Download Air Masses and Fronts

The Fronts and Backs of Weather
 Air Masses
– similar characteristic of temperature, moisture
• centers of high pressure
– acquire characteristic of source region
• needs uniform surface (mountain regions - no good)
 Four Basic Source Regions
– Maritime (m) versus Continents (c)
– Polar (P) versus Tropical (T)
The Fronts and Back of Weather
 Continental Air Mass
• low moisture content
• few clouds
– Winter (cP)
• Very cold, dry
• Temperature varies
much within air mass
• Active weather at edge
– Summer (cT)
• Very hot
• Associated with drought
• limited source - NA
 Maritime Air Mass
• high moisture content
• abundant clouds
– Winter (mP)
• Chilly, damp
• Temperature varies
some within air mass
• Active weather at edge
– Summer (mT)
• Hot and humid
• Associated with HHH
• abundant source - NA
The Fronts and Back of Weather
 Fronts (low pressure zones)
– valleys between domes of air masses
• separate air masses of different density
– density differences due to Temperature, Moisture
» biggest difference: mT (hot, humid) & cP (cold, dry)
• Many weather parameters vary across a front
– Temp, Moisture, Pressure, Wind, Clouds, Precipitation
– front type is totally dependent on winds in the
colder (more dense) air mass
• winds blow toward boundary - cold front
• winds blow away from boundary - warm front
The Fronts and Back of Weather
 Cold Fronts
– denser air moving
toward the boundary
– Temperature highest at
the front, then falls off
– Most active weather
with front (T-storms)
Steep slope to front
– RH rises, Visibility up,
Pressure rises
– mT to cP - common
 Warm Fronts
– denser air retreating
from the boundary
– Temperature rises as
front approaches then
steady after front
– Most active weather
precedes the front
Gentle slope to front
– RH steady, Visibility
down, Pressure drops
– cP to mT - common
The Fronts and Back of Weather
 Stationary Front
– winds in denser air mass blow parallel to front
– unsettled weather - mainly on cold side
– breeding ground for cyclone development
 Speed of front
– determined by surface winds in colder air mass
– overrunning determined by speed of winds in
the warmer air mass