Wednesday June 1, 2011
Severe Weather Outbreak - Supercells with Large Hail

A surge of heat and humidity (air temperatures blasting into the upper 80s to lower 90s and dewpoints climbing to between 65° and 70°) coming in on a gusty southerly flow, coupled with cooling temperatures and difluent flow aloft, along with strong speed shear in the atmosphere all with an inbound cold front acting as a trigger, set the stage for widely scattered severe thunderstorms during primarily the afternoon and early evening. I say primarily during the afternoon because the passage of an early morning warm front triggered thunderstorms in the northern Catskills, Mohawk valley, and Adirondacks between 5am and 8am, a few producing up to quarter sized hail near Tomantown Fulton County, Galway, Fonda, and West Milton between 6am and 7:05am.

Thunderstorms in the event remained fairly scattered as the convergence along the inbound cold front was not optimal to support a more widespread and organized event with surface winds gradually shifting from southerly during the morning to westerly during the afternoon, parallel to the front. More of a southerly flow, however, remained in place in the Hudson valley and western New England well into the afternoon which acted to increase the overall directional wind shear along with convergence along the front which coupled with high instability in the atmosphere was sufficient to trigger and sustain a series of supercell thunderstorms in that region which primarily produced huge hail along with locally torrential rain and frequent lightning from the late morning into the evening.

There were a total of eight severe supercell thunderstorms (rotating thunderstorms) that developed from the late morning through the evening in primarily the Mohawk and Hudson valleys and Bennington, Berkshire, and Litchfield counties in western New England from the mid to late morning through the early evening. These storms generally tracked from west to east at 40-50 mph with several storms taking similar tracks over the same communities through the day. The Adirondacks, Catskills, and Schoharie valley were largely left out of this outbreak.

Springfield, MA EF3 Tornado (Max winds 160 mph): Explosive supercell thunderstorm development occurred in western and central MA through the late afternoon and evening. The first in a series of storms running along and south of the Mass Pike produced a deadly EF3 tornado which put down an incredible continuous thirty nine mile severe damage path up to a half mile wide from Westfield through downtown Springfield to Monson, Brimfield, Charlton and Sturbridge. Environmental conditions over the Connecticut river valley were similar to those across eastern New York, with CAPE (convective available potential energy) values of 3500 to 4000, high heat and dewpoints and strong speed shear, accounting for the supercell thunderstorm development. Low level wind shear, however, was considerably stronger in the Connecticut valley vs. over New York allowing the lead supercell in Hampden County, MA to produce the violent long track tornado. It is possible that the associated pressure falls and inflow from the supercells over eastern New York, Bennington, and Berkshire counties from the mid to late afternoon increased the low level south to southeast flow in the Connecticut river valley to make the difference between the non-tornadic supercells over New York and the tornadic supercells in western and central Massachusetts.

The Local Storms: Storms marked with an "*" were particularly intense long track supercells producing significant hail.

Supercell #1:*
This thunderstorm formed in the Mohawk valley during the late morning and was the first isolated cell to develop. It became severe between 12pm and 12:10pm producing 1" diameter hail in Ephratah, Fulton County. The storm continued to track east through Saratoga County through 1pm, displaying a classic hook echo on the Doppler radar reflectivity display and producing up to baseball sized hail in Saratoga Springs at 1pm.

STORM REPORTS FOR SUPERCELL #1

Town County Storm Report Time
Ephratah Fulton 1" diameter hail (Quarter Sized) 12:03pm
Gloversville Fulton 1/2" hail 12:12-12:15pm
Near Ballston Spa Saratoga 1.25" Hail (Half Dollar Sized), estimated 60 mph winds 12:55pm
Barkersville Saratoga Estimated 0.88" sized hail 1:00pm
Saratoga Springs Saratoga 2.75" diameter hail (Baseball sized) Gick Road, buses dented 1:00pm
Galway Saratoga 1" Hail (From a smaller separate storm on the supercell's flank) 1:10pm
4 miles SW of Schuylerville Saratoga 1.75" diameter hail (Golf ball sized) 1:10pm

Supercell #2:
This thunderstorm appeared to form along the outflow of the lead supercell in the Mohawk valley, tracking east from Fulton County into Saratoga County. This storm was not as strong or long lived producing penny to nickel sized hail in Johnstown at 1:16pm, and then hail up to the size of quarters (1" diameter) five miles SSE of Saratoga Springs at 2:03pm.

Supercell #3:
Another supercell developed in the outflow region of the lead storm over Rensselaer County quickly moving east into Bennington County, VT between 1:30pm and 2pm. Two large hail reports came out of this storm locally, with 1" hail measured at Hoosick Falls at 1:40pm and 1.25" hail at Arlington, VT in Bennington County at 2:03pm.

