Wednesday July 1, 2009 Isolated Severe Weather,
Capital Region Flash Flood Event

A stagnant weather pattern featuring a strong closed upper air low pressure system located over southern Ontario was responsible for this second consecutive day of severe weather and torrential over the region. The players on this day consisted of a weak occluded frontal boundary that lined up along and just west of the Hudson valley, allowing a moist flow of air to continue over eastern New York and western New England with dewpoints ranging through the lower to middle 60s. The boundary also acted as a weak surface focusing mechanism for the afternoon and evening convection that formed. Dense fog and low clouds during the early to mid morning burned away for a couple of hours allowing partial sunshine during the late morning and early afternoon. The subsequent surface heating pushing temperatures into the middle and upper 70s combined with cooling temperatures aloft (500 mb temperature at 8:00pm over Albany of -17° Celsius) created sufficient instability for strong thunderstorm updrafts to form.

The event began with a small cluster of slow moving thunderstorms over northern Schoharie and western Schenectady counties during the early afternoon. This one small thunderstorm cluster essentially remained parked, through a process of back building propagation, over western and central Schenectady County between 1pm and 3pm producing between 2.00" and 3.75" of rain on Delanson and Duanesburg leading to flash flooding. At approximately 2:45pm the storm became severe over Glenville producing large hail and a damaging downburst of wind. A subsequent quick burst of additional severe thunderstorms occurred in and around the Capital Region, Washington County, and the mid Hudson valley between 2:45pm and 5:00pm before the t-storms over the Capital Region consolidated into a slow moving line which dumped torrents of rain over southern and eastern Saratoga, western Washington, eastern Schenectady, northeast Albany, and northwest Rensselaer counties causing significant flash flooding between approximately 3:00pm and 7:00pm. Many road closures were reported in and around Schenectady, Clifton Park, Cohoes, Easton, and North Troy to name just a few of the harder hit communities. In Schenectady, Broadway and a part of Union Street were closed, Northern Drive in Troy was closed between Gurley Avenue and 7th Avenue due to rushing water with debris coming down the road. Sewer caps in North Troy were reported to have been blown off due to jets of flood water coming up from the sewer system with flooding on 125th Street and 2nd Avenue as well. In Easton, two bridges along County Route 113 were reported to have been washed out by flash flood waters.

The following two images are the Albany Doppler weather radar storm total rainfall estimates for the Capital Region as the event was ending. Note, Doppler weather radar will often overestimate rainfall amounts when hail is present, as it was in this event, as the algorithm can not determine from the reflectivity a difference between heavy rain and hail. In this case, however, based on WeatherNet 6 ground spotter rainfall observations, the radar estimates were pretty close, except in the five inch pocket in southwest Washington County, (the purple shaded area in figure #1) where the estimate was a little high.


#1: ENX (Albany NWS Doppler Radar) Storm total Rainfall Estimate: Storm total rainfall estimate for the Wednesday, July 1, 2009 Flash Flood Event. Ground spotter truth from the WeatherNet 6 spotters indicated 2.50" to 4.00" of rain fell in the most saturated zone. The rain fell in approximately a three hour time frame creating the flash flood situation.

Albany National Weather Service Doppler Radar Storm Total Rainfall Estimate, Wednesday July 1, 2009 

#2: ENX (Albany NWS Doppler Radar) Storm total Rainfall Estimate: A closer shot of the immediate Capital Region

Albany National Weather Service Doppler Radar Storm Total Rainfall Estimate, Wednesday July 1, 2009 

WeatherNet 6 Storm Total Rainfall Reports

Town County Rainfall Report Town County Rainfall Report
Sharon, CT Litchfield 0.19" Savoy, MA Berkshire 0.15"
Lanesborough, MA Berkshire 0.10" Pittsfield, MA Berkshire 0.24"
           
Green Island Albany 3.36" Colonie Albany 1.38"
Latham Albany 2.95" Albany (Airport) Albany 2.76"* (Record)
Albany (NWS) Albany 1.50" Voorheesville Albany 0.57"
Berne Albany 1.90" Cohoes Albany 3.45"
           
Kinderhook Columbia 0.42" Livingston Columbia 0.42"
Hudson Columbia 0.20" Ancramdale Columbia 0.23"
           
Speigletown Rensselaer 3.60" Schaghticoke Rensselaer 3.05"
Brunswick Rensselaer 2.09" Wynantskill Rensselaer 0.99"
Center Brunswick Rensselaer 1.04" Melrose Rensselaer 2.82"
Troy Rensselaer 2.60"      
           
