A vertically stacked upper level low moved slowly over eastern Pennsylvania, New Jersey and southern New York on Friday, May 20th. The surface low moved to near Long Island by the early afternoon.
Every event with a place to put it. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS ALY wrote it up.
A vertically stacked upper level low moved slowly over eastern Pennsylvania, New Jersey and southern New York on Friday, May 20th. The surface low moved to near Long Island by the early afternoon. Showers and thunderstorms developed in a moist and unstable airmass across the region. Storms trained or repeatedly moved over the same areas across a portion of Litchfield County resulting in flash flooding in the Waterbury area.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Albany, NY wrote its last area forecast discussion before the first event at May 20, 4:17 PM EST, 18 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE ALBANY NY 517 PM EDT FRI MAY 20 2011 .SYNOPSIS... A VERTICALLY STACKED LOW PRESSURE CENTER OVER LONG ISLAND WILL CONTINUE TO DRIFT EASTWARD AND BE SOUTH OF CAPE COD ON SATURDAY AND...AND WELL OUT TO SEA BY SUNDAY. A THREAT OF AFTERNOON SHOWERS AND THUNDERSTORMS WILL LINGER SATURDAY. AN APPROACHING FRONTAL SYSTEM WILL BRING A RENEWED THREAT OF SHOWERS AND THUNDERSTORMS STARTING SUNDAY AFTERNOON. THE FRONT IS FORECAST TO STALL OVER THE REGION WHICH WILL RESULT IN UNSETTLED WEATHER FOR MUCH OF THE COMING WEEK. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... SHOWERS AND THUNDERSTORMS OCCURRING ACROSS THE REGION THIS AFTER NOON WILL DIMINISH THIS EVENING WITH THE LOSS OF SOLAR HEATING. AN EASTERLY FLOW OF COOL MOIST AIR OFF THE ATLANTIC ALONG WITH CONVECTION TO THE EAST WILL RESULT IN LOTS OF CLOUDS TONIGHT. THE SHOWERS SHOULD PRETTY MUCH BE OVER WITH BY MIDNIGHT. THERE MAY BE SOME LIGHT FOG DUE TO THE LARGE AMOUNT OF LOW LEVEL MOISTURE...ALTHOUGH LOW STRATUS LOOKS TO BE MORE LIKELY. LOWS TONIGHT WILL BE IN THE LOW TO MID 50S IN THE VALLEYS WITH SOME UPPER 40S ACROSS COOLER REGION SUCH AS THE ADIRONDACKS AND HIGHER ELEVATIONS OF THE CATSKILLS AND WESTERN NEW ENGLAND. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/... SATURDAY WILL START OUT WITH PARTLY TO MOSTLY CLOUDY SKIES. THE CLOUDS WILL DIMINISH SOME DURING THE MORNING HOURS BUT THEN INCREASE DUE TO DIURNAL HEATING...WITH A CHANCE OF SHOWERS AND A FEW THUNDERSTORMS DURING THE AFTERNOON DUE TO LOW LEVEL MOISTURE AND INSTABILITY. HIGHS WILL RANGE FROM THE MID 60S TO NEAR 80. USED THE MAV/MOS WITH A FEW MODIFICATIONS. THE THREAT OF SHOWERS WILL END AND CLOUDS DIMINISH SOME DURING THE EVENING HOURS WITH THE LOSS OF SOLAR HEATING. SATURDAY NIGHT WILL FEATURE PARTLY CLOUDY SKIES WITH DRY WEATHER. WINDS WILL VEER AROUND TO THE SOUTHEAST. LOWS WILL RANGE