- Slides: 32
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
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.
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 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 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
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.