Winter Storm & Extreme Cold

Please visit the City's "Know Snow" website for more information regarding parking, snow removal, and information updates.

Terms

Winter Weather Advisory: Winter weather conditions are expected to cause significant inconveniences and may be hazardous. When caution is used, these situations should not be life threatening.

Winter Storm Watch: A winter storm is possible in your area. Tune in to NOAA Weather Radio, commercial radio, or television for more information.

Winter Storm Warning: A winter storm is occurring or will soon occur in your area.

Blizzard Warning: Sustained winds or frequent gusts to 35 miles per hour or greater and considerable amounts of falling or blowing snow (reducing visibility to less than a quarter mile) are expected to prevail for a period of three hours or longer.

NWS: National Weather Service.

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Winterize Your Home:

  • Extend the life of your fuel supply at home by insulating walls and attics.
  • Caulk and weather-strip your home doors and windows, install storm windows, and consider covering your windows with plastic.
  • Outfit fireplaces with a tight-sealing damper and keep it closed when not in use. If a fireplace is used infrequently, use a chimney block to elimiate heat loss.
  • Make sure kitchen and bathroom vent dampers close properly.
  • Additional Home Safety Tips

Winterize Your Car:

  • Battery and ignition system should be in top condition and battery terminals clean.
  • Ensure antifreeze levels are sufficient to avoid freezing.
  • Ensure the heater and defroster work properly.
  • Check and repair windshield wiper equipment; ensure proper washer fluid level.
  • Ensure the thermostat works properly.
  • Check lights and flashing hazard lights for serviceability.
  • Check for leaks and crimped pipes in the exhaust system; repair or replace as necessary. Carbon monoxide is deadly and usually gives no warning.
  • Check brakes for wear and fluid levels.
  • Check oil for level and weight. Heavier oils congeal more at low temperatures and do not lubricate as well.
  • Consider snow tires, snow tires with studs, or chains.
  • Replace fuel and air filters. Keep water out of the system by using additives and maintaining a full tank of gas.
  • Additional Driving Tips 

Guidelines for Action:

  • Listen to your radio, television, or NOAA Weather Radio for weather reports and emergency information.
  • Sign up for the City of Boston's Emergency Alert System Alert Boston.

 

Winter Weather Terms

Weather Term

Definition

Blizzard

A blizzard means that the following conditions are expected to prevail for a period of three hours or longer:

Sustained wind or frequent gusts to 35 miles an hour or greater; and

Considerable falling and/or blowing snow (i.e., reducing visibility frequently to less than ¼ mile)

Blizzard Warning

Issued for winter storms with sustained or frequent winds of 35 mph or higher with considerable falling and/or blowing snow that frequently reduces visibility to 1/4 of a mile or less. These conditions are expected to prevail for a min3imum of three hours.

Blowing Snow Advisory

Issued when wind-driven snow reduces surface visibility, possibly hampering traveling. Blowing snow may be falling snow or snow that has already accumulated but is picked up and blown by strong winds.

Drifting Snow

Drifting snow is an uneven distribution of snowfall/snow depth caused by strong surface winds. Drifting snow may occur during or after a snowfall. Drifting snow is usually associated with blowing snow.

Flurries

Snow flurries are an intermittent light snowfall of short duration (generally light snow showers) with no measurable accumulation (trace category).

Freeze

A freeze is when the surface air temperature is expected to be 32°F or below over a widespread area for a climatologically significant period of time. Use of the term is usually restricted to advective situations or to occasions when wind or other conditions prevent frost. "Killing" may be used during the growing season when the temperature is expected to be low enough for a sufficient duration to kill all but the hardiest herbaceous crops.

Freeze Warning

Issued during the growing season when surface temperatures are expected to drop below freezing over a large area for an extended period of time, regardless whether or not frost develops.

Freeze-up Date

In hydrologic terms, the date on which the water body was first observed to be completely frozen over.

Freezing Drizzle

A drizzle that falls as a liquid but freezes into glaze or rime upon contact with the cold ground or surface structures.

Freezing Drizzle Advisory

Issued when freezing rain or freezing drizzle is forecast but a significant accumulation is not expected. However, even small amounts of freezing rain or freezing drizzle may cause significant travel problems.

Freezing Fog

A suspension of numerous minute ice crystals in the air, or water droplets at temperatures below 0º Celsius, based at the Earth's surface, which reduces horizontal visibility; also called ice fog.

Freezing Level

The altitude at which the air temperature first drops below freezing.

Freezing Rain

Rain that falls as a liquid but freezes into glaze upon contact with the ground.

Freezing Rain Advisory

Issued when freezing rain or freezing drizzle is forecast, but a significant accumulation is not expected. However, even small amounts of freezing rain or freezing drizzle may cause significant travel problems.

Freezing Spray

An accumulation of freezing water droplets on a vessel caused by some appropriate combination of cold water, wind, cold air temperature, and vessel movement.

Freezing Spray Advisory

An advisory that may be issued within the Offshore Waters Forecast, the Coastal Waters Forecast, the Near shore Marine Forecast, and the Open Lake Forecast (GLF). An accumulation of freezing water droplets on a vessel at a rate of less than 2 centimeters (cm) per hour caused by some appropriate combination of cold water, wind, cold air temperature, and vessel movement.

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 falls 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.

Frost Advisory

Issued during the growing season when widespread frost formation is expected over an extensive area. Surface temperatures are usually in the mid-30s.

