A warm and humid air mass was over the region and had been in place for several days. A slow moving surface boundary was draped across the North Country and extended westward towards western New York and Lake Ontario. This boundary was  the focus for convection on May 26th and 27th and again on May 28th.
A combination of individual storms and merging storms trained over the same area of central Warren county in a southwest-northeast direction, with at least 10 or so  storms moving over the same area Saturday afternoon, May 28th. This resulted in a swath of heavy rainfall which fell in just a few hours causing flash flooding resulting in road closures with significant damage to many roadways, washed-out culverts and a least a couple of washed-out bridges. Thurman, Stoney Creek, Warrensburg, and Chester were impacted with some residents displaced from their homes. The worst flooding and damage occurred in Thurman where about a quarter of the roads were closed due to the flash flooding.  It was reported that seven area fire departments, three EMS crews, the Warren County Sheriff's Office, State Police, along with state, county and local highway departments all responded to the flooding.
Damage in Warren County from the May 28th flooding were estimated at 12.6 million dollars.
In addition, a few of the storms were severe producing large hail up to the size of a golf ball and some trees were downed by strong thunderstorm winds.

Hail in WARREN, NEW YORK
From 28-MAY-11 12:30:00 to 28-MAY-11 12:35:00 (EST-5)
Location: KNOWLEHURST
Magnitude: 0.88 
Crop damage: 0.00K
Reported by: Public

Nickel size hail was reported in Knowelhurst (Stony Creek) during a thunderstorm.

Thunderstorm Wind in WARREN, NEW YORK
From 28-MAY-11 12:45:00 to 28-MAY-11 12:45:00 (EST-5)
Location: STARBUCKVILLE
Magnitude: 50.00 EG
Crop damage: 0.00K
Reported by: Law Enforcement

A tree was reported down on Landon Hill Road in Chestertown due to strong thunderstorm winds.

Thunderstorm Wind in WARREN, NEW YORK
From 28-MAY-11 12:50:00 to 28-MAY-11 12:50:00 (EST-5)
Location: ATHOL
Magnitude: 50.00 EG
Crop damage: 0.00K
Reported by: Law Enforcement

A tree was reported down on High Street near Athol due to strong thunderstorm winds.

Flash Flood in WARREN, NEW YORK
From 28-MAY-11 16:07:00 to 28-MAY-11 20:30:00 (EST-5)
Location: WARRENSBURG
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

The Northway, Interstate 87, was closed between Exits 23 and 25 due to water and debris covering the road. The southbound lanes were re-opened just before 6:30 pm EDT, however the northbound lanes remained closed until 9:30 pm EDT.

Flash Flood in WARREN, NEW YORK
From 28-MAY-11 15:07:00 to 28-MAY-11 20:30:00 (EST-5)
Location: ATHOL
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Flash flooding reported at Glen Athol Road and Valley Road in Warrensburg with part of the road washed away.

Thunderstorm Wind in WARREN, NEW YORK
From 28-MAY-11 13:06:00 to 28-MAY-11 13:06:00 (EST-5)
Location: THE GLEN
Magnitude: 50.00 EG
Crop damage: 0.00K
Reported by: Law Enforcement

A tree was reported down on Route 28 in Warrensburg one mile north of Golf Course Road due to strong thunderstorm winds.

Hail in WARREN, NEW YORK
From 28-MAY-11 13:32:00 to 28-MAY-11 13:37:00 (EST-5)
Location: HAGUE
Magnitude: 1.00 
Crop damage: 0.00K
Reported by: Park/Forest Service

Quarter size hail was reported at the Rogers Rock Campground in Hague during a thunderstorm.

Hail in WARREN, NEW YORK
From 28-MAY-11 15:15:00 to 28-MAY-11 15:20:00 (EST-5)
Location: WARRENSBURG
Magnitude: 1.75 
Crop damage: 0.00K
Reported by: Public

Golf ball size hail was reported in Warrensburg during a thunderstorm.

Flash Flood in WARREN, NEW YORK
From 28-MAY-11 15:35:00 to 28-MAY-11 20:30:00 (EST-5)
Location: BRANT LAKE
Flood cause: Heavy Rain
Property damage: 12.60M
Crop damage: 0.00K
Reported by: Public

Numerous roads were closed due to flash flooding and damage from heavy rainfall from training thunderstorms in Thurman, Stony Creek, Warrensburg and Chestertown including the following: Mountain Road, High Street, River Road, Harrisburg Road, South Garnet Road, Combs Road (severe damage), Dippikill Road, Green Mansions Road, Stock Farm Road, and Route 9 between Warrensburg and Chestertown.
In Stony Creek, an elderly woman was rescued from her trailer alongside a creek off Murray Road; her home and another trailer were destroyed by the flood waters. Also, a man was rescued from the roof of his home on Warrensburg Road. Some residents of South Garnet Road were stranded in their homes and some students missed several days of school due to a washed out bridge. The Warrensburg Central School District had to reroute bus routes due to damaged roads.
The Lake George Schroon Valley Resort flooded. Visitors to Camp DippiKill, a retreat owned by the University at Albany student association, were stranded as all access roads were reported washed out. A farm off near Mountain Road suffered flooding, no animals were harmed.

Hail in WARREN, NEW YORK
From 28-MAY-11 12:39:00 to 28-MAY-11 12:44:00 (EST-5)
Location: THURMAN
Magnitude: 1.50 
Crop damage: 0.00K
Reported by: Public

Ping-pong ball size hail was reported in Thurman during a thunderstorm.

Hail in WARREN, NEW YORK
From 28-MAY-11 13:05:00 to 28-MAY-11 13:10:00 (EST-5)
Location: ATHOL
Magnitude: 1.25 
Crop damage: 0.00K
Reported by: Park/Forest Service

Half dollar size hail was reported at the Daggett Lake Campsites in Warrensburg during a thunderstorm.