Chapter 20 Weather Patterns Severe Storms Standards Concept

Chapter 20 Weather Patterns & Severe Storms Standards: Concept 2 PO: 11, 12, 13

Air mass • Large section of air with the same temperature and moisture throughout • Can stay in the same spot for days and weeks

Movement of Air Masses • As an air mass moves away from where it formed it takes the temperature and moisture conditions with it • As an air mass moves the characteristics change and so does the weather in the area over which the air mass moves.

Classifying Air Masses • Air masses are named according to their source region

Classifying Air masses Temperature Humidity • Polar (P) ▫ Formed near the poles at high latitudes ▫ Cold air • Tropical (T) ▫ Formed near the equator at low latitudes ▫ Warm air • Continental ( c ) ▫ Formed over land ▫ Dry air • Maritime (m) ▫ Formed over ocean ▫ Wet air *Temperature is always written first with a capital letter. Humidity is written second with a lower case letter

Air Masses

Formation of Fronts • When two air masses meet they form a front • Associated with some form of precipitation

Warm Front • Forms when warm air moves into an area formerly covered by cooler air

Cold Front • A cold front forms when cold, dense air moves into a region occupied by warmer air • Brings more violent weather, moves quickly

Stationary Front • The air flow is neither toward or away from the air masses it moves parallel to the front • Brings gentle to moderate rain

Occluded Front • When an active cold front overtakes a warm front. • Produces complex weather systems

Weather Map Symbols

Thunderstorms • Generates lightning and thunder • Produce gusty winds heavy rain and hail • From when warm, humid air rises in an unstable environment • At any given time there about 2, 000 thunderstorms in progress

Stages of a Thunderstorm

Fun Facts • Earth as a whole is struck by an average of more than a hundred lightning bolts every second. • The odds of becoming a lightning victim in the U. S. in any one year is 1 in 700, 000. The odds of being struck in your lifetime is 1 in 3, 000.

More Fun Facts • Lightning is not confined to thunderstorms. It's been seen in volcanic eruptions, extremely intense forest fires, surface nuclear detonations, heavy snowstorms, and in large hurricanes. • Use the 30 -30 rule. When you see lightning, count the time until you hear thunder. If that time is 30 seconds or less, the thunderstorm is within six miles of you and is dangerous. Seek shelter immediately.

Thunderstorm Arizona

Thunderstorm Phoenix

Tornados • Violent windstorms that take the form of a rotating column of air called a vortex. The vortex extends downward from a cumulonimbus cloud. • In the US occur most often from Nov. – June

Tornado Development

Tornado Intensity

Tornado Safety Watches Warnings • Alert people to the possibility of tornadoes in a specified area for a particular time period • Issued when a tornado has actually been sighted in an area or is indicated by weather radar

Joplin, MO Tornado 2011

Tornado Damage

Tornado Damage Joplin, MO

Tornado Damage Joplin, MO

Hurricanes (typhoons, cyclones or tropical cyclones) • Whirling tropical cyclones that produce winds of at least 119 km per hour • Most powerful storms on Earth • Develop in that late summer when water temperatures are warm enough to provide the necessary heat and moisture in the air • Eye Wall – greatest wind speed • Eye – center of storm, no rain, calm • Storm Surge – most dangerous part water comes ashore

Hurricane Katrina Eye Wall

Storm Surge

Hurricane Irene 2011

Hurricane Fun Facts • Names are alphabetically and alternate between male and female names • Deadliest hurricane was the Great Galveston Hurricane in Texas (1900) category 4 storm with 8, 000 deaths.

Hurricane Intensity