Severe Weather Watcher Handbook

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The flashing within the rain core provides good background illumination for low cloud banks and scud along a sharp gust front. Separate flashes may change the shape and position of silhouetted clouds, but after a while you will recognize the repeating shapes as reliable and abiding storm features. A large updraft base will show up as a dark region,and if a lowering is present it will be a bowl-shaped "dark hole "through which no light passes. The underside of these dark regions can be studied over time for signs of a funnel or tornado. Quick, frequent bolts mark the core region or the site of a new,maturing cell.

Always remain aware of wind conditions,too.If the S-SE wind becomes calm,the rain-free base and main updraft may be overhead.As soon as a cool wind from the W-NW begins,you have moved into the outflow region and the threat for severe effects will quickly diminish.The only other thing could be a strong wind before precipitation begins,or hail as it peaks,but these threats will only last a few minutes longer and are usually apparent from the other clues mentioned earlier.

Severe winter weather

Although the emphasis for severe weather watchers and spotters is on summer severe weather, MSC also appreciates receiving reports of winter conditions which may threaten public safety. These include low visibilities due to blowing snow or dust, the rate and amount of snowfall, dense fog, and freezing rain. Areas such as the Maritimes and B.C. receive far fewer summer severe events but are battered by frequent bouts of severe winter weather and high winds in the cooler half of the year.

From time to time weather warnings are issued in the winter, and you can be our eyes and ears for your local area. The dangers associated with severe winter weather should not be underestimated. Treacherous roads and bitterly cold temperatures and/or windchills have killed many people. Canadians are sometimes surprisingly ill-prepared for the "normal "extremes of our northern clime.

Weather warnings in winter

The criteria for issuing the following winter weather warnings vary from region to region. Use these descriptions as a general guide only.
Blizzard Warning - Snow or blowing snow with a wind of 40km/hr or more is expected, with visibility reduced to less than one kilometer and a windchill of more than 1600 watts/m. All these conditions are expected to last six hours or more (four hours in Alberta and Ontario).
Freezing Rain Warning - Slippery walking and driving conditions are expected, with possible damage to trees and overhead wires (due to rain freezing on contact to form a coating of ice).
Heavy Snowfall Warning - A snowfall of 10cm or more is expected over a period of 12 hours or less.(In urban areas such as Vancouver a snowfall of more than 5cm may occasion a warning.)
Snowsquall Warning - A snowfall of 15cm or more is expected over a period of 12 hours or less, or visibilities are expected to be near zero for 4 hours or more.
Windchill Warning - Windchills of at least 2000watts/m (or 40km/hr winds and -25 °C) are expected,making all outdoor activity dangerous.
Winter Storm Warning - When two or more winter conditions reach warning proportions (for example,wind and snow, or freezing rain and a heavy snowfall)a winter storm warning is issued.

You may also hear cold wave advisories from time to time.These are issued when temperatures are expected to drop by 20 °C or more within 18 hours.(There is some variation from region to region in the criteria for issuing cold wave advisories or warnings, especially in British Columbia, where Arctic outbreaks are of particular concern.) Hypothermia is always a risk under winter conditions, but cold waves can catch people unprepared and exposed to both hypothermia and frostbite.

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