2013–14 North American winter

The 2013–14 North American winter was one of the most significant for the United States, due in part to the breakdown of the polar vortex in November 2013, which allowed very cold air to travel down into the United States, leading to an extended period of very cold temperatures. The pattern continued mostly uninterrupted throughout the winter and numerous significant winter storms affected the Eastern United States, with the most notable one being a powerful winter storm that dumped ice and snow in the Southeastern United States and the Northeastern United States in mid-February. Most of the cold weather abated by the end of March, though a few winter storms did affect the Western United States towards the end of the winter.

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 2013 occurred on December 21, and ends at the March equinox, which in 2014 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.

Seasonal forecasts
On November 21, 2013, the National Oceanic and Atmospheric Administration's Climate Prediction Center issued its U.S. Winter Outlook. Sea surface temperatures had been near average since spring 2012, and forecasters expected these conditions to continue through winter 2013–14, with neither El Niño nor La Niña conditions expected to affect the season's climate. In the outlook, little rainfall was anticipated in the Southwestern United States, and the development of drought was expected in the Southeastern United States. Below-average levels of precipitation and below-average temperatures were expected in the Alaskan panhandle. Below-average temperatures were also favored in the Northern Plains, while above-average temperatures were favored in New England, the South-Central, Southeastern, and Southwestern United States, and western Alaska. The remainder of the country fell into the outlook's "equal chance" category, with an equal chance of above-average, below-average, and near-average temperatures and/or precipitation.

Seasonal summary
The 2013–14 winter season was characterized by prolonged periods of extremely cold temperatures across the eastern half of United States, as well as numerous high-impact winter storms, caused by a persistent pattern of strong mid-level ridging over the western half of the continent and mid-level troughiness over the eastern half – due in part to the weakening of the phenomenon known as the polar vortex. Many areas saw some of their coldest temperatures in decades or broke said records. Additionally, notable events and below-average temperatures continued well into March and past the official end of winter, with total damages as a result of thr winter weather and cold temperatures exceeding $5 billion (2014 USD). Significant winter weather events began early, with a major storm system affecting the Great Plains and Deep South in early October. Some of the mountainous areas received nearly 4 ft of snow along with gusty winds creating blizzard conditions, while a significant tornado outbreak occurred further southeast in the warm sector. Afterwards, little activity occurred until mid-November, where an arctic front brought the first snowfall and cold temperatures to much of the Northeastern United States. Shortly before and throughout the Thanksgiving holiday, a widespread and large winter storm caused numerous impacts in areas ranging from the Texas panhandle to the interior Northeastern U.S., with heavy snow totals and ice accumulations occurring in the state; the same storm would then bring mostly rain to the Northeast.

October storm complex
The first winter storm of the season, a significant system, was forecast by the National Weather Service, which issued a Blizzard Warning on October 3 preceding the storm. The storm occurred as an early season blizzard, and, according to the Weather Prediction Center, was an event of a magnitude unseen for the past decade. Many locations in Colorado, Nebraska, Montana, Wyoming,, and received near or over 10 in of snow. Some areas in South Dakota received nearly 4 ft of snow, with receiving 47 in. In many locations, there were high winds of over 50 mph, with some locations reporting winds of nearly hurricane force, being 74 mph.

Late November storm complex
On November 22, an upper-level trough located over northern California moved southward offshore the southern California coast, with its pressure deepening to a closed low-pressure area and also was cut off from the main upper-level jet. Mixed precipitation developed ahead of an occluded front that was attached to the low, causing impacts across the Western United States. The low-pressure area initially remained nearly stationary; however the low weakened and moved eastward across California and Arizona, while producing snow across southern portions of California and Nevada. The low then dissipated along a surface front, though an upper-level vortex produced mixed precipitation ahead of the vortex across areas from Arizona to Texas. The upper-level low-pressure area then ejected into the southern Great Plains on November 25, as the precipitation associated with the upper-level low began to organize into a linear structure. A low-pressure area then formed in the Gulf of Mexico on November 26 and began interacting with the upper-level low, as, at the same time, a phase began between the upper-level low and a northern stream system. As a result, a broad area of ascent developed across the Eastern United States. A southerly low-level jet across the Southeastern United States pulled moisture into the East Coast of the United States, and, with the combination of the phased upper-level low and the moisture drawn from the southerly low-level jet, broadened a precipitation shield northeastward. Snow fell across the Northeastern United States and southeastern Canada on November 27 and 28.

