SECOND LINE APPROACHING THE EAST SHORE OF LAKE HURON. SOME OF THESE STORMS HAVE BEEN EXHIBITING SIGNS OF ROTATION ON DOPPLER RADAR AND THERE IS POTENTIAL FOR THESE STORMS TO PRODUCE A TORNADO. AS OF THIS MOMENT THERE HAVE BEEN NO REPORTS OF ACTUAL TORNADOES. THESE STORMS WILL ALSO BE CAPABLE OF PRODUCING DAMAGING WIND GUSTS IN EXCESS OF 90 KM/H..LARGE HAIL IN EXCESS OF 2 CENTIMETRES AND LOCALLY HEAVY RAINFALL IN EXCESS OF 50 MILLIMETRES IN ONE HOUR.

, At this time, both the NWS Storm Prediction Center and the Ontario Storm Prediction Center were composing updated severe weather outlooks. No severe weather had occurred up to this point.

A coordination call was placed to the Toronto Office from Buffalo….describing What was being depicted on the KBUF Radar. Moments later…calls were being received of a tornado on the ground.

WFCN11 CWTO TORNADO WARNING ISSUED BY ENVIRONMENT CANADA AT 1:35 PM EDT FRIDAY 19 AUGUST TORNADO WARNING FOR: =NEW= KITCHENER - CAMBRIDGE - REGION OF WATERLOO =NEW= GUELPH - ERIN - SOUTHERN WELLINGTON COUNTY =NEW= MOUNT FOREST - ARTHUR - NORTHERN WELLINGTON COUNTY =NEW= ORANGEVILLE - GRAND VALLEY - SOUTHERN DUFFERIN COUNTY. SEVERE THUNDERSTORM WARNING UPGRADED TO TORNADO WARNING FOR: KITCHENER - CAMBRIDGE - REGION OF WATERLOO GUELPH - ERIN - SOUTHERN WELLINGTON COUNTY MOUNT FOREST - ARTHUR - NORTHERN WELLINGTON COUNTY ORANGEVILLE - GRAND VALLEY - SOUTHERN DUFFERIN COUNTY ==DISCUSSION== RADAR IS DETECTING A SEVERE ROTATING STORM NEAR JUST EAST OF CONESTOGO LAKE. OPP HAVE RECEIVED A REPORT OF A TORNADO WITH THIS STORM. THIS STORM IS MOVING EASTWARD AT 70 KM/H. THIS IS A WARNING THAT SEVERE THUNDERSTORMS WITH TORNADOES ARE IMMINENT OR OCCURRING IN THESE REGIONS. MONITOR WEATHER CONDITIONS.TAKE IMMEDIATE SAFETY PRECAUTIONS.NOTE..A SUMMARY OF ALL WARNINGS AND WATCHES FOR SOUTHERN ONTARIO ISAVAILABLE IN THE WWCN11 CWTO BULLETIN ISSUED IMMEDIATELY FOLLOWING THIS BULLETIN. END/TUGWOOD

Strong Mesocyclone

Strong Mesocyclone

But a Funny Thing Happened on the Way to Toronto…

The Supercell Seemed to Change ‘Character’ Tornadic Storm Evolved into Wind and Flood Producer Mesocyclone (general circulation) remained intact Marine Layer from Lake Ontario may have come into play Mesocyclone approaching Toronto (20m West YYZ)

Moderate Meso

Storm Reports from Toronto Brampton…Torrential Rain/Flooding 100mm (4”) Rain Toronto…Severe Flooding; Golf Ball Sized Hail; Localized Straight Line Wind Damage Downsview (EC)…136mm (5.4”) Rain; Flooding (Partial Evacuation of the Storm Centre) Toronto…175mm (7”) Rain Ajax to Oshawa…Torrential Rain; Flash Flooding

Lightning Characteristics

1625z1700z1730z1800z1830z1900z2000z1930z Two F2 Tornadoes Flash Flooding Relatively High Strike Count 46% Ave Positive LTGCG Nearly 60% Positive During 2 nd F2 Relatively High Strike Count 22% Ave Positive LTGCG Transition Zone?

Studies Worth Citing The Relationship between Cloud to Ground Lightning Polarity and Surface Equivalent Potential Temperature during Three Tornadic Outbreaks (Smith, LaDue, MacGorman 2000) Southern Ontario 18Z Aug 19, 2005 Southern Ontario 20z Aug 19, – Strikes Strikes 2490 – Strikes Strikes

Lightning Characteristics Ramped up lightning during touchdowns High Percentage of Positive Lightning Strikes…Particularly During ‘Second” F2 Tornado F2 Tornadoes

Studies Worth Citing Positive CG Lightning Associated with the Spencer F4 Tornado of 30 May 1998 (Carey, Petersen, Rutledge 2000) Spencer, SD May 30, 1998Southern Ontario, Aug 19, 2005

Exeter 16z Toronto 18z Now…… Why did the storm change character? LI km Helicity SBCape BRN 20 9

A Change in Character? Did elevation have anything to do with the severe weather produced? Was the placement of Theta E Ridge a factor (other than LTGCG)? Did a Lake Ontario marine layer weaken or change the storm? Was this a ‘normal’ progression in the lifecycle of a supercell … tornadic to HP? 1500’ 500’

Lessons Learned Be aware of the lightning characteristics and trends within the storm. Watch for significant changes. Make informative calls to surrounding offices…regardless of how obvious the situation may seem to be. Be flexible enough to change severe weather modes during a single event.

Special Thanks To: Dave Zaff…SOO BUF Thomas.Niziol…MIC BUF Jim LaDue…WDTB Developer/Researcher Pat King and Dave Sills… Research Env Canada George Kourounis/Keith Fletcher…Spotters