FROM THE UPPER 40S TO THE MID 50S. SUNDAY WILL START OUT DRY BUT AN APPROACHING WARM FRONT IS LIKELY TO SPREAD SOME CLOUDINESS AND A SLIGHT CHANCE OF SHOWERS INTO THE REGION BY MID DAY. HIGHS WILL BE IN THE 60S AND LOW 70S WITH SOUTHERLY WINDS 10 TO 15 MPH. THERE WILL BE A HIGHER CHANCE OF SHOWERS SUNDAY NIGHT AS THE FRONTAL SYSTEM GETS CLOSER. LOWS WILL MOSTLY BE IN THE LOWER 50S UNDER CLOUDY SKIES. && .LONG TERM /MONDAY THROUGH FRIDAY/... AN UNSETTLED WEATHER PATTERN WILL CONTINUE INTO MUCH OF THE UPCOMING WORK WEEK. THE FLOW AT 500 HPA WILL BECOME WEST TO SOUTHWEST AS A TROUGH AXIS SETS UP ACROSS THE GREAT LAKES AND OHIO VALLEY AND RIDGING DEVELOPS ACROSS THE WESTERN ATLANTIC. WITH THE SOUTHWEST FLOW OVER THE AREA...TEMPS WILL BE WARMER THAN THIS WEEK...AS 850 HPA SIT AT AROUND 12-16 DEGREES C FOR MUCH OF THE WEEK. THIS WILL ALLOW FOR MAX TEMPS TO REACH THE UPPER 70S TO MID 80S FOR MUCH OF THE WEEK...ALTHOUGH THEY FINALLY MAY DROP A BIT BY FRIDAY AS THE TROUGH MOVES TOWARDS THE NORTHEAST. WITH THE SOUTHWEST FLOW...NEARBY UPSTREAM TROUGH...AND A WEAK SFC BOUNDARY SLOWLY MOVING TOWARDS THE AREA...THE THREAT FOR SHOWERS AND THUNDERSTORMS WILL BE IN PLACE FOR THE ENTIRE WEEK...ESP FOR NORTHWESTERN PARTS OF THE CWA. HAVE GONE WITH CHC POPS FOR MONDAY THROUGH FRIDAY FOR SHRA/TSRA...WITH THE BEST THREAT PROBABLY IN THE DIURNALLY FAVORED AFTN THROUGH EVENING HOURS. HAVE INCLUDED THUNDER...AS THE GFS FORECASTED SHOWALTER VALUES ARE NEGATIVE FOR MUCH OF THE WEEK. BOTH THE 12 UTC ECMWF/GFS SHOW A GOOD AMOUNT OF PRECIP OCCURRING DURING THE WEEK...ESP FOR NORTHWESTERN AREAS...WITH THE REPEATED ROUNDS OF SHRA/TSRA. WILL HAVE TO MONITOR MODELSTRENDS OVER THE NEXT FEW DAYS FOR NEXT WEEK FOR THE POTENTIAL FOR ANY HYDRO/FLOODING CONCERNS...ESP IF TRENDS CONTINUE REGARDING THE CURRENT MODEL FORECASTED QPF. && .AVIATION /21Z FRIDAY THROUGH WEDNESDAY/... VFR CONDITIONS SHOULD PREVAIL...BUT SOME BRIEF SHOWERS AND THUNDERSTORMS COULD PRODUCE SOME BRIEF INTERVALS OF IFR VISIBILITIES AND MVFR CEILINGS AT KALB AND KGFL. BASED ON RADAR TRENDS...KPOU SHOULD BE RAIN FREE MUCH OF THE AFTERNOON...BUT KEEPING VCSH IN CASE SOMETHING DEVELOPS MORE IN LINE WITH KPOU...AS SOME SHOWERS AND THUNDERSTORMS ARE ALREADY NEAR THE KPOU VICINITY...BUT NOT TRACKING TOWARD KPOU. COVERAGE OF SHOWERS AND STORMS SHOULD DECREASE WITH TIME THROUGH THE LATE AFTERNOON AND EVENING. BETWEEN 06Z-12Z...MVFR CEILINGS AND VISIBILITIES SHOULD DEVELOP WITH ALL THE LOW LEVEL MOISTURE AND LIGHT WINDS IN THE REGION. CEILINGS AND VISIBILITIES SHOULD IMPROVE TO VFR TOMORROW MORNING. WINDS WILL BE LIGHT NORTH AT 5 KT OR LESS THIS AFTERNOON AND EVENING...AND NEAR CALM TONIGHT. LIGHT NORTH TO NORTHEAST WINDS AT LESS THAN 10 KT SHOULD OCCUR TOMORROW MORNING. OUTLOOK... SAT...VFR/MVFR. CHC -SHRA/TSRA. SUN...VFR. NO SIG WX. MON-WED...VFR/MVFR. CHC -SHRA/TSRA. && .FIRE WEATHER... SHOWERS AND THUNDERSTORMS WILL DIMINISH TONIGHT WITH A LOSS OF HEATING FROM THE SUN. RAINFALL AMOUNTS WILL VARY WIDELY AS IS TYPICAL WITH CONVECTION. HIGH LOW LEVEL MOISTURE WILL LIKELY RESULT IN LOTS OF LOW STRATUS OR STRATOCU DURING THE NIGHTTIME HOURS...WITH HUMIDITY VALUES NEAR 100 PERCENT AROUND DAYBREAK. WINDS WILL BE LIGHT FROM THE NORTH OR NORTHWEST. SKIES WILL BE PARTLY CLOUDY SATURDAY WITH A CHANCE OF SHOWERS AND THUNDERSTORMS DURING THE AFTERNOON HOURS. MIDDAY HUMIDITY VALUES WILL RANGE BETWEEN 45 AND 65 PERCENT. WINDS WILL BE NORTH OR NORTHEAST 6 TO 12 MPH. CLOUDS WILL DIMINISH SOMEWHAT SATURDAY NIGHT AND AGAIN HUMIDITY VALUES WILL INCREASE TO NEAR 100 PERCENT AFTER MIDNIGHT. ON SUNDAY...AN APPROACHING FRONTAL SYSTEM WILL BRING ABOUT ANOTHER CHANCE OF SHOWERS AND THUNDERSTORMS STARTING IN THE AFTERNOON. MIDDAY HUMIDITY VALUES WILL RANGE FROM 45 TO 70 PERCENT...WITH SOUTHERLY WINDS 5 TO 15 MPH. PRECIPITATION AMOUNTS WILL BE HIGHLY VARIABLE OVER SHORT DISTANCES...WITH MOST AREAS GETTING LESS THAN A HALF INCH OF RAIN...BUT SOME SPOTS COULD GET WELL OVER AN INCH. && .HYDROLOGY... SHOWERS AND THUNDERSTORMS WERE OCCURRING OVER THE REGION THIS AFTERNOON. WHILE AVERAGE AMOUNTS OVER LARGER AREAS ARE NOT LIKELY TO EXCEED A HALF INCH THERE IS POTENTIAL FOR LOCALLY HEAVY RAINFALL OF WELL OVER AN INCH FROM TRAINING CELLS. THESE CAN PRODUCE SIGNIFICANT PONDING OF WATER...ESPECIALLY WHERE LARGE PAVED AREAS SUCH AS SHOPPING AND INDUSTRIAL AREAS SURROUNDED BY LARGE PARKING LOTS. HEAVY DOWNPOURS WILL ALSO CAUSE SHARP RISES ON STREAMS. THE SHOWERS WILL HAVE LESS OF AN EFFECT ON LARGER RIVERS. SHOWERS AND THUNDERSTORMS WILL DIMINISH THIS EVENING AND THE THREAT SHOULD BE OVER WITH AROUND MIDNIGHT. A FLOOD WARNING CONTINUES FOR THE ESOPUS CREEK BELOW THE ASHOKAN RESERVOIR. ABOUT A FOOT AND A HALF OF WATER WERE SPILLING FROM ASHOKAN RESERVOIR FROM HEAVY RAINFALL WEDNESDAY NIGHT. THE ESOPUS WAS STILL ABOVE FLOOD BUT RECEDING AT MOUNT MARION EARLY FRIDAY AFTERNOON BUT MORE SHOWERS AND THUNDERSTORMS WERE STREAMING INTO THE AREA SO ADDITIONAL RAIN MAY CAUSE IT TO LEVEL OFF. THE MOHAWK RIVER BETWEEN LAKE DELTA AND UTICA WAS RECEDING AFTER RISING TO NEAR BANKFULL FROM TORRENTIAL RAINS THURSDAY AFTERNOON. IT WAS STILL RISING AT LITTLE FALLS EARLY FRIDAY AFTERNOON BUT IS ONLY TWO TO THREE FEET ABOVE NORMAL AND WELL BELOW FLOOD. THE FLOOD WARNING ISSUED FRIDAY EVENING FOR UTICA WAS CANCELLED EARLY THIS AFTERNOON. MORE SHOWERS...AND A FEW THUNDERSTORMS...ARE POSSIBLE SATURDAY ...PARTICULARLY DURING THE AFTERNOON...BUT THE AIR WILL BE DRIER SO FOR THE MOST PART RAINFALL AMOUNTS WILL BE LIGHT. AGAIN...HEAVY RAINFALL IS POSSIBLE OVER SMALL AREAS...WHICH COULD PRODUCE LOCALIZED