Clouds Forecast Snow Day in Advance, Head of Blue Hill Observatory Finds

Humans may be raised to a par with tree-toads, crickets, and other animals that can foretell a storm without inspecting a barometer. This encouraging announcement came from the Blue Hill Meteorological Observatory, where C. F. Brooks, professor of Meteorological and director of the Observatory since 1931, and E. Monroe Harwood, Jr., research assistant, have been studying the indications given by clouds.

In short term forecasting of snowstorms, certain clouds foretell a day ahead and give rough indications of when the snowfall will begin, how heavy it will be, and how long it will last. The clouds which have been found most useful for weather predictions are feathery formations of snow crystals called "cirrus," and are ordinarily from four to six miles above the ground.

Before any snowstorm of six inches or more, the first cirrus clouds some either from between west-by-north and northwest, or from between west-by-south and south-west. Cirrus clouds from 10 degree to 19 degrees north of west, or from 11 degrees to 50 degrees south of west are almost a sure sign of a storm in about 24 hours, the scientists reported. These conclusions have been made from records kept over a period of 33 years.

If the high cirrus clouds are going faster than the winter average of 35 miles per hour, the storm is likely to be short and light. "This larger proportion for the lesser storms is to be expected," says Professor Brooks, "since fast air-currents usually go with fast-moving storms, which would not yield such a quantity of snow in their brief stay as the slow-moving ones would."

Altostratus, altocumulus, and secondary altocumulus clouds have also been found to indicate approaching storms, but only by a margin of from a few minutes to two hours. The altostratus cloud is a dense mass of falling snow, and by computing its height and rate of fall, the approximate time of its arrival at the ground can be told.