Heavy snow can immobilize a region and paralyze a city, stranding commuters, closing airports, stopping the flow of supplies, and disrupting emergency and medical services. The weight of snow can cause roofs to collapse and knock down trees and power lines. Homes and farms may be isolated for days and unprotected livestock may be lost. In the mountains, heavy snow can lead to avalanches. The cost of snow removal, repairing damages, and the loss of business can have severe economic impacts on cities and towns. See weather.gov for the latest forecast.
- Blizzard: Sustained winds or frequent gusts of 35 mph or more with snow and blowing snow frequently reducing visibility to less than a quarter mile for 3 hours or more.
- Blowing Snow: Wind-driven snow that reduces visibility. Blowing snow may be falling snow and/or snow on the ground picked up by the wind.
- Snow Squalls: Brief, intense snow showers accompanied by strong, gusty winds. Accumulation may be significant.
- Snow Showers: Snow falling at varying intensities for brief periods of time. Some accumulation is possible.
- Flurries: Light snow falling for short durations with little or no accumulation.
- Avalanche: A mass of tumbling snow. More than 80 percent of midwinter avalanches are triggered by a rapid accumulation of snow and 90 percent of those avalanches occur within 24 hours of snowfall. An avalanche may reach a mass of a million tons and travel at speeds up to 200 mph.
A Nor’easter is a storm along the East Coast of North America, so called because the winds over the coastal area are typically from the northeast. These storms may occur at any time of year but are most frequent and most violent between September and April. Some well known Nor’easters include the notorious Blizzard of 1888, the “Ash Wednesday” storm of March 1962, the New England Blizzard of February 1978, the March 1993 “Superstorm” and the recent Boston snowstorms of January and February 2015. Past Nor’easters have been responsible for billions of dollars in damage, severe economic, transportation and human disruption, and in some cases, disastrous coastal flooding. Damage from the worst storms can exceed a billion dollars.
Nor’easters usually develop in the latitudes between Georgia and New Jersey, within 100 miles east or west of the East Coast. These storms progress generally northeastward and typically attain maximum intensity near New England and the Maritime Provinces of Canada. They nearly always bring precipitation in the form of heavy rain or snow, as well as winds of gale force, rough seas, and, occasionally, coastal flooding to the affected regions. The heavily populated region between Washington D.C., Philadelphia, New York and Boston, the “I-95 Corridor,” is especially impacted by Nor’easters.
The U.S. East Coast provides an ideal breeding ground for Nor’easters. During winter, the polar jet stream transports cold Arctic air southward across the plains of Canada and the United States, then eastward toward the Atlantic Ocean where warm air from the Gulf of Mexico and the Atlantic tries to move northward. The warm waters of the Gulf Stream help keep the coastal waters relatively mild during the winter, which in turn helps warm the cold winter air over the water. This difference in temperature between the warm air over the water and cold Arctic air over the land is the fuel that feeds Nor’easters.
Weather forecasters at NWS local forecast offices around the country and at the National Centers for Environmental Prediction near Washington, D.C., monitor conditions conducive for Nor’easters, especially during the fall and winter. When they see conditions are favorable in the upcoming days, forecasters may issue winter storm, blizzard, high wind and coastal flood watches to alert the public that some of the worst effects of Nor’easters might be possible. If conditions are imminent, those watches are changed to warnings.
Follow weather.gov to get the latest forecasts and warnings. If a Nor’easter threatens your home town, take steps to prepare, such as having three days of food, water and other provisions in a disaster supplies kit. A Nor’easter could cut power and leave you in the dark. Also, sit down with your family and create an emergency communications plan so your loved ones know how to stay in touch if you are separated. Stay off the roads if advised by local authorities and never drive into flood waters. These simple actions will help you stay safe during a Nor’easter.
Heavy accumulations of ice can bring down trees and topple utility poles and communication towers. Ice can disrupt communications and power for days while utility companies repair extensive damage. Even small accumulations of ice can be extremely dangerous to motorists and pedestrians. Bridges and overpasses are particularly dangerous because they freeze before other surfaces.
