Snow squalls can be beautiful and dangerous, but what exactly are they?
By Alex Sosnowski, AccuWeather senior meteorologist
You may have heard or seen weather forecasts calling for snow squalls, but what exactly are these and why is there reason for concern?
By definition, a squall is a sudden violent wind, often accompanied by rain, hail or snow. Another definition describes a squall as a short-lived commotion. Both are relevant.
Snow squalls are like wintertime thunderstorms
Snow squalls are the wintertime equivalent of summertime showers or thunderstorms. Snow squalls can occur anytime from mid-October to late-April.
They are often small in size, but they can bring intense snowfall, just as thunderstorms bring intense rainfall to a small area.
These wintertime showers form when the air near the ground is much warmer than the air aloft. First, towering clouds develop. Next, that moisture is released in the form of snow.
Sometimes snow squalls become aligned with the wind.
These snow squall streets may hit the same area multiple times within a few hours. In this situation, several inches of snow may pile up in part of a community, while a neighboring location less than a mile away may stay completely dry.
Occasionally, snow squalls may form into a solid line that extends 100 miles or more and advances to the east and south. Squalls of this nature are often associated with a press of Arctic air. After the initial covering of snow, a freeze-up may quickly follow.
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Snow squalls occur most often near and downwind the Great Lakes, but they can occur hundreds of miles away from a source of water, even in the middle of the nation. All that is needed is enough moisture in the low levels of the atmosphere to initiate cloud formation and very cold air aloft.
Gusty winds and plunging temperatures often accompany snow squalls. Downdrafts within the squall bring colder air from high in the atmosphere down to near the ground. A sunny midday with temperatures in the lower 40s F may quickly turn sour with a burst of heavy snow and temperatures near 32.
In the strongest snow squalls, thunder and lightning may occur.
Snow squalls and interstate highways: A dangerous combination
As fascinating as snow squalls are, they can be dangerous for motorists traveling on the highway.
For example, when on a highway such as Interstate 80 or 70, a squall can approach at a speed of 100 mph or more. In this case, traffic is moving west at 70 mph, while the squall is moving east at 30 mph. This gives motorists little time to react. Sudden braking may cause the vehicle to slide and begin a chain reaction accident involving dozens of vehicles.
Like thunderstorms, the squalls often move swiftly along at 25-50 mph. It can literally be sunny one minute, then a complete whiteout the next. In a matter of seconds, road conditions can transition from dry to wet to snow-covered.
"It is essential that motorists pay attention to the horizon and reduce their speed ahead of the approaching snow squall," according to AccuWeather Chief Meteorologist Elliot Abrams. "When AccuWeather forecasts call for flurries, snow showers or snow squalls motorists need to be alert for rapidly changing weather conditions."
Both flurries and snow squalls are technically snow showers. However, meteorologists try to distinguish the intensity by using flurries in the forecast when the intensity of the snow shower will be light.
Snow squalls are the heaviest of the snow showers. The use of snow showers covers a more broad range. Both may occur when snow showers are in the forecast, but most of the intensity of the snowfall will fall somewhere in between flurries and snow squalls.
When snow squalls are in the vicinity, a safe alternative may be to pull into a designated rest area or take the nearest exit off the highway and let the squall pass to avoid becoming a statistic in a chain-reaction accident. Most often, the snow will melt off in the wake of a squall as fast as it accumulated.
Pulling off to the shoulder of the road during a squall is not advised as oncoming traffic may not realize that your vehicle has stopped even if your emergency flashers are on.
Motorists may want to consider that on a day where snow squalls are in the forecast, taking a secondary highway, with a lower speed limit, instead of a major interstate might be a safer option or could save hours if an accident has occurred and traffic has been halted.
Often the same weather pattern that promotes snow squalls by day brings a clear sky and plummeting temperatures at night.
Even in the wake of a day with snow squalls, roads that were made wet by passing squalls may quickly freeze during the evening.
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