The winter storm was responsible for at least 14 deaths. The Weather Channel meteorologist Jonathan Erdman described the storm as "about as expansive a winter storm as it get," On November 24, 2013, 300 flights were cancelled at Dallas/Fort Worth International Airport. Flagstaff, Arizona recorded 11 inches of snow, and near the Four Corners as much as 4 feet fell. As much as a foot of snow fell in Colorado and Utah, and 13 people had died as of November 25. The serious winter storm that was expected did not materialize. As of November 27, 2013, 475 flights had been cancelled, with 3,600 delays, many in the New York City and Philadelphia areas. Snow turned to rain in Pittsburgh despite an ominous forecast, but 9 inches fell in Mercer County, Pennsylvania, and 4.5 inches in Buffalo. Atlanta had less than an inch of snow, but it was the third November snow since 1930. Morehead City, North Carolina had serious damage, and damage was also reported in Atlantic Beach, North Carolina, from an EF2 tornado.

December cold wave
On December 1, 2013, the weakening of the polar vortex led to the beginning of an abnormally cold trend in the Eastern and Central United States. On December 6, the continued deterioration of the polar vortex led to the jet stream pushing southward, bringing record cold temperatures across the Eastern U.S. During the cold wave, which extended from December 6–10, over 150 daily precipitation records and close to 100 daily snowfall records were broken across the northeastern, southeastern and south central United States. Jordan, Montana dipped down to -42 F on the morning of December 7, and Great Falls, Montana dipped down to -33 F, the coldest so early in the season. Eugene, Oregon had their second snowiest December day on record. Several cities had 3+ days of record lows. On December 4, the record low on December 4 in Denver of -13 F broke the record by 8 °F (4 °C). Burns, Oregon saw an all-time record low of -30 F. Numerous airline flights were canceled and there were reports of power outages. The cold blast led to a monthly average temperature of only 7.5 F in Rhinelander, Wisconsin, the 8th coldest December for the state on record.

Early December winter storm
On December 2, a Pacific storm system entered the Western United States, and it spread heavy rain and snow from the Pacific coast to the Rocky Mountains. As the storm continued to move east, high snow totals fell in its wake. Maximum reported snowfall totals in this area were found to have occurred in Idaho, Wyoming, and Montana, where 30 in or greater were reported. High winds were widespread as well, with multiple locations in the mountainous regions of the western US reporting winds of greater than 60 mph. As reported by the National Weather Service's Weather Prediction Center, the surface low reached its peak strength at approximately 6:00 UTC on December 3 while it was over western Wyoming, where a central pressure of 994 hPa was observed.

Pre-Christmas storm complex
On December 19, a strong cold front moved southward across much of the Great Plains. By daybreak on December 20, temperatures in many parts of Oklahoma had dropped to mostly between 10 and 30 °F. However, despite the freezing temperatures, the depth of the cold air was rather shallow, with a depth of generally no more than 1500 ft. As a result of the shallow depth of the front, once the front reached parts of the higher terrain in northwestern Arkansas, the front stalled, leaving areas just ahead of the front significantly colder than areas behind it. While temperatures in much of the Plains remained at or below freezing, an upper low was forming over the Southwestern United States. As the low pushed eastward and northeastward across parts of eastern New Mexico and West Texas, it interacted with moisture over the Southern Plains; there was an unusually high amount of moisture across the area for December, and the low drew much of it over the cold air-mass near the surface. With the moisture in place, light rain began to fall in some locations prior to sunset. The rain persisted and spread from southwest to northeast overnight, with moderate rain beginning to fall across much of Southwest, Central, and northeastern Oklahoma and Southeast Kansas. By late morning on December 21, much of the rain had ended in Southwest and Central Oklahoma, where many areas had received over 0.25 in of ice accumulation with some locations receiving over 0.50 in or even, in localized areas, 0.75 in of ice; isolated power outages occurred, and multiple trees and tree limbs were broken and/or pulled down by the weight of the ice. Heavy icing continued along the Interstate 44 corridor and parts of Osage County in Oklahoma; in these areas, there were reports of 0.50 - 0.75 in of ice, and in southeastern Oklahoma and extreme northwestern Arkansas, there were lesser reports of 0.25 - 0.50 in of ice. Additional ice totals occurred in Southeast Kansas, where there were isolated locations which received ice accumulations of as high as 0.75 in.

Early January blizzard
On January 3, Boston had a temperature of 2 °F with a -20 °F wind chill, and over 7 in of snow. Boxford, Massachusetts recorded 23.8 in. Fort Wayne, Indiana had a record low of -10 °F. In Michigan, over 11 in of snow fell outside Detroit and temperatures around the state were near or below 0 °F. New Jersey had over 10 in of snow, and schools and government offices closed. Over a dozen deaths were attributed to the cold wave, with dangerous roadway conditions and extreme cold cited as causes.

