Thunderstorm Outlook for Canada and the United States for Saturday May 26, 2018.

Canada
There is a slight chance of severe thunderstorms over southwestern Ontario, damaging winds and locally heavy rainfall are the main threats. Severe thunderstorms are also possible in southern Saskatchewan and southern Alberta.

United States
Isolated severe storms with hail and strong wind gusts are possible on Saturday across Montana into the western Dakotas.  A marginal severe threat may also develop across parts of eastern Wisconsin into upper Michigan. A tornado or two may also occur over parts of the southern and western Florida peninsula.

The thunderstorm forecast is issued daily from April 1 to September 30.
Definition of a Severe Thunderstorm 
In Canada, a rainfall rate greater than 50 millimetres (2 in) in one hour, or 75 millimetres (3 in) in three hours, is also used to indicate severe thunderstorms. Severe thunderstorms can occur from any type of storm cell. However, multicell, supercell, and squall lines represent the most common forms of thunderstorms that produce severe weather.

A thunderstorm is classed as severe if winds reach at least 90 km/h (58 mph), hail is 25 millimetres (1 in) in diameter or larger, or if funnel clouds or tornadoes are reported. Although a funnel cloud or tornado indicates a severe thunderstorm, a tornado warning is issued in place of a severe thunderstorm warning. A severe thunderstorm warning is issued if a thunderstorm becomes severe, or will soon turn severe.
Thunderstorm Safety Tips:
  • Move to a sturdy building or car.
  • Do Not take shelter under isolated trees.
  • Get out of boats and away from water.
  • Unplug appliances. Avoid using the telephone or any electrical appliances. 
  • Do not take a bath or shower.
  • Remember when thunder roars go indoors!

The Enhanced Fujita Scale (EF-Scale) rates the strength of tornadoes in Canada and the United States based on the damage that they cause. 

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