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Reading the Sky Before the Squall Hits
💡 A rapidly falling barometer plus building dark clouds and shifting wind means shorten sail and seek shelter early — before the squall arrives, not after.
Weather forecasts (your pre-departure check from earlier cards) tell you what should happen. But conditions can shift faster than any forecast, so a skipper must also read the sky and sea in real time. The classic warning sign is a falling barometer: a rapid pressure drop (roughly more than 1–2 hPa per hour) signals an approaching low and strengthening wind. Pair that with the old adage — "red sky at morning, sailor's warning" — and darkening cumulonimbus (towering anvil-topped clouds) building to windward.
On the water, watch for a chain of small signs: a sudden wind shift or drop (an ominous calm before a squall), whitecaps forming where the sea was smooth, a line of dark, ruffled water advancing toward you, and a noticeable temperature drop. A halo around the sun or moon, and high wispy cirrus thickening into a lowering grey deck, often precede a front by several hours. Any one sign is weak evidence; several together is a decision.
The seamanship rule is simple: decide early, while you still have options. A squall that looks 20 minutes away can arrive in 10. Once you commit, reduce sail (reef) or throttle back before the wind hits, note your position and nearest sheltered harbour, and remember that a lee shore — coast downwind of you — becomes dangerous fast. It is always better to shorten sail or seek shelter too early than one gust too late.