One minute it's sunny — albeit frigid — outside and the next you can't even see two feet in front of you due to strong winds blowing snow every which way. And then, just as quickly as it arrived, the snow and wind are gone and there doesn't even seem to be any snow left behind.
Congratulations. You just experienced a snow squall!
Thar she squalls
The brevity and suddenness of snow squalls are what differentiates them from snow storms. Snowstorms are largely predictable events that can last for hours or even days, depending on conditions. Snow squalls, however, sweep in and out of an area quickly, lasting no longer than an hour in many cases, according to the National Weather Service (NWS).
Think of snow squalls as the wintertime equivalent of a summer thunderstorm or a squall on an ocean. All are localized events that can occur without much warning, and this is especially true for snow squalls, as their clouds are often difficult to spot on radar due to how close to the ground they are.
There are two types of snow squalls. The first is a lake-effect snow squall. This squall occurs when cold Arctic air sweeps over warmer open waters, like lakes. Clouds form between the two bodies, and the result is often a large amount of snow. These kinds of squalls are particularly common around the Great Lakes in the U.S. but can occur elsewhere. Certain conditions, including the differences in temperature and the air pressure, must be met before a lake-effect squall can form.
The second type is a frontal snow squall. These squalls may form a little bit in front of a cold front and don't often last particularly long as they move across a small area. Near-freezing temperatures on the surface are necessary along with enough moisture.
The video below, from ABC7NY, offers a time-lapse view of the snow squall that swept through some of New York on Wednesday. Despite it being a time-lapse, you do get a sense of just how quickly a snow squall can move and what effects it can have on a street. (It also shows that New Yorkers will brave just about anything to go to the newsstand.)
Safe squall driving
Given that snow squalls can kick up in a brief amount of time and drop a moderate amount of snow, they can be very dangerous for just about any traveler unlucky enough to be in it. It isn't so much the amount of snow — a snow squall rarely results in much accumulation. It's the combination of wind and snow that poses a danger. This mix of strong winds and snow can reduce visibility quickly, resulting in a whiteout.
Between the lack of visibility and how suddenly they arrive, snow squalls are responsible for multiple traffic incidents. On Wednesday, more than two dozen vehicles were involved in a "chain-reaction crash" in central Pennsylvania due to a snow squall, USA Today reports. Similar incidents happened in New York and New Jersey.
Despite their suddenness, snow squalls can be predicted, and NWS will often issue advisories about them. In the event of one, NWS encourages people to delay and avoid any sort of motor travel until the squall passes. If you're already driving, reduce your speed, turn on your headlights and hazard lights and avoid slamming on your brakes.