Module 13 - Meteorology
Fronts
What you will learn
Recognise warm, cold, occluded and weakening fronts, anticipate a plausible sequence and test it against the current forecast and observations.
Fronts mark transitions between air masses. They support a change model, but their cloud, rain, wind and visibility sequences vary.
A warm front marks warmer air replacing colder air at the surface. A broad lowering cloud sequence, falling pressure and persistent precipitation are common, but the strength and timing depend on the front and air masses involved.
A cold front marks colder air replacing warmer air and may bring a sharper band of rain or showers, gusts and a wind change, followed by cooler air. Some cold fronts are weak or nearly dry. An occlusion forms when a cold front catches a warm front; it does not produce one universal temperature or wind outcome.
Front symbols show the direction of movement. Troughs can bring showery unstable weather without being air-mass boundaries. Use the chart, area forecast and observations together rather than treating one cloud or memorised sequence as proof.
| Feature | Common clues | Important limitation |
|---|---|---|
| Warm front | Broad lowering cloud, pressure fall, persistent precipitation | Timing and detail vary |
| Cold front | Sharper rain/showers, gusts, wind and temperature change | Can be weak or nearly dry |
| Occlusion | Mixed frontal weather around a mature low | No single warm- or cold-type outcome |
| Trough | Showers and unstable weather | Not necessarily an air-mass boundary |
Use the front to plan decision points
A cold front is forecast to reach the route near the final headland, with southwest 5 or 6 veering west, rain then showers and moderate visibility becoming good.
1. Build a hypothesis
Expect a possible rain band, gusts and wind change near the forecast passage.
2. Map consequences
Check the post-front westerly exposure, opposing tide and harbour entrance.
3. Set evidence
Watch pressure, cloud, temperature, visibility and wind for the expected change.
4. Retain an alternative
Use a nearer harbour or delay if the front and tide remove the margin.
Sense check: The wind may veer at this front, but the chart and forecast wording—not a universal rule—set the expected change.
Common mistake or limitation
- Treating a memorised warm- or cold-front sequence as guaranteed timing and severity.
- Assuming every cold front veers the wind by the same amount or immediately improves visibility.
- Using one cloud type as proof of a front instead of combining sequence, pressure, forecast and observations.
Recap
- Fronts organise a plausible change sequence, not a guaranteed script.
- Cold-front wind and visibility changes are not universal.
- Test the forecast model against pressure, cloud, wind, temperature and visibility.
Optional quick check
Section 5 of 13
Which is the best use of an approaching cold front on a passage plan?
Sources and factual review
Reviewed 20 August 2026 - Compass Revision editorial review.
Continue studying Meteorology
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