Late Season Nor'easter in the USA

  • Forecast snow amounts and visible satellite image showing the storm. Photo credit: MeteoGroup.

    Forecast surface pressure at 00:00 UTC on March 15 2017. Photo credit: MeteoGroup.

  • Late Season Nor'easter in the USA
    18.03.2017 17:49

    The northeastern states of the USA had a rude reminder of winter earlier this week, as a late season winter storm brought over a metre of snow to some areas from March 13-14. New York City itself received 20 cm of snow.

    Residents in the north-east of the USA could have been forgiven for thinking that winter was finally coming to an end, with several warm spells of weather earlier this month. But the weather has a funny habit of turning the seasons on their head.  A winter storm formed in the Gulf of Mexico on March 13, and underwent explosive cyclogenesis as it moved north-east, when its central pressure dropped by 31 hPa in less than 24 hours.  This type of storm is known as a “nor'easter”, because of the strong north-easterly winds that tend to blow ahead of the storm centre.

    Precipitation fell as snow for the northeastern states of the USA, as the storm drew in cold air from the north and north-east. New York State declared a state of emergency in preparation for the storm. Predicting snowfall totals from such winter storms is notoriously tricky, since the boundary between where rain, sleet and snow falls can be very narrow.

    The highest storm snowfall was at a ski resort in Vermont, with 147 cm recorded, but 30 – 90 cm accumulations piled up quite widely inland across the northeast US, although Boston only saw 17cm. Snow fell as far south as Wilmington, North Carolina. Wind gusts topped 70 mph in several coastal locations, and strong winds combined with the weight of the snow downed tree branches in Pennsylvania and New York, resulting in tens of thousands of people losing power.  The strong winds also resulted in coastal flooding in New Jersey, due to a combination of heavy rain draining out to sea, a coastal storm surge and high tides.

    Further south, warmer air aloft resulted in freezing rain falling in parts of Virginia and Maryland. The rain froze onto exposed surfaces, downing further trees and causing severe damage to the delicate cherry blossom in Washington D.C.

    Parts of the Midwest were also hit by heavy snowfall , as a separate storm moved across the Great Lakes region.  Snow accumulation for Chicago from this storm, and lake-effect snow as cold air moved across the warm water of Lake Michigan in the storm’s wake, approached 20 cm. This fell on the back of an unprecedented January and February, when no measurable snow was recorded in Chicago for the first time in 146 years.

    By: Richard Martin-Barton