Small Craft Advisory, explained
When the National Weather Service posts a marine advisory or warning for your waters, it's telling you something specific. Here's what each one means, the conditions behind it, and how seriously to take it.
Small Craft Advisory (SCA)
A Small Craft Advisory is the most common marine headline you'll see, and the one most relevant to recreational boaters. On the Great Lakes it's typically issued for sustained winds (or frequent gusts) of about 22 to 33 knots, or for waves hazardous to small craft — often around 4 feet or more, depending on the local NWS office and the body of water. Some offices also issue SCAs for hazardous conditions like heavy freezing spray or strong currents.
Crucially, "small craft" has no official size cutoff. It's a judgment call: the advisory means conditions are dangerous for inexperienced boaters or less-capable boats. A seasoned skipper on a large, seaworthy boat may operate safely in an SCA; someone in a 16-foot runabout, a kayak, or a personal watercraft should treat it as "stay in." If you're asking whether you're experienced enough to ignore an SCA, you're not.
Special Marine Warning (SMW)
A Special Marine Warning is short-fuse and serious: it's issued for sudden, severe, usually brief conditions — most often thunderstorms producing winds of 34 knots or more, dangerous lightning, waterspouts, or hail. These come with fast-moving storm fronts and can hit with little warning. An SMW means get off the water or into shelter now. The wind can slam from calm to 40+ knots in minutes as the gust front arrives.
Gale, Storm and Hurricane-Force Warnings
| Warning | Sustained wind | Meaning |
|---|---|---|
| Gale Warning | 34–47 kt | Dangerous for all recreational boats — do not go out |
| Storm Warning | 48–63 kt | Extremely dangerous; even large vessels at serious risk |
| Hurricane-Force Wind Warning | 64 kt+ | Life-threatening; rare on the lakes but it happens (e.g. November storms) |
These are unambiguous: recreational boaters have no business on the water during a Gale Warning or worse. The Great Lakes' notorious November gales, which have sunk large freighters, live in this category.
Watch vs. Warning vs. Advisory
- Watch — conditions are possible; a Gale Watch means a gale may develop. Start planning to be off the water.
- Advisory — hazardous conditions are occurring or imminent but less severe (this is where the SCA sits). Caution strongly advised.
- Warning — dangerous conditions are occurring or imminent. Take action.
What to do when one is posted
- SCA: Small and inexperienced — stay in. Larger, experienced, well-found boat — go only with a clear plan, a reason, and a bail-out.
- SMW: Get to shelter immediately; do not try to outrun a storm across open water.
- Gale or worse: Do not launch. If you're already out, head in well before it arrives.
On shouldiboat.com, active marine warnings for a spot are shown at the top of its page and fold straight into the verdict: a Small Craft Advisory pushes the day to CAUTION, and a Gale, Storm or Special Marine Warning forces NO-GO no matter what the raw numbers say. The warning always wins.
Thresholds vary slightly by NWS office and water body and can change — this is a general explainer, not the official criteria. Always read the current NWS marine forecast and warnings for your area.