Feb 6, 2013: Friday Storm Forecast Update

Forecast Highlights:

Warmer temperatures were observed today, returning closer to average with highs in the upper 30s to low 40s. The main focus at this time is on a storm expected to affect the region on Friday into Friday night; while there remains uncertainty regarding exact impacts in the NYC area, this storm has the capability of producing a significant snowstorm for the Northeast US region, including the NYC area.



Latest Friday Storm Forecast:

After a relatively uneventful winter, with snowfall below average so far across large parts of the region, the first significant frozen precipitation event since late December is expected to affect the region with widespread significant impacts. The last time a widespread snowstorm affected the region with significant accumulations was back in October 2011; the last time the Interstate 95 corridor was included in these significant accumulations was over 2 years ago, in January 2011. While uncertainty continues regarding the specifics of this storm, confidence continues to increase that this ends up as the most significant snow event to affect the area since November, with the potential for heavy snow or even blizzard conditions for parts of New England.

Since starting to show the significant storm yesterday, most of the model guidance has not been very consistent today. After the 0z ECMWF run last night showed a major snowstorm across the area, the 12z run backed away. The GFS was initially further southeast, before trending northwest to show a major snowstorm with its 18z run, and then back east with the latest 0z run. Despite the overall trend east with the coastal low with the 0z guidance, the latest 0z ECM run that just came in showed a major snowstorm for the area again, leaving it once again in the position of being the westernmost model. The overall idea remains at this time for a significant storm to affect the region, although there is still uncertainty regarding exactly how significant the impacts are and where the worst of the storm ends up.

The storm is the result of two shortwaves phasing over the northeastern US; this takes place under a rather marginal pattern, with a western US ridge axis east of the ideal location for a major storm along with a lack of blocking near Greenland. There remains uncertainty regarding the specifics of the phasing, which also result in additional model differences; should the northern stream dig more with earlier phasing, a more significant storm would end up taking place with a stronger coastal low closer to the area, with major snow accumulations from NYC to southern New England. It is also possible the timing and location of the phasing is unfavorable for the area to receive a major storm, with the coastal low pressure staying mostly east and most of the snow in the NYC area coming in from wraparound snows as the storm exits the region. The model guidance is still struggling with these specifics, resulting in different scenarios ranging from the 18z GFS and 0z ECM runs today showing a major snowstorm just east of NYC to the 0z UKMET which was considerably southeast with the coastal low pressure.

The main aspects of this storm that have high confidence are that moderate to significant snow accumulations are still expected across most of New York state into southern-central New England, with a coastal low tracking close to the region. At least some rain is likely to be involved especially near and east/south of NYC until the primary low is absorbed into the coastal low which then takes over, and at the very least light-moderate accumulations are expected across the area. The small differences with the coastal low pressure, however, will have a larger impact regarding whether the area ends up with a major snow event, or simply rain/snow changing over to moderate wraparound snow accumulations at the back end of the storm. At this time, there is not enough confidence to fully side with a single scenario, and later updates on Thursday will narrow this spread down into a high confidence outlook as the model guidance gradually trends towards a consensus.

Forecast for NYC Area: Despite the overall uncertainties regarding the coastal low pressure, there is moderate-high confidence on the first part of the storm