Thunderstorms

1. At any one time, nearly 2,000 thunderstorms are occurring around the world.

2. The three conditions necessary for a thunderstorm to form are: 1) lots of moisture in the lower atmosphere 2) The now warmer air begins to rise 3) the atmosphere must be unstable

3. There are air mass thunderstorms that form due to differences in air masses.

4. Frontal thunderstorms form by an advancing cold front usually.

Stages of a Thunderstorm

Stages of thunderstorm development

13.2-Severe Weather

6. A supercell is a self-sustaining, extremely powerful storm that has intense, rotating updrafts.

Mammantus

7. Lightening is electricity caused by the rapid rush of air in a cumulonimbus cloud.

8. When lightening occurs, the air expands out rapidly, causing the sound of thunder.

9. A downburst is a violent damaging thunderstorm wind concentrated in a local area.

Downburst

Hail10. Hail is precipitation in the form of balls or

lumps of ice. They form in severe storms. Indicator of tornadoes!

Hail formation

11. A tornado is a violent, rotating column of air in contact with the ground.

12. A change in wind speed and direction cause wind shear which creates a horizontal rotation. When it’s close enough to an updraft, it becomes vertical and thus a tornado.

Anatomy of a tornado

First photographed tornado- 1884

Salt Lake City Tornado

A dual funnel tornado

14. Weak tornadoes (F0-F1) make up 80% of all tornadoes. Last 1-10 minutes. On ground up to 3 miles. Wind speeds- 60-115 mph

15. Strong ones (F2-F3) make up 19%. Last up to 20 min. On ground up to 15 mi. Winds- 110-205 mph

16. Violent ones (F4-F5) make up only 1%. Last up to 1 hour. On ground up to

50 mi. Winds- over 200!

Hook Echo

Wind shear & Hook Echo

April 3-4, 1974 Tornado Outbreak

Waterspout

Three Waterspouts!

Tornado Alley!

18. More than 700 tornadoes occur each year in the U.S.

Tornadoes & Hurricanes

13.3 Tropical Storms1.  A tropical cyclone is a large, rotating, low-

pressure storm formed over warm, ocean water in the summer or fall.

2.  Our storms form off the coast of Africa near the equator and move west/northwest.

Hurricane formation

3.  A tropical depression is an organized system of clouds and thunderstorms with a defined surface circulation and maximum sustained winds of 38 mph or less.

4.  A tropical storm has maximum sustained winds of 39-73 mph.

5.  A hurricane is an intense tropical weather system of strong thunderstorms with a well-defined surface circulation and maximum sustained winds of 74 mph or higher.

Saffir-Simpson Scale

25. Some famous hurricanes to strike NC are: Hugo (1989), Fran (1996), Floyd (1999), Isabel (2003)

26. Record hurricanes in the US: Andrew (1992), Katrina (2005)

 27. The 2005 hurricane season set new records with 28 storms. With only 24 names, the last 4 storms were given letters (Alpha, Beta, etc.) Fifteen of these became hurricanes, seven were major hurricanes, with five that were category fours and four became category fives!!

• A hurricane watch is issued when hurricane conditions are possible within 36 hours. Begin family's disaster plan, needed supplies, evacuation routes, etc.

• A hurricane warning is issued when hurricane force winds are expected within 24 hours. Complete planning process and prepare for the storm.

Hurricane Isabel (infrared)

Isabel Radar

Inland during a hurricane, it’s the rainfall that does the most damage!

Flooding from Isabel

Overwash from Isabel

Fran approaching …

Infrared Image of Floyd

Hurricane Wilma

August 1995 Satellite image

Storm Surge

Katrina and Sea Surface Temperatures

Saffir-Simpson