January 21, 2014 Snow
The third major snowstorm of the winter and biggest snowstorm since February 2013 affected the NYC area on January 21-22, producing a narrow swath of heavy snow along with strong winds and cold temperatures. The storm was notable for its difficult forecasting, having only shown up in its entirety on the model guidance just 2 days before the onset of snow. Snow totals ranged from 3-5″ in interior central CT to 6-11″ in coastal CT; 2-4″ in NW NJ/interior SE NY; 9-13″ in northeast NJ and Westchester county; 7-13″ in NYC; and 9-14″ in Long Island.
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January 21, 2014 Storm Archive
This storm originated as an Alberta clipper-type system in western Canada as a strong arctic air mass surged southward over Canada, the first to do so since early January, with the clipper diving southeast into the Midwest US but with a lack of a well defined surface low pressure. The system was associated with a strong shortwave trough, which amplified and became neutrally tilted as it reached the southeast US near Tennessee and North Carolina.
Two low pressure centers were initially present on Tuesday afternoon, 1/21, one ahead of the shortwave near western North Carolina and the other near SE Virginia, which later shifted off the coast while reaching a minimum pressure of 996 mb. As the trough gained a neutral tilt near the coast, the low near western North Carolina reached the coast and became the dominant low pressure center, with the broad area of low pressure beginning to consolidate as the focus of heavy precipitation shifted from the NYC area into the coastal Mid Atlantic. The shortwave then became negatively tilted, with the low pressure beginning to rapidly deepen as it tracked northeast parallel to the coast, reaching a minimum pressure near 982 mb while off the coast of New Jersey, and ultimately reaching 968 mb on Wednesday evening as it became occluded and began weakening while passing through Newfoundland.
Forecasting The Storm
January 18 – Cold Returns Next Week
January 20 – Snow Tomorrow, Then Cold Again
January 21 – Heavy Snow, Windy, Cold Tonight
January 21 Storm Updates
1/18 18z run of the GFS at hour 78 (0z Wed), depicting a weak low pressure with light snow brushing southeast Virginia (image credit: PSU e-Wall).
Medium Range: The forecasting of this storm system was mostly notable for the lack of a consistent storm signal from the model guidance until the short range, making the forecasting of this storm more difficult than usual. In the medium range, the ECM originally depicted a strong coastal low affecting the region with its 1/15 0z and 12z runs but had a different setup than what was observed, with moderate to heavy snow mostly setting up from Long Island into New England while extending westward into NY state with the 12z run. The 1/16 0z run still had a storm signal but was suppressed and weaker, keeping light snow limited to the coastal regions. The GFS generally depicted a weak low pressure offshore, with only one run, the 1/16 6z run, depicting a deepening clipper system tracking over NYC with a general 2-5 inches of snow from the area into southern New England. The 12z model suite generally saw the ECM and GFS back off from their earlier depictions with the system staying offshore, while the 12z CMC depicted a major storm but with again with a different setup than actually observed, with a 967mb low near Boston producing widespread heavy snow over the area extending northward into eastern NY state. The following model runs on 1/17 and 1/18 were somewhat more consistent with a weaker low pressure remaining offshore, possibly brushing coastal areas with light snow.
1/20 18z run of the GFS at hour 30 (0z Wed), depicting the heavy snow setting up over the NYC area (image credit: PSU e-Wall).
Short Range: A common theme with storms leading up to this event was for the model guidance to underestimate shortwaves emerging out of western Canada, and this system ended up being a similar case where the correction helped to result in a gradual trend towards a stronger and further west low pressure. Stronger signals for a widespread snowstorm only began to re-emerge with more consistency on 1/19, just two days before the storm, with the full magnitude of the snowstorm not being properly depicted until only 30-36 hours prior to the onset of precipitation. The GFS first depicted the low pressure tracking close enough for widespread snow in the area with its 1/19 6z run, about 60 hours out, with about 0.10 inch of liquid-equivalent precipitation over NYC, but with the vorticity maximum too strung out. A slow northwest trend continued with the following runs with the 18z run depicting 0.20″ of precipitation, while the ECM and CMC continued to support a weaker system staying offshore with little to no snow over the area.
