mT Air Mass:

• largely originates in Gulf of Mexico, western Atlantic - affecting eastern 2/3 of country
• also originates in tropical eastern pacific (SW monsoons in summer)
• warm, moist, unstable
• confined to southern US in winter
• important source of moisture feeding storms all year round

cT Air Mass:

• originates over Mexican Plateau region and desert SW
• hot, dry, unstable at low levels, stable at upper levels
• boundary between cT and mT is often called the dryline
  • The dryline is often seen in surface and satellite data and is a favored location for storm initiation:
  • Examples: | static visible satellite image | satellite/surface loop |