30 September through 1 October 2010 Record rainfall across the northeastern U.S.

 

After a rather warm dry summer (and most of September) a big synoptic pattern change took place across the Northeastern Conus. Instead of ridge overhead or nearby, an unusually deep trough and cutoff low began building into the region on the closing days of September.

The GFS forecasted a very wet event 10 days (or more) out, developing some sort of tropical system and bringing it up the coast on the leeside of the trough. At least one model run made it looks a little like the "Perfect" storm, some sort of intense surface low hugging the coast as it raced up from Florida, bringing massive rainfall. Apparently this model was the very first to indicate an unusual event possibly forthcoming, although it backed off the solution while the ECMWF model was more consistent in the Day 5-7 range of forecasting a potentially heavy rainfall event.

Tropical Storm Matthew formed in the Caribbean on September 23rd. This storm then went west into Central America and Southern Mexico, producing massive rainfall. While the storm never affected our region in any direct way, its remnants might have begun to establish an impressive tropical feed that began to form shortly after its demise around September 26th.

At the same time, an upper air low that had brought an unusual rain event to portions of California, opened up and move toward the southeast and eventually cut off again. This system began transporting the remnants of tropical moisture northward. Also, another trough began buckling the jet stream further north, causing heavy rainfall across the Great Lakes. Energy from this system merged with the initial upper low system. At the surface, a slow moving cold front began moving from the Ohio Valley to the east. Aloft, an exit region underneath an increasing upper level jet, formed from the Gulf of Mexico, northward to New York State. Both these forcing mechanisms, along with a low level jet, transported PWAT air over 2.5 inches into our region by late September 30th.

To make things more interesting, yet another tropical storm formed, Nicole, near Cuba on September 28th, right in the tropical fetch. This disturbance was technically a tropical storm for less than 12 hours. However, it remained a depression and eventually rode northward along the slow moving front which at this point lined up from just west of Wilmington, NC northward to just west of the Hudson Valley.

Initially a synoptic low pressure and its associated warm front, located well north of the tropical stream of heavy rain, produce isentropic lift and a band of moderate to heavy rain of its own, during the morning hours of September 30. Up to two inches of rain fell across portions of the Litchfield County and portions of the Mohawk Valley. Most other areas received an inch or less of rainfall with this first surge of rain.

Thursday looked to be the day of our biggest weather problems. There were legitimate concerns on the possibility of high winds, torrential rainfall and possibly even severe weather with isolated supercells, due to very strong low level wind shear. A Flood Watch has been issued early Thursday morning by the midnight shift. A Wind Advisory was also issued, upgraded to a High Wind Warning across the higher terrain to the east of the Hudson Valley.

As it turned out, a dry slot actually moved into most of our region as the warm begrudgingly lifted north of the Mohawk Valley by Thursday afternoon. After the initial shot of rain, much of the remainder of Thursday saw just occasional light rain or showers. The atmosphere remained too stable for any thunderstorms to form.

However, things began to change by nightfall. An impressive heavy swath of rain was moving slowly eastward right along and just behind the cold front, into our region from the west. Dewpoints surged into the low 70s, ambient temperatures into the upper 70s. A few thunderstorms did form along this line, one of which proved to be severe in Hamilton County. The winds increased out of the south, gusting to near 40 mph in the valleys, and possibly over 55 mph across the Higher Terrain where there were some scattered reports of power outages (especially in Bennington County) as well as downed tree and limbs.

The remnants of Nicole moved right along the front as it crossed into our region overnight. Massive rainfall rates and accumulation ensued. Rain easily fell at an inch an hour or more much of the overnight across much of the region. Rain continued well into Friday, but at lesser rates, closer to a third to half an inch per hour.

When the rains left by Friday afternoon, 6-8 inches of rainfall had fallen across our region, much of that in the western portions of the Capital region! As of 900 PM on the evening of September 30th, Albany was working on its 6th driest September on record, the driest since 1964. By 1AM, the end of the climatological month, we had a wetter than normal September!

Two consecutive days of record breaking rain fell on September 30th and October 1. The last time there have been two back to back record rainfalls on the record books, were the last two days of December 1948.

Minor to moderate flooding occurred across our entire HSA, but not until October 1st. There were water rescues in places like Central Avenue in Colonie as the road became quickly flooded. Our entire region was under an aerial flood warning, with many river point warnings issued as well. The flooding was the worst in September since the passage of Tropical Storm Floyd back in 1999. Had it not been for unusually dry antecedent conditions prior to the rainfall, the flooding would have likely been much worse.

Above: Liquid equivalent precipitation forecasts from the GFS (upper left), NAM (upper right), ECMWF (lower left) and GGEM (lower right) for 4 consecutive runs valid 0000 UTC 2 October. Note the bands of extreme values of 5 or more in all the guidance. However, some guidance was suggesting one broad band of rainfall, while other guidance was suggesting multiple bands. The multiple bands of extreme rainfall were predicted by guidance initialized closer to the observed event.

