The National Weather Service has developed a multi-tier concept for forecasting hazardous weather which includes outlooks, watches, warnings and advisories.
An outlook is issued to indicate that a hazardous weather or hydrologic event may occur over the next several days.
A watch is issued whenever that risk has increased significantly but the occurrence, location or timing are still uncertain. Marine Watches for “GALE” “STORM”, and “HURRICANE FORCE” wind conditions, not related to tropical cyclones, can be highlighted in extended range forecasts beyond 24-hours for coastal inland waters, and offshore waters (does not include high seas forecasts).
A warning is issued when the hazardous condition or event is either occurring, imminent or likely (for the marine forecasts, within 24-hours).
A weather advisory is issued when a hazardous weather condition or event is occurring, imminent or likely but for less serious conditions than those that would warrant a warning.
A small craft advisory (SCA) is issued by the National Weather Service whenever conditions in the coastal waters or Great Lakes meet specific thresholds that are defined locally and can include wind, waves and sometimes ice. This is issued within 24-hours of expected small craft advisory conditions.
It is important to note that there is NO precise definition of “small craft” and the interpretation is left to the vessel operator. This might include considerations of the operator’s experience level, vessel type, overall size and sea worthiness.
Small Craft Advisories are normally issued for sustained winds or frequent gusts between 20 and 33 knots except that the minimum wind criteria may be as high as 25 knots and as ow as 18 knots, depending on local criteria. Minimum wave heights for a Small Craft Advisory also vary regionally from as little as 5 feet to as much as 10 feet, also depending on local criteria considerations.
Small Craft Advisories can also be issued for winds and waves below the local minimum criteria if hazardous sea conditions exist due to wave period, wave steepness, swell direction or ice. In addition, in or near bars (e.g. Grays and Columba River), advisories might also be issued due to the interaction of swell and currents in shallow water interacting with ebb tides.
Fred Pickhardt, chief meteorologist,
Ocean Weather Services
Lee S. Chesneau
Lee Chesneau’s Marine Weather