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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

Tornadoes to Torrents

The Southern Ontario Severe Weather Event of Aug 19, 2005

social aspects of the event
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
The Journey Across Southern Ontario “Tornadoes to Torrents”
  • Define Two Part Event
  • Synoptic Set Up
  • The Tornadoes
  • Flooding Rains
  • Interesting Lightning Features
  • Conclusions/Summary
slide4

Flash Flooding

Tornadoes

Supercell Track

Fergus

slide6

Lake Nipigon

Lake

Superior

Geo

Bay

Lake

Huron

Lake Ontario

Lake Erie

Environment Canada

slide7

Flash Flooding

Tornadoes

Supercell Track

Fergus

slide15

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.

slide18

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.

slide19

MDT

MDT

slide20

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:

slide21

==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.

slide22

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.

,

slide25

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.

slide26

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

slide31

Strong

Mesocyclone

slide32

Strong

Mesocyclone

the supercell seemed to change character
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)

storm reports from toronto
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

slide45

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

studies worth citing
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

lightning characteristics47
Lightning Characteristics
  • Ramped up lightning during touchdowns
  • High Percentage of Positive Lightning Strikes…Particularly During ‘Second” F2 Tornado

F2 Tornadoes

studies worth citing48
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

slide50

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

a change in character
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
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
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