What is the Hazard?
Extratropical cyclones, the most frequent type of storm in the Northeast, commonly cause rain, snow, and wind that combine to create severe winter weather storms that threaten New York City.
Temperature differences between the subtropics and the polar regions cause these frontal storm systems. The storm’s surface wind strength is primarily determined by surface pressure gradients created between the low pressure of the storm and surrounding area of high pressure.
Subgroups of extratropical cyclones include Nor’easters, winter storms, blizzards, and bomb storms (storms that intensify rapidly). In addition to storms, periods of extremely cold temperatures also present a risk to New York City throughout the winter.
Winter Weather Types
According to the National Climatic Data Center, New York City averages 26.7 inches of snowfall annually. Heavy snow, one of the primary winter hazards affecting New York City, is defined as either a six-inch-or-more accumulation of snowfall within 12 hours or less, or a eight -inch-or-more accumulation within a 24-hour period.
Several types of winter-weather conditions have the potential to affect New York City.
Winter Weather Definitions
|Snow||Precipitation in the form of ice crystals that form directly from water vapor freezing in the air|
|Sleet||Pellets of ice composed either of fully or partially frozen raindrops, or refrozen, partially melted snowflakes|
|Snow Showers||Snow falling at varying intensities for brief periods with accumulations of one inch or less|
|Blizzard||A combination of conditions prevailing for three hours or more:
|Snow Squalls||Intense, brief periods of moderate-to-heavy snowfall, accompanied by strong, gusty surface winds and possibly lightning, with risk of significant snow accumulation|
|Thundersnow||A snowstorm accompanied by thunder and lightning, which can occur over intense low pressure systems or other similar conditions of relatively strong instability and abundant moisture|
|Ice Storms||Freezing rain with potential accumulations of one-quarter of an inch or more|
|Bomb Cyclones||A low-pressure system that intensifies very rapidly with a fall in pressure of at least 24 millibars in 24 hours|
The hazards inflicted upon New York City by winter storms can be significant. Snow and ice hazards can compromise public safety and health and prevent the normal, day-to-day functioning of infrastructure and services. Snow accumulations that block roadways, public transit infrastructure, and sidewalks impede people and vehicles’ mobility and access to critical services and places of work. Snow accumulation is hazardous when it damages overhead power and telecommunications lines, and its weight causes trees and limbs to fall onto roofs and vehicles.
All types of wintry precipitation – snow, sleet, and freezing rain – contribute to hazardous travel conditions, although freezing rain is considered among the most treacherous, since it falls initially as rain, but freezes on contact with a surface, forming a glaze of ice.
Ice storms present potentially greater hazards for infrastructure in New York City than heavy snowfall, because ice storms develop quickly and have a greater chance of downing overhead power and telecommunications lines, leaving New Yorkers without power and communications. Ice accumulation is a hazard that makes walking and driving extremely dangerous, makes roads impassable, and even affects commuter train rail beds and switches in the mass transit system.
Winter storms are also especially hazardous for people who work outdoors, the homeless population of New York City, people with inadequate heat at home, children traveling to school, and seniors and other vulnerable populations.
An extreme cold event typically involves an extended period with temperatures at or below 32°F. These extended periods of subfreezing temperatures commonly occur in New York City between December and March. Although wind gusts and frigid temperatures often accompany winter storms, extremely cold temperatures can occur in New York City independent of these other types of winter weather events.
As the temperature drops and wind speed increases, heat drains from people’s bodies more rapidly than normal, creating a "wind-chill effect" that can make people feel even colder than the actual temperature.
This National Weather Service (NWS) wind-chill chart shows the temperature that a person feels on their exposed skin due to the combination of falling air temperature and increased wind speed. As shown, hazard of frostbite increases as people’s exposure to freezing temperatures and bitter wind increases.
Wind Chill Chart
When winter weather conditions warrant, the NWS issues wind-chill advisories or wind-chill warnings for the New York City region. NWS issues an advisory when wind-chill values are expected to fall to between 24°F and minus 15°F. NWS issues a wind-chill warning when values are expected to fall to minus 25°F or below.
Winter Weather Attributes/Characteristics
The severity of a winter storm depends on the temperature, its wind speed, the nature of associated precipitation, its rate of accumulation, and its timing. For example, a storm that occurs in early winter, when leaves are still on the trees, has the potential to cause more trees and power lines to topple as the extra snow and ice accumulate on the tree leaves or poles and weigh them down.
El Niño and La Niña are two parts of a natural climate cycle that affect winter weather -- the warm and cool phases of a recurring climate pattern across the tropical Pacific. The pattern can shift back and forth irregularly every two to seven years. Each phase can trigger predictable disruptions of temperature, precipitation, and winds that have the potential to intensify winter weather affecting New York City.
