Tuesday, September 18, 2012
Excessive Rain - High Wind - Severe Convective Event

A powerful storm, more typical for later autumn than the very end of summer, developed through the phasing of a moisture rich system evolving out of the gulf of Mexico, and an energetic system dropping south out of Canada through the day on the 17th. The resulting new storm on Tuesday September 18 tracked through the St. Lawrence valley dragging a series of strong cold fronts through eastern New York and western New England during the evening and overnight period. The rapid deepening of the storm, coupled with strong high pressure off shore, caused a tight pressure gradient across the Northeast leading to a prolonged period of strong SSE gradient winds gusting from 30-40 mph on average with localized gusts, especially across the higher elevations of the Taconics and western New England, to 50 mph during the afternoon and early evening. The flow pushed a tropical air mass into the Northeast with dewpoints climbing into the middle and upper 60s through the afternoon along with temperatures into the upper 60s and low 70s. The moisture rich air acted to fuel what would become a torrent of rain for a time during the afternoon and evening.

Rain
Periods of light to at times moderate stratiform rain fell through the morning and early to mid afternoon priming the region for the big dump of rain from the mid afternoon through the evening as strongly forced, but shallow convective lines of torrential downpours, developed along the lead wind shift line or pre-frontal trough late in the day. Initially one strong convective line, to shallow to produce lightning, developed over central New York during the afternoon and moved into the Mohawk valley and the Adirondacks weakening some with time as a new zone of torrential rain developed over the Catskills and Capital region during the late afternoon. For approximately one to two hours during the late afternoon and early evening, the new zone of tropical rain over the Catskills and Capital Region remained quasi-stationary waiting for the pre-frontal trough to run into it and move it east through the Hudson valley and western New England, which it did through 9pm. One to two inches of rain fell in just two hours in parts of Greene, Albany, Schenectady, and southern Saratoga counties from this band of rain before it began moving off to the east, causing one of the rainfall bullseyes across the region. Upslope flow along the south to southeast facing slopes of the Catskills enhanced rainfall through the entire day in parts of Delaware, Ulster, and Greene counties where in some places 5"-7" of rain fell in approximately twelve hours , much of it coming during the late afternoon and evening. Fortunately, with only a few exceptions in Greene and western Ulster Counties, flooding was generally confined to the urban and poor drainage type as dry conditions across the region preceding this event allowed plenty of room in streams and creeks to absorb the tremendous runoff.

Wind - Severe Weather
The storm was characterized by strong wind fields through a deep layer in the atmosphere with 50-60 mph winds dropping as low as 1500 to 2000 feet in elevation during the mid to late afternoon with a passing strong low level jet. Strong turning of the wind from southeast at the surface to southwest and west aloft along with considerable increases in the speeds with height was also present. The set-up is characterized by strong directional and speed shear, which are favorable ingredients for severe convective storms. Instability in the atmosphere, however, was almost completely absent which prevented the convective elements which developed to only grow to heights of 15,000 to 20,000 feet, which is considered quite shallow. The convective cells were so shallow that there was little if any lightning with the exception of brief period of cloud to ground strikes with a slightly taller cell in southern Dutchess County during the evening. The concern for severe weather in terms of damaging convective winds, however, was high, due to the strength of the wind fields so low in the atmosphere. Even shallow convective cells with tops to 15,000' would be sufficiently tall to interact with the high momentum air from 2000 to 5000 feet to bring some of it down to the ground in bursts resulting in pockets of wind damage as the convective lines moved through. There, however, was also some concern for isolated and brief spin up type tornadoes, due to the existence of the strong low level directional wind shear. A tornado watch was issued by the Storm Prediction Center from the mid afternoon through the early evening for that potential.

In the end, there were forty six reports of wind damage, combined reports of trees and wires being blown down from both gradient and convective winds with the event, making it a significant event. Much of the gradient wind damage occurred in Columbia County in the form of downed trees and power lines in many communities. No tornadoes occurred due to the lack of instability which prevented the convective updrafts from becoming tall or producing any sustained circulations.