Mechanicville Saratoga 1.72" Clifton Park Saratoga 2.34"
Clifton Park (The Oaks) Saratoga 1.60" Round Lake Saratoga 1.20"
Charlton Saratoga 0.85" Malta Saratoga 1.10"
Wilton Saratoga 0.82"      
           
Delanson Schenectady 2.28" to 3.65" Scotia Schenectady 1.29"
Niskayuna Schenectady 1.07" Schenectady Schenectady 1.32"
           
Jefferson Schoharie 0.30" Fulton Schoharie 0.30"
Richmondville Schoharie 0.39"      
           
Kingston Ulster 0.35" West Shokan Ulster 0.09"
           
Lake Luzerne Warren 0.12" Bolton Landing Warren 0.25"
           
Cossayuna Washington 0.76" Fort Edward Washington 0.75"
Granville Washington 0.25"      

Albany Doppler Radar Images at the Peak of the Torrential Rain

#3: ENX base reflectivity image 4:37pm Wednesday July 1, 2009: A multicell complex of thunderstorms in the process of consolidating into a solid slow moving torrential rain making line. Severe weather at this point at just about ended with the storm complex transitioning into a flash flood producer.

Multicell thunderstorm complex consolidating over the Capital Region, 4:37pm, Wednesday July 1, 2009 

#4: ENX base reflectivity image 5:19pm: At this time the line had consolidated into a solid zone of slow moving torrential downpours. Rainfall rates at times in portions of the line exceeded an inch per hour.

Multicell thunderstorm complex producing torrential rain over the Capital Region, 5:19pm, Wednesday July 1, 2009 

Severe Weather and Flash Flood Reports

The reports listed in the table were compiled by the Albany National Weather Service office for the purpose of verifying the severe thunderstorm and flash flood warnings that were issued for this event and does not necessarily represent the total number of severe weather or flash flood occurrences that materialized with this event.
Town County Storm Report Time
East Glenville Schenectady Quarter Sized Hail (1.00" diameter) 2:47pm
Glenville Schenectady Quarter Sized Hail 2.:50pm
Ballston Lake Saratoga Penny Sized Hail (3/4" diameter) 2:50pm
Glenville Schenectady Wind damage, trees blown down 2:50pm
East Glenville Schenectady Nickel Sized Hail (0.88" diameter) 2:50pm
Charlton Saratoga Quarter Sized Hail (1.13" diameter) 2:58pm
Burnt Hills Saratoga Nickel Sized Hail 3:03pm
Glenville Schenectady FLASH FLOOD, Three to Four Feet of Water on Glenville Road 3:04pm
Glenville Schenectady Wind damage, trees blown down on Glenridge Road 3:04pm
Duanesburg Schenectady FLASH FLOOD, Duanesburg Churches Rd. closed 3:30pm
Copake Columbia Nickel Sized Hail 3:37pm
Snake Hill Saratoga Ping Pong Ball Sized Hail (1.50" diameter) 3:45pm
Delanson Schenectady FLASH FLOOD, Turnbull Road closed 3:45pm
Cohoes Albany Lightning strike on a home 4:35pm
Cohoes Albany 58 mph wind gust 4:35pm
5 Miles West of Cohoes Albany Penny Sized Hail 5:04pm
Roessleville Albany Nickel Sized Hail 5:05pm
One Mile North of Troy Rensselaer FLASH FLOOD, Many roads closed in North Troy, extensive flash flooding 5:18pm
Cohoes Albany FLASH FLOOD, many roads closed, vehicles stranded in the water 5:18pm
Brunswick Rensselaer Heavy Rain, 1.33" in an hour ending at 5:51pm 5:51pm
3 Miles NW of Albany Albany FLASH FLOOD, Central Avenue closed underneath I-90 5:55pm
2 Miles No. of Albany Albany FLASH FLOOD, Sand Creek Rd. and Everett Rd. closed due to flooding 5:59pm
Latham Albany FLASH FLOOD, Route 2 closed due to high water 6:10pm
Easton Washington FLASH FLOOD, Cheese Factory Road closed, seven foot deep trough cut through the road, Route 113, Old Schuylerville Road, and Meeting House Road among the flooded 6:13pm
Waterford Saratoga FLASH FLOOD, Fonda road washed out, peopled rescued from homes 6:20pm
Near Reynolds Rensselaer FLASH FLOOD, Route 67 bridge closed on the Rensselaer side 6:20pm
Stillwater Saratoga FLASH FLOOD, Durham Road washed out, Route 4 flooded and closed 6:20pm
2 MIles West of Cohoes Albany Heavy Rain, 3.47" measured in three hours, two feet of water covering Windmill Way, flooding on Truman Way 6:40pm