A small craft advisory is a warning that the day will be rough enough to be hazardous for smaller boats, and for most recreational skippers it is the flag that turns a planned trip into a judgement call. There is no single national threshold. Each National Weather Service forecast office sets its own for the waters it covers, broadly somewhere in the range of 20 to 33 knots of sustained wind, with sea criteria running anywhere from 4 to 10 feet depending on the area. On the US East Coast it is commonly 25 to 33 knots or seas of 5 to 7 feet; on the Great Lakes it can be 22 knots and 4 feet. Check what your own forecast office uses rather than carrying one number everywhere.
There is no single legal definition of a small craft and the advisory is not binding, so nobody stops you at the ramp. That is exactly why it deserves respect rather than a shrug. There is also no length that makes a boat a small craft. The Weather Service's position is that any vessel likely to be adversely affected by the stated conditions should treat itself as one, and that the boat's type, size and seaworthiness and the crew's experience all bear on it.
Whether it applies to you depends on more than length. An experienced crew on a heavy, well found hull may find an advisory day merely unpleasant, while the same water is dangerous for an open boat, a shorthanded crew, anyone prone to seasickness, or a skipper who has not seen that much wind before. Sea conditions, not wind speed alone, usually decide it.
If you do go, plan the exit. Advisory conditions make inlets and bar crossings the riskiest part of the day, and wind against an outgoing tide steepens waves sharply. Our guide explains who a small craft advisory really applies to and how to read one against your own boat.