PONDING OF WATER. SATURDAY NIGHT AND EARLY SUNDAY WILL PROBABLY BE DRY. THERE IS A SLIGHT CHANCE OF SHOWERS OR THUNDERSTORMS SUNDAY AFTERNOON. A FRONTAL SYSTEM IS FORECAST TO APPROACH THE REGION FIRST AS A WARM FRONT MONDAY. IT IS THEN EXPECTED TO STALL NEAR THE REGION MONDAY NIGHT OR TUESDAY. THIS WILL AGAIN BRING ABOUT UNSETTLED WEATHER. IT WILL BE DRY MUCH OF THE TIME BUT THERE WILL BE A THREAT OF SHOWERS AND THUNDERSTORMS...WITH THE GREATEST THREAT DURING THE AFTERNOON AND EARLY EVENING HOURS. PRECIPITABLE WATER AMOUNTS WILL BE HIGH...SO THERE WILL BE A POTENTIAL FOR HEAVY DOWNPOURS. FOR DETAILS ON SPECIFIC AREA RIVERS AND LAKES...INCLUDING OBSERVED AND FORECAST RIVER STAGES AND LAKE ELEVATIONS...PLEASE VISIT THE ADVANCED HYDROLOGIC PREDICTION SERVICE /AHPS/ GRAPHS ON OUR WEBSITE. && .ALY WATCHES/WARNINGS/ADVISORIES... CT...NONE. NY...NONE. MA...NONE. VT...NONE. && SYNOPSIS...RCK NEAR TERM...RCK SHORT TERM...RCK LONG TERM...FRUGIS AVIATION...KGM FIRE WEATHER...RCK HYDROLOGY...RCK
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE ALBANY NY 1044 AM EDT FRI MAY 20 2011 CTZ001-013-MAZ001-025-NYZ032-033-038>043-047>054-058>061-063>066- 082>084-VTZ013>015-211100- NORTHERN LITCHFIELD-SOUTHERN LITCHFIELD-NORTHERN BERKSHIRE- SOUTHERN BERKSHIRE-NORTHERN HERKIMER-HAMILTON-SOUTHERN HERKIMER- SOUTHERN FULTON-MONTGOMERY-NORTHERN SARATOGA-NORTHERN WARREN- NORTHERN WASHINGTON-SCHOHARIE-WESTERN SCHENECTADY- EASTERN SCHENECTADY-SOUTHERN SARATOGA-WESTERN ALBANY-EASTERN ALBANY- WESTERN RENSSELAER-EASTERN RENSSELAER-WESTERN GREENE-EASTERN GREENE- WESTERN COLUMBIA-EASTERN COLUMBIA-WESTERN ULSTER-EASTERN ULSTER- WESTERN DUTCHESS-EASTERN DUTCHESS-NORTHERN FULTON-SOUTHEAST WARREN- SOUTHERN WASHINGTON-BENNINGTON-WESTERN WINDHAM-EASTERN WINDHAM- 1044 AM EDT FRI MAY 20 2011 THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTHWESTERN CONNECTICUT...WESTERN MASSACHUSETTS...EAST CENTRAL NEW YORK AND SOUTHERN VERMONT. .DAY ONE...THIS AFTERNOON AND TONIGHT. THERE IS A CHANCE OF MAINLY NON SEVERE THUNDERSTORMS THIS AFTERNOON THROUGH THE EARLY EVENING. ANY THUNDERSTORM THAT DOES FORM WILL MOVE SLOWLY FROM SOUTHEAST TO NORTHWEST AROUND 15 MPH. THUNDERSTORMS COULD PRODUCE LOCALLY SMALL HAIL AND COULD SLOWLY TRAIN OVER THE SAME FEW LOCALITIES...PRODUCING IN EXCESS OF TWO INCHES OF RAINFALL AND SIGNIFICANT PONDING OF WATER. .DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY. THERE IS A CHANCE OF THUNDERSTORMS SATURDAY AFTERNOON AND AGAIN MONDAY THROUGH THURSDAY. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ALBANY NY
355 PM EDT FRI MAY 20 2011
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0317 PM FLASH FLOOD MILLBROOK 41.78N 73.69W
05/20/2011 DUTCHESS NY TRAINED SPOTTER
ROUTE 44 FLOODED IN SEVERAL PLACES BETWEEN MILLBROOK AND
AMENIA.
