- Originates over land in high-latitude regions.

- Cold and dry air mass.

2. Maritime Polar (mP):

- Originates over oceans in high-latitude regions.

- Cool and moist air mass.

3. Continental Tropical (cT):

- Originates over land in low-latitude regions.

- Warm and dry air mass.

4. Maritime Tropical (mT):

- Originates over oceans in low-latitude regions.

- Warm and moist air mass.

5. Arctic (A):

- Originates over the Arctic Ocean.

- Extremely cold and dry air mass.