Winter Weather Explained: Snow, Sleet & Freezing Rain

Winter storms are some of the hardest storms to forecast and some of the most disruptive. A difference of one or two degrees, sometimes thousands of feet above the ground, decides whether a storm brings a beautiful snowfall, a slushy mess, or an ice storm that knocks out power for a week. This guide explains what controls precipitation type, how to read the alerts, and what to watch for on the map.

Snow, sleet, and freezing rain: it's all about the layers

Most precipitation in the mid-latitudes, even in summer, starts as snow high in the cloud. What reaches the ground depends on the temperature of the layers it falls through on the way down:

These layers are often arranged geographically along a storm's path. In a typical winter storm moving across the eastern U.S., you might find rain to the south and east, then a band of freezing rain, then sleet, then snow to the north and west, sometimes within 50 miles. As warm air pushes in aloft during the storm, the bands shift, so a location can change from snow to sleet to freezing rain in a few hours. That's why winter forecasts so often say "a wintry mix," and why snow totals can bust when warm air arrives sooner or later than expected.

Why ice storms are so destructive

Freezing rain is the most damaging winter precipitation because ice is heavy and accumulates on everything: trees, power lines, cars, and roads. A rough guide to ice accumulation:

• A light glaze (under a tenth of an inch) makes roads, bridges, sidewalks, and steps treacherous.
• A quarter inch or more starts to break tree limbs and bring down power lines, especially with wind.
• Half an inch or more can cause widespread, long-lasting power outages and major tree damage.

Many of the costliest winter storms in U.S. history have been ice storms rather than snowstorms, with power out for days or weeks across entire regions.

Winter weather alerts

Criteria vary by region, because six inches of snow is routine in Buffalo and paralyzing in Atlanta. In general:

• Winter Storm Watch: significant snow, sleet, or ice is possible, usually issued one to three days ahead. Time to prepare.
• Winter Storm Warning: significant snow, sleet, or ice is expected. Travel may become very difficult or impossible.
• Winter Weather Advisory: winter weather is expected to cause significant inconvenience, such as slippery roads, but at a lower level than a warning.
• Ice Storm Warning: heavy freezing rain accumulation is expected, enough to cause damage to trees and power lines.
• Blizzard Warning: sustained winds or frequent gusts of 35 mph or more with blowing or falling snow reducing visibility to under a quarter mile for three hours or more. A blizzard is defined by wind and visibility, not by how much snow falls; a "ground blizzard" can happen with no new snow at all.
• Cold Weather Advisory and Extreme Cold Warning: dangerously cold temperatures or wind chills. (These replaced the older Wind Chill Advisory and Wind Chill Warning.)

On the RadarBug map, Winter Storm Watches are blue, Winter Weather Advisories are green, and every warning, including Winter Storm, Ice Storm, and Blizzard Warnings, is red.

Wind chill and frostbite

Wind chill describes how cold it feels on exposed skin, because wind strips away the thin layer of warm air next to your body. At an air temperature of 0 °F with a 15 mph wind, the wind chill is about −19 °F, and exposed skin can get frostbite in about 30 minutes. At wind chills around −35 °F, that time falls to roughly 10 minutes.

Wind chill doesn't make objects colder than the air temperature: a car radiator or pipes won't drop below the actual temperature. It describes how fast your body loses heat.

• Frostbite: skin becomes numb, white, or grayish-yellow, firm, or waxy, most often on fingers, toes, ears, nose, and cheeks. Warm the area gradually with body heat or warm (not hot) water, and don't rub it.
• Hypothermia: shivering, confusion, slurred speech, drowsiness, and fumbling hands. Core body temperature has dropped below 95 °F. It's a medical emergency; call 911 and warm the person's core first.

Winter weather on radar

Radar shows snow, but it reads it differently from rain, and it helps to know the quirks:

• Snow looks weaker than it is. Snowflakes reflect less radar energy than raindrops, so heavy snow often shows up as light-to-moderate green and blue echoes. Light green over a snowy area can mean a steady inch an hour.
• The bright band. Where snow is melting into rain, wet snowflakes look like giant raindrops to the radar. That produces a ring or band of exaggerated yellows and oranges around the radar site at the melting level, which can be mistaken for heavier precipitation. It's also a useful clue: rain is falling outside that band and snow beyond it, higher up.
• Overshooting. Far from the radar, the beam passes above shallow winter clouds entirely, so light snow and especially lake-effect snow can be missed or underestimated (see How to Read a Weather Radar).
• Lake-effect snow shows as narrow, intense bands streaming off the Great Lakes when very cold air crosses the warmer water. A single band can drop several inches an hour on one town while the next town over stays sunny.

Staying safe in winter weather

• Black ice: bridges and overpasses freeze first, because cold air reaches them from above and below. Be especially careful on them, in shaded spots, and on roads that look wet when the temperature is near freezing.
• Car kit: blankets, a phone charger, water and snacks, a flashlight, an ice scraper, a small shovel, and sand or kitty litter for traction. If you get stranded, stay with your car, run the engine about ten minutes each hour for heat, and keep the exhaust pipe clear of snow to prevent carbon monoxide buildup.
• Shoveling is strenuous exercise in cold air and triggers heart attacks every winter. Take breaks, push snow rather than lifting it, and don't shovel if you have heart problems without asking a doctor first.
• Heating safety: never use an oven, grill, or generator to heat your home. Keep space heaters three feet from anything that can burn, and use carbon monoxide detectors.
• Pipes: in hard freezes, especially in the South where pipes are often less insulated, let faucets drip and open cabinet doors under sinks on exterior walls.