Thursday, May 18, 2017
Regional Severe Thunderstorm Event

Photographer: Jeff Hart - Major damage to trees in Kingsbury, Washington County due to a 90 mph macroburst. (severe thunderstorm downburst) The downburst of wind began in Queensbury at 7:30pm on Thursday May 18 traveling 3 miles to Kingsbury through 7:40pm producing this and other damage along a three mile path.

Wind damage in Kingsbury, Washington County


A significant severe thunderstorm event unfolded across eastern New York and western New England, primarily from Otsego, Schoharie, Albany, and Rensselaer counties on north through the Mohawk valley, Adirondacks, Lake George-Saratoga Region and southern Vermont from the late afternoon through the early evening with fast moving multi-cell thunderstorm clusters producing areas of significant wind damage. Major damage to trees and power lines occurred between 7:30 and 7:40pm from Queensbury in Warren County to Kingsbury in Washington County when a, estimated by NWS, 90 mph downburst (macroburst in this case due to the damage field extending over 2.5 miles, vs a microburst where the wind damage is generally confined to an area of 2 miles or less) occurred. Although wind damage was spotty in nature and very localized across the region, which is typical with severe thunderstorms which are quite small in overall scale, violent cloud to ground lightning was quite widespread in both the severe and non-severe thunderstorms which occurred. The light show throughout the region was described by many as "Epic" with frequent to continuous flashes in many areas as the storms moved through.

Rainfall, however, was not particularly heavy with the greatest amounts measured generally ranging from 1/2" to 0.60" with most areas that were affected by the storms generally receiving 0.30" or less. A relatively dry atmosphere in place and the fast forward motion of the storms (35-50 mph) precluded excessive amounts of rain which often can accompany convective outbreaks.

SET UP

Record breaking heat through the day preceded the thunderstorm event with temperatures surging into the upper 80s to lower and mid 90s during the afternoon (Albany's high of 94° tied the record for the date.) However, humidity levels were not particularly high with dewpoints generally ranging through the mid and upper 50s, climbing modestly directly in advance of the evening thunderstorms to near 60°. A significant amount of dry air aloft also existed which contributed to a lack of heavy rainfall with the thunderstorms and also helped to prevent any development during the day. The dry air aloft, however, also contributed to enhancing the damaging surface wind gusts as cooling of the air occurred aloft due to the evaporation of rain as it developed and fell through the cloud. This evaporative cooling process caused dense heavy layers of air to form aloft in the thunderstorms which gravity then pulled quickly to the ground causing an acceleration to the wind and contributed to gusts over 60 mph in some places. This was, however, not the only process at play. Another mechanism a thunderstorm has to produce damaging surface winds is through momentum mix down of strong winds aloft to the surface. This occurs as a thunderstorm's updraft and downdraft interact with that higher speed air aloft, tapping into that flow and then essentially mixing some of it down to the ground in strong localized surface blasts. So, it was the combination of accelerations due to evaporative cooling as well as momentum mix down that were the two primary damaging wind mechanism at play in this event.

THUNDERSTORM INITIATION
Conditions locally were not favorable for thunderstorm initiation despite the high heat in place. There were no surface convergence boundaries near the region to act as a thunderstorm trigger and the fact that dewpoints were marginal at best (50s), meant the heating, as great as it was, was not sufficient to overcome a mid level cap (warm air aloft) allowing for sunny skies to prevail through the day with very little cloud development. A trigger, however, did develop over western New York by the mid afternoon as a lake breeze front/pre-frontal trough acted as a surface convergence boundary in an environment where the atmosphere was more weakly capped (cooler aloft), which allowed storms to fire. Once the storms were triggered, the ball was set rolling as fast jet stream winds aloft quickly steered them to the east into eastern New York and western New England where ample energy aloft (CAPE values of around 1500 j/kg) existed to support the storm's and subsequent severe weather.

The first storms of the event, however, were not associated with the main clusters that formed over western New York. An apparent differential heating boundary, created by cloudier conditions over the Adirondacks vs. in the Mohawk valley allowed for enough convergence to pop a small storm over SE Herkimer County late in the afternoon. That storm weakened as it quickly moved NE through Fulton and NW Saratoga counties through 5:30pm with a second cell forming on it's outflow. That second storm went on to produce some damaging wind and large hail in Montgomery and Fulton counties between 5:30pm and 6:15pm and was one of only two large hail producing storms of the event, with the other over northern Hamilton County between 7 and 7:30pm. This storm developed some mid level rotation for a brief period allowing for a very strong updraft which produced the hail.


