Air masses defined: What type of weather we have depends on what type of air we have

Weather Glossary

ROCHESTER, NY (WROC) – As the sun heats the earth in different ways based on the earths angle, geography, land types, and other factors, different types of air masses develop. It is these air masses that clash and create weather. Within individual air masses there is little change and as a certain air mass remains over one area over a long period of time, it takes on more characteristics of said air mass. Temperature and moisture are the two main factors that determine the type.

In terms of moisture, there are two main types. If the air is over land, it is called continental and represented with a lower-case c. If the air is over water, it is called maritime and represented with a lower-case m.

In terms of temperature, there are several different options. This correlates well with location as the equator is generally warmer than the poles.

  • A: Arctic air mass – This is a very cold airmass that originates over the poles. It is often dry.
  • P: Polar air mass – Usually a colder air mass, but not as cold as the arctic and can originate over areas like Canada or Russia. It can also originate over bodies of water.
  • T: Tropical air mass – Found over the tropics and near the equator. This air mass is warmer and most often contains a lot of moisture

Here are a few examples from the NWS of where a certain air mass may originate.


cP: Continental Polar air mass would be something like we experience in the northeast after a cold front. It can be a drier and cooler air mass that may have originated from Canada. It is not as cold as cA.

mT: Maritime Tropical air mass would be something like the air over the Gulf of Mexico. Occasionally during summer in the Northeast a mT air mass can take over and temperatures surge into the 90s with very high humidity levels.

cT: Continental Tropical is drier than mT, but it is still plenty warm and can originate over the desert southwest. This air mass can result in extended droughts if it lingers over one area for a long period of time.

cA: Continental Polar may hide behind an arctic front and dive southward across the Great Lakes in winter. This can bring blasts of cold air and snow when the air mass clashes with, for example, mP. It is often where the polar vortex is held.

mP: Maritime Polar can be found in areas like the North Atlantic and bring rain or snow along a back-door cold front.

We get weather when these air masses clash and create fronts.

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