Snow squalls are dramatic and sudden weather events, representing a brief but intense period of heavy snow and strong winds. They move quickly, creating localized whiteout conditions with little to no warning. The entire event is typically very short-lived, but the exact time a squall lasts can vary based on atmospheric conditions. Understanding their duration is key to recognizing their hazard potential.
Characteristics and Defining Criteria
A snow squall is essentially an intense snow shower, characterized by a rapid onset of heavy snowfall and accompanied by strong, gusty winds. The defining feature is the speed and intensity of the event, which often causes visibility to drop to a quarter mile or less in a matter of minutes, creating whiteout conditions. They are distinct from a blizzard, which is defined by sustained winds of 35 miles per hour or more and low visibility lasting for three hours or longer.
The mechanism behind a snow squall is typically a narrow band of convection, similar to a summer thunderstorm, triggered by a strong cold front passage. These systems often form along a fast-moving cold front, or in the case of lake-effect snow, where cold air moves over a relatively warmer body of water. The intense snowfall rate can exceed one to two inches per hour, though total accumulation is often minor because of the short duration.
Typical Duration and Influencing Factors
Snow squalls are generally very short-lived, with a typical duration lasting between 30 and 60 minutes at any single location. Some frontal squalls can pass over a specific point in less than 30 minutes. Several meteorological factors determine where the duration falls within this range.
The most significant factor influencing the duration is the speed at which the entire system is moving. A squall line or cold front advancing quickly, perhaps at 30 to 40 miles per hour, will pass over any given area much faster than a slower-moving band. The width of the precipitation band also plays a direct role, as a narrower band of intense snow will clear out more quickly than a wider one.
The atmospheric setup, specifically the source of moisture and instability, also affects the longevity of the squall. Frontal snow squalls rely on the sharp temperature contrast and lifting provided by a cold front. Lake-effect squalls, by contrast, can sometimes persist longer or repeat in waves because they are continually fueled by the open water of a lake.
Immediate Hazards and Safety During a Snow Squall
The most immediate hazard of a snow squall is the severe reduction in visibility, which can turn a clear highway into a complete whiteout in seconds. This abrupt loss of sight, combined with strong winds that create blowing snow, makes it nearly impossible for drivers to see the road or other vehicles. This often leads to high-speed, multi-vehicle collisions, especially where drivers cannot react quickly enough to the rapid deterioration of conditions.
The rapid temperature drop associated with the cold front can also cause a flash freeze, turning wet pavement or slush into a sheet of ice almost instantly. This makes stopping distances up to ten times longer than normal, compounding the danger of the poor visibility. Because of the short duration of the event, the most effective safety measure is to avoid or delay travel until the squall has passed.
If caught driving when a snow squall strikes, the immediate action is to slow down gradually and turn on low-beam headlights and hazard lights to increase visibility to others. It is safest to exit the road at the next opportunity and wait for the squall to pass, which should happen in under an hour. If pulling over is not possible, drivers should avoid slamming on the brakes, as this can cause a skid on the suddenly slick surface, increasing the risk of a chain reaction crash.