Weather Whys; Squalls

This is weather wise. As long as men have sailed to the sea, the squal has inspired respect and even fear in the hearts of those who encounter it. The strong winds have been known to toss ships about like toys in a vast bathtub and dangering the lives of those aboard. A squal is a sudden but very intense wind that lasts for several minutes, then fades away as abruptly as it arrived. The winds are often associated with the heavy thunderstorm activity which builds ahead of a cold front. In fact, those lines of rain and thunderstorms are called squal lines. That activity can occur over land or at sea, but when squal lines do strike land these days, they're more commonly known as gust fronts. They often produce a low, dark cloud known as a roll cloud that hovers at the leading edge of the thunderstorm, and in many ways that is the signature of the squal. The strong winds are the result of rain-cooled air that rushes down out of the cloud.

Squals are common in the plains and Ohio Valley and rarely inspire much comment unless accompanied by very severe weather. But one squal in turn of the century San Francisco was unusual in both its strength and duration. It hit suddenly on the afternoon of November 21, 1910. Eyewitnesses said that a profound quiet settled over the city. Then the thunder began accompanied by winds that shook brick buildings. The wind was estimated to have exceeded 60 miles per hour, but then, strangely, the squal died as quickly as it came. In many locations, it lasted less than a minute. And otherwise, our writer is Christine Harbour, our editor is Brian Walkie, and our executive producer is Karen Hope. Or otherwise, I'm Drew Barlow.