Four Major Air Masses Affecting North American Weather

1. Continental Polar (cP) – Cold, dry; from Canada/Alaska; clear skies.
2. Maritime Polar (mP) – Cool, moist; from N. Pacific; steady rain/snow.
3. Continental Tropical (cT) – Hot, dry; from SW US/Mexico deserts; clear, hot.
4. Maritime Tropical (mT) – Warm, moist; from Gulf/Caribbean/Atlantic; heavy rain, storms.

Collisions between these air masses create fronts and drive most weather changes.