Module 13 - Meteorology
Fronts
Warm-front semicircles and cold-front triangles point in the direction the front is moving. At a warm front, warmer air advances over colder air; at a cold front, denser cold air replaces warmer air at the surface. An occlusion forms when a cold front catches a warm front and lifts the warm air away from the surface.
A typical Atlantic warm-front approach may bring progressively lowering cloud, pressure fall, persistent rain or drizzle and reduced visibility. A cold front may bring a sharper band of rain or showers, gusts, a wind change, pressure rise and cooler air behind. These are useful recognition patterns, not a guaranteed script: weak fronts may give little rain, active fronts can be severe, and visibility need not improve immediately.
Chart symbols also communicate uncertainty and development. Crosses through a front indicate weakening. A waving front can slow and prolong rain, while a trough can bring unstable showers without being an air-mass boundary. Use the latest area forecast and actual trend to decide when and where the route may be affected.
| Chart feature | Typical meaning | Planning limitation |
|---|---|---|
| Warm front | Warm air replacing colder air; often broad cloud and persistent precipitation | Timing, visibility and wind change vary with the system |
| Cold front | Cold air replacing warmer air; often a sharper band of showers or rain | A veer, squall or rapid clearance is common but not guaranteed |
| Occluded front | Cold front has overtaken the warm front, lifting warm air | Can retain widespread cloud and rain; do not assume a simple mixed sequence |
| Weakening front | Crosses mark diminishing air-mass contrast | Weakening does not mean no operational effect |
| Waving front | A wave slows or changes the frontal movement | Rain can last longer and timing can become less certain |
| Trough | Line of unstable air, often with showers | Not an air-mass boundary, but still relevant to the passage |
Optional quick check
Section 5 of 6
What is the safest way to use a cold-front symbol on a forecast chart?
Sources and factual review
Reviewed 19 August 2026 - Day Skipper Revision.
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