STORM REPORTS September 18, 2012 (Both Gradient and Convective Wind Damage Reports, Flash Flood Reports)


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
Chatham Columbia Gradient Wind Damage: Tree blown down on roadway 12:55pm
Livingston Columbia Gradient Wind Damage: Tree blown down on roadway 1:15pm
Watervliet Albany Gradient Wind Damage: Tree limbs on power lines between 3rd and 4th Avenue 1:25pm
Austerlitz Columbia Gradient Wind Damage: Trees and wires down, spotter report of peak gust of 48 mph 1:25pm
Canaan Columbia Gradient Wind Damage: Trees and wires blown down 1:36pm
Hillsdale Columbia Gradient Wind Damage: Wires blow down 1:40pm
Chatham Columbia Gradient Wind Damage: Trees and wires blown down, fence blown over 1:47pm
Ghent Columbia Gradient Wind Damage: Trees and wires blown down 2:04pm
Chatham Columbia Gradient Wind Damage: Tree blown down onto a road 2:31pm
Valatie Columbia Gradient Wind Damage: Trees and wires blown down 2:31pm
Canaan Columbia Gradient Wind Damage: Trees blown down on roadway 2:39pm
New Milford, CT Litchfield Gradient Wind Damage: Limbs down on Route 37 and one tree down in a horse field adjacent to Candlewood Mountain Road 3:00pm
Canaan Columbia Gradient Wind Damage: Tree down on roadway 3:00pm
Great Barrington, MA Berkshire Gradient Wind Damage: Tree down on a house and car 300pm
Greenport Center Columbia Gradient Wind Damage: Tree down on roadway 303pm
Taghkanic Columbia Gradient Wind Damage: Tree and power line down 3:05pm
Kinderhook Columbia Gradient Wind Damage: Tree down on roadway 3:05pm
Hillsdale Columbia Gradient Wind Damage: Trees and wires down 3:13pm
Gallatinville Columbia Gradient Wind Damage: Trees down on roadway 3:33pm
Ghent Columbia Gradient Wind Damage: Tree down on roadway 3:56pm
Hillsdale Columbia Gradient Wind Damage: Tree down on roadway 3:58pm
Ancram Columbia Gradient Wind Damage: Trees and wires down 4:06pm
Claverack Columbia Gradient Wind Damage: Trees and wires down 4:11pm
Stockport Columbia Gradient Wind Damage: Trees and wires down on a house 4:23pm
Stockport Columbia Gradient Wind Damage: Tree down on roadway 4:24pm
North Blenheim Schoharie Gradient Wind Damage: Trees and wires down 4:53pm
Torrington, CT Litchfield Gradient Wind Damage: Trees blown down 5:54pm
Shandaken Ulster FLASH FLOOD: Oliverea Road closed due to flash flooding 6:15pm
Jewett Greene Convective Wind Damage: Trees and wires blown down 6:15pm
Lexington Greene Convective Wind Damage: Trees and wires down 6:15pm
Rosendale Ulster Convective Wind Damage: Trees down 6:30pm
Kingston Ulster Convective Wind Damage: Trees and wires blown down 6:35pm
Niskayuna Schenectady Convective Wind Damage: Trees reported down 6:40pm
Clifton Park Saratoga FLASH FLOOD: Roads reported closed due to flooding 6:50pm
Easton Washington Convective Wind Damage: Numerous trees reported blown down 6:55pm
Catskill Greene Convective Wind Damage: Trees and wires blown down 6:57pm
Jewett Greene FLASH FLOOD: Roads closed due to flooding 7:10pm
Windham Greene FLASH FLOOD: Roads closed due to flooding 7:10pm
Fort Edward Washington Convective Wind Damage: Trees blown down 7:11pm
Kinderhook Columbia Convective Wind Damage: Numerous trees blown down 7:15pm
Livingston Columbia Convective Wind Damage: Numerous trees blown down 7:20pm
West Lebanon Columbia Convective Wind Damage: Numerous trees blown down 7:39pm
Greenwich Washington Convective Wind Damage: Numerous trees blown down 7:59pm
Colonie Albany FLASH FLOOD: Flooding on NY-5, road closed 8:05pm
1 Mile NE of N. Adams, MA Berkshire Convective Wind Damage: Trees blown down 8:21pm
Sharon, CT Litchfield Convective Wind Damage: Trees blown down, power out 8:21pm
Torrington, CT Litchfield Convective Wind Damage: Trees blown down 8:40pm
New Hartford, CT Litchfield Convective Wind Damage: Trees blown down 8:51pm

