Feb 5, 2013: Significant Storm Possible Friday

Forecast Highlights:

Mainly cloudy skies continued across the area with occasional snow showers, with highs reaching the upper 20s to low 30s across the area. Snow totals fell in the low end of the forecast range, generally under 1/2 inch. Partly sunny skies will return for Wednesday and Thursday with warmer temperatures, ahead of the next storm to affect the region on Friday, which has the makings of a significant storm for parts of the region. After a brief warm up for early next week along with a rain event, a colder pattern is expected to return.


Tonight – Thursday: Dry, Slightly Warmer

Additional light snow showers are expected tonight, with accumulations remaining below 1/2 inch. Following this light snow event, warmer temperatures will return into the region as the cold air mass over the region begins to slightly retreat north, with highs expected to reach the mid to upper 30s inland and upper 30s to low 40s for the rest of the area on Wednesday, along with a west/WNW wind at 5-15 mph. Cold overnight lows are expected again, dropping back into the 10s away from NYC, with colder temperatures for Thursday peaking in the low to mid 30s inland and the mid to upper 30s for the rest of the area.

Friday – Weekend: Moderate-Significant Storm More Likely

Until this point, the forecast for Friday was complicated; what initially looked to be nothing more than a weak clipper was changed after an ECMWF run 3 days ago showed a major storm affecting the region, but it was a significant outlier compared to the models back then and even now – the low pressure tracked over the NYC area, with only central-northern New England receiving a significant snowstorm. Since then, the rest of the models continued to show a weak low pressure while the ECM held to its solution of a significant coastal low pressure developing. Last night’s update, despite staying more on the conservative side due to uncertainty and trends so far this season, noted that while the ECM may have been too strong, the possibility was there it was onto something with a coastal low pressure developing. With the ECM holding steady with a major storm and the other model trending towards the same direction, a significant snowstorm is now increasingly likely to affect the region.

The storm is the result of two shortwaves phasing over the northeastern US; this takes place under a rather marginal setup, however, with a western US ridge axis east of the ideal location for a major storm along with a lack of blocking near Greenland, which favors New England receiving the most significant impacts of the storm as opposed to the NYC area. The northern stream has been shown to have more digging throughout today’s runs, with the GFS and ECM currently supporting a moderate storm affecting the NYC area and a major storm in New England. The 12z ECM was the most bullish model run of the day, with rain changing to snow with several inches for parts of the area, developing into a blizzard in New England northeast of the area.

There are two main factors regarding why the worst of the snowstorm is likely to be more towards New England as opposed to NYC; one is the aforementioned setup, with a trough in the western US and a ridge axis a little east of a position that would ideally support a major snowstorm for the NYC area. This would generally favor the storm peaking in intensity a little too late and too far east for the heaviest snows to focus nearby. Additionally, this is not a pure coastal low pressure, as there is a weak primary low pressure heading into Pennsylvania, which then dies out as phasing takes place and the coastal low intensifies. This part, however, is more uncertain and where potential exists for changes to either turn this into a light-moderate rain/snow event or a major snowstorm for the area; although at this time, it appears phasing will take place a little too late for the storm to develop early and far west enough for NYC to receive the worst of the storm, this can still change slightly which would have an impact on the location of heavier snow. The axis of heavy snow is still subject to some revisions, potentially to the point where the area ends up with moderate-significant accumulations, and this potential needs to be monitored closely at this time.

Preliminary Forecast: While confidence is not very high yet regarding the exact outcome, the latest thinking is for a coastal low to develop near eastern North Carolina and move northeast, with a rain/snow mix inland and mostly rain further south, perhaps starting out with a period of snow. As the storm intensifies and heads towards New England by the evening, the rain/snow line is likely to shift south, likely changing back to snow across the area with additional accumulations, although exactly how much snow accumulates from this point is uncertain at this time. Overall, at the very least, light to moderate snow accumulations are likely for most of the area, with the best chance of significant accumulations over 6 inches currently towards interior SE NY and Connecticut, possibly including parts of Long Island.

There is still uncertainty regarding the exact development of this storm, however, and this needs to be monitored for the possibility that most of the area ends up observing a significant snowstorm, which is a real concern at this time; the possibility exists that should phasing take place earlier, the low pressure may also track close enough to result in a widespread moderate-significant snow event for the majority of the NYC area in addition to New England, in which case snow totals could easily exceed 6-12 inches across the area. Stay tuned for more information on this storm with Wednesday’s forecast discussion.

Longer Range: Briefly Warmer, Then Colder

Slightly cooler temperatures will briefly return for Saturday, followed by a warm up for Sunday and early next week with highs returning into the 40s. A storm is expected to track well north of the area, with rain followed by a cold front moving through, bringing a colder pattern back into the region. The latest model guidance indicates another storm potential towards mid-late next week, although the storm is too far out in the long range to determine potential impacts. Stay tuned for more information on the longer range.

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