A wintry mix is a combination of liquid and frozen precipitation, including snow, sleet, and freezing rain. This blend of weather conditions is dangerous because it introduces multiple hazards simultaneously, often shifting rapidly between precipitation types. Wintry mix signals a complex atmospheric event where temperatures hover around the freezing point, setting the stage for severe consequences affecting transportation, utilities, and personal safety.
Defining the Components of Wintry Mix
A wintry mix results from a layered temperature profile in the atmosphere. Snowflakes fall through different temperature layers before reaching the ground. The difference between the main components—sleet and freezing rain—depends on the thickness of the warm layer and the final cold layer near the surface.
Sleet, or ice pellets, occurs when a snowflake melts completely in a warm layer, then refreezes into a hard pellet as it falls through a deep, sub-freezing layer near the ground. These pellets bounce upon impact and create a coarse, slushy accumulation on roads and sidewalks.
Freezing rain is considered the most hazardous component. It happens when the final sub-freezing layer near the surface is too shallow for the melted droplet to freeze completely before impact. The liquid water, known as supercooled water, instantly freezes upon contact with any surface at or below 32 degrees Fahrenheit, creating a thick, clear glaze of ice.
Immediate Hazards on Roadways
The primary risk from a wintry mix is the immediate loss of traction for vehicles and pedestrians. Freezing rain forms a transparent layer on pavement, commonly called black ice, which offers virtually no grip. This nearly invisible glaze leads to a sudden loss of control for drivers.
Bridges, overpasses, and elevated roadways are particularly susceptible to icing because cold air circulates both above and below them, causing them to freeze faster than ground-level roads. Stopping distances increase dramatically, and attempting to brake or steer suddenly on black ice can cause a vehicle to skid uncontrollably.
Pedestrians face an equal threat, as the clear glaze makes sidewalks and driveways extremely slippery, leading to dangerous slips and falls. Even small accumulations of ice are enough to make travel hazardous.
Impacts on Utilities and Property
Ice accretion from freezing rain poses a physical threat to stationary infrastructure and property. As supercooled water freezes on contact, it coats power lines, tree branches, and communication towers, adding immense weight. Just a half-inch of ice accumulation can add up to 500 pounds of extra weight to utility lines and increase the strain on tree branches by up to 30 times.
This cumulative weight often causes tree limbs to snap and power lines to break, resulting in widespread and prolonged power outages. Ice accumulation can also damage structures, particularly roofs, where one inch of ice adds about 57 pounds of weight per square foot. This ice load increases the risk of structural damage or collapse.
Preparing for and Responding to Wintry Mix
Preparation for a wintry mix begins with monitoring weather forecasts closely for advisories indicating freezing precipitation. The most effective response is to avoid travel, as rapidly changing conditions make roads unpredictable.
Emergency Kit Supplies
It is advisable to have an emergency kit stocked with supplies for several days, including:
- Non-perishable food
- Water
- Flashlights
- Warm blankets
- Charged cell phones and battery packs
Charging cell phones and battery packs before the storm arrives helps maintain communication in case of a power outage.
Travel and Post-Storm Safety
If travel is necessary, drivers should ensure their fuel tank is full to prevent fuel line freezing and carry a vehicle emergency kit. After the storm, property owners should clear walkways carefully and remain vigilant for downed power lines, which should never be approached.