Saturday, September 8, 2012
Severe Weather Outbreak

An outbreak of severe thunderstorms occurred between 2pm and 6:30pm across eastern New and western New England on Saturday September 8. A moderate risk for severe thunderstorms had been outlooked by the Storm Prediction Center for the region on the 7th with that forecast continued through the 8th for the anticipation of a widespread and significant damaging wind event associated with a strongly forced squall line and for the potential of discrete supercells in advance of the line creating an isolated tornado threat. A tornado watch was issued for the region at 1pm on the 8th and continued through 6:15 pm in New York and through 7pm in western New England. There were 42 official reports of damaging wind in the twenty one county CBS 6 coverage area, no tornadoes, and no hail.

Set Up:
Strong dynamics (atmospheric elements in the mid and upper levels such as jet stream disturbances and wind) were in place across the region as a potent upper air disturbance broke off from a developing long wave trough and surged east across New York and New England through the afternoon. This disturbance enhanced the mid and upper level wind fields in the atmosphere to strong levels and also caused a strong surface low pressure system to form along an advancing powerful cold front. The surface storm tracked up the St. Lawrence valley through the early afternoon and, coupled with a strong high pressure system off shore, caused a strong south to southeast surface wind all day with gusts from 30-35 mph common. Wind with height turned in a clockwise fashion with height in the atmosphere and strengthened to 45-50 mph from 5, 000 to 10,000 feet (very low in the atmosphere for winds this strong.) Strong wind shear (wind increasing in speed with height as well as turning with height) is a highly favorable parameter for severe weather production if other mechanisms for creating and sustaining thunderstorms are in place. Mechanisms such as the region being in the favorable right rear quadrant of a strong upper level jet (200 to 300 mb level in the atmosphere), with moderately diffluent flow aloft. These parameters cause lift and allow thunderstorm updrafts to develop. The region was also in a warm and very humid air mass with temperatures climbing into the lower 80s in the Hudson valley with dewpoints generally ranging from 65°-70°, ingredients which increase the overall instability.

So, all the big parameters were coming into place for a large severe event. likely marked by some discrete thunderstorms running in advance of a strongly dynamically forced squall line immediately along the leading edge of the cold front. However, there was one exception, one missing ingredient which in the end was the reason why the event was not more widespread and damaging than it was. The missing ingredient was a lack of overall instability with convective available potential energy values (CAPE) running from 500 to a maximum in the Hudson valley of 1000 j/kg. Despite very warm and humid surface conditions, temperatures aloft were not particularly cold. The colder the air aloft the more instability and thus taller stronger updrafts. Also, lapse rates were meager, meaning the temperature drop with height was nominal, another indicator of the lack of significant cold air aloft. So, the big forecast challenge for this event was how much would the strong dynamics in the atmosphere compensate for the fairly weak and meager instability.

In the end, the weak instability prevented much of any severe thunderstorm development from occurring in advance of the main squall line. This was a positive for the region as any discrete thunderstorms would have spun like tops and likely produced tornadoes. This scenario in fact did play out over and near New York City during the morning as discrete cells developed in a more unstable and strongly sheared environment and went on to produce several tornadoes. Instead, locally from the late morning through the early afternoon, low topped showers developed in Dutchess and Columbia counties quickly spreading north through eastern Rensselaer, Berkshire, and Bennington counties before moving out of the region early in the afternoon. Had greater instability been in place, these showers would likely have grown into damaging thunderstorms.

The squall line itself did materialize as expected and went on to produce pockets of damaging wind as it advanced. Storm tops, however, were shallow, generally 20,000 feet on average or lower at times. In fact through much of the squall line's existence very little lightning occurred due to the shallow tops which meant there was limited mixing of rain drops and ice crystals which is necessary to cause charge separation and cloud electrification. Storm tops, however, grew a bit to near 30,000' on average late in the afternoon, especially in the mid Hudson valley where instability was a little higher. These taller storms caused a marked increase in lightning in this region. Storms to 30,000' also developed in the squall line across southeast Hamilton, northern Saratoga, Warren, northern Washington, and Rutland counties where frequent lightning also occurred. These taller storm segments in the line also produced pockets of damaging wind. No hail occurred, likely due to the shallow nature of the t'storms in the squall line.

The squall line was narrow and generally moved through any one location quite quickly with anywhere from a half and hour to an hour of trailing strata form rain behind it. Temperature drops of approximately twenty degrees occurred with the line's passage with decent shelf clouds noted along its leading edge. The following three Instant Doppler 6 images show the progress of the classic squall line as it moved into and through the region.

Instant Doppler 6 Radar Images

3:08 pm September 8, 2012

Instant Doppler 6, 3:08pm 9/8/2012

3:43 pm September 8, 2012

Instant Doppler 6, 3:43pm 9/8/2012 

4:43 pm September 8, 2012

Instant Doppler 6, 4:43pm 9/8/2012  

STORM REPORTS September 8, 2012


Note: These are the reports that National Weather Service Offices use to verify warnings that are issued and are not meant as a comprehensive list of all the storm damage which may have occurred

Town County Storm Report Time
Ilion Herkimer Wind damage, tree reported down on North Street 2:10pm
Dolgeville Herkimer Wind damage, tree blown down on wires 2:12pm
Little Falls Herkimer Wind damage, trees blown down 2:30pm
Schuyler Lake Otsego Wind damage, metal roofing blown off a house, trees down 2:38pm
Oneonta Otsego Estimated 60 mph wind gust 2:45pm
St. Johnsville Montgomery Wind damage, trees blown down 2:48pm
Canajoharie Montgomery Wind damage, trees blown down 2:57pm
Indian Lake Hamilton Wind damage, trees and wires down 3:02pm
Near Treadwell Delaware Wind damage, trees down, blocking a roadway 3:05pm
Gloversville Fulton Wind damage, numerous trees reported down 3:16pm
1 Mile No. of Fonda Montgomery Wind damage, trees blown down 3:20pm
Mayfield Fulton Wind damage, numerous trees blown down 3:21pm
Delhi Delaware Wind damage, trees down throughout the town 3:25pm
Downsville Delaware Wind damage, trees down 3:25pm
Thurman Warren Wind damage, numerous trees and wires reported down 3:30pm
Edinburg Saratoga Wind damage, trees blown down 3:35pm
Richmondville Schoharie Wind damage, trees down on wires 3:35pm
Cleverdale Warren Wind damage, trees and wires down blocking a road 4:00pm
Queensbury Warren Estimated 60 mph wind gust 4:00pm
Glenville Schenectady Wind damage, trees blown down 4:03pm
Schenectady Schenectady Wind damage, trees blown down 4:07pm
Schoharie Schoharie Wind damage, trees and wires blown down 4:10pm
Scotia Schenectady Wind damage, trees and wires blown down 4:12pm
Clifton Park Saratoga Large maple tree blown down over Ashdown Road 4:12pm
Windham Greene Wind damage, trees blown down 4:21pm
Greenville Greene Wind damage, trees blown down 4:30pm
Lansingburgh Rensselaer Wind damage, multiple trees and wires blown down 4:32pm
Brunswick Rensselaer Wind damage, multiple trees and wires blown down 4:36pm
Nassau Rensselaer Wind damage, multiple trees and wires blown down 4:54pm
Galeville Ulster Wind damage, trees blown down 4:58pm
Esopus Ulster Wind damage, trees blown down 5:00pm
Stuyvesant Falls Columbia Wind damage, numerous branches down 5:04pm
Bennington, VT Bennington Wind damage, multiple trees and wires blown down 5:08pm
Poughkeepsie Dutchess Wind damage, several trees and wires blown down 5:32pm
Near North Landgrove, VT Bennington Wind damage, trees blown down 5:32pm
Dalton, MA Berkshire Wind damage, trees blown down 5:46pm
Dover Plains Dutchess Wind damage, numerous trees blown down 5:46pm
Becket, MA Berkshire Wind damage, trees reported down 5:55pm
Sheffield, MA Berkshire Wind damage, trees and wires blown down 6:00pm
Sheffield, MA Berkshire Wind damage, trees blown down on wires 6:21pm
Kent, CT Litchfield Wind damage, trees blown down on wires 6:23pm

This is a local storm report map generated at the Albany National Weather Service office, showing the storm reports (wind damage) as well as the severe thunderstorm (yellow) and Tornado (red) warning polygons that were issued by the Albany office for this event.

Local Storm Report Map, September 8, 2012 

This is the Storm Prediction Center (SPC) national severe reports map for September 8, 2012 illustrating the significant number of damaging wind reports over the Northeast.

SPC National Severe Reports Map for September 8, 2012 

 

 

WeatherNet 6 Rainfall Reports for September 8, 2012

Town County Rainfall Report Town County Rainfall Report
Savoy, MA Berkshire 0.80" Pittsfield, MA Berkshire 0.70" to 1.06"
Alford, MA Berkshire 0.30"      
           
Voorheesville Albany 0.42" Glenmont Albany 2.25"
Feura Bush Albany 2.20" Guilderland Albany 0.50"
Colonie Albany 0.32"      
           
Livingston Columbia 1.54" North Chatham Columbia 1.42"
Ancramdale Columbia 0.92" Germantown Columbia 2.00"
Hudson Columbia 1.50"      
           
Arkville Delaware 1.20"      
           
Broadalbin Fulton 0.40"      
           
Catskill Greene 1.38"      
   
     
Wells Hamilton 0.70" Piseco Hamilton 0.75"
           
Amsterdam Montgomery 0.70" Glen Montgomery 0.48"
Fonda Montgomery 0.75"      
           
Oneonta Otsego 0.79"      
           
Center Brunswick Rensselaer 0.87" Speigletown Rensselaer

1.10"

Brunswick Rensselaer 0.87"      
           
Malta Saratoga 0.31" Charlton Saratoga 0.20"
Milton Saratoga 0.45" Clifton Park (Oaks) Saratoga 0.50"
           
Duanesburg Schenectady 0.35" Scotia Schenectady 0.26"
           
Jefferson Schoharie 0.90" Richmondville Schoharie 0.56"
Fulton Schoharie 0.35" Summit Schoharie 0.75"
Huntersland Schoharie 0.60"      
           
Ulster Park Ulster 0.38" West Shokan Ulster 0.67"
           
Queensbury Warren 0.75"      
           
Cossayuna Washington 0.65"      
           
Landgrove, VT Bennington 0.85" Danby, VT Rutland 0.56"