Wednesday, May 16, 2018

Severe weather season in Montreal - watch vs warning

Severe thunderstorms result in millions of dollars in damages every year across Canada. The threats are many with summer thunderstorms, including flash floods, strong winds, large hail, lightning and tornadoes.
Temperatures are slowly warming up across southern Quebec, and it won't be long before thunderstorms begin rattling around. With the increase in heat and humidity, will come the inevitable thunderstorm. Southern Quebec averages 15 to 17 thunderstorm days every year, most occurring between late May and early September. Severe thunderstorms are particularly menacing, because they come with several different high impact threats that can occur in any one region. They form very quickly, in lines or even as single cells. Tornadoes and lightning are among the greatest dangers within a thunderstorm. Lighting kills an average of 10 Canadians each year, while injuring 150 more. That being said, it is flash flooding, hail and strong winds that cause the greatest damage in Montreal.

Here are just a few examples of strong storms in Montreal. On August 22, 2017, a severe thunderstorm and microburst in the Borough of NDG, levelled thousands of trees and snapped hydro poles like twigs. On May 29, 1986, and again one year later on the same date, strong thunderstorms produced copious amounts of large hail, up to 12mm in diametre. The result was over $75 million dollars in damages to homes and cars across metro Montreal, and millions more in crop losses in southern Quebec. Of course the most famous thunderstorm in Montreal, occurred on July 14, 1987, when over 100mm of rain in less than 2 hours, flooded large portions of the city, including the Decarie Expressway. Known as the Decarie Flood, the storm resulted in two fatalities and $200 million in damages.

The best way to protect yourself and property from summer storms is through awareness and vigilance. During hot and humid weather, listen for updated watches and warnings. Environment Canada will post a Severe Thunderstorm Watch, typically for a large area and a wide time frame. They are posted when conditions are favourable for severe thunderstorm development, but none are occurring yet. The watch is simply to advise the public that a threat does exist for severe weather. A Severe Thunderstorm Warning is an immediate call to action for a smaller portion of the watch area. The watch means strong storms have developed and are being tracked by Environment Canada. These storms are expected to impact the warned region. Keep in mind that thunderstorms form and dissipate very quickly. They are micro scale weather events, impacting a small geographical region at any given time. Therefore it is important that you check the time and source of the warning. Often social media will share information that is dated. Warnings are typically in effect for short periods of time for any given region, often less than one hour. They are updated often as the storms move through the area. The best course of action during severe thunderstorms, is to move inside, away from windows and doors. If outside, find the lowest point, make yourself as small as possible to avoid being struck by lightning.  More lightning safety tips can be found here.

Environment Canada continues to upgrade the doppler radar network across Canada, which will greatly improve severe weather forecasts as well as watch and warning times. You can read more on the new radar technology here.

No comments: