November 26-27, 2013 Storm Summary

November 26-27, 2013 Rain/Ice/Snow/Wind

0308The most significant storm since June affected the region as a low pressure tracked up the East Coast, producing widespread heavy rain, ice, snow and wind, easing the moderate drought and preventing the fall of 2013 from ending up as the driest fall on record. Widespread rain totals of 1 to 3 inches were recorded across the region, locally up to/over 4 inches along the axis of heavy rain, along with significant snow and ice accumulations in the interior Northeast and wind gusts up to 55 mph.

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November 26-27, 2013 Storm Archive

NWS Regional Radar
WPC Surface Analysis


Storm Synopsis

nov27trackAn area of low pressure formed near the Gulf of Mexico on the 25th as an upper level low tracked east through the southern US. As this low pressure developed, a northern stream trough began to dig SSE through the central US, picking up and phasing with the southern system, bringing the surface low pressure up the East Coast.

By Tuesday evening, November 26, the low was located near South Carolina, but became increasingly elongated as the system entered the Northeast US in two waves, with the northern wave entering the region on Wednesday morning and the southern wave lagging behind near the Carolinas. As phasing between the two energies took place, the surface low pressure began to consolidate as it tracked through New England while deepening at a faster rate, with a minimum pressure near 994 millibars over NYC and 986 mb over Maine. The storm quickly tracked north out of the region by Wednesday night as it continued to rapidly deepen over eastern Canada. While the track appears to resemble that of a nor’easter, it was not exactly one, especially considering that due to the strung-out low pressure setup, there were few in the region who actually experienced northeasterly winds.



Forecasting The Storm

November 22 – Very Cold, Possibly Stormy Week Ahead
November 23 – Frigid Week Ahead; Rain Tuesday Night
November 24 – Heavy Rain, Wind on Wednesday
November 25 – Significant Storm Tomorrow, Wednesday
November 26-27 Storm Updates


Post-Storm Analysis

11/21 12z ECMWF run at hour 144, showing a strong low pressure near NYC with widespread heavy rain. It incorrectly handled most storms this fall at the hour 144 time range, but in this case was more accurate with the storm. (image credit: PSU e-Wall)

f144Long Range: Signs for a storm around the November 27-30 time frame have showed up well in advance, with some long range GFS runs signaling the potential for a coastal storm as far back as November 15-16, and was first mentioned in the November 19 forecast discussion. As the time frame entered the 180 hour range on November 20, most of the operational models were in agreement of a significant storm affecting the region, with the GFS showing a coastal low with heavy rain near the coast and heavy snow just inland, the ECM showing a rain/snow event, and the CMC initially showing a similar storm to that of the GFS before trending further amplified and inland. Initially, this was noted with caution as throughout most of the fall of 2013, almost every single low pressure near the Northeast US was significantly exaggerated by the medium range ECMWF especially beyond the hour 144 range. The November 20 discussion noted that the progressive flow and lack of north Atlantic blocking could prevent a significant storm from developing, but that should the storm affect the region, the pattern setup supported rain near the coast and snow inland.

11/22 0z run of the GFS at hour 144 (0z Thurs); this run showed a significant storm, but incorrectly depicted a major snowstorm just inland of the coast and a more consolidated surface low (image credit: PSU e-Wall).

f144_2Medium Range: The model guidance is known for having more difficulties with handling storms in the medium range, and this was no exception; by late November 20, the GFS sided with a weaker and more suppressed storm, a theme which continued into November 21 with support from the CMC, while the ECM continued to show phasing of the northern and southern streams with a coastal low pressure producing widespread heavy rain. Despite the GFS remaining offshore, however, the majority of its ensemble members depicted a much more amplified scenario, signaling the operational run may be too suppressed; this was noted in the November 21 forecast discussion, when the forecast placed a 50% chance of rain.

By November 22, the CMC began to depict an amplified storm phasing and tracking up the coast or just inland, and continued with this solution with occasional minor changes until the short range, despite being too amplified and too far west at times, a typical recurring CMC bias. The GFS temporarily resumed showing a major storm, with heavy rain near the coast and heavy snow inland, but had some inconsistencies with its handling of the phase, as it depicted a fairly consolidated low pressure quickly intensifying as it tracked up the coast, when in reality the low was more strung out and took longer to quickly intensify. The ECM depicted a two-wave scenario with some similarities to the final outcome, with heavy rain on the morning of November 27 and the second wave mostly staying north/east on the 27th.

11/23 18z run of the GFS at hour 96 (18z Weds), showing its incorrect handling of the setup by keeping the northern and southern streams separate, with the southern energy later phasing with the northern shortwave depicted over Montana (image credit: PSU e-Wall).

f96The support from the GFS was short lived, however, as by November 23, it trended again towards a more suppressed storm as a result of incorrectly handling the energies involved, as it was too slow with the southern stream and too flat/progressive with the northern stream; in its 11/23 18z run, it actually depicted the southern stream slow enough that it phased with a separate northern stream shortwave coming in from behind, producing some snow in the southeast US and a major storm in Newfoundland. By that point, however, the remainder of the model guidance was fairly consistent with its handling of the storm, showing an elongated low pressure tracking roughly along the I-95 corridor, but with the main uncertainty regarding the setup of the second wave during the day on Wednesday.

Short Range: By November 24, the model guidance was in full agreement on a major storm affecting the region as the GFS sided with its ensemble members and gradually trended towards a more amplified storm. At that point, the main uncertainty was regarding the exact track, precipitation totals and wind speeds, with most models generally depicting between 1.5 and 4 inches of rain; the NAM entered the storm time range on the 24th and depicted at least 3-6 inches of rain across the area, showing its typical wet bias, before backing down on rain totals the day before the storm. The models gradually narrowed down these differences up until the day of the storm, with otherwise relatively decent agreement on the storm in the short range.



Storm Timeline in the Northeast

Regional radar image from 6:18 AM EST 11/26, from the National Weather Service. Widespread light snow fell from central PA into southern NY and New England, with the main storm entering Virginia.

11.26.13_1118Precipitation initially began to fell in the region early on the morning of Tuesday, 11/26, as widespread light snow spread through central PA into eastern NY and central New England associated with a weak low pressure over southern Canada tracking northeast. This round of precipitation continued for a few hours before exiting as the main precipitation shield entered the Mid Atlantic towards 7-9 AM. Most locations observed rain, but with snow and freezing rain falling towards the higher elevations of West Virginia and western Virginia. The storm continued to spread northeast into Pennsylvania and New Jersey by 10 AM-12 PM, starting out as light snow across most of Pennsylvania and rain in New Jersey. In the NYC area, this started with light snow/sleet in northern NJ/SE NY and rain/sleet in NYC and western Long Island, but quickly changed over to rain by 1-2 PM for most except for interior NW NJ/SE NY.

Regional radar image from 12:08 AM EST 11/27, from the National Weather Service. Heavy rain fell across the area, with snow in northwestern NY and freezing rain in central Pennsylvania.

11.27.13_0508As the precipitation continued to expand northeastward with mid level warm air advection, the rain/snow line continued to progress northeast, gradually covering the entire region except for western PA and NY. With the surface low pressure east of the mid level trough axis, however, colder air remained near the surface north and west of the low pressure track, with central-northern Pennsylvania, NW NJ and the higher elevations of New York and New England changing over to freezing rain by the mid-late afternoon hours. This freezing rain was heavy at times, especially over Pennsylvania, with a gradual changeover to rain occurring by the evening but with surface temperatures making little progress beyond the low-mid 30s.

Heavy rain entered the NYC area towards 9 PM, and continued through most of the overnight hours. Initially, interior NW NJ continued to see freezing rain, but quickly changed over to rain as temperatures slowly warmed up. By 12 AM, the warm front entered Long Island and NYC, continuing to spread inland until reaching its most interior extent by 4 AM, over north central NJ into SE NY. This set up for a tight temperature gradient, with the warm sector surging into the low 60s with a strong SE wind, gusting up to 40-55 mph. Just inland of the front, however, temperatures remained in the low 40s with light winds.

Regional radar image from 2:18 PM EST 11/27, from the National Weather Service. The second wave affected the region, with rain in the area and snow starting to fall in eastern Pennsylvania.

11.27.13_1918The cold front cleared NYC by 7 AM and the rest of Long Island and CT by 10 AM, with temperatures falling back into the 50s and 40s as a steady west wind picked up in intensity. Following the passage of a front, drier conditions were observed for the rest of the morning aside from a brief wave of light-moderate rain around 9-11 AM. As the second wave moved into the region, precipitation redeveloped over the Mid Atlantic and entered the area around 2 PM; with colder air moving in aloft from the west, snow started falling over central Pennsylvania, with the rain/snow line gradually shifting east until reaching western NJ around 4 PM and central NJ by 6 PM. At that point, however, the main precipitation shield began to move out, and the rain/snow line failed to advance further east; precipitation ended for most of the area around 6-7 PM with lingering rain/snow showers for some afterwards.


Storm Impact and Precipitation Totals

Below is an estimated snow accumulation map, based on snow reports from the National Weather Service. An estimated rainfall map will be added soon.

11.26.13_snowThe storm was the most significant system to affect the region in an extended period of time, during which a moderate drought developed over the northeast US; the last 2+ inch rain event in NYC was with tropical storm Andrea in June, almost half a year prior to this event, and the last 1+ inch event, or more specifically 1/4 inch, was on September 22. One of the most notable aspects of this storm was its rain totals, with the axis of heavy rain setting up from central VA into east PA, northern NJ/NYC, southern New England and downeast Maine, where 2 to 4 inches of rain fell. Elsewhere across the region, liquid-equivalent precipitation totals of at least 1 to 2 inches were observed. In the warm sector of the storm, strong wind gusts were observed especially towards Long Island and southern CT, with widespread gusts in the 40-55 mph range, including 54 mph in Bridgeport, CT; locally higher gusts were observed, with a report as high as 64 mph in Stony Brook, NY (Suffolk) and 56 mph in Jericho, NY (Nassau).

In addition to the rain, the storm also produced significant snow and ice totals over the interior Northeast. An initial wave of light snow moved through Pennsylvania into NY and New England on Tuesday morning, producing up to 1-2 inches of snow, with the main storm producing over 1 inch of snow mainly northwest of an axis from central PA into central NY and VT/NH/Maine. Snow totals were relatively light for the main part, but with the axis of heaviest snow over western PA/NY, where at least 6-12 inches of snow accumulated. Widespread light freezing accumulations of under 0.1 inch were observed in the interior Northeast, including NW NJ, with an area of 1/4 to 1/2 inch of freezing rain over south central Pennsylvania.

Below is a list of rain totals from airport observations across the area from the National Weather Service:

Northern NJ:
2.68″ – Teterboro, NJ (Bergen)
2.48″ – Newark, NJ (Essex)
1.72″ – Andover, NJ (Sussex)
1.40″ – Sussex, NJ (Sussex)

Southeast NY:
2.85″ – White Plains, NY (Westchester)
1.62″ – Montgomery, NY (Orange)

New York City:
2.49″ – Central Park, NY (Manhattan)
2.21″ – LaGuardia, NY (Queens)
1.97″ – JFK Airport, NY (Queens)

Long Island:
2.09″ – Islip, NY (Suffolk)
1.98″ – Montauk, NY (Suffolk)

1.82″ – Shirley, NY (Suffolk)
1.47″ – Farmingdale, NY (Nassau)
1.32″ – Westhampton Beach, NY (Suffolk)

Southern CT:
2.81″ – Meriden, CT (New Haven)
1.81″ – Bridgeport, CT (Fairfield)
1.37″ – New London, CT (New London)
1.27″ – New Haven, CT (New Haven)

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