What Makes a Winter Storm?
First of all, temperatures need to be at or below freezing at either the cloud level, ground level, or both to produce snow or ice. Secondly, moisture is needed to form clouds and pecipitation. Finally, a lifting mechanism, such as a frontal boundary is needed to lift warm moist air over the colder air to form the clouds and precipitation.
Winter Storms with Strong Winds
Sometimes winter storms are accompanied by strong winds which create blizzard conditions with blinding wind-driven snow, severe drifting, and dangerous wind chill. These storms can knock down trees, utility poles, and power lines. Storms near the coast can cause coastal flooding and beach erosion.
Extreme cold often accompanies a winter storm or is left in its wake. Prolonged exposure to the cold can cause frostbite or hypothermia and is life threatening. Infants and the elderly are most susceptible. Extreme cold can cause pipes to burst and freeze. Long cold spells can cause rivers to freeze and cause ice jams which can lead to flooding.
Heavy accumulations of ice can bring down trees, electrical wires, telephone poles and lines, and communications towers. Communications and power can be disrupted for days while utility companies work to restore service. Even small accumulations of ice may cause hazards to motorists and pedestrians.
Heavy Snow Storms
Heavy snow can immobilize an entire region, strand motorists, stop the flow of supplies, and disrupt emergency services. Accumulations of snow can collapse buildings and knock down trees and power lines. Homes and farms may be isolated for days. The cost of snow removal, repairing damages, and the loss of business can have a drastic economic impact on our cities and towns.
A WINTER STORM WATCH is issued by the National Weather Service when a storm is still in its development stage, and conditions are favorable for the possibility of six inches of snow or more in a 12 hour period, significant or damaging accumulation of ice, or a combination of both. Watches are normally issued when these conditions are expected in future forecast periods and are not yet occurring.
A WINTER STORM WARNING is issued by the National Weather Service when a storm is expected to produce heavy snow of six inches or more in a 12 hour period, or a significant or damaging amount of ice within the first period of the forecast.
A SNOW ADVISORY is issued by the National Weather Service when snowfall amounts are expected to be below the warning criteria, however, pose a hazard to the public. Snow Advisories are issued for the first period of the forecast for forecasted average snowfall amounts of 3 to 5 inches.
A WINTER WEATHER ADVISORY is issued when a mixture of precipitation such as snow, sleet, and freezing rain is expected, but is expected to remain below the warning criteria. If only freezing rain or freezing drizzle is expected, then the product would be issued as a FREEZING RAIN ADVISORY.
A HEAVY SNOW WARNING is issued when heavy snowfall is expected (generally more than 6 inches in a 12 hour period), or 8 inches or more in a 24 hour period.
A BLIZZARD WARNING is issued when winds within the winter storm are expected to be 35 MPH or greater, and considerable snow or blowing snow is expected to reduce visibilities to 1/4 mile or less. These conditions should last more than 3 hours.
A WIND CHILL ADVISORY is issued when wind chill temperatures are expected to reach 20 to 30 degrees below zero.
A WIND CHILL WARNING is issued when wind chill temperatures are expected to reach 35 degrees below zero or lower.