Wednesday, May 5, 2010

Winds, Hail and Lightning are Topics on Day #3 of Weather Awareness Week

It's spring in the Pacific Northwest and that means an unstable air mass can bring thunderstorms that include lightning, wind, and hail. Just this week, the National Weather Service sent out a brief alert for a severe cell over the southern Skamania/Clark county border.


Straight line winds: Downburst winds from a thunderstorm usually result when evaporation of raindrops cools air within a storm. Winds generated from this process can exceed 100 mph. Weather forecasters call these bursts of wind "microbursts" if they are less than 2 1/2 miles across and "macrobursts" if they are greater than 2 1/2 miles across. These downbursts of air can be detrimental to aircraft and can cause extensive damage, injuries and fatalities.

Hail: Another thunderstorm threat, also occurs in the northwest. Hail forms within thunderstorms as liquid water freezes in the cold mid and upper levels of storms. This ice is kept aloft by strong updrafts (convection). Large hail can easily damage vehicles and buildings and can be life-threatening to animals and people. Even small hail can be dangerous to motorists when it accumulates on roadways.

Lightning: Each year over 300 people in the U.S. are struck by lightning while working outside or during other outdoor activities. Over the past 30 years in the United States, an average of 58 people per year are killed by lightning. Hundreds of others are injured and left to cope with permanent disabilities.

It takes thunder about 5 seconds to travel one mile. So, if you count the seconds from the flash to the thunder you can calculate the distance. A 10 second flash to thunder count would mean the lightning strike was 2 miles away.

Try to get indoors during all thunderstorms. When thunderstorms threaten you this season, tune to NOAA Weather Radio, The Weather Channel, or your local radio or television stations for up-to-date information.

If caught outside and lightning is in the immediate area, and there are no safe locations nearby, the following steps will help decrease your chances of being struck by lightning. Do not seek shelter in partially enclosed building, or tall objects such as an isolated or small group of trees. Stay at least 15 feet apart from other members of your group so the lightning won't travel between you if hit. If you can possibly run to a vehicle or building, do so! Sitting or crouching on the ground is not safe and should be used only as a last resort if an enclosed building or vehicle is not available.

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