Straight Line Winds are responsible for most thunderstorm wind damage winds can exceed 100 mph one type of straight line wind is called the downburst; it can cause damage equivalent to a strong tornado and can be extremely dangerous to aviation damage from straight line winds is often incorrectly attributed to a tornado

As thunderstorm downdrafts increase, winds are pushed along the ground.

Straight line winds in a thunderstorm.

Straight line wind damage to forested land

Analysis of straight line wind damage

Tornado!

What is a tornado? A tornado is a violently rotating column of air extending from a supercell thunderstorm to the ground. (Only 1 in 1000 thunderstorms becomes a supercell and only 1 in 6 supercells spawns a tornado.) Tornadoes can stay still, hop/skip places, or move forward at speeds up to 70 mph. Their average speed is 30 mph. Damage paths can be in excess of 1 mile wide and 50 miles long. (Longest known path was 219 miles in 1925.)

Where do tornadoes form? Tornadoes occur in many parts of the world but are most frequent in the United States east of the Rocky Mountains during the spring and summer months. In the Central Plains, thunderstorms develop along a "dryline" as it moves east during the afternoon. This area is called Tornado Alley. Tornadoes may form as air near the ground flows "upslope" toward higher terrain. Tornadoes occasionally accompany tropical storms and hurricanes that move over land.

40% of all US tornadoes occur in Tornado Alley

The sun heats dry air more. Winds push the dry air eastward into the humid air during the afternoon. A dry line separates the two air masses. Most tornadoes occur between 3 and 9 PM

A tornado usually forms in the wall cloud, the dark base cloud, of a supercell.

Cumulonimbus clouds often grow to over 40,000 feet. Some even pop through the tropospause to the stratosphere! A column of warm, humid air rises very quickly. How the column of air begins to rotate is not completely understood by scientists, but one way the rotation appears to happen is that winds at two different altitudes blow at two different speeds. Tornado Formation: Step 1

If this column gets caught in an updraft, the column’s spin tightens and it speeds up (much like a skater spins faster when arms are pulled close to the body). A funnel cloud is created. Tornado Formation: Step 2

The rain and hail in the thunderstorm cause the funnel to touch down, creating a tornado. Tornado Formation: Step 3

Tornado!

Tornado Strength Weak Tornadoes –69% of all tornadoes –Less than 5% of tornado deaths –Lifetime minutes –Winds less than 110 mph

Strong Tornadoes –29% of all tornadoes –Nearly 30% of all tornado deaths –May last 20 minutes or longer –Winds mph Tornado Strength

Violent Tornadoes –Only 2% of all tornadoes –70% of all tornado deaths –Lifetime can exceed 1 hour –Winds greater than 205 mph New computer models suggest that the winds at the surface could exceed the speed of sound. One probe sent into a tornado registered an air pressure drop of 100 mb! Tornado Strength

Damages cause an average of 80 deaths and 1500 injuries each year most fatalities occur because people do not leave mobile homes and automobiles when told to do so cause $400 million in property damages each year

Why you should leave when told to.

Why you should leave your car!

National Weather Service Announcements TORNADO WATCH: Tornadoes are possible in your area. Remain alert for approaching storms. TORNADO WARNING: A tornado has been sighted or indicated by weather radar. (Warning time averages only 13 minutes.)

Tornado Safety Move to a basement. If an underground shelter is not available, move to an interior room or hallway on the lowest floor and get under a sturdy piece of furniture. Stay away from windows. Get out of automobiles. Do not try to outrun a tornado. Abandon mobile homes.

Tornado Safety in School Have drills for your severe weather action plan. Schools without basements should use interior rooms and hallways on the lowest floor and away from windows as tornado shelters. Use air horn or megaphone in case of power failure. Turn off electricity and gas if school is damaged. Move students out of gymnasiums, cafeterias, and auditoriums.

Tornado Safety in School Students should assume the tornado protection position.

This map shows the number of days of thunderstorm activity. NJ has 10 – 20 such days.

This map shows the average number of tornadoes. NJ has one or fewer.

Waterspouts Waterspouts are weak tornadoes that form over warm water. Waterspouts are most common along the Gulf Coast and southeastern states. Waterspouts occasionally move inland becoming tornadoes causing damage and injuries.

Waterspout

May 9, 2012 Grand Isle, LA

Top 10 Twisters in History March 18, 1925 May 7, 1840 May 27, 1896 April 5, 1936 April 6, 1936 April 9, 1947 April 24, 1908 June 12, 1899 June 8, 1953 May 11, 1953 Update: On May 23, 2011, the Joplin, Missouri tornado killed 117 people, making it the 8 th worst in US history.

Joplin, MO tornado May 23, 2011 One Year Later

Tornado Tidbits A tornado lifted a child and put him down unharmed in a tree. A plane was carried 35 miles. This is the heaviest piece of debris ever carried. A check was found 305 miles away, the longest distance debris has been carried. A baby was found unhurt on her mattress under a wall of her wrecked home. Horses hitched to a rail were found ¼ mile away unhurt and still hitched to the rail. Sometimes it rains fish, frogs, snails or salamanders.

I’ll Get You!