The rest of the model guidance only began to catch up with the northwest trend with the 1/20 0z runs, the day before the storm. The GFS first supported widespread moderate to heavy snow accumulations, depicting just under 0.50″ of precipitation in NYC which along with higher snow to liquid ratios supported at least 6-10 inches of snow, as it corrected towards a stronger and sharper shortwave and a more consolidated vorticity maximum near eastern New Jersey. The 0z CMC then followed along, with the heaviest snow over central NJ into NYC with 0.50 to 0.70 inch of precipitation; the CMC generally continued to depict similar precipitation totals through the day of the storm. The ECM, not having performed very well with snowstorms during the winter, was too slow to catch up with the trend again, with the 0z run only keeping 2+ inch accumulations southeast of NYC, not fully depicting widespread moderate to heavy snow in line with the other models until the 12z run.
1/20 18z run of the GFS at hour 36 (left), and 1/22 0z run at hour 6 (right), focusing on the same frame, depicting the short range differences with the handling of the system (image credit: PSU e-Wall).
Focusing on the GFS from the 1/20 0z run through 1/21, each run continued to reflect minor adjustments to the shortwave trough, leading to continuous changes until precipitation was already ongoing. As previously noted, the vorticity maximum was modeled to set up near eastern New Jersey, but the shortwave continued to trend sharper with a further south vorticity max with each run until initialization, when in reality it passed through North Carolina. The incorrect handling of the shortwave led to the GFS initially depicting the second round of precipitation in the Mid Atlantic as a consolidated precipitation shield with heavy snow extending into NYC and Long Island, as opposed to a strung out precipitation shield with heavy snow over the southeast Mid Atlantic and North Carolina which would later shift offshore. Partially as a result of this, the 1/21 18z to 1/22 6z runs expanded the moderate snow coverage area too far inland, with over 3″ of snow extending as far north as Albany, NY into east central Maine, while slightly overdoing precipitation totals over the area with nearly 0.70″ of precipitation over NYC. This scenario also kept precipitation over the area for too long, extending into 4-7am over the immediate NYC area, when in reality the strung-out nature of the precipitation shield following the further south than anticipated development of the low pressure pushed most of the snow east of NYC by 10pm.
Another source of error in the forecasting of the system came from the handling of the northern end of the precipitation shield, as the GFS often tends to smooth out precipitation gradients too much due to its lower resolution, but even when accounting for this on higher resolution models such as the NAM, modeled snow totals were too high northwest of the heavy snow band, where persistent subsidence resulted in light snow rates for the entire duration of the storm.
Storm Timeline in the Northeast
Regional radar image from 2:18 PM EDT 1/21, from the National Weather Service, showing the heavy snow band as it expanded north through NYC.
As a clipper-type system shifted southeast towards the region accompanied by an arctic air mass, temperatures steadily fell in the morning and the early afternoon into the mid-upper 10s as light snow gradually began to fall towards 7-9am. With the aid of strong lifting and frontogenesis at 700mb overlapped with the dendritic growth zone, a narrow band of heavy snow developed over Philadelphia into central NJ around 11am-1pm, which along with high snow to liquid ratios up to 20:1 resulted in snow rates up to 2-3″/hour. As the more favorable dynamics shifted north into the NYC area, the heavy snow band lifted north, first into Long Island and NYC by 1pm and northeast NJ, Westchester county and southern CT by 2-3pm.
Regional radar image from 7:18 PM EDT 1/21, from the National Weather Service, showing the heavy snow band as it shifted southeast through NYC while the coastal low pressure organized near North Carolina.
With the favorable dynamics situated over the area, the heavy snow band remained in place through at least 7pm, continuing to produce heavy snow over the aforementioned locations, while a tighter pressure gradient in response to the deepening coastal low pressure led to a strengthening northerly wind, especially in Long Island, coastal CT and NYC where near blizzard conditions were observed at times. With the strong banding focused over the immediate NYC area, however, subsidence persisted just inland of the main band, keeping northwest NJ and SE NY under light snow rates.
By the evening and early overnight hours, the trailing low pressure began to organize near eastern North Carolina, with the precipitation shield pivoting towards a SSW-NNE orientation as the shortwave trough passing through NC gained a neutral and eventually a negative tilt. As this occurred, heavier precipitation developed over North Carolina and the southeast Mid Atlantic region, with the more favorable dynamics weakening over the area and shifting south towards the developing low pressure. The heavy snow band gradually shifted east through NYC into west-central Long Island and southern CT after 7pm before largely collapsing by 9-10pm as locations north and west of NYC dried up with only isolated snow showers persisting. The heavy snow from the second round stayed off the coast overnight as the low pressure began to rapidly intensify while tracking northeast, although light snow persisted over central-eastern Long Island and SE CT through the early morning hours before moving out of the region.