Thunderstorms and Severe Weather

All Thunderstorms begin as Cumulus Clouds

This is runaway convection – cumulonimbus over the Plains. These clouds can grow to 70,000 feet (14 miles) high!

Mature thunderstorms have both downdrafts and updrafts. The precipitation forms in the updraft and falls out into the downdraft.

Thunderstorm Hazards  Lightning  Tornadoes/downbursts  Hail  Flash Floods

Every year people die from lightning strikes

There are actually nine cloud-to-cloud strokes for each cloud-to-ground stroke

In the U.S., the greatest number of thunderstorms and lightning fatalities (5-10 per year) occur annually in Florida.

Cloud-to-Ground strokes are the most dangerous.

Notice the segmented pathway to the ground. Also, some of the lighting didn’t contact the ground.

Lightning doesn’t always hit the tallest object…

but it often does. In the middle ages, the church towers were used to store gunpowder, with predictable results. Mosques, on the other hand were struck but rarely suffered damage. Can you see why?

Did Franklin really do this?

“Benjamin Franklin Drawing Electricity from the Sky" by Benjamin West ( ). The Philadephia Museum of Art

The cloud-to- ground stroke heats the air to around 30,000 K, making it the brightest stroke.

By holding the shutter open, several strokes are captured in this image. There were also lots of air discharges.

An air discharge is a stroke which peters out in the air.

Florida gets a lot of lightning and we used to launch the space shuttle from there.

Lightning can hit outside the thunderstorm!

Notice the positive streamers at a, b, and c

When the stepped leader’s charge is approaching, you might give off positive streamers! Don’t be the lightning’s conduit. Get inside during thunderstorms. Read survivor stories here: gov/survivors.htm.

The fellow inside the metal cage is safe. It’s called a Faraday Cage. Lightning travels around him, not through him.

Inside your vehicle is actually a safe place. It’s a kind of Faraday Cage. Don’t touch the metal parts.

Out on the golf course is NOT a safe place during a thunderstorm.

Lightning in the ground is so hot it will fuse sand. The resulting formations are called Fulgarites

The heating of the air causes rapid expansion. The compession is sound. We hear it as thunder. The sound of thunder travels at right angles to the lightning bolt. It travels at 1100 ft/sec so count to 5. The sound has traveled about one mile.

Tornadoes

Blue dots are high winds, Green dots are large hail, Red dots are tornadoes

Tornadoes never occur without a parent thunderstorm. There are over 1000 tornadoes in the U.S. most years.

Miami, Florida tornado

A large, cone tornado. It might be a mile wide at the ground.

Oklahoma City F5 tornado May 3, 1999

Here are all the 2011 tornadoes (1894)

All the tornadoes in 2014 so far (1000)

The number of tornadoes observed in the U.S. appears to be increasing. Or are we just getting better at finding them?

Tornadoes in the Great Plains tend to be the most destructive

On radar, often big tornadoes are seen with a “hook echo”

Greensburg, KS tornado hook echo

Greensburg High School (

Watches and Warnings

Damage from the May 31, 1998 tornadoes in Albany, NY. On the Fujita scale, where does this fit?

In 2006, the NWS introduced the Enhanced Fujita Scale, an updated version of the F-scale

House damaged House untouched Houses demolished Houses untouched Tornadoes do damage on a very small scale

In 2011, almost 1900 tornadoes were reported in the U.S.!

Tuscaloosa EF

Where don’t you want to be when a tornado strikes?

Large hail is not a killer, but does considerable damage Hail

Falling from 20,000 feet or higher, large hailstones pack quite a punch!

Average annual number of days with hail

This is the biggest hailstone known. It fell at a town called Aurora, NE on June 22, 2003.

The Aurora hailstone was 7 inches in diameter. Imagine that falling on your head from 20,000 feet up !

This is the previous record-holder, the Coffeyville hailstone with some props (egg, hand) for comparison.