Boating when it’s nice out is fun; boating when the weather conditions aren’t perfect is challenging. Boaters who most easily adapt to the conditions usually have a knack for anticipating them. Anticipating and giving yourself some time to prepare for or avoid bad weather will be more intuitive if you become proficient at interpreting the changing cloud cover. Next time you head to your boat, take a good look at the cloud cover. Compare it to the weather forecast you’ve checked on TV, or on your smartphone. Compare what you’re seeing in real life to what the forecasters are telling you is on the way. Clouds indicate the kind of weather you’ll encounter when you’re on the water, but are also a visible sign of weather to come. A skilled boater should be able to identify cloud types, know what weather changes are associated with different types, and be in step with forecasts — or even a step ahead.
There are three basic groups of clouds based on structure and height, Cirrus clouds are high and feathery, stratus are the layer clouds which tend to be flat and uniform when covering most of the sky, and finally there are cumulus which are heaped, lumpy masses. Within those groups are the principal types: Cirrus, Cirrostratus, cirrocumulus—20,000 to 40,000 feet; altostratus, altocumulus — 8,000 to 20,000 feet; and stratus, stratocumulus, and nimbostratus below 8,000 feet. A further breakdown of cloud forms fall into 10 genera with many subtypes and combinations. For a more thorough description, visit the NOAA/NASA Cloud Chart (PDF file), or any edition of the International Cloud Atlas (PDF file). Or check out cloud types on Wikipedia.
Cloud types are significant only when you consider the timing of their development, structural changes, and particularly the sequence in which they occur. For instance, cirrus clouds are usually the first sign of an approaching storm, but to be a real indicator of approaching weather, they should increase in number and be followed by cirrostratus clouds.
If cirrostratus exist, an indicator of a storm would be for them to thicken and be followed by altostratus. Altostratus are followed by nimbostratus and precipitation that started with the altostratus continues. Storm conditions are present with both altostratus and nimbostratus.
The end of storm conditions is often signaled by breaks in the low clouds and clearing skies to the west. Since storms in the mid-latitudes generally move from west to east, a storm’s approach is indicated by clouds gathering to the west, and a storm’s passing by clearing in the western sky.
Cumulus clouds forming in the morning indicate moist conditions, and convection will likely continue during the day, resulting in more numerous and higher-building clouds by afternoon. Watch out for thunderstorms.
Altostratus clouds are the most reliable weather indicator. They almost always indicate a front approaching, and impending, continuous, all-day rain or snow, if they continue to thicken.
My tips for boaters interested in weather prediction are to combine your knowledge of local forecasts with cloud observations. Notice the wind direction of the clouds and their sequence. It will give you a leg up on being a better, more prepared boater.
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