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Secrets of the St. Lawrence

Sailors take warning - White-outs

Sailors take warning (PDF; 2.41 MB)


- "Oh, no! Not fog! All our careful planning for nothing. The locals were right in saying we might well be completely blanketed in cloud this morning, after that lovely warm yesterday!"

In summer, on the St Lawrence, you may sometimes run into persistent fog so thick you could cut it with a knife.

Sailing in such conditions is very difficult, unless you have radar. A ship might well be lurking behind each fog bank.

Three types of fog

The worst type of fog, because it is the most persistent, is created by cold waters and warm, moist wind from the South. It will remain until it is blown off by a dry wind from another direction - Advection fog.

The fog that appears on rainy days with light winds may be just as dense. Once the rain stops, a Southwesterly or Westerly wind should follow and sweep it away - Frontal fog.

The third type of fog forms along the shore on a clear night but doesn't last long. The land breeze will carry it a short distance offshore. The morning sun will generally dissipate it - Radiation fog.

Because of their particularly cold waters, the Tadoussac, Pointedes- Monts, Havre-Saint-Pierre and Strait of Belle Isle areas are especially prone to fog.

White-outs - Thick fog obscures a barely visible boat.

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