Early January winter storm
2014 began on an active note, with another major winter storm affecting much of the United States on January 6–7, days after the previous blizzard. Between 6 and 12 in of snow fell with this system across a wide area spreading from central Missouri across Illinois and Indiana to Lower Michigan. Snowfall totals of near 18 in were recorded across northern Indiana, and additional accumulations occurred downwind from the major Great Lakes. This storm was accompanied by some of the coldest temperatures to affect the Central and Eastern United States in 20 years. Upper flow which was meridional all the way up to the Arctic Circle provided a direct path for cold air advection to occur southward to the United States. The average temperature of the contiguous United States was 17.9 F, the coldest day since January 12–13, 1997 and the 40th-coldest day in the United States since 1900. During the event, wind chills dropped as low as the -60s °F (-50s °C) across the Northern High Plains. The event was short-lived, with the portion of the polar vortex that had traveled across the Great Lakes lifting northeastward into Quebec soon after.

January–March cold wave
Following the initial cold blast in early January, multiple periods of extended cold, some with record-low temperatures, continued throughout much of the remaining winter into early to late March. The NOAA's National Climatic Data Center found that since modern records began in 1895, the period from December 2013 through February 2014 was the 34th-coldest such period for the contiguous 48 states as a whole. They also found 91% of the Great Lakes were iced over, the second highest percentage on record. Ice on the Great Lakes did not fully melt until early June. That was the latest date of ice on the Great Lakes ever.

The average temperature for the contiguous U.S. during the winter season was 31.3 F, one degree below the 20th-century average, and the number of daily record-low temperatures outnumbered the number of record-high temperatures nationally in early 2014.

Late January blizzard
On January 19, a weak Alberta clipper exited out of Canada, and quickly moved through the Upper Midwest on January 20, dropping little to no accumulations of snowfall. As it moved eastward early on January 21, frontogenesis occurred, and precipitation expanded from Indiana to western Pennsylvania. Then, as it neared the coast, a new area of low pressure developed off the Outer Banks and began to move northwards, as snowfall expanded into parts of the Mid-Atlantic; consequently, by 15:00 UTC on January 21, the Weather Prediction Center (WPC) initiated storm summary bulletins for the developing winter storm. A heavy band of precipitation set up from the cities of Philadelphia to New York City as a result of rapid deepening, leading to high snowfall rates along this corridor and the heaviest accumulations of the event.

Near-blizzard conditions occurred up and down the Interstate 95 corridor, with blizzard warnings issued for southeastern New England. The system, which was not well-forecast in advance and was stronger then anticipated by many, also struck at or near rush hour, which created hazardous conditions and impacts from Washington D.C. to Boston, Massachusetts. States of emergencies were declared in the states of New Jersey, Maryland and more due to the blizzard, which also caused thousands of flights nationwide to be either cancelled or delayed. At least one death was confirmed due to the storm, in Maryland. In the wake of the storm, bitterly cold temperatures pushed into the Northeast once again, causing dangerously low wind-chills.

Late January southern winter storm
Early on January 27, a cold front crossed into the Gulf of Mexico, with temperatures ahead of the front in Texas and Louisiana in the 60s °F (10s °C) dropping to below freezing only one day later. As this occurred, a southern stream upper-level trough translated in an eastward direction across northern parts of Mexico. This also coincided with the backing of low-level winds along the western Gulf Coast. Relatively warm and humid air overrode the colder air near the surface, resulting in precipitation falling in Texas, Louisiana, and parts of the Southeastern U.S. as a mixture of rain, freezing rain, and snow. Late in the day, a broad northern stream upper-level trough containing a trough axis was located over the Central and Eastern United States, and the storm began to develop as this trough axis, initially reaching from the Upper Midwest to the northern Rocky Mountains, sharpened and moved in a southeastward direction during the following 24-hour period. This activity coincided with the movement of additional cold air at the surface. Many areas experiencing liquid precipitation falling at the surface saw rain switch over to freezing rain by 12:00 UTC January 28 as temperatures dropped. A mixture of frozen to partly frozen precipitation spread eastward over the following period into the early hours of January 29, impacting much of the Deep South. Widespread ice accumulations in excess of .25 in occurred as a result of the event. As the southern stream trough axis weakened while it moved eastward across the western Gulf of Mexico, a northern stream trough amplified as it headed toward the Southeastern U.S. Overrunning wintry precipitation affected the area as a weak surface low traveled along the front and crossed into the Atlantic.

Mid-February nor'easter
On February 11, a quick-moving area of low pressure moved across the Southeast, bringing rain and snow to areas like Atlanta, interacting with some of the cold air to the north of it. It then quickly moved offshore by roughly 3 p.m. This part of the storm was only the beginning of a crippling 2-day streak of winter nightmares across the South. Accumulations from this half of the winter storm ranged anywhere from 1–3 in of snow and a glaze of icing across the South.

