Sea Science: by Jordanna Sheermohamad
Clouds provide some of the best observational information when scanning the sky for a hint of impending weather. The most obvious example of that is a cumulonimbus cloud. Given that its name comes from the Latin root “cumulus,” meaning “heap,” and “nimbus,” meaning “rain,” it appears exactly as one would imagine: a piled heap reaching high into the sky. This cloud is often the culprit when there is hail, heavy rain, lightning and possible tornados or waterspouts.
To the trained eye, some of the less obvious clouds can also provide useful information about the atmosphere, leaning towards a pretty dependable 24-hour forecast.
The invention and inclusion of satellites and computer models allowed weather forecasting to take giant leaps forward in expanding a dependable forecast beyond the one-day time frame. However these tools are not always at our disposal, and one has to wonder how our forefathers were able remain safe from weather hazards.
First scientifically named by pharmacist Luke Howard, clouds are primarily classified by their altitude, or height in the atmosphere, which also indicates whether their composition is of water droplets, ice crystals or a combination of the two. The atmosphere generally gets colder as you rise, so the higher the cloud, the more supercooled water droplets or ice crystals it may contain.
Furthermore, sunlight is transmitted through water and ice differently, so the way a cloud edge looks from the ground can also indicate the cloud’s composition. During the accumulation process, when water droplets and/or ice crystals gather, enough particles may form that sunlight is absorbed rather than transmitted through the cloud, which is often what occurs during a fog.
The ability of light to reflect or absorb through the cloud is what gives us the range of cloud colors, from white through grey to black. Some clouds appear dark, while others appear brighter in color. This could be, in addition to composition, a result of the clouds height in the atmosphere and the sun’s angle on the horizon. Cloud composition also can create halo-like affects around the sun and the moon as a result of the refraction of light off the ice crystals associated with high clouds.
Many other Latin root words can be found in cloud names, such as “alto,” meaning “high”; “cirro,” meaning “curl”; and “stratus,” meaning “layer.” Aggregating these basic words allows for cloud names that describe both their attitude and their appearance in the sky from a ground observation.
The moisture content of the different levels of the atmosphere also determine the possibility of the cloud formation, because without the moisture, there is no potential for cloud formation. Knowing the wind direction will then tell you where the moisture is coming from and where it’s headed to, therefore allowing a vague forecast to predict elevated chances of rain versus clear skies.
Modern observational tools such as satellites afford the opportunity to see real-time weather disturbances from thousands of miles away, increasing the chance for more accurate forecasts. But basic knowledge of cloud and sky observations is a pretty significant tool in the short term.
Jordanna Sheermohamed is president and lead meteorologist of Weather Forecast Solutions, a weather-forecasting firm (WeatherForecastSolutions.com). Comments are welcome below.