Clouds Over the Keys: A Primer

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Some Florida Keys residents and visitors perhaps first encountered the enchanting Florida Keys skyscape during a morning drive on the Overseas Highway. Others may have noticed the puffy, white clouds set against turquoise waters while peeking out of a window during an afternoon plane ride. Millions have enjoyed the mosaics of cloud and color that are Florida Keys sunsets. Many among you have wondered at a “Florida mountain,” a vast, turbulent, electrically charged mass known as a cumulonimbus cloud (a thunderstorm). These huge masses of liquid, vapor, and ice weigh millions of pounds and can grow nearly twice as high as Mount Everest. The unique terrain of the Florida Keys, coupled with intense subtropical sunshine, abundant moisture, and ubiquitous clear air, have yielded a bounty of cloud varieties which have enchanted generations of residents and visitors. Human beings have observed clouds for millennia. Indeed, clouds have fancied generations of painters, writers, and photographers, from the great Dutch landscape painters of the 17th Century, to poet Percy Bysshe Shelley who wrote The Cloud in 1820, to Florida photographer Clyde Butcher, famous for his panoramic black and white photographs of “Florida Mountains.” Clouds have stimulated the interest of scientists as well, including, of course, meteorologists! Clouds possess helpful clues concerning the properties and motions of the air within which they float, and thus the impending weather. Father Benito Viñes, the head of the meteorological observatory at Belen College in Havana, Cuba (1870–1893), studied the motions of clouds at different altitudes in the vicinity of hurricanes. Father Viñes made some of the earliest successful hurricane track predictions using cloud observations from a network of weather stations he set up across Cuba and portions of the Caribbean. Mr. Harry B. Boyer, a former official-in-charge of the U.S. Weather Bureau in Key West, wrote a paper in 1896 about hurricane structure based on Boyer’s observations of clouds in and around hurricanes near Key West. Even today, both professional and amateur meteorologists observe clouds routinely. For example, meteorologists at the Florida Keys National Weather Service take two detailed cloud observations each day, prior to launching weather balloons. In addition, clouds are observed from space via weather satellites. Some clouds even can be detected by Doppler radar. A cloud is defined as a visible aggregate of minute water droplets and/or ice particles in the atmosphere above the earth’s surface. Clouds develop as water vapor in the atmosphere condenses in rising currents of air aloft. Clouds of varying sizes, shapes, and colors are found at different altitudes. The British pharmacist, Luke Howard, created a classification system for clouds in 1802. This system has been incrementally improved upon by others in the two centuries since Howard came up with the three basic cloud types: cirrus, stratus, and cumulus. Howard’s classification system utilized Latin, as was common with scientific classification schemes of the time (think medicine or botany). The International Cloud Atlas is the reference on clouds. It was first published in 1896 as a training aid for meteorological observers, and it remains in print today. The descriptions contained within the Atlas are impressive both in their clarity and brevity: Cirrus “Detached clouds in the form of white, delicate filaments or white or mostly white patches or narrow bands. These clouds have a fibrous (hair-like appearance, or a silky sheen, or both).” Stratus “Generally grey cloud layer with a fairly uniform base, which may give drizzle, ice prisms or snow grains. When the sun is visible through the cloud, its outline is clearly discernible. Stratus does not produce halo phenomena except, possibly, at very low temperatures. Sometimes stratus appears in the form of ragged patches.” Cumulus “Detached clouds, generally dense and with sharp outlines, developing vertically in the form of rising mounds, domes, or towers, of which the bulging upper part often resembles a cauliflower. The sunlit parts of these clouds are mostly brilliant white; their base relatively dark and nearly horizontal. Sometimes cumulus is ragged.” Nearly all cloud types have been observed at one time or another over the Florida Keys, with the possible exception of the “lenticular” cloud, a high-altitude, lensshaped cloud that forms near mountains. Cumulus clouds occur with great regularity around the Keys thanks to the prevalence of warm, moist trade winds. Cumulus clouds often thicken vertically, transforming into “cumulus congestus,” the most common rain-shower cloud in the Keys. Occasionally, the cumulus congestus clouds grow into cumulonimbus, the thunderstorm cloud. The Atlas describes the cumulonimbus as a “heavy and dense cloud, with a considerable vertical extent, in the form of a mountain or huge towers. At least part of its upper portion is usually smooth, or fibrous or striated, and nearly always flattened; this part often spreads out in the shape of an anvil or vast plume. Under the base of this cloud which is often very dark, there are frequently low ragged clouds either merged with it or not, and precipitation sometimes in the form of virga.” The ocean adjoining the Florida Keys makes for a great cloud observatory. Many guides and other captains who spend most of their daylight hours on Florida Keys coastal waters likely have developed an appreciation for clouds, and maybe even some skill at using them to predict local weather. If you would like to learn more about Florida Keys clouds, visit our online cloud chart at http://www.srh.noaa.gov/key/?n=cloudchart. In the meantime, be weather-ready, and stay safe!