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Tornadoes to Torrents

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

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Tornadoes to Torrents

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

  2. 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

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

  4. Flash Flooding Tornadoes Supercell Track Fergus

  5. Environment Canada

  6. Lake Nipigon Lake Superior Geo Bay Lake Huron Lake Ontario Lake Erie Environment Canada

  7. Flash Flooding Tornadoes Supercell Track Fergus

  8. CENTER NORMAN OK 0755 AM CDT FRI AUG 19 2005 VALID 191300Z - 201200Z SPC AC 191255 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.

  9. MDT

  10. SPC AC 191646 DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1146 AM CDT FRI AUG 19 2005 VALID 191630Z - 201200Z ...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.

  11. MDT MDT

  12. Upgraded from Sev Tstorm Watch WWCN11 CWTO 191650 SEVERE WEATHER BULLET INISSUED BY ENVIRONMENT CANADA AT 12:50 PM EDT FRIDAY 19 AUGUST 2005. -------------------------------------------------------------------- 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:

  13. ==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.

  14. 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. ,

  15. 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.

  16. WFCN11 CWTO 191735 TORNADO WARNING ISSUED BY ENVIRONMENT CANADA AT 1:35 PM EDT FRIDAY 19 AUGUST 2005. --------------------------------------------------------------------- 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

  17. Strong Mesocyclone

  18. Strong Mesocyclone

  19. But a Funny Thing Happened on the Way to Toronto…

  20. 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)

  21. Moderate Meso

  22. 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

  23. Lightning Characteristics

  24. Two F2 Tornadoes Flash Flooding Transition Zone? 1625z 1700z 1730z 1800z 1830z 1900z 1930z 2000z Relatively High Strike Count 46% Ave Positive LTGCG Nearly 60% Positive During 2nd F2 Relatively High Strike Count 22% Ave Positive LTGCG

  25. Studies Worth Citing The Relationship between Cloud to Ground Lightning Polarity and Surface Equivalent Potential Temperature during Three Tornadic Outbreaks (Smith, LaDue, MacGorman 2000) 1512 – Strikes 1225 + Strikes 2490 – Strikes 803 + Strikes Southern Ontario 18Z Aug 19, 2005 Southern Ontario 20z Aug 19, 2005

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

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

  28. Now…… Why did the storm change character? LI -6 -2.5 0-3km Helicity 225 200 SBCape 1560 600 BRN 20 9 Exeter 16z Toronto 18z

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