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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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Created :
2002-08-26
Modified :
2002-12-31
Reviewed :
2002-12-31
Url of this page : http://www.msc.ec.gc.ca /education/severe_weather/page45_e.cfm
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