Summer Weather in Canada

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Summer Severe Weather

Geoff Coulson Warning Preparedness Meteorologist Environment Canada Sept 11 2009 ICLR Friday Forum

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Contents
• • • • Ontario Storm Prediction Centre Forecasting Technology Watch/Warning Program A closer look at August 20th tornado outbreak

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Ontario Storm Prediction Centre Toronto

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Radar data…

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Weather Technology

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Satellite Data…

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Computer Models…

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Forecast Area of Responsibility

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Scale of a Summer Storm

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One storm covering part of a county

Scale of a Winter Storm

Snow

L

Heavy Snow Freezing Rain X Rain Showers

One storm covering thousands of square kilometres

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Severe Weather Lead Times
• Summer Severe Weather (severe thunderstorms, tornadoes etc..) minutes to hours • Winter Severe Weather (heavy snow, freezing rain, strong winds etc..) – hours to days

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Weather Watch vs. Weather Warning


Weather Watch means there is the potential for severe weather --- Be Alert Weather Warning means that severe weather will soon occur or is occurring --- Take Action Ron Gravelle



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Severe Thunderstorms – A Breed Apart
• 5% of Ontario thunderstorms are categorized as severe each year… • Severe thunderstorm has one or more of the following characteristics – Wind gusts of 90 km/h or more – Hail of 2 cm diameter or larger (size of a nickel or larger) – Flooding rains – Tornado(s) 13

By the Numbers

• On average around 120 summer severe events in Ontario each season (late April to early October) – – – – 70 due damaging winds 20 heavy rain/flooding 20 hail 11 tornadoes 14

Fujita Wind Damage Scale
• F0 – winds up to 115 km/h – Shingle, siding damage • F1 – winds 120 to 170 km/h – Numerous shingles, partial roof removal • F2 – winds 180 to 240 km/h – Roof removed from well-built home • F3 – winds 250 to 320 km/h – Roof and some exterior walls removed • F4 – winds 330 to 410 km/h – 2 storey brick house left with only a few walls remaining • F5 – winds 420 to 510 km/h – Brick house destroyed to foundation 15

Tornado Characteristics
• Duration
• 5 minutes to 120 minutes

• Speed of Motion
• 30-70 km/h

• Path length
• Less than 1 km-150 km

• Path Width
• 10’s of metres - 2 km

• Direction of travel
• Usually southwest to northeast

• IMPORTANT – Appearance of Tornado NOT an indication of its strength

Ontario Tornadoes
• Vast majority are either F0 or F1 • 1 F2 every year or so • 1 F3 every 8 years or so – Last confirmed Ontario F3 Violet Hill, April 20, 1996 – OVERDUE!

• 1 F4 every 15 years or so
– Last confirmed Ontario F4 Barrie and Grand Valley tornadoes, May 31, 1985 – OVERDUE!

• No confirmed F5’s in Ontario – OVERDUE?
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Tornado Warnings
• Strong evidence on radar
– Rotation at multiple levels in storm…however… – “hook” echo

• Credible Eyewitness/Video Report
– CANWARN trained spotter – Police/Fire/Municipal Official – Multiple public reports/videos…right place at right time 18

CANWARN Storm Spotters

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Project OPPortunity

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CANWARN/OPP reports important…
• Ground-truth info from radars, lightning detector and satellites • Help protect members of the affected community and communities where storm may be headed • Information could be used to issue/update Watches and Warnings

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August 20th 2009 Tornado Outbreak

Jeff Scheper

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Staying on Top of the Weather
Media

Internet Weatheradio

Cell Phone/PDA

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Time to React
• May be a few minutes or less • Not all storms will have a watch/warning • Not all storms will be easily visible – Haze – Rain – Surrounding hills or trees

• Preparation before event is key
– Check weather before going out…keep an eye on the sky – Where is my best shelter? – React… 28

Ways Forward
• How do you alert people for the most significant of events? – National Alert System?
• Red banner on TV • Interrupt radio broadcasts (syndicated...
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