Air Masses, Fronts and Frontal Weather
What the exam tests
This domain tests air-mass classification and the weather associated with fronts, including cloud sequences and post-frontal changes.
Core rules
- Air masses are classified by source region and track: tropical or polar, maritime or continental. Maritime air is moist; continental air is dry.
- A warm front has a shallow slope, a long cloud sequence (cirrus, cirrostratus, altostratus, nimbostratus), steady rain ahead of the surface front and a gradual wind veer.
- A cold front is steeper and narrower, with cumuliform cloud, showers, squalls and a sharp wind veer; pressure rises after passage and visibility often improves.
- An occluded front occurs when a cold front catches a warm front; it can produce complex cloud and precipitation.
Worked example
A station reports cirrus, then altostratus, then continuous rain, with pressure falling steadily and wind backing. The sequence and falling pressure point to an approaching warm front. After the front passes, expect the wind to veer, temperature to rise and rain to become patchy or cease. The reasoning is based on the order of cloud types and the pressure trend, not on a single observation.
Traps
Reversing the warm-front cloud sequence; expecting heavy showers from a warm front; confusing wind veer with backing; assuming all cold fronts produce the same weather.