&&
11PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ALBANY NY
405 PM EDT FRI MAY 20 2011
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0353 PM FLASH FLOOD 3 NW POLAND 43.26N 75.10W
05/20/2011 HERKIMER NY TRAINED SPOTTER
SMALL CREEK RUNNING OVER RUSSIA RD ONE HALF MILE WEST OF
MILITARY ROAD
&&
FRUGISPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ALBANY NY
410 PM EDT FRI MAY 20 2011
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0350 PM FLASH FLOOD COXSACKIE 42.36N 73.81W
05/20/2011 GREENE NY LAW ENFORCEMENT
MANSION ST. CLOSED BETWEEN BAILEY ST. AND LAWRENCE AVE
DUE TO FLOODING
&&
FRUGISPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ALBANY NY
412 PM EDT FRI MAY 20 2011
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0338 PM HAIL VALATIE 42.41N 73.68W
05/20/2011 E0.75 INCH COLUMBIA NY PUBLIC
&&
FRUGISPRELIMINARY LOCAL STORM REPORT...CORRECTED
NATIONAL WEATHER SERVICE ALBANY NY
419 PM EDT FRI MAY 20 2011
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0345 PM FLASH FLOOD 2 NE COXSACKIE 42.38N 73.78W
05/20/2011 COLUMBIA NY 911 CALL CENTER
ONE LANE CLOSED ON RT 9J DUE TO FLOODING AND DEBRIS.
NEARBY RAILROAD TRACKS FLOODED.
0358 PM FLASH FLOOD CLAVERACK 42.22N 73.72W
05/20/2011 COLUMBIA NY 911 CALL CENTER
FLOODING OF RT. 217 NORTH OF ROUTE 23
&&
FRUGISSPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE ALBANY NY
502 PM EDT FRI MAY 20 2011
NYZ065-202130-
WESTERN DUTCHESS NY-
502 PM EDT FRI MAY 20 2011
...A STRONG THUNDERSTORM IN
DUTCHESS COUNTY IN EAST CENTRAL NEW YORK...
AT 501 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
THUNDERSTORM CAPABLE OF PRODUCING...AROUND HALF INCH HAIL...WINDS
UP TO 50 MPH...FREQUENT LIGHTNING. THIS STORM WAS LOCATED NEAR
FISHKILL...OR ABOUT OVER BEACON...AND MOVING WEST AT 5 MPH.
THE THUNDERSTORM WILL BE NEAR...
BEACON BY 530 PM EDT
LAT...LON 4145 7400 4152 7401 4158 7396 4159 7378
4150 7376 4149 7392 4144 7398 4144 7399
TIME...MOT...LOC 2102Z 073DEG 6KT 4153 7390The Brookhaven radar (KOKX), 85 km away, was scanning. The volume nearest the first event began at 21:34 UTC.
1 flash flood. Local standard time, as filed.
Flooding was reported northwest of Waterbury in Litchfield County at the intersection of Route 6 and Route 63, on Route 63 between Echo Lake Road and Woodruff Avenue and on portions of Woodruff Avenue and Scott Avenue.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Connecticut in 2011Every state in 2011This day in weather historyWarnings in Connecticut, May 2011
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 311308.