Supercell #4:*
Yet another supercell developed in the wake of the lead storm over Saratoga County around 2pm, tracking east into Vermont through approximately 3pm. This storm was a prolific hail producer developing a strong rotating updraft which may have yielded a funnel cloud along its track over Buskirk along with up to baseball sized hail.

STORM REPORTS FOR SUPERCELL #4

Town County Storm Report Time
Stillwater Saratoga Estimated 1" diameter hail 2:16pm
Easton Washington 3/4" diameter hail 2:20pm
Eagle Bridge Washington 2.75" diameter hail (Baseball sized) 2:35pm
1 mile So. of Cambridge Washington 1.5" diameter hail 2:35pm
Buskirk Washington 3/4" diameter hail, storm spotter indicated rotating cloud 2:40pm
Buskirk Washington Funnel Cloud 2:47pm
Shaftsbury, VT Bennington 0.88" to 1.75" diameter hail 2:48pm-2:50pm
Shaftsbury, VT Bennington 3.25" diameter hail (Teacup sized) 3:00pm
1 mile E. of Shaftsbury, VT Bennington 1" hail, trees blown down 3:07pm
Sunderland, VT Bennington Wind damage, two trees blown down 3:07pm

Supercell #5*
While the Washigton-Bennington County supercell was producing giant hail and damaging wind bursts along its path, this supercell was developing over Berkshire County producing large hail over the northern and central parts of the county between 2:45pm and 3:45pm as well as flash flooding in an around Pittsfield, MA

STORM REPORTS FOR SUPERCELL #5

Town County Storm Report Time
Pittsfield, MA Berkshire 1" diameter hail 2:45pm
Adam, MA Berkshire Estimated 2" diameter hail (Hen Egg Sized) 2:45pm
New Ashford, MA Berkshire 0.88" diameter hail 2:50pm
Pittsfield, MA Berkshire 3/4" diameter hail, local street flooding in progress 2:58pm
Pittsfield, MA Berkshire 1" diameter hail 3:00pm
Pittsfield, MA Berkshire 3/4" diameter hail 3:02pm
Becket, MA Berkshire 1.5" diameter hail (estimated) 3:15pm
Pittsfield, MA Berkshire 0.88" diameter hail 3:15pm
Dalton, MA Berkshire 3/4" diameter hail 3:25pm
Hinsdale, MA Berkshire 1.75" diameter hail 3:30pm
2 miles SW of Windsor, MA Berkshire Wind damage, wires down 3:45pm

Supercell #6:
This storm developed over southern Bennington County between 3:45 and 4pm, putting down 1" diameter hail in Bennington, VT at 3:55pm. This storm then tracked into Windham County, VT producing large hail and damaging wind gusts through 6:00pm

Supercell #7:
This storm formed over east central New York tracking into and through western and central Otsego County on a northeast path between 5:45pm and 6:30pm before weakening. Large hail generally accompanied this storm along its track through Otsego County

STORM REPORTS FOR SUPERCELL #7

Town County Storm Report Time
Otego Otsego Estimated 1.25" diameter hail 5:52pm
Gilbertsville Otsego 3/4" diameter hail 5:55pm
Richfield Springs Otsego 0.88" diameter hail 5:58pm
Springfield Center Otsego Measured 1" diameter hail 6:16pm

Supercell #8:
The final storm over the local area of the day developed over the higher terrain in Ulster County between 6pm and 6:30pm tracking east through Ulster, Dutchess and Litchfield counties through 8:30pm. A combination of large hail and damaging wind gusts occurred along the path of this storm

STORM REPORTS FOR SUPERCELL #8

Town County Storm Report Time
Saugerties Ulster Measured 1" diameter hail 6:45pm
Saugerties Ulster Estimated 1" diameter hail 6:48pm
Saugerties Ulster Estimated 1" diameter hail 6:50pm
Salisbury, CT Litchfield Wind damage, trees and wires blown down 7:45pm
Burrville, CT Litchfield Measured 1" diameter hail 8:13pm

Pictures


#1: Photographer: WeatherNet 6 spotter Spencer Conlin, Very large hail stones in Eagle Bridge, Washington County, June 1, 2011 (Hail up to baseball size was reported in Eagle Bridge)

Large Hail from Eagle Bridge, Washington County June 1, 2011 

#2: Photographer: WeatherNet 6 spotter Spencer Conlin, Very large hail stones in Eagle Bridge, Washington County, June 1, 2011

Large Hail, Eagle Bridge, NY Washington County June 1, 2011 

#3: CBS6 Viewer Cheryl Catlin: An evening view of the back edge of one of the New England supercells taken from East Poestenkill, NY Rensselaer County

The back edge of a supercell thunderstorm during the evening