Above: NAM12 liquid equivalent precipitation forecast initialized 1200 UTC 29 September and valid 1800 UTC 2 October. Note the multiple bands of extreme rainfall being predicted as well as the extreme values well over 5 within the bands. Also note the relative minimum through the Hudson Valley through the Capital District.

Above: Winds and isotachs at 925 hPa for the GFS (upper left), NAM (upper right), ECMWF (lower left) and 850 hPa from the GGEM (lower right) for 4 consecutive runs. Note that NY and western New England were in the cyclonic convergent region of a strong low level jet segment.

 

Above: Surface winds and isotachs from the NAM12 initialized at 0600 UTC 30 September valid 1800 UTC 30 September, 0000 UTC 1 October and 0600 UTC 1 October. Note the predicted surface winds were much weaker than the predicted 925 hPa winds. However, due to the southerly wind direction, some channeling through the Hudson Valley could be expected, increasing the surface winds and the potential for winds to reach wind advisory criteria.

 

Above: GEFS winds and anomalies at 925 hPa and 850 hPa initialized 1200 UTC 30 September and valid 1200 UTC 1 October. Note that NY and western New England were in the cyclonic convergent region of the low level jet segment. Also note the V winds were > 5 SD above normal, suggesting significant moisture advection and convergence.

 

 

Above: GEFS MSLP and PWAT and anomalies initialized at 1200 UTC 29 September (left), and 1200 UTC 30 September (center and right), valid at 0000 UTC 1 October (left and center) and 1200 UTC 1 October (right). Note the PWAT values between 3 SD and 5 SD above normal. These were originating in the subtropics and tropics, were values very rarely seen, and suggested extreme amounts of moisture streaming over the northeastern U.S.

 

 

Above: GEFS probabilities for 3.00 in 36 hours (left), 4.00 in 48 hours (center left and center right), and 5.00 in 48 hours (right), initialized between 1200 UTC 29 September and 1200 UTC 30 September, valid at various times on 1 October to early morning on 2 October. Note the probabilities above 60% over a large area for all the amounts. Large areas of > 60% probabilities for these QPF values is extremely rare, and suggests high confidence for widespread rainfall amounts at or above these QPF values.

Above: SREF 850 winds and anomalies initialized 09Z 30 September and valid 1200 UTC 1 October. Note that NY and western New England were in the cyclonic convergent region of the low level jet segment. Also note the V winds were > 5 SD above normal, suggesting significant moisture advection and convergence.

 

 

Above: SREF MSLP, PWAT and anomalies initialized at 0900 UTC 30 September and valid 0000 UTC 1 October (left) and 1200 UTC 1 October (right). Note the PWAT values between 3 SD and 5 SD above normal. These were originating in the subtropics and tropics, were values very rarely seen, and suggested extreme amounts of moisture streaming over the northeastern U.S.

 

 

 

 

Above: SREF probabilities for 3.00 in 36 hours and 4.00 in 48 hours initialized at 0900 UTC 30 September and valid 1200 UTC 1 October (left) and 0000 UTC 1 October (right). Note the probabilities above 60% over a large area for all the amounts. Large areas of > 60% probabilities for these QPF values is extremely rare, and suggests high confidence for widespread rainfall amounts at or above these QPF values.

 

 

Above: GEFS plume loops for Albany, NY, Binghamton, NY, Montpelier, VT, and Montgomery, NY. Notice the clustering above 3 inches in most cases, which is extremely rare, and suggests exceptional rainfall totals.

 

 

Above: SREF plume loops for Albany, NY, Binghamton, NY, Montpelier, VT, and Montgomery, NY. Notice the clustering above 3 inches in most cases, which is extremely rare, and suggests exceptional rainfall totals.

 

 

 

Above: Soundings from Upton, NY (OKX) at 0000 UTC 1 October (left) and 1200 UTC 1 October (right). Note the extreme PWAT values, and the instability.

 

 

Above: MSAS loops of MSLP and wind barbs showing the development and progression of the surface low pressure center.

 

 

 

Above: Loops of water vapor satellite imagery. Note the plume of tropical moisture surging through the northeastern U.S.

 

 

 

Above: Loops of visible satellite imagery. Note the stream of tropical moisture into the northeastern U.S.

 

 

Above: Loop of radar reflectivity through the event.

 

 

Above: Stage 4 total rainfall through the event. Note the widespread 5.00+ rainfall amounts, and in some cases above 8.00.

 

 

 

Above: Hydrographs from Rosendale on Rondout Creek, Prattsville on Schoharie Creek and Coldbrook on Esopus Creek.

 

 

Above: Hydrographs from Mount Marion on Esopus Creek, Little Falls on the Mohawk River, and Kast Bridge on West Canada Creek.

 

 

Above: Hydrographs from Hope on Sacandaga River, Hinckley on West Canada Creek and Gilboa Dam on Schoharie Creek.

 

 

Above: Hydrographs from Delta Dam on the Mohawk River, Burtonsville on Schoharie Creek, and Brookfield on Still River.

 

 

Above: Hydrographs from Utica on the Mohawk River and Troy on the Hudson River.

 

Any comments, questions or suggestions, please mail to:Neil.Stuart@noaa.gov