Black Ice: Black ice is a deadly driving hazard defined as patchy ice on roadways or other transportation surfaces that cannot easily be seen. It is often clear (not white) with the black road surface visible underneath. It is most prevalent during the early morning hours, especially after snow melt on the roadways has a chance to refreeze over night when the temperature drops below freezing. Black ice can also form when roadways are slick from rain and temperatures drop below freezing overnight.
Ice Jams: Long cold spells can cause rivers and lakes to freeze. A rise in the water level or a thaw breaks the ice into large chunks which become jammed at manmade and natural obstructions. Ice jams can act as a dam, resulting in severe flooding.
Ice Recreation: Ice on lakes and streams can be deadly. Before fishing, skiing, snowmobiling or engaging in any other activities on ice, check with local officials, such as your State Department of Natural Resources, who monitor the body of water. If you see any of the following conditions, do NOT go out on the ice:
Cracks, holes or breaks in the ice Flowing water around the edges, just below the surface, or over the top of the ice Ice that appears to have thawed and refrozen
White or “snow” ice is only about half as strong as new, clear ice. Double these thickness guidelines when traveling on white ice. For more information on ice thickness and safety, visit mndnr.gov/icesafety
Frost: Frost describes the formation of thin ice crystals on the ground or other surfaces in the form of scales, needles, feathers, or fans. Frost develops under conditions similar to dew, except the temperatures of the Earth's surface and earthbound objects fall below 32°F. As with the term "freeze," this condition is primarily significant during the growing season. If a frost period is sufficiently severe to end the growing season or delay its beginning, it is commonly referred to as a "killing frost." Because frost is primarily an event that occurs as the result of radiational cooling, it frequently occurs with a thermometer level temperature in the mid-30s.
- For ice fishing, ice skating and walking, you need 4 inches or more of ice.
- For snowmobiles and ATVs, you need at least 5 inches.
- To drive a car or small pickup on ice you need at least 8 to 12 inches of ice.
- For medium-sized trucks, there must be at least 12 to 15 inches.
If you decide to venture out on the ice, remember the following guidelines:
Stay off the ice if it is less than 2 inches thick!
The most well-known blizzards are winter storms that produce several inches occurring with strong winds that cause blowing snow and whiteout conditions, but not all blizzards happen this way. In the Midwest, ground blizzards develop with little or no concurrent (or new) snowfall. One of the most infamous ground blizzards was the Children's Blizzard of 1888, which killed an estimated 235 people in the Great Plains. This ground blizzard was extremely dangerous because it was preceded by unseasonably warm air, which caused people to let their guard down. Many people ventured outside without proper winter clothing, but the relatively warm weather did not last long. Since then, there have been countless other ground blizzards, many of which were deadly.
The typical ground blizzard occurs when an Arctic cold front moves through the region, causing temperatures to drop and winds to increase quite rapidly, often reaching gusts of 50 to 60 mph. If there are several inches of deep fresh snow on the ground, this strong wind will quickly pick up the snow and create whiteout conditions. Another reason these blizzards are dangerous is the cold temperatures that follow behind the Arctic front. Anyone stranded in their vehicle or forced to walk outside is at risk of frostbite or hypothermia.
Snow squalls, often associated with strong cold fronts, are a key wintertime weather hazard. They move in and out quickly, and typically last less than an hour. The sudden white-out conditions combined with falling temperatures produce icy roads in just a few minutes. Squalls can occur where there is no large-scale winter storm in progress and might only produce minor accumulations. Snow squalls can cause localized extreme impacts to the traveling public and to commerce for brief periods of time. Unfortunately, there is a long history of deadly traffic accidents associated with snow squalls. Although snow accumulations are typically an inch or less, the added combination of gusty winds, falling temperatures and quick reductions in visibility can cause extremely dangerous conditions for motorists.
What is the difference between a snow squall and a snow storm?
The difference between a snow squall and a snowstorm is the duration of the event. Snow squalls are usually very short-lived (on the order of 30-60 minutes) and extremely intense. A snow storm could last for several hours or even days.
Snow Squall Warnings
Snow squall warnings are short-fused and focused on distinct areas (like tornado and severe thunderstorm warnings). These warnings provide critical, highly localized life-saving information. If a snow squall warning is issued for your area, avoid or delay motor travel until the squall passes through your location. Read the Impact-Based Snow Squall Warnings factsheet.