Wednesday July 14, 2021
Major Flash Flood Event - Rensselaer County

On Wednesday July 14, Rensselaer County government officials estimated infrastructure damage to roads, bridges, buildings, and utilities in central and western Rensselaer County in and around the communities of Troy, Brunswick, East Greenbush, Schodack, Averill Park, Sand Lake, Wynantskill and Poestenkill to range into the millions in the aftermath of destructive flash flooding. Anywhere from 2.00" to 4.50" of rain fell in two to three hours, with an estimated 1"-2" falling in as little as thirty minutes, between 3 and 6pm resulting in tremendous runoff with the county's complex terrain playing a role in both diverting runoff into the lower elevations to the west as well as aiding in the behavior of the thunderstorm complex responsible for the event.

Flooding was widespread in the areas shaded in green on the graphic below which includes a zone across northern Columbia into west central Berkshire County where more localized and less impactful flash flooding occurred between 7 and 8pm as the thunderstorm complex slowly moved south.

4.56" of rain measured in Averill Park
2.23" of rain measured in Brunswick
2.56" of rain measured in Canaan - Columbia County
2.11" of rain measured in Pittsfield, MA
1.45" of rain measured at Woodford, VT
1.37" of rain measured at Castleton
1.12" of rain measured at Greenwich

Roads that Rensselaer County Emergency management officials reported with flooding impacts included:
-Moonlawn Road
-Tamarac Road
-Miller Road in East Greenbush and Schodack
-Averill Park Road, First Dyke and Teal roads in Sand Lake
-State Route 150 and State Route 66 in Sand Lake
-Snyder's Corners and Oak Hill roads in Poestenkill
-Plank and Blue Factory Roads in Poestenkill
-Main Street in Poestenkill
-Old Hickory
-North Nassau Road
-Luther Road
-Creek Road
-Rabie Road
-Gentile Road
-Burden Lake Road

Flooding zone map, Wednesday July 14, 2021 

THE EVENT:
Hot humid weather prevailed across the region with air temperatures climbing in response to considerable sunshine into the mid and upper 80s and dewpoint temperatures ranging from the upper 60s to around 70°. Aloft, there was not much wind to speak of, but instability was high with CAPE (convective available potential energy) values ranging up to 2500 j/kg, as a weak upper level disturbance dropped mid level temperatures a little bit to set up an environment of moderately steep lapse rates.

An initial batch of showers, which tracked across the Adirondacks during the late morning, put out an outflow boundary that helped to trigger clusters of showers and t'storms during the afternoon further south. One batch of thunderstorms rooted itself in the unstable air mass from southern Warren and Saratoga counties by 2pm and intensified as it expanded east into Washington county and south into eastern Albany and NW Rensselaer counties by 3pm. Intense updraft cores developed in what was a short line, producing frequent violent cloud to ground lightning as well as torrential rainfall. A cell in the northern part of the line exhibited some mid level updraft rotation over south central Washington and Bennington counties where pockets of wind damage occurred with trees blown down from Cambridge to Shaftsbury, VT between 3:15 and 3:30pm.

In Rensselaer County, the thunderstorm complex slowly propagated south through the county between 3 and 6pm as the initial thunderstorm merged with new cells that developed over southern Saratoga and Albany counties. Cells within the new multi-cell cluster moved east with the southward propagation of the complex produced by new cells which continuously developed along the southern leading edge. The higher terrain in the eastern part of the county likely played a role in the southward propagation as convergence along the east facing slopes of the Rensselaer plateau aided in the development of the new cells. The propagation south continued through 8-9pm with the storm complex evolving into Columbia and central Berkshire counties before weakening. The high moisture content of the atmosphere and the slow propagation of the thunderstorms yielded the excessive rainfall amounts in the short 2-3 hour window resulting in the rapid flooding. The Wynantskill creek flooded in Wynantskill after 9pm and prompted home evacuations.

The following series of radar images chronicle the event from 3 to 8:30 pm.

Albany Doppler Radar Image around 3pm Wednesday July 14, 2021 - Strong thunderstorms with heavy rain from southern Washington County into far northeast Albany County


Albany Doppler radar base reflectivity image, 3pm July 14, 2021 

Albany Doppler Radar Image around 3:30pm Wednesday July 14, 2021 - Intense lightning cores around Shaftsbury, VT and from Troy, East Greenbush to Grafton indicated intensification across the storm cluster. Wind damage had occurred in Shaftsbury, VT with a few trees also blown near Troy.

Albany Doppler radar base reflectivity image, 3:30pm July 14, 2021 

Albany Doppler Radar Image around 4:00pm Wednesday July 14, 2021 - A break away cell in Bennington County, responsible for the wind damage in Shaftsbury progressed to the eastern part of the county with the strong cell in Rensselaer County continuing to produce intense frequent lightning and torrential rainfall.