Later on February 11, another area of low pressure formed on the extreme southern edge of the Gulf Coast, near the TX–LA border. Drawing moisture from the Gulf of Mexico, it was able to fire up a small area of showers and thunderstorms near the coastline. As it tracked eastward, it began to interact with the cold air above it, producing an area of ice and snow on its backside as it moved to the east. On February 12, the swath of ice exploded in size as the conditions for freezing rain began to come together. Areas from eastern Alabama, including Atlanta in Georgia to the Southeast coast and South Carolina were included in this swath of icy precipitation. Meanwhile, to the south, near the Gulf Coast, heavy showers and thunderstorms were consisted in a streak of rain stretching up to southern parts of Georgia. As the low moved east, it then dissipated as a new area of low pressure developed off the South Carolina coast late on February 12, and that began to strengthen as it tracked to the north, placing the Northeast in the fire zone for the winter storm.

Early on February 13, more snow began to develop on the northern side of the storm as the precipitation shield approached the New York metropolitan area in colder air. Heavy bands of snow set up as the system began its transition into a nor'easter, with some of these bands containing snowfall rates of up to 1–2 in per hour. At the same time, warmer air was beginning to funnel into the storm system, and as a result the rain/snow line slowly creeped up the state of New Jersey as the warm air began to further intrude into the winter storm. By 10 a.m, most of the precipitation had moved north of New York City, and began to reach into areas like Boston. Even though the area of low pressure, which had now deepened to 988 mbar late on February 13, was offshore of the East Coast, little to no precipitation was falling as a result of dry air to funnel its way into the storm. Most of the snow totals in these areas ranged anywhere from 6–24 in, as a result.

Early March winter storm
On February 28, an extratropical cyclone moved near California, intensifying as it did so. Showers and thunderstorms began spreading into California early on March 1 which is the atmospheric river with heavy snowfall in the mountains, torrential rainfall, triggering numerous flash floods, and even spawning two EF0 tornadoes in Arizona and California The storm weakened somewhat as it began to pass through the southwestern United States, but maintained its structure as it began to move towards the central part of the country.

At the same time, an Alberta clipper was moving through the Upper Midwest, dropping relatively light to moderate snow through the areas. The energy between the clipper system and the remains of the extratropical cyclone combined to produce energy for a long tracked winter storm. Late on March 2, snow and ice began to develop along a weak area of low pressure near Texas and Oklahoma. Numerous locations reported thunderstorms with sleet and freezing rain due to the intense upper-air dynamics and Arctic air at the surface. A small squall line began to set up ahead of the cold front. Snow and ice began to reach into the Mid-Atlantic near midnight, which eventually started to sag southwards, keeping most of the heaviest snow accumulations to the south of the Northeast. The system then moved off by evening on March 3. Snowfall accumulations ranged from 3–7 in from the winter storm. At least 16 fatalities were reported.

Late March bomb cyclone
Late on March 25, a winter storm emerged off the coast of the Southeastern United States and began to undergo explosive intensification, becoming a meteorological bomb by March 26. Powered by moisture coming from the Gulf of Mexico, the storm quickly became an unusually powerful nor'easter four times the size of, and reached a maximum low pressure of 954 mbar. The system produced powerful sustained winds up to 89 mph, and wind gusts up to 119 mph, with unofficial amounts reaching 129 mph. After making landfall on Nova Scotia, the system weakened to a 960 mbar nor'easter on March 27, before weakening further to a 975 mbar storm on March 28. On March 29, the system deteriorated into a weak winter storm over Greenland, where it would remain for the next few days while slowly dissipating.

Eastern United States
The NOAA's National Climatic Data Center found that since modern records began in 1895, the period from December 2013 through February 2014 was the 34th-coldest such period for the contiguous 48 states as a whole. They also found 91% of the Great Lakes were iced over, the second highest percentage on record. Ice on the Great Lakes did not fully melt until early June. That was the latest date of ice on the Great Lakes ever. The average temperature for the contiguous U.S. during the winter season was 31.3 F, one degree below the 20th-century average, and the number of daily record-low temperatures outnumbered the number of record-high temperatures nationally in early 2014. In addition, while December through February was the ninth driest on record for the contiguous 48 states dating to 1895, chiefly due to extremely dry conditions in the West and Southwest, yet Winter snow cover areal extent was the 10th-largest on record for same 48 states, dating to 1966. New York City, Philadelphia, and Chicago all had one of their ten snowiest winters, while Detroit had its snowiest winter on record.

The first week of March 2014 also saw remarkably low temperatures in many places, with 18 states setting all-time records for cold. Among them was Flint, Michigan, which reached -16 F March 3, and Rockford, Illinois at -11 F.

Western United States
In contrast, California had its warmest winter on record, being 4.4 °F (2.4 °C) above average, while the first two months of 2014 were the warmest on record in Fresno, Los Angeles, San Francisco, Las Vegas, Nevada, Phoenix and Tucson, Arizona.