Discreet hail producing thunderstorm over Fulton County May 18, 2017 - Hail up to 1" to 1.5" in diameter reported at Kingsbury, Bleecker, Broadalbin, Mayfield, Vail Mills and Riceville

Discreet severe hail producing thunderstorm over Fulton County around 6pm May 18, 2017

Photograph contributed via facebook by Victoria Bouffard - Large hail stones in Broadalbin, Fulton County

Large hail in Broadalbin, Fulton County Thursday May 17, 2017

Photograph contributed via facebook by Kyle Schoonmaker - Large hail stones in Mayfield, Fulton County

Large hail in Mayfield, Fulton County Thursday May 17, 2017

Instant Doppler 6 image at 7:08pm Thursday May 18, 2017 - showing the fast moving line of multi-cell thunderstorms extending from SW Warren County through NW Saratoga, Fulton, western Montgomery, and eastern Otsego counties. Albany Doppler radar (ENX)
a short time prior to this image indicated winds a couple of thousand feet off the ground in northern Otsego County of up to 75 mph.

Instant Doppler 6 image at 7:08pm Thursday May 18, 2017 showing inbound multi-cell severe thunderstorms 

Albany Doppler radar reflectivity image (approximately 7:45pm) showing bowing line segments of severe thunderstorms extending from Rutland County, VT through Saratoga County into into Schenectady County. Severe wind damage had occurred in Queensbury and Kingsbury just prior to this image between 7:30 and 7:40pm. Damaging wind was occurring in and around Saratoga Springs at this time with a 64.8 mph wind gust measured by the CBS6 camera and weather instrument mount located on top of the MVP building (150' elevation) in Schenectady at 7:41pm


Albany Doppler radar reflectivity image at approximately 7:45pm, Thursday May 18, 2017

The main cluster of severe thunderstorms at this time were pulling out of Washington County and moving into and through Bennington County, VT. An additional cell at this time over SE Schoharie County went on to straddle the Albany Greene County line producing some pockets of wind damage in that region through 9:15pm.

Instant Doppler 6 image at 8:25pm Thursday May 18, 2017 

Instant Doppler 6 image at 9:14pm Thursday May 18, 2017 - strong, but weakening thunderstorms were moving through eastern Rensselaer, northern Columbia and northern Berkshire counties. Additional thunderstorms through Schoharie, Delaware, and western Greene counties at this time remained below severe limits as they moved into the mid Hudson valley through 10:30pm, but did produce frequent cloud to ground lightning. One cell developed out of that cluster becoming severe across eastern Dutchess and Litchfield counties around 11:30pm.

Instant Doppler 6 image at 9:14pm Thursday May 18, 2017 

Cloud to ground lightning strike over Rotterdam, Schenectady County - photograph contributed by Collin Kellogg, Thursday May 18, 2017

Cloud to ground lightning strike over Rotterdam, Schenectady County, Thursday May 18, 2017 

Cloud to ground lightning strike over Boght Corners, Albany County, looking east into Rensselaer County, Thursday May 18, 2017 - Photograph by Sean Organ

Cloud to ground lightning over Boght Corners, Albany County, Thursday May 18, 2017 

Photograph contributed via facebook by Cassandra Jones - In cloud lightning and a rainbow, Hartford, Washington County Thursday May 18, 2017

In cloud lightning and a rainbow, Hartford, Washington County Thursday May 18, 2017 

Storm Prediction Center Storm Reports Graphic for Thursday May 18, 2017 showing the locations of reported storm damage. (Over 50 reports in the local area)

SPC Storm Reports for Thursday May 18, 2017 


NWS Storm Reports for Thursday May 18, 2017. Note, these reports are used to verify the NWS warnings which were issued for this event and therefore do not necessarily represent an accounting for all of the wind damage which may have occurred.

