Download Air Masses

Air Masses
Air Masses
• Large bodies of air characterized by similar
temperatures and amounts of moisture at a
given altitude
• So large they can take days to move over an
area causing constant weather
• Can be 1600 km (~1000 mi) wide and several
km thick
Movement of Air Masses
• A moving air mass
carries temperature
and moisture with it
• As it moves, the
characteristics of an
air mass change – and
so does the weather
over the areas it
passes
Classifying Air Masses
• Source region – the area over which an air
mass gets its properties
• Named by source region
– Polar (P) air masses
• Form at high latitudes
• Are cold
– Tropical (T) air masses
• Form at low latitudes
• Are warm
Classifying Air Masses (cont.)
• Also classified by surface
– Continental (c ) air masses
• Form over land
• Dry air
– Maritime (m) air masses
• Form over water
• Humid air
Classifying Air Masses (cont.)
• Thus, there are 4 types of air masses
–
–
–
–
cP – continental polar – dry and cold
cT – continental tropical – dry and warm
mP – maritime polar - ? and ?
mT – maritime tropical - ? and ?
• Well, actually there is a 5th
– Arctic Polar (aP) – dry and cold
Air Masses
Continental Polar (cP) Air Masses
• Begin in northern Canada, Alaska’s interior,
& Siberia
• Cold and dry in winter – clear skies and cold
temps
• Cool and dry in summer – days with cooler
weather
• Not usually associated with ↑ precipitation
except for “lake effect snow”
Lake Effect Snow
Maritime Tropical (mT) Air Masses
• Warm, ↑ moisture content, unstable
• Source of most precipitation in eastern part
of US
• The high temps and
icky humidity found
in FL, LA, etc. are
caused by mT air
masses
Rain storm over Florida keys
Maritime Polar (mP) Air Masses
• Some air masses affecting North America
begin in Siberia
– cP changes into mild, humid, unstable mP air
– Brings low clouds
& precipitation
– Uplift  rain &
snow on windward
side of mountains
Maritime Polar (mP) Air Masses
• mP air masses also from North Atlantic off
coast of eastern Canada
• In winter, New England is on the northern or
northwestern edge of a low-pressure system
– Remember low pressure system cyclones rotate
counterclockwise
– This brings in mP air with snow and low temps
– These are called “nor’easters”
Continental Tropical (cT) Air Masses
• These don’t affect North America too much
• Well, except in the southwestern US and
Mexico
• Sometimes they affect areas outside their
sources causing
– Hot temps and drought in the summer
– Warm and mild temps in fall
Arctic Polar (aP)
• Source region for Arctic (a) air is northern
Canada, Siberia, and the Arctic
• Colder than polar air masses
• Develop over ice and snow covered ground
• Dry
Summary
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What is an air mass? How large are they?
How are air masses classified?
Which air masses are typically dry?
Which air masses are typically warm?
What causes lake effect snow?