Albany Doppler radar base reflectivity image, 4:00pm July 14, 2021 

Albany Doppler Radar Image around 4:30pm Wednesday July 14, 2021 - Intense rainfall continued at this time over southern Rensselaer County with a drop in lightning activity across the complex..


Albany Doppler radar base reflectivity image, 4:30pm July 14, 2021

Albany Doppler Radar Image around 5:00pm Wednesday July 14, 2021 - New thunderstorm cells had developed over southeast Saratoga, southeast Schenectady and northern Albany counties with torrential rain continuing over southern Rensselaer County at this time.


Albany Doppler radar base reflectivity image, 5:00pm July 14, 2021

Albany Doppler Radar Image around 6:00pm Wednesday July 14, 2021 - The thunderstorms that had formed in Saratoga and Albany counties between 4:30 and 5pm had merged with the Rensselaer County cell at this time adding to the rain that had already fallen. New thunderstorm cells were also in the process of developing over northeast Greene, northern Columbia and central Berkshire counties and around Pittsfield, MA

 Albany Doppler radar base reflectivity image, 6:00pm July 14, 2021

Albany Doppler Radar Image around 7:00pm Wednesday July 14, 2021 - The thunderstorm complex had moved south into northern Columbia County and into the Pittsfield, MA area by 7pm. Pockets of flash flooding were reported from Chatham to Canaan and Austerlitz.

Albany Doppler radar base reflectivity image, 7:00pm July 14, 2021 

Albany Doppler Radar Image around 8:00pm Wednesday July 14, 2021 - Heavy rain was easing over northern Columbia County at this time with smaller, weakening thunderstorm cells over east central Columbia, southern Berkshire and northern Dutchess counties.

Albany Doppler radar base reflectivity image, 8:00pm July 14, 2021 

NWS Storm Reports for Wednesday July 14, 2021. 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
Center Brunswick Rensselaer Wind Damage: Several reports of trees and wires blown down in Center Brunswick 3:10pm
Cambridge Washington Wind Damage: Trees down blocking Coila Road 3:21pm
Shaftsbury, VT Bennington Wind Damage: Multiple reports of trees and wires blown down in town 3:23pm
Brunswick Rensselaer Flash Flood: Route 278 and 7 flooded with 2-3 feet of moving water the intersection and route 278 impassable and closed 3:35pm
Poestenkill Rensselaer Wind Damage: Several reports of trees and wires down 3:43pm
Brunswick Rensselaer Flash Flood: Widespread road flooding 4:15pm
Eagle Mills Rensselaer Flash Flood: Several reports of roads flooded 4:20pm
Poestenkill Rensselaer Flash Flood: Numerous flooded roads 4:30pm
East Greenbush Rensselaer Flash Flood: One lane of the Columbia Turnpike closed with rocks and debris washed onto some roads 4:34pm
West Sand Lake Rensselaer Flash Flood: Several inches of moving water flowing over Route 43 in several locations between West Sand Lake and Averill Park 4:47pm
Schodack Rensselaer Flash Flood: Numerous reports of flooded roads 5:15pm
Averill Park Rensselaer Flash Flood: Route 66 washed out 5:15pm
East Greenbush Rensselaer Flash Flood: Water reaching homes and flooding basements along Berkshire Drive and Evergreen Way 5:30pm
Chatham Columbia Flash Flood: New Concord Road flooded between State Route 295 and County Route 9 7:17pm
Austerlitz Columbia Flash Flood: County Route 24 flooded between Route 9 and Stonewall Road 7:47pm
Chatham Columbia Flash Flood: State Route 66 flooded at the intersection of Dardess Drive 8:05pm
Wynantskill Rensselaer Flood: Wynantskill creek flooded with evacuations of 10 homes near Brookside Avenue 9:41pm

Albany National Weather Service Rainfall Observation Analysis an Distribution Map - Wednesday July 14, 2021

Albany National Weather Service Rainfall Analysis July 14, 2021 


Flooding on Taborton Road - Sand Lake - Wednesday July 14, 2021 - Craig Adams

 

Flooding along Taborton Road in Sand Lake, Wednesday July 14, 2021

Flooding on Route 66 near Crooked Lake, Averill Park - Wednesday July 14, 2021 - Craig Adams

Flooding along Route 66 near Crooked Lake, Wednesday July 14, 2021 

Flooding on Glass Lake Road - Wednesday July 14, 2021 - Craig Adams

Flooding along Glass Lake Road, Wednesday July 14, 2021 

Cloud to ground lightning strike over Albany - Wednesday July 14, 2021 - Trevor English

Cloud to ground lightning strike over Albany, Wednesday July 14, 2021