Town County Severe Weather Report Time
1 Mile SE of Kringsbush Montgomery Measured 1.5" diameter hail 5:38pm
Bleecker Fulton Measured 1" diameter hail 6:02pm
Mayfield Fulton Measured 0.88" diameter hail 6:07pm
1 Mile W of Vail Mills Fulton Measured 1" diameter hail 6:08pm
1 Mile NW of Riceville Fulton Measured 1.25" diameter hail 6:18pm
West Winfield Herkimer Thunderstorm wind damage, trees and wires down 6:23pm
1 Mile WSW Eagle Bay Herkimer Measured 0.88" diameter hail 6:33pm
Van Hornesville Herkimer Thunderstorm wind damage, trees and wires down 6:41pm
Ames Montgomery Thunderstorm wind damage, trees, wires, and transformer down 7:02pm
Indian Lake Hamilton Measured 1.5" diameter hail 7:09pm
Indian Lake Hamilton Measured 1" diameter hail 7:11pm
Queensbury to Kingsbury Warren - Washington 90mph macroburst, 3 mile path length, 1.5 mile path width, major damage to trees and power lines, thousands without power, barn roof blown off and moved 1/4 of a mile, trees on buildings with road closures, damage began at the Floyd Bennett Memorial Airport 7:30-7:40pm
1 Mile SSE of Oneida Corners Warren Wind damage, trees and wires down blocking Ridge Rd 7:30pm
1 Mile NE of Queensbury Warren Tree blown down on a house 7:30pm
1 Mile WSW of South Amsterdam Montgomery Tree blown down blocking the intersection of Verbraska Road and Route 5S 7:32pm
1 Mile WNW Walling Corners Montgomery Wind damage, tree blown down onto a trailer 7:35pm
2 Mile SE Oneida Corners Washington Thunderstorm wind damage: Large portion of a metal roof blown off, tree uprooted flipping over two vehicles 7:35pm
3 Miles NNW of Hudson Falls Washington Measured 68 mph wind gust (Glens Falls NY Mesonet site) 7:35pm
East Galway Saratoga Wind damage, large tree limbs blown down 7:37pm
2 Miles SSE of Hawthorne Hill Schenectady Wind damage, tree blown down on a house on Pearse Road 7:40pm
Schenectady Schenectady Measured 64.8 mph gust on top of the MVP building on State Street (150' elevation) 7:41pm
2 Mile NNE of Saratoga Springs Saratoga Large oak tree uprooted 7:45pm
Eddy Corners Saratoga Wind damage, tree down on an unoccupied van 7:45pm
1 Mile N of Saratoga Lake Saratoga Wind damage, trees blown down between Lake Lonely and Saratoga Lake 7:47pm
Saratoga Springs Saratoga Wind damage, large tree limbs down 7:52pm
1 Mile ENE of Flagler Corners Saratoga Wind damage, trees limbs down on Route 9 7:52pm
Cohoes Albany Wind damage, tree blown down onto a house on Mohawk Street 7:52pm
2 Mile NNE of Saratoga Springs Saratoga Wind damage to trees and power lines 7:54pm
1 Mile NNE of Niskayuna Schenectady Trees and wires down just west of Balltown Road 7:56pm
Latham Albany Thunderstorm wind damage, numerous trees and wires blown down, power outages 7:56pm
1 Mile SSW of Troy Rensselaer Wind damage, tree blown down 7:57pm
Rensselaer Rensselaer Wind damage, tree blown down 7:57pm
1 Mile SE of Paradise Beach Warren Wires down resulting in a structure fire 8:00pm
1 Mile south of Eddy Corners Saratoga Wind damage, multiple trees down blocking to lanes of I-87 8:00pm
1 Mile W of South Troy Rensselaer Wind damage, trees and power lines down 8:00pm
2 Miles ESE of Defreestville Rensselaer Wind damage, trees and wires down across Morner Road 8:00pm
2 Miles S. of North Petersburg Rensselaer Tree limbs down from wind and lightning 8:13pm
North Hoosick Rensselaer Multiple reports of trees and wires blown down 8:17pm
1 Mlle NE of Newtonville Albany Wind damage, tree blown down 8:25pm
Bennington, VT Bennington Wires blown down 8:27pm
Stockport Columbia Wind damage, trees down on wires 9:10pm
Slingerlands Albany House struck by lightning catching on fire 9:45pm
Dover Furnace Dutchess Wind damage, numerous trees down near Route 22 and East Duncan Hill Road 11:48pm
Oniontown Dutchess Wind damage, trees and wires down on Old Route 22 11:50pm