WHAT TO REPORT

This section explains the specific events or sky conditions we want you to report on. Previously in this booklet we presented background information to familiarize you with storm features and characteristics. Understanding them will help you to assess the severe potential of each storm situation.

It is not necessary to report all of these features and characteristics, but MSC appreciates hearing about key characteristics and any unusual things you see. (See box.) However, it is important to bear in mind that on a busy severe weather day the forecaster won't be able to stay on the phone with you for long - so be brief and concise.

For the purposes of spotting and reporting,a severe weather event is one that threatens life or property. The most common hazards are hail and wind damage, but occasionally tornadoes and serious flooding also occur. These are the obvious effects, but of equal importance is the accurate recognition and reporting of potential danger signs - funnels, rotation, and other indicators - which precede tornadic development.

Do not go looking for damage or wander around in an area hit by a serious storm. That's a job for emergency personnel or MSC authorized persons only. If you happen to come across damage, report on all types - hail, wind, flooding and tornado .Let the forecasters determine the cause unless it was obvious in the sky beforehand.

Hail

Hailstones form in the strong updrafts within thunderstorms. They are curious little ice sculptures that remind us of the size and strength of these gigantic clouds. Alternating clear and frosted rings bring us back a crystalline time capsule from a long, turbulent ride on updrafts and downdrafts reaching speeds of 160 km/hr. Large hailstones are evidence of very powerful updrafts, and therefore, stronger storms. When very large hail occurs, you should definitely be watching for other severe events, including tornadoes.

There are three aspects of hail that merit reporting:

size - if 2cm diameter or larger (Check with your reporting contact to see if all hail events should be reported.)
quantity - if hailfall covers the ground
impact - if noticeable, widespread damage occurs

Sizes are often given by comparison with familiar items such as pea size (0.5cm), marble (1cm), grape (1.5cm), nickel size (2cm), walnut (3cm), golfball (4-5cm), tennis ball (6cm) and baseball (7-8cm).Weaker storms may produce large quantities of pea size stones that can cause extensive damage,especially when driven by high winds. On the other hand, very large stones may be widely scattered and require some hunting in the grass to determine the biggest reportable size. Falling hailstones are dangerous and have been known to kill livestock. Extreme crop and property damage can occur when hail is accompanied by strong winds,even if the size or number of stones is modest.

About watches and warnings

A severe thunderstorm watch is issued for a region when the potential exists for the development of such storms. This is a good day to observe the sky and keep an eye on growing thunderheads.

A severe thunderstorm warning will be issued for local areas in the path of individual torms when they intensify to the severe stage. Thunderstorm cells are small (5-25 km dia.)compared with the satellite and radar views available to the weather office, so the watcher's role as an "early warning system" verifying local severe events is invaluable. Many warnings are issued as a direct result of reported sightings.

Occasionally a tornado watch is issued - when conditions suggest that the potential exists for tornadoes to develop.When you hear a tornado watch you should be alert and keep a close eye on the weather.

Tornado warnings are usually issued only after confirmed tornado sightings, but severe thunderstorm warnings also imply the risk of tornado development. Every severe storm should be taken seriously and watched carefully for signs of rotation, strong outflow winds,or other characteristics worth reporting.

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Meteorological Service of Canada - Environment Canada - Government of Canada

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