6-7 March 2011 Significant multi-hazard winter storm


A cold front moved gradually southeastward across the region during the day on Sunday, March 6th, as a wave of low pressure moved northeastward along the boundary Sunday night into Monday, March 7th. To the south of the boundary, it was mild as the area was in the warm sector of the low pressure system. The storm tapped into both Atlantic and Gulf moisture, resulting in heavy rainfall of 1 1/2 to 4 inches across the central and southeastern Catskills, mid Hudson Valley, Taconics, Washington County, Berkshires, southern Vermont and Litchfield County Sunday, March 6th, into Monday, March 7th. The heavy rainfall, combined with runoff from snowmelt due to the mild temperatures, resulted in widespread flooding of rivers, streams, creeks, and roads. Ice jams occurred resulting in flooding on the East Canada Creek and Sacandaga River in east central New York and on the Rocky River and West Branch Deerfield River in southern Vermont.


Colder air was drawn into the area in the wake of the boundary, changing the ongoing rain to mixed precipitation, freezing rain and sleet, then to snow. The period of mixed precipitation only lasted a couple hours, except for across a portion of the Capital District where a prolonged period of mostly sleet occurred and across a portion of the Taconic where a prolonged period of freezing rain occurred. Once again, similar to the 25 February storm, it was a big forecast challenge determining where the mixed precipitation within the precipitation transition zone was going to be. There were conflicting model/ensemble data, with the GEFS showing run-to-run consistency, and the SREF shifting the precipitation transitions zone a little east within 12 hours of the precipitation onset, making for another exceptionally challenging forecast, similar to the 25 February storm.


Heavy snow accumulated across the western Adirondacks, Mohawk and Schoharie Valleys, the central and eastern Catskills, the Lake George Saratoga region, and across the Capital District. One to 2 feet of snow was reported across the southern Adirondacks and Mohawk Valley, 8 to 18 inches across the Lake George Saratoga region, Helderbergs, and Schoharie Valley, with 5 to 8 inches of snow and sleet across the Capital District on top of the quarter to about a half of an inch of ice accretion. Up an in inch of ice accumulated in portions of the central and southern Taconics particular in the Towns of Amenia, Northeast and Dover. Numerous power lines were downed, trees and power poles snapped resulting in power outages and numerous road closures in the area.


The snow came down heavy at times, with snowfall rates of 1 to 2 inches per hour. In addition, brisk northerly winds resulted in blowing and drifting of the snow during the morning hours. This combination of heavy snow, along with blowing and drifting of the snow made it difficult for snow plows to clear the roads. The heavy snow and sleet resulted in widespread power outages, school closures, traffic accidents and even a few roof collapses.



Above: GEFS 925 hPa and 850 hPa temperature forecasts. Note the tight temperature gradients through central and eastern NY and central and northern New England.




Above: GEFS 850 hPa winds (top row) and 925 hPa winds (bottom row). Note the separate wind maxima over the Carolinas in the right panels (initialized 12Z 06 March) represented by the 3-4 SD above normal contour, suggesting a second southern stream upper impulse approaching the northeastern U.S. that was not captured in earlier guidance.



Above: GEFS probability for 1.00 inches liquid equivalent precipitation in 24 hours. Note the more widespread and higher probabilities indicated in the near term guidance in the right panel (initialized 00Z 6 March). In fact the probabilities expanded inland.



Above: GEFS precipitation type forecasts, showing the west and northwest shift of the precipitation transitions zone and mixed precipitation in the nearer term guidance in the right panel (initialized 12Z 6 March).




Above: GFS 850 hPa temperatures and heights (top row) and 925 hPa temperatures and heights (bottom row). There was very little change in the position of the tight thermal gradient, but the heights were forecasted to be lower in the near term guidance (initialized 12Z 6 March) implying a stronger system tracking toward the northeastern U.S.



Above: SREF 850 hPa temperatures (left) and winds (center and right). Note the tight thermal gradient is a little west of where the gradient is in the GEFS. Also note that the SREF is showing the developing system in the Carolinas in the 09Z 6 March initialization, similar to the GEFS.




Above: NAM 850 hPa temperatures (top row) and 925 hPa temperatures (bottom row). Note the tight thermal gradient shifts a little east in the near term guidance (right panels initialized 12Z 6 March), implying the precipitation transition zone would be a little further east.



Above: SREF probability for 1.00 inch liquid equivalent precipitation in 24 hours. Note the westward expansion of the high probabilities, similar to the GEFS.



Above: SREF precipitation type. Note the probabilities for various precipitation types shifted a little eastward in the near term guidance (initialized 09Z 6 March).




Above: GEFS (top row) and SREF (bottom row) plume diagrams for Albany NY, Watertown NY, Binghamton NY and Burlington, VT. Note the trend in each loop for more snow, sleet and freezing rain as the storm gets nearer.



Above: Soundings from Albany, NY showing the elevated layer above freezing, indicating mixed precipitation.



Above: Loop of surface maps showing the movement of the frontal systems and high and low pressure centers.




Above: Pictures of ice accumulation in the mid Hudson Valley (courtesy Rick Bodin).





Above: Pictures of ice accumulation from Dutchess County in NY.



Above: Pictures of flooding in the mid Hudson Valley of NY (Courtesy of Rick Bodin).



Above: Flooding at Wappingers Creek near Clinton (left) and Horstman Farm near the SI plant (right).



Above: Ice jam forming near the Stockade in Schenectady.