Definition
An air mass classification letter used on weather charts to identify air that originated over the arctic region. Arctic air is extremely cold and dry at its source, colder and drier than polar (P) air, and forms over the permanent ice and snow surfaces north of the polar front.
Plain English
The letter A on a weather chart tells you the air came from the far north — the arctic. That air starts out extremely cold and very dry because it formed over ice and snow.
Context Anchor
Seen on weather charts and in FAA discussions of North American air mass source regions.
Derivation
From the Greek 'arktikos,' meaning 'of the north' or 'near the Bear,' referring to the constellation Ursa Major (the Great Bear) which sits over the northern sky. Knowing this helps lock in that arctic air comes from the far north — the region under the Bear.
Why Pilots Care
An Arctic air mass produces the lowest temperatures, clear skies, and high risk of frost or carburetor icing during winter operations.
Grounding Statement
Picture a large pool of very cold air sitting over snow and ice, then sliding south across Canada and the United States.
Intuition Check
Do not read “arctic” here as just a casual word for “cold.” In this context, it identifies the air mass source region: the far northern Arctic area where the air formed.
Example Sentence 1
The forecaster identified the incoming system as an A air mass, warning pilots of extreme cold and possible engine starting difficulties on the ramp.
Example Sentence 2
Before a cross-country flight in January, the pilot checked whether an Arctic air mass would affect the route.