Air Mass Designations And Terms Used In WEATHERAmerica Discussions, Saturday, January 15, 2022

[Larry Cosgrove]

Air Masses

The first letter of the abbreviation (lowercase "m" or "c") outlines whether the air mass is a dry, continental air mass or a moist, maritime air mass. The second letter in the abbreviation (capital "I", "P", "T" or "A") gives an indication of the temperature or character of the air mass. A third designation, "w" (warmer) or "k" tells the reader if the regime is warmer or colder than normal or the comparison between other air masses. After Vilhelm and Jacob Bjerknes (1926).

ImP Integrated/Modified maritime polar (used to describe air of Pacific Ocean origin that has been warmed/dried after crossing the Rocky Mountains.

IcP Integrated/Modified continental polar (polar air mass that has stabilized and warmed over the interior of North America)

cPk (polar air mass that is colder than the regime which preceded its passage)

cP (polar air mass with origins over central or southern Canada, northern U.S.)

cA (Arctic air mass which originates near or above the Arctic Circle; may be Alaska, northern Canada, or Siberia)

cAk (Arctic air mass which is sharply colder than regime which preceded its passage; often associated in the media with the term "Siberian Express")

mA (Arctic air mass that originates over northern Pacific Ocean, northern Atlantic Ocean, or Hudson Bay; tends to marginally warmer than continental source)

mAk (Arctic air mass originating over water that is associated with either a very strong upper vortex, or has some inclusion of air from Alaska, Greenland or Iceland)

mP (polar air mass originating over a water body, such as the Pacific Ocean, Hudson Bay, or Atlantic Ocean)

mPk (polar air mass originating over water which is colder than the air mass which preceded its passage; term often used in damming/wedge scenarios or a flow signature involving passage of the air over sea ice.

cT (continental tropical air, usually originating over deserts from dry topography or dry High Plains, such as western Texas)

cTw (continental tropical air, with extreme dryness as well as rapid temperature rises noted).

mT (maritime tropical air, with high relative humidity and noted for instability that fuels diurnal thunderstorms)

mTw (warmer/hotter tropical regime under a subsident heat ridge or in a strong low-level jet stream; source regions: Bay of Campeche and Caribbean Sea)

A three-way or "triple point" convergence (cP/cT/mT) of air masses is often associated with severe weather outbreaks

Occasionally, synoptic meteorologists and climatologists term humid regimes along the Inter Tropical Convergence Zone as "equatorial"; rapid drainage of this highly unstable and moisture-laden air in the Pacific Basin into California is often termed the "Pineapple Express"

Rapid cold air mass advection and ingestion in concert with a bombogenesis event is sometimes called a "bomb drop"; the standout examples of this phenomenon are the January 26-27 1978 Blizzard and the March 11 1993 Superstorm

A similar process is a cold air mass "Dam Break" (in Texas termed a "Blue Norther"), where severe cold reaches very low latitudes (such as the February 12-15 2021 surge through the Great Plains and Mississippi Valley into Texas and the Deep South).