Weather Fronts Explained for Sailors — Warm, Cold and Occluded

A depression typically brings a warm front then a cold front. Ahead of the warm front the cloud thickens, the barometer falls and the wind backs and freshens, then rain sets in and the wind veers. The warm sector is mild and murky with a steady barometer. The cold front brings squalls, heavy rain and a sharp veer, then the barometer rises and the air clears, with showers and good visibility.

Dark storm clouds approaching over a rocky coastline with breaking waves — A front arriving: the cloud thickens and lowers, and the wind and sea build. Photo: Marika Caruana, CC BY-SA 4.0.

Sequence as a depression passes north of you

A northern hemisphere depression with a warm front, a cold front and the warm sector between them, with winds blowing anticlockwise round the low — A typical Atlantic depression. The fronts pass from west to east.

Typical sequence in the northern hemisphere.
Stage	Barometer	Wind	Cloud and weather	Visibility
Ahead of warm front	Starts to fall	Backs, freshens	Cirrus, then cirrostratus	Good
Warm front close	Falling steadily	Backs further, increases	Altostratus, rain starting	Moderate
Warm front passes	Fall slows	Veers (e.g. SE to SW)	Nimbostratus, steady rain	Poor
Warm sector	About steady	Steady SW	Stratus, drizzle	Moderate or poor, fog possible
Cold front passes	Rises sharply	Veers sharply (SW to NW), squally	Cumulonimbus, heavy rain	Poor in rain
Behind the front	Rising	NW, gusty	Cumulus, showers	Very good

Occluded fronts

As a depression matures, the faster cold front catches the warm front and lifts the warm sector off the ground: an occlusion. You get a mixture of both fronts' weather, often a long band of rain, without the warm sector between.

Close-up of an aneroid barometer dial — An aneroid barometer. A steady fall warns that a depression and its fronts are coming. Photo: Ka23 13, CC BY 4.0.

Which way will the wind shift?

If the centre of the low passes north of you (the usual UK case), the wind veers. If it passes south of you, the wind backs. Buys Ballot's law helps: with your back to the wind in the northern hemisphere, the low is on your left.

Scrub through a frontal passage hour by hour in the Weather School simulator.

Related guides

Frequently asked questions

Does the wind veer or back at a cold front?

In the northern hemisphere it veers, often sharply, typically from south-west to west or north-west.

What is the warm sector?

The wedge of warm, moist air between the warm front and the cold front. It brings mild, cloudy weather with drizzle and often poor visibility.

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