Saturday-Sunday October 29-30, 2011
Historic Nor'easter: Damaging Early Season Snow Storm
The scope and magnitude of the October 29-30th, 2011 snow storm for the Northeast was both epic and historic with as much as 30" of snow reported in some higher elevations communities in Berkshire County, MA and an estimated 2.5 million utility customers throughout the Northeast without power due to downed trees on power lines from heavy snow weighting on trees still in full fall leaf. Snow of course is not unprecedented in the Northeast in October, with the destructive October 4, 1987 snow storm in the Capital Region coming to mind which dumped a record 6.5" of snow on Albany and over 12" in the higher elevations. That storm left the region devastated from fallen trees and power lines with power outages lasting several weeks in the most heavily impacted areas. The 1987 event, although significant for the local area, was far less wide reaching than this storm which brought damaging accumulations of snow to parts of twelve states from West Virginia and Virginia through Maine. As just one example of the enormous societal impacts of the storm, at one point it was reported that the electricity was knocked out to an estimated 86% of the state of Connecticut. The visible satellite picture below was taken on Sunday October 30 after the storm and clearly shows the extent of the snow pack left in the storm's wake.
Locally, the heaviest snow fell in Berkshire and Litchfield counties where the highest elevations were impacted by the most significant accumulations. Fortunately, in these higher elevation areas, most of the leaves had fallen from the trees, greatly mitigating a major power outage occurrence, although many outages were still reported. A general 15"-24" of snow fell in Berkshire and Litchfield counties (elevation dependent) with locally up to 30" reported in some of the highest elevations. Surrounding that, 10"-15" of snow piled up into the higher elevations of extreme southern Vermont and throughout the Taconic range in New York and across much of Dutchess County, with 6"-10" fairly widespread across the remainder of the mid Hudson valley and eastern Catskills. Another small snow maximum of 10"-15" occurred in the highest elevations of southeast Delaware and Greene counties. With the Nor'easter tracking a bit south of Cape Cod and the Islands and the system doing battle with a pool of dry air over northern New York and northern New England a sharp cut-off to the snow developed on the northern and western edge of the system. This resulted in a rapid and sharp decrease in snowfall amounts just north and west of the heavy snow zone. In the Capital Region a general 2"-4" of snow fell, with 1"-3" in the western Catskills north through the Mohawk valley, Lake George-Saratoga region through much of Rutland County, VT, with little more than a coating across most of the Adirondacks. Up to an estimated 20,000 National Grid customers locally lost power for generally less than a day in parts of Saratoga, Albany, Rensselaer, Columbia and eastern Greene counties where snow weighting did bring some trees and power lines down.
WeatherNet 6 Snowfall Distribution Map for the October 29-30, 2011 Nor'easter
WeatherNet 6 and National Weather Service Spotter Snowfall Reports
Storm Set Up:
Strong Nor'easters are not uncommon in October. What is uncommon, however, is the availability of a large chunk of air cold enough to support snow. In this case the cold air had been in place over a period of a couple of days (supporting a snow event on the 27th) and extended far enough south so that snow fell in the major cities of Washington, Baltimore, Philadelphia, New York, Hartford, and Boston. Surface temperatures during the storm, however, did generally remaine at or above freezing creating heavy wet and sticky snow. Air temperatures aloft, however, at roughly the 5000 foot level dropped down to -6° to -8° C, which represents an anomalously cold air mass for the time of the year. The storm itself, due to the rapid vertical motions in the atmosphere it created coupled with the cooling processes of snow melting as it fell through the atmospheric column further cooled the air to a point where it could support snow through the duration of the storm, with only a brief mix with rain reported in the lowest elevations in the Hudson valley at the onset.
The storm bombed, meaning its central pressure dropped dramatically over a short period of time. And it did this while it was tracking south of Long Island Saturday afternoon and into the night which allowed it to produce a zone of exceptionally heavy snow which impacted portions of Pennsylvania, southeast New York, southern Vermont, Massachusetts, Connecticut, New Hampshire and Maine. With the storm track a tad off shore, the northern and western edge of the heaviest snow zone stopped just short of the Albany area. However, the higher elevations of southern Bennington County, VT, the Taconic range in New York, and much of north central and eastern Dutchess County, and all of Berkshire, and Litchfield counties were in the zone most favorable for heavy snow. In that zone through the mid Hudson valley, to Berkshire an Litchfield counties significant small scale banding developed due to the storm's rapid intensification. Snowfall rates of 2"-4" per hour occurred for many hours leading to snowfall accumulations of two feet or more in the higher elevations of especially Berkshire County. Amounts were lower In valley locations despite the heavy banding and the fact that a lot of the snow fell at night as temperatures remained at or above freezing through the duration which promoted considerable melting on the way down. In fact in the Capital Region, where snowfall rates were generally much lighter, road conditions for the most part remained wet even after dark, never deteriorating to a slippery snow packed condition as roads did in the heavier snow zones south and east of the city.