Small Craft Advisory and Lake Wind Advisory explained

The National Weather Service has two alerts that matter most to lake boaters.

Small Craft Advisory

A Small Craft Advisory is issued for coastal waters and the Great Lakes when wind or waves are expected to be hazardous to small boats. The exact trigger varies by region, but it usually starts around 20 to 25 kt of sustained wind or frequent gusts, or when waves reach a set height. It ends below gale strength, at which point a Gale Warning takes over.

There is no legal definition of “small craft.” In practice the advisory means conditions are rough for any boat under about 33 ft and for inexperienced crews in larger boats.

Lake Wind Advisory

Inland lakes and reservoirs are not part of the marine forecast zones, so many inland NWS offices use a Lake Wind Advisory instead. Criteria are set locally. A typical office issues one when sustained wind of about 20 mph (17 kt) or more is expected for several hours, or when gusts are strong enough to make small-boat handling dangerous.

How to use them

• An advisory is a floor, not a ceiling. No advisory does not mean it is safe for your boat. A kayak can be in trouble at 12 kt.
• Check the timing. Many advisories run only for the afternoon, when wind peaks. An early start can get you home before it builds.
• Look at the direction. On a long lake, wind blowing down its length builds bigger waves than the same speed across it. See fetch.

Lakeglance shows the forecast wind and gusts for each lake hour by hour, so you can see whether conditions approach advisory levels even when no alert has been issued.