Severe Weather 101 - Hail and Wind

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April 28, 6:41 AM

by Tony Hake, Denver Weather Examiner

 

 

This is part four of a five part series on Colorado’s severe weather.

Straight line winds are winds out of a thunderstorm and are classified as severe when they hit 58 mph. These winds can reach tornado and hurricane force and as a result, cause property damage and can injure and even kill animals and humans. These winds are usually the result of air cooling rapidly due to precipitation or evaporation. As the cooler air is heavier than the surrounding warmer air, it rushes downward, accelerating toward the ground and spreads out as it hits, much like pancake batter being poured onto a griddle.

These winds can exceed 100 mph which obviously present a danger to life and property. Flying debris picked up by the winds can wreak havoc. Airports and pilots need to be aware of these conditions and precautions are usually taken when these conditions exist.

One term many of you may have heard is microburst - this is a straight line wind less than 2 ½ miles across. If it is more than 2 ½ miles across, it is called a macroburst.

Because these winds are so strong, the damage from them can oftentimes be mistaken as a result of a tornado. When the National Weather Service inspects such damage, they look for telltale signs to determine what the real cause is. A tornado due to its rotating nature will throw debris in a circle and haphazardly. Straight line winds are just as the name implies - straight - so the damage will be in a straight pattern out from where it initially strikes the ground. The image at the right depicts just this situation when an 80mph straight line wind struck a park in Tennessee.

Another thunderstorm threat that almost everyone in Colorado is familiar with is hail. Hail is quite simply frozen water that is held aloft by the updraft winds of a thunderstorm, going up and down, getting bigger and bigger until it simply weighs too much to stay in the air. Small, pea-sized hail is pretty common in Colorado but softball sized can and does happen.

Oftentimes clouds will exhibit a green color cast when hail is present and small hail can be the harbinger of bigger stones to come so it is always wise to seek shelter when hail if falling, even if it doesn’t seem that bad. The bigger hailstones provide a great risk for crops, property and can result in injury and death.

How big can hail get? On June 22, 2003 in the south central Nebraska town of Aurora, the world’s largest hailstone fell. This stone measured a whopping 7 inches in diameter and over 18 inches in circumference! See the picture at right or click here for more information.

The National Weather Service issues severe thunderstorm warnings for winds of 58 mph or higher and for large hail 3/4 of an inch in diameter or larger. Realize that some storms are capable of much larger hail and much higher wind so when you hear about a severe thunderstorm warning, seek shelter.

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