Tornadoes Fergus 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. MDT
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. MDT MDT
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: 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 latercalls were being received of a tornado on the ground. 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 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 BramptonTorrential Rain/Flooding 100mm (4) Rain TorontoSevere Flooding; Golf Ball Sized Hail;
Localized Straight Line Wind Damage Downsview (EC)136mm (5.4) Rain; Flooding (Partial Evacuation of the Storm Centre) Toronto175mm (7) Rain Ajax to OshawaTorrential Rain; Flash Flooding Lightning Characteristics
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 Southern Ontario
18Z Aug 19, 2005 2490 Strikes 803 + Strikes Southern Ontario 20z Aug 19, 2005
Lightning Characteristics CG Lightning 350 # S tr i k e s
300 250 200 150 100 50 0
Time F2 Tornadoes Ramped up lightning during touchdowns High Percentage of Positive Lightning Strikes Particularly During Second F2 Tornado
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 Now Why did the storm change character? LI -6 0-3km Helicity 225
SBCape BRN Exeter 16z 1560 20
-2.5 200 600 9 Toronto
18z 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 ZaffSOO BUF Thomas.NiziolMIC BUF Jim LaDueWDTB Developer/Researcher
Pat King and Dave Sills Research Env Canada George Kourounis/Keith FletcherSpotters
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