Equipment Outfitters

While storms generally affect large portions of an area and are usually forecast in advance, the powerboat skipper should be aware of two conditions that can affect his well-being and safety on a more local scale: fog and squalls. Since these weather conditions can be isolated and very localized, they may be unannounced on VHF weather forecasts. The best way to cope with them is to anticipate their arrival.

Fog

Fog is actually a low cloud caused by differences between the air temperature and land or water temperature. The most common fogs on the ocean are advection fogs, the result of warm air flowing over cooler water or land. These usually occur in the summer on northern coastal waters and on the Great Lakes. Steam fog appears more often on rivers and lakes when cool air sinks onto warm waters to produce rising columns of mist. Since fog depends on high humidity to form, keep an eye out for a combination of high humidity, warm wind and cool water. It’s a surefire combination, certain to produce fog.

Squalls

A thunder squall may be the forerunner of an approaching cold front or it may be an extremely local storm caused by unstable cool air above a hot land mass. Squalls are unpredictable, can bring winds of gale force and usually appear in hot, humid summer weather. They are marked by fast-moving black cumulus clouds, often with lightning and a line of rain underneath.

Clouds

Clouds are nature’s tell-tales, often providing clues to oncoming weather patterns. While there is considerably more to forecasting than simply watching clouds, boatmen have found that the appearance of distinctive cloud types suggest certain weather possibilities. But clouds change constantly, and the skipper who can read the patterns has a decided advantage in recognizing good and had weather news.

Types of Clouds:

Latin names describe basic cloud types: Cirrus means plumed and feathery wisps; Stratus means sheetlike; and Cumulus means heaped.

Cirrostratus, a high and hazy cloud that causes halos around the sun, usually warns of impending rain or snow.

Cirrocumulus, sometimes called a “mackerel sky,” indicates changeable weather.

Altostratus, darker, thicker and lower than cirrostratus, bring rain.

Altocumulus, the traditional cottonball puff clouds of summer, indicate fair weather. Darkening bases can mean light rain.

Cumulus, a fair weather sign, should be watched to make sure it doesn’t turn to sudden cumulonimbus and bring thunderstorms.

Nimbostratus is a low dark cloud that often precedes either a cold or warm front and brings steady rain.

If you have trouble distinguishing between one type of cloud and another, don’t despair. There are some basic rules for weather. Isolated, wispy or white clouds mean good weather. Dense, dark or tall clouds mean bad weather. And don’t forget the old seagoing adage: “Red sky in morning, sailors take warning. Red sky at night, sailors’ delight.” It can be surprisingly accurate in predicting what’s ahead.

Cirrus clouds are high and, moving from the northwest, indicate good weather. But if thick, low clouds appear at the same time, it may forecast rain or drizzle.

Cumulonimbus is the classic thunderhead, bringing wind and rain below.

Stratocumulus clouds in scattered tufts mean good weather but if they join into a solid base, they can bring rain.

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