Glaze

Ice formed by freezing precipitation covering the ground or exposed objects.

Heavy Snow

This generally means:

Snowfall accumulating to 4" or more in depth in 12 hours or less

Snowfall accumulating to 6" or more in depth in 24 hours or less

In forecasts, snowfall amounts are expressed as a range of values, e.g., "8 to 12 inches." However, in heavy snow situations where there is considerable uncertainty concerning the range of values, more appropriate phrases are used, such as "up to 12 inches" or alternatively "8 inches or more".

Heavy Snow Warning

Issued by the National Weather Service when snowfall of 6 inches (15 cm) or more in 12 hours or 8 inches (20 cm) or more in 24 hours is imminent or occurring. These criteria are specific for the Midwest and may vary regionally.

Ice Jam

In hydrologic terms, a stationary accumulation that restricts or blocks stream flow.

Ice Storm

An ice storm is used to describe occasions when damaging accumulations of ice are expected during freezing rain situations. Significant accumulations of ice pull down trees and utility lines resulting in loss of power and communication. These accumulations of ice make walking and driving extremely dangerous. Significant ice accumulations are usually accumulations of ¼" or greater.

Ice Storm Warning

This product is issued by the National Weather Service when freezing rain produces a significant and possibly damaging accumulation of ice. The criteria for this warning varies from state to state, but typically will be issued any time more than 1/4" of ice is expected to accumulate in an area.

Nor'easter

A strong low-pressure system that affects the Mid-Atlantic and New England states. It can form over land or over the coastal waters. These winter weather event are notorious for producing heavy snow, rain, and tremendous waves that crash onto Atlantic beaches, often causing beach erosion and structural damage. Wind gusts associated with these storms can exceed hurricane force in intensity. A nor'easter gets its name from the continuously strong northeasterly winds blowing in from the ocean ahead of the storm and over the coastal areas.

Severe Icing

The rate of ice accumulation on an aircraft is such that de-icing/anti-icing equipment fails to reduce or control the hazard. Immediate diversion is necessary.

Sleet

Sleet is defined as pellets of ice composed of frozen or mostly frozen raindrops or refrozen partially melted snowflakes. These pellets of ice usually bounce after hitting the ground or other hard surfaces. Heavy sleet is a relatively rare event defined as an accumulation of ice pellets covering the ground to a depth of ½" or more.

Sleet Warning

Issued when accumulation of sleet in excess of 1/2" is expected; this is a relatively rare scenario. Usually issued as a winter storm warning for heavy sleet.

Snow

Precipitation in the form of ice crystals, mainly of intricately branched, hexagonal form and often agglomerated into snowflakes, formed directly from the freezing [deposition] of the water vapor in the air.

Snow Advisory

This product is issued by the National Weather Service when a low pressure system produces snow that may cause significant inconveniences but do not meet warning criteria and if caution is not exercised could lead to life threatening situations. The advisory criteria vary from area to area. If the forecaster feels that it is warranted, he or she can issued it for amounts less than the minimum criteria. For example, it may be issued for the first snow of the season or when snow has not fallen in a long while.

Snow Flurries

Snow flurries are an intermittent light snowfall of short duration (generally light snow showers) with no measurable accumulation (trace category).

Snow Shower

A snow shower is a short duration of moderate snowfall. Some accumulation is possible.

Snow Squall

A snow squall is an intense but limited duration period of moderate to heavy snowfall, accompanied by strong, gusty surface winds and possibly lightning (generally moderate to heavy snow showers). Snow accumulation may be significant.

Wind Chill

Reference to the wind chill factor; increased wind speeds accelerate heat loss from exposed skin and the wind chill is a measure of this effect. No specific rules exist for determining when wind chill becomes dangerous. As a general rule, the threshold for potentially dangerous wind chill conditions is about -20°F.

Wind Chill Advisory

The National Weather Service issues this product when the wind chill could be life threatening if action is not taken. The criteria for this warning vary from state to state.

Wind Chill Factor

Increased wind speeds accelerate heat loss from exposed skin. No specific rules exist for determining when wind chill becomes dangerous. As a general rule, the threshold for potentially dangerous wind chill conditions is about -20°F.

Wind Chill Warning

The National Weather Service issues this product when the wind chill is life threatening. The criteria for this warning vary from state to state.

Wind Gust

Rapid fluctuations in the wind speed with a variation of 10 knots or more between peaks and lulls. The speed of the gust will be the maximum instantaneous wind speed.

Wind Shear

The rate at which wind velocity changes from point to point in a given direction (such as vertically). The shear can be speed shear (where speed changes between the two points, but not direction), direction shear (where direction changes between the two points, but not speed) or a combination of the two.

Wind Speed

The rate at which air is moving horizontally past a given point. It may be a two-minute average speed (reported as wind speed) or an instantaneous speed (reported as a peak wind speed, wind gust, or squall).

Winter Storm Warning

This product is issued by the National Weather Service when a winter storm is producing or is forecast to produce heavy snow or significant ice accumulations. The criteria for this warning can vary from place to place.

Winter Storm Watch

This product is issued by the National Weather Service when there is a potential for heavy snow or significant ice accumulations, usually at least 24 to 36 hours in advance. The criteria for this watch can vary from place to place.

Winter Weather Advisory

This product is issued by the National Weather Service when a low pressure system produces a combination of winter weather (snow, freezing rain, sleet, etc.) that presents a hazard, but does not meet warning criteria.

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