Query: Snowfall is increasing in the fall and winter in the Northern Hemisphere and North America with many records being set.

Relevant passages:
Snow <=SEP=> Snow pertains to frozen crystalline water throughout its life cycle , starting when it precipitates from clouds and accumulates on surfaces , then metamorphoses in place , and ultimately melts , slides or sublimates away . Snowstorms organize and develop by feeding on sources of atmospheric moisture and cold air . Snowflakes nucleate around particles in the atmosphere by attracting supercooled water droplets , which freeze in hexagonal-shaped crystals . Snowflakes take on a variety of shapes , basic among these are platelets , needles , columns and rime . As snow accumulates into a snowpack , it may blow into drifts . Over time , accumulated snow metamorphoses , by sintering , sublimation and freeze-thaw . Where the climate is cold enough for year-to-year accumulation , a glacier may form . Otherwise , snow typically melts seasonally , causing runoff into streams and rivers and recharging groundwater .   Major snow-prone areas include the polar regions , the upper half of the Northern Hemisphere and mountainous regions worldwide with sufficient moisture and cold temperatures . In the Southern Hemisphere , snow is confined primarily to mountainous areas , apart from Antarctica .   Snow affects such human activities as transportation : creating the need for keeping roadways , wings , and windows clear ; agriculture : providing water to crops and safeguarding livestock ; such sports as skiing , snowboarding , snowmachine travel ; and warfare : impairing target acquisition , degrading the performance of combatants and materiel , and impeding mobility . Snow affects ecosystems , as well , by providing an insulating layer during winter under which plants and animals are able to survive the cold .

2014–15 North American winter <=SEP=> The 2014 -- 15 North American winter refers to winter as it occurred across the continent from late 2014 through early 2015 . While there is no well-agreed-upon date used to indicate the start of winter in the Northern Hemisphere , there are two definitions of winter which may be used . Based on the astronomical definition , winter begins at the winter solstice , which in 2014 occurred on December 21 , and ends at the March equinox , which in 2015 occurred on March 20 . Based on the meteorological definition , the first day of winter is December 1 and the last day February 28 . Both definitions involve a period of approximately three months , with some variability .   While both the meteorological and astronomical definitions of winter involve the onset of winter occurring in December , many places in North America experienced their first wintry weather during mid November . A period of below-average temperatures affected much of the contiguous United States , and several records were broken . An early trace of snowfall was recorded in Arkansas . There were greater accumulations of snow across parts of Oklahoma as well . A quasi-permanent phenomenon referred to as the polar vortex may have been partly responsible for the cold weather . Temperatures in much of the United States dropped 15 to below average by November 19 following a southward `` dip '' of the polar vortex into the eastern two-thirds of the country . The effects of this dip were widespread , bringing about temperatures as low as 28 F in Pensacola , Florida . Following a significant snowstorm there , Buffalo , New York received several feet of snow from November 17 -- 21 . During the 2014 -- 15 winter season , Boston broke its all-time official seasonal 107.6 in snowfall record from the winter of 1995 -- 96 , with a total snowfall record of 108.6 in as of March 15 , 2015 .   Many records for snowfall and temperature were broken , many for the month of February , with every state east of the Mississippi River being colder than average , some for the entire winter . However , this meteorological winter was the 19th-warmest of the past 120 winters over the lower 48 states , largely due to persistent warm weather in the West .

Cold wave <=SEP=> A cold wave ( known in some regions as a cold snap ) is a weather phenomenon that is distinguished by a cooling of the air . Specifically , as used by the U.S. National Weather Service , a cold wave is a rapid fall in temperature within a 24-hour period requiring substantially increased protection to agriculture , industry , commerce , and social activities . The precise criterion for a cold wave is determined by the rate at which the temperature falls , and the minimum to which it falls . This minimum temperature is dependent on the geographical region and time of year .   In the United States , a cold spell is defined as the national average high temperature dropping below 20 F.