Thunderstorms

THUNDERSTORMS

Nature's violence unleashed

Thunderstorms

In Malaysia, thunderstorms are a common phenomenon occurring all year round, frequently during the afternoon and early evening. Despite their small size, all thunderstorms are dangerous. Every thunderstorm produces lightning which has the potential to kill people.

Heavy rain from thunderstorms can lead to flash flooding and landslides. Strong winds and hail are also dangers associated with some thunderstorms.

Flash floods caused by thunderstorms

Landslides caused by thunderstorm rain

What is a thunderstorm ?

Thunderstorm is defined by the World Meteorological Organization as one or more sudden electrical discharges, manifested by a flash of light (lightning) and a sharp or rumbling sound (thunder).

¤	A thunderstorm usually develops in an unstable and moist atmosphere.
¤	A cumulus cloud is formed when warm moist air from the surface rises and is lifted to higher altitude and condenses.
¤	It grows laterally and vertically into a large dense cloud called cumulonimbus, with strong turbulence within the cloud and strong outflow below the base of the cloud.
¤	The mature thunder cloud often has a cellular structure with diameter that can reach 3 to 5 kilometers and its top exceeding 10 kilometers. Thunderstorm cells may occur singly, in clusters, or in lines.
¤	Thunderstorms last an average of 15 to 30 minutes but may last much longer in some storms.

Thunderstorms are capable of producing hail, heavy rain, frequent lightning and strong gusty winds. Some of the most severe weather occurs when a cluster of thunderstorms affect an area for a prolonged period of time.

Downburst

Downburst is a term used to describe a small area of rapidly descending air beneath a thunderstorm. The strong winds can reach very high speeds causing significant damage along its path and is extremely dangerous to aviation.

What is lightning ?

The action of rising and descending air within a thunderstorm cloud separates positive and negative charges. Lightning is the discharge produced when differences between ground and atmospheric electrical charges are large enough to overcome the insulating effect of the air. Lightning can occur within cloud, cloud to cloud, and between cloud and ground. Lightning often strikes outside of heavy rain and may occur as far as 10 miles away from any rainfall.

Air near a lightning strike is heated to above 20,000 ^oC - hotter than the surface of the sun. Rapid heating and cooling of air near the lightning causes a shock wave that results in thunder.

Lightning can damage electrical installations and induce fires. Most lightning deaths and injuries occur when people are caught outdoors.

Most Frequent Period For Thunderstorms

Thunderstorms can occur throughout the year but are most likely to happen in the intermonsoon periods, namely April to May and October to November. Over land, thunderstorms frequently develop in the afternoon and evening hours while over the sea, thunderstorms are more frequent at night.

Thunderstorm and Lightning Safety - What To Do !

Before the Storm ....
¤	Check the weather forecast before leaving for extended periods outdoors.
¤	Watch for signs of approaching storms.
¤	Postpone outdoor activities if thunderstorms are imminent.

When the Thunderstorm Approach ....
¤	Move to a sturdy building or car. Do not take shelter in small sheds or under isolated trees
¤	If lightning is occurring and a sturdy shelter is not available, get inside a car and keep the windows up.
¤	Get out of boats and away from water.
¤	Telephone lines and metal pipes can conduct electricity. Avoid using the telephone or electrical appliances. Use phones only in an emergency. Unplug electrical appliances which are not in use.
¤	Do not take a bath or shower .
¤	Turn off air conditioners. Power surges from lightning can overload the compressors.
¤	If you are driving on highways and flyovers be alert to strong gusts.
¤	Get to higher ground if flash flooding is possible.

If Caught Outdoors and No Shelter is Nearby ....
¤	Shelter in a low spot away from trees, fences and poles, that is not subject to flooding.
¤	If you are in a forested area, take shelter under the shorter trees.
¤	If you feel your skin tingle or your hair stand on end, squat low to the ground. Place your hands on your knees with your head between them. Make yourself the smallest target possible, and minimize your contact with the ground.
¤	If you are boating or swimming, get to land and find shelter immediately!

Role of the Malaysian Meteorological Service

The Malaysian Meteorological Service maintains a constant surveillance on the weather and broadcasts regular weather forecasts via the mass media. Information from its network of ground observation stations, weather radars, satellite, and other sources track the development of thunderstorms in the country. Listen for severe weather advisories and warnings!

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Source Dest.: http://www.my-hut.com/default2.asp?tree=558

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