This is the Storm Prediction Center (SPC) national severe reports map for September 18, 2012 illustrating the extent of the event. Note: Damage plots are for convective wind only, not gradient wind

SPC National Severe Reports Map for September 18, 2012 

WeatherNet 6 Storm Total Rainfall Reports for September 18, 2012

Town County Rainfall Report Town County Rainfall Report
Savoy, MA Berkshire 2.20" Pittsfield, MA Berkshire 2.30" to 2.80"
Alford, MA Berkshire 0.90" Lanesborough, MA Berkshire 2.40"
Sharon, CT Litchfield 2.09"      
           
Voorheesville Albany 4.58" Guilderland Albany 4.28"
Cohoes Albany 2.60" Colonie Albany 4.08"
Coeymans Hollow Albany 3.50" Latham Albany 3.34"
Glenmont Albany 2.50" East Berne Albany 3.25"
Newtonville Albany 2.28" Feura Bush Albany 3.65"
Preston Hollow Albany 3.75"      
           
Taghkanic Columbia 1.90" Kinderhook Columbia 2.30"
Germantown Columbia 3.75" Ancramdale Columbia 2.36"
Chatham Center Columbia 1.60" Hudson Columbia 2.65"
Austerlitz Columbia 2.05"      
           
Arkville Delaware 5.40" Margaretville Delaware 4.50"
           
Broadalbin Fulton 1.70" Johnstown Fulton 3.00"
           
Freehold Greene
4.88"
South Cairo Greene 3.56"
Maplecrest Greene 4.70" Cairo Greene 4.66" to 5.20"
Greenville Greene 2.61" Halcott Greene 3.10"
           
Piseco Hamilton 3.50" Wells Hamilton 3.56"
           
Glen Montgomery 1.00" Fonda Montgomery 1.23"
Palatine Bridge Montgomery 0.75"      
         

 

Oneonta Otsego 1.12" Worcester Otsego 1.47"
Cherry Valley Otsego 1.60" East Worcester Otsego 1.33"
           
Speigletown Rensselaer 2.75" Berlin Rensselaer 2.71"
Stephentown Rensselaer 2.10"      
           
Saratoga Springs Saratoga 2.70" Milton Saratoga 1.46" to 1.71"
Clifton Park (Oaks) Saratoga 3.86" Wilton Saratoga 2.33"
           
Duanesburg Schenectady 1.70" Scotia Schenectady 2.08"
Princetown Schenectady 1.30"      
          0.67"
Summit Schoharie 1.90" North Blenheim Schoharie 2.30"
Huntersland Schoharie 2.40" Jefferson Schoharie 1.80"
Richmondville Schoharie 1.48" Charlotteville Schoharie 1.50"
Gilboa Schoharie 4.25"      
           
Saugerties Ulster 2.60" Kingston Ulster 2.15"
Whiteport Ulster 1.99" Phoenicia Ulster 7.08"
Big Indian Ulster 7.48" West Shokan Ulster 5.78"
Ulster Park Ulster 1.98"      
           
Queensbury Warren 3.76" Lake Luzerne Warren 2.92"
           
Kingsbury Washington 2.61" Cossayuna Washington 2.31"
Fort Edward Washington 2.77" Granville Washington 2.60"
Hudson Falls Washington 2.97"      
           
Landgrove, VT Bennington 2.23" West Arlington, VT Bennington 2.08"
Woodford, VT Bennington 2.21" West Rutland, VT Rutland 1.32"