Historically, El Niño events are more likely to intensify warm-weather events in the Northeast, whereas La Niña events are more likely to affect colder weather events there. Predicting the potential impact of El Niño and La Niña is complicated due to the variability of other natural weather phenomenon that affect temperature and weather in the Northeast, such as the cycles of the North Atlantic Oscillation and Artic Oscillation.
Winter storms are classified by meteorological measurements and their societal impacts. The Northeast Snowfall Impact Scale (NESIS), a post-event classification, characterizes and ranks high-impact Northeast snowstorms – those with large areas of snowfall accumulations of 10 inches and more – on a scale of one to five.
The National Climatic Data Center developed the NESIS scale to indicate the impact that Northeast snowstorms might have upon the transportation systems and economy of the region and potentially the rest of the United States. The NESIS index is different from other meteorological indices, because it incorporates population data and meteorological measurements to assess a storm's overall societal impact.
NESIS scores are derived from the size of the area affected by the snowstorm, the amount of snow accumulation, and the number of people living in the path of the storm. Snowfall and population factors are combined into an equation that calculates a NESIS score, which is associated with a range of storms, classified from small to extreme. Storms generating heavy snowfall over large areas that include major metropolitan centers would generate raw scores with the highest values.
The raw score is then converted into one of the five NESIS categories -- Notable, Significant, Major, Crippling, and Extreme.
Since 1798, New York City has experienced 19 snowstorms with snowfall totaling 16 inches or more. When the data from these historic storms was analyzed via NESIS, only one storm was classified as extreme. Of the remaining storms on the list, five were classified as crippling, five as major, one as significant, and one as notable. Data from the remaining six historical snowstorms did not generate a sufficiently high value to qualify for a NESIS rank.
Winter storms are frequent occurrences in New York City. Based on historical frequency, New York City is likely to experience a winter storm with snow accumulation of 16 inches or more approximately once every nine years.
Historically, there are only a few reported instances of thundersnow in New York City. However, the most recent thundersnow event occurred here on March 7, 2018. Thundersnow events are less likely to occur in extremely cold winter months than in warm-weather months.
According to the New York City Panel on Climate Change, the city currently experiences an average of 72 days per year with temperatures at or below 32°F, which could decrease over the next several decades.
All areas of New York City are susceptible to winter storms. However, during these events, snowfall totals can vary widely across the city. For example, during the winter storm on December 26 and 27, 2010, snowfall ranged from 13 inches in Queens to 29 inches on Staten Island .
|Variations in Measured Snowfall Across NYC, December 26 - 27, 2010|
|Great Kills||Central Park||LaGuardia Airport||Kennedy Airport|
New York City generally experiences less severe cold than other places in the greater metropolitan area for two reasons -- the urban heat-island effect and its proximity to the ocean. Areas near shorelines often have slightly warmer temperatures during colder months than inland areas. However, even with warmer temperatures in coastal areas, strong winds near the shore can still create hazardous wind-chill conditions that affect residents.
Neighborhoods in New York City with relatively low population density, lots of trees and natural ground cover, and low amounts of heat-absorbing asphalt typically remain a few degrees cooler than other neighborhoods in summer months, but this warming effect is less pronounced during colder winter months.
New York City has experienced a range of major winter storms from 1798 through January 2018. For more information on winter weather events, use the Hazard History and Consequence Database, an interactive tool developed for this website.
Over the last 25 years, three winter snowstorms and blizzards were sufficiently damaging to earn presidential disaster declarations for New York City and the surrounding region:
|Top Five Snowstorms in New York City|
|Date||Inches of snow||NESIS rating|
|January 22 to 24, 2016||30.3 inches||4|
|February 11 to 12, 2006||27 inches||3|
|December 26 to 27, 1947||26 inches||2|
|March 12 to 14, 1888||21 inches||4|
|February 25 to 26, 2010||21 inches||3|
|Source: Weather 2000/Forecast Research|
- The Blizzard of 1996 in January 1996
- The President’s Day Snowstorm II in February 2003
- The Blizzard of 2010 in December 2010
Of the top five snowstorms recorded in New York City’s history, the Blizzard of 2016 broke the record for total snowfall accumulation in January 2016. As the top-five list shows, record snowfall accumulations in New York are not confined to recent years.
Although the Blizzard of 2016 is remembered for the hazards caused by over 30 inches of snowfall, a secondary hazard created by this winter weather event is worth noting. This January winter storm, also called Winter Storm Jonas, occurred during spring tide, which contributed to moderate storm surge and flooding in coastal areas throughout the region.
This graphic compares the cumulative height of the water during Hurricane Sandy with the impact of Winter Storm Jonas and other historic coastal storm events.
Historic High Water Events at NYC’s Battery vs. Winter Storm Jonas
Source: NOAA; UCAR, courtesy of NOAA Office of Response and Restoration
Although the surge associated with the winter storm is lowest among the storm events shown here, it demonstrates that the accumulation of water from coastal storm surge, sea level rise, and tide levels during a winter storm can flood coastal areas and simultaneously bury the city in massive, unprecedented amounts of snow.