Weather Systems Vocabulary Air mass – huge body of air with the same temperature and moisture characteristics Front – a boundary between two air masses Hurricane – a tropical cyclone of low pressure and very strong winds Thunderstorm – Cumulonimbus cloud possessing thunder and lightning, usually accompanied by strong winds, rain and sometimes hail Tornado _ whirling funnel of air of very low pressure and very strong winds; must touch the ground to be called a tornado

Air Masses Usually 1,000 miles across or more Has the same temperature and moisture characteristics When it travels out of its area it carries the characteristics (front from Alaska will be cold and dry) Usually from a Tropical or polar region They are classified by their source region, such as (P) Polar, (A) artic, (T) tropical and (E) equatorial

FRONTS They are classified as warm, cold, stationary or occluded. When warm air moves in this is a warm front When cooler (cold) air moves in this is a cold front When two air masses bump into each other and neither moves it is called stationary. An occluded front is when three air masses meet. Cold fronts are indicated in blue, warm fronts in red

Severe weather There are three main weather phenomena Thunderstorms Tornadoes hurricanes All three are associated with cumulonimbus clouds All three are potentially deadly

Thunderstorms Come from cumulonimbus clouds and always have thunder and lightning Lightning is a flash of light produced by electrical discharges in a thunderstorm. It discharges millions of volts and heats the air to 60,000 degrees F. Thunder is the sound sent out by rapidly expanding gases along the lightning's trail They usually contain heavy rain, strong winds and sometimes hail Hail is small balls of ice

Thunderstorm stages They have three stages: building, mature, and dissipating Building stage has updrafts as the storm builds and grows vertically. Mature stage the moisture that is carried up gets heavier and starts to fall, this creates downdrafts… there are still updrafts so the moisture moves up and down several times Dissipating, contains only downdrafts (the storm is blowing itself out) In the US alone 200 people are killed by lightning each year and 400-500 are injured.

Safety rules for thunder and lightening Stay away from windows and doors Don’t use electrical appliances Don’t use the phone or take a shower or bath If outside, go inside if possible Move away from water such as pools, lakes and the ocean If you are in a boat, go ashore Stay away from metal objects like gold clubs, fishing poles, bicycles, farm equipment or motorcycles Don’t stand in an open field, a hilltop or golf course, stay low by sitting. Don’t stand under a single tree (if you must be under a tree, look for a group of trees of similar height) If in a group of people, stay low and spread out If in a car, stay there.

How do thunderstorms affect aviation? Cumulonimbus clouds mean the air is unstable Thunderstorms have violent up and down drafts Unstable air causes turbulence which raises havoc with planes Hail can do serious damage to airplanes Lightning can cause electrical devices on the plane to go out or even shut down engines Pilots usually fly above or around thunderstorms

Tornadoes

Tornadoes Destructive and devastating to life, property and nature Occur in every month of the year About 700 annually in the US Unstable air of low pressure Most are counter-clockwise Air is sucked into the center (vortex) of the storm The funnel of a tornado appears dark because of the dirt and debris it picks up

Tornado winds They can be stronger than 261 mph They can be as big as 500 yards (5 football fields) across They are measured on the Fujita wind damage scale F-0 light up to 72 mph F-1 moderate 72 to 112mph F-2 considerable 113 to 157 mph F-3 severe 158 to 206 mph F-4 devastating 207 to 260 mph F-5 incredible above 261mph

HURRICANES Produce many thunderstorms and tornadoes within them Their winds are not as strong as tornadoes usually but still devastating Affect hundred of miles wide Flood coastal cities and dump many inches of rain The eye of the hurricane can be 15 miles wide! Before storms become hurricanes they are first tropical depressions then tropical storms Judged on the saffir-simpson scale Cat 1 Cat 2 Cat 3 Cat 4 Cat 5