Cirrus Cloud - Use in Forecasting

Use in Forecasting

See also: Weather forecasting and Tropical cyclone track forecasting

Random, isolated cirrus do not have any particular significance. A large number of cirrus clouds can be a sign of an approaching frontal system or upper air disturbance. This signals a change in weather in the near future, which usually becomes stormier. If the cloud is a cirrus castellanus, there might be instability at the high altitude level. When the clouds deepen and spread, especially when they are of the cirrus radiatus variety or cirrus fibratus species, this usually indicates an approaching weather front. If it is a warm front, the cirrus clouds spread out into cirrostratus, which then thicken and lower into altocumulus and altostratus. The next set of clouds are the rain-bearing nimbostratus clouds. When cirrus clouds precede a cold front, it is because they are blown off the anvil, and the next to arrive are the cumulonimbus clouds. Kelvin-Helmholtz waves indicate extreme wind shear at high levels.

Within the tropics, 36 hours prior to the center passage of a tropical cyclone, a veil of white cirrus clouds approaches from the direction of the cyclone. In the mid to late 19th century, forecasters used these cirrus veils to predict the arrival of hurricanes. In the early 1870s, the president of Belen College (located in Havana, Cuba), Benito Vines, developed the first hurricane forecasting system, and he mainly used the motion of these clouds in formulating his predictions. He would observe the clouds hourly from 4:00 am to 10:00 pm. After accumulating enough information, Vines began accurately predicting the paths of hurricanes, and he eventually summarized his observations in his book, Apuntes Relativos a los Huracanes de las Antilles.