Transcript WEATHER PATTERNS AND SEVERE STORMS

WEATHER PATTERNS AND
SEVERE STORMS
AIR MASSES
• Body of air of similar temperature and
moisture content
• Creates fairly constant weather over an
area
• As an air mass moves, the conditions of
the air mass change
CLASSIFYING AIR MASSES
• Air masses are classified by the source
region
• Eastern North America is influenced by
continental polar and maritime tropical air
masses
Continental Polar – cP – uniformly cold and
dry in winter bringing cold temperature and
clear skies to an area
• cool and dry in summer bringing cool
temperatures
Maritime Tropical – mT – warm, loaded with
moisture, and usually unstable
• Source of much of the precipitation in the
Eastern two-thirds of the US
• In summer maritime tropical brings hot
temperatures with high humidity!
Maritime Polar – mP – in winter the maritime
polar that affects the US is from the Pacific
NW
• Cool, moist and unstable air mass, low
clouds and showers
• Produces heavy rain and snow on
windward side of mountains
• Maritime Polar in the Atlantic can form a
low pressure storm called a nor’easter
Continental Tropical – cT – form in
Southwest US and Mexico in summer,
brings very hot and dry weather
• In fall the movement brings warm
conditions in fall called the Indian Summer
3. FRONTS
• A boundary that separates two air
masses
Warm Front – warm air moves into area
formerly covered by cool air
• Slope is gradual
• Sequence of clouds: cirrus, cirrostratus,
altostratus, nimbostratus
• Produce light-to-moderate precipitation
• Gradual warming of temperature
• Wind shift from east to southeast
Cold front – forms when cold, dense air
moves into a region occupied by warmer
air
• Twice as steep as warm fronts and
advance more rapidly
• Associated with violent weather,
thunderstorms and tornadoes
• Forms cumulonimbus clouds
• The temperature drops with the passage
of a cold front and the weather clears
• Stationary Front – the cold air mass and warm
air mass move parallel to each other; brings
gentle to moderate precipitation
• Occluded Front – an active cold front
overtakes a warm front and wedges the
warm front upward
4. MIDDLE-LATITUDE CYCLONES
• Main weather producers in the US
• Large centers of low pressure that travel from
west to east and cause stormy weather
• Rotate counterclockwise
• Cold front and warm front, abundant
precipitation
• Forms when a cold front overtakes a warm
front and lifts the warm front forming an
occlusion
• As the occlusion begins, the storms gets
stronger, the pressure falls, and the wind
speed increases
5. THUNDERSTORMS
• Storm that generates thunder and
lightning; can produce gusty winds,
heavy rain and hail
• Associated with cumulonimbus clouds
• Thunderstorms are common
• Thunderstorms form when warm, humid
air rises in an unstable environment
• Strong updrafts cause the cloud to grow
vertically
6. TORNADOES
• Tornadoes are violent windstorms that take the
form of a rotating column of air called a vortex.
Te vortex extends down from a cumulonimbus
cloud
• Frequency is greatest from April through June
• Most tornadoes are associated with severe
thunderstorms
• A mesocyclone begins when strong winds aloft
cause the surface winds to roll. Updrafts
cause the rolling winds to tilt up
7. HURRICANES
•
Tropical cyclones that produce winds of at least 119
km/hour
•
Growing threat because more and more people live
near coast
•
Form between 5 and 20 degrees north and south
latitude
•
Develop most often in late summer when surface
water temperatures are warm enough to provide the
necessary heat and moisture to the air
•
Eye wall has the highest wind speeds and heaviest
precipitation
•
Eye is a zone where precipitation and winds stop
•
Most damage occurs with storm surge
•
A hurricane weakens over cold water or over land
2008 Hurricanes for Atlantic
Arthur
Bertha
Cristobal
Dolly
Edouard
Fay
Gustav
Hanna
Ike
Josephine
Kyle
Marco
Nana
Omar
Paloma
Rene
Sally
Teddy
Vicky
Wilfred