The December 15–17, 2020 nor'easter was a powerful nor'easter that hammered the Northeastern United States and produced widespread swaths of over of snow in much of the region from December 15–17, 2020, ending a 1,000+ day high-impact snowstorm drought in much of the Mid-Atlantic and coastal New England regions. The system developed out of a weak area of low-pressure that first developed over the Central United States producing some snowfall before moving eastward, and by December 16, a new, dominant area of low pressure began to develop along the Southeast coast. This low steadily deepened as it moved along and impacted the Mid-Atlantic coastline, prompting several winter-related advisories and warnings for much of the Northeast.
Multiple states that were expected to be impacted by the nor'easter, including New Jersey, Pennsylvania, and Virginia declared states of emergencies on December 15–16 in advance of the storm. New York and Boston declared a snow emergency the day of the storm as well. The nor'easter brought significant snowfall to metropolitan areas such as New York City, Philadelphia, and Washington, D.C., which eclipsed the entire snowfall total from the previous winter season, as well as Boston and Portland that saw over a foot of snow from the storm. Tens of thousands lost power during the storm, and the storm caused high wind gusts along the Jersey Shore, in addition to rough surf and even storm surge in coastal Massachusetts. At least 7 people have been confirmed killed as a result from the storm, and it is estimated to have caused over $125 million (2021 USD) in damages. The winter storm was rated Category 2 winter storm on the Regional Snowfall Index (RSI) scale, the first such storm for the Northeastern United States since a nor'easter in March 2018. The system was unofficially named Winter Storm Gail by The Weather Channel.
Meteorological history
The nor'easter originated from a disorganized winter storm in the Southern Plains of the United States, late on December 14. The winter storm became more widespread the next day, as a low-pressure system developed, and it began to spread snowfall in Oklahoma and Kansas. The system slowly moved eastward across the Southern Plains throughout the day on December 15. On the next day, the system reached the Eastern United States and began spreading snow, ice, and rain across the region. Early on December 17, the system then moved off the coast and developed strong winds and heavier precipitation, while the snowfall spread northward. As the low-pressure system began to strengthen, the rain-snow line pushed northward as well. The center of low pressure moved northeastward, parallel to the coast, before reaching its peak intensity at 12:00 UTC on December 17, while situated off the coast of New Jersey, with a minimum central pressure of . The nor'easter also developed an eye-like feature around this time. A combination of moisture from the tropical eastern Pacific and the Gulf of Mexico, very strong low- to mid-level warm air advection, and strong frontogenesis led to strong mesoscale banding, which resulted in heavy snowfall rates for several hours over parts of the Northeastern United States. The nor'easter developed a secondary low to the east later that day and gradually began to weaken, as it began moving away from the Northeastern U.S. A high-pressure system to the east of Atlantic Canada then steered the nor'easter away from the coast, after it passed south of New England, and the storm raced off eastward into the Atlantic. For the next couple of days, the nor'easter continued moving eastward, before the original low was absorbed into the developing secondary low to the east, on December 20. This new storm subsequently strengthened, and the system was named Greta by the Free University of Berlin on the same day.
Preparations
On December 14, Winter Storm Watches were placed into effect in a large swath from Virginia up through southern New England. Early the next day, watches located from Virginia to Western New Jersey were updated to Winter Storm Warnings. Simultaneously, Winter Weather Advisories were issued for the southern end of the storm. Later winter storm warnings were issued up through most of southern New England.
Mid-Atlantic states
On December 16, Governor Ralph Northam of Virginia declared a state of emergency.
300 snow plows were deployed to apply salt to many major roads and bridges due to expected snowfall.