A small craft advisory is a type of warning issued by the National Weather Service in the United States, most frequently in coastal areas. It is issued when winds have reached, or are expected to reach within 12 hours, a speed marginally less than that which is considered gale force.
Exact parameters for what wind speed triggers the advisory have been changed over time. Until the late 1960s, a range of 32 to 38 miles per hour (or 28 to 33 knots) was observed; then the lower limit was reduced to 23 miles per hour (20 knots). Today, however, it is more common in most places to use 25 to 38 miles per hour (22 to 33 knots) as the standard, thus neatly encompassing the combined ranges of forces 6 and 7 on the Beaufort scale.
Occasionally an informal lesser advisory, known as "small craft exercise caution", is issued for wind speeds that are somewhat lighter than those which call for a small craft advisory. Criteria for this vary in different localities; sometimes a range of 19 to 24 miles per hour (17 to 21 knots) is observed, or in some places 17 to 23 miles per hour (15 to 19 knots) may be used.
The insignia denoting a small craft advisory is one red, triangular flag (two such flags, one placed above the other, signify a gale warning).
The National Weather Service does not specifically identify what constitutes a "small craft", although the United States Coast Guard informally assigns the designation to boats with a total length of less than 33 feet (10 m).
Sometimes the term wind advisory is used in place of "small craft advisory" when winds of the same force are occurring at, or being forecast for, inland locations. A formal lake wind advisory is issued for winds just below this range, because unobstructed winds across the open waters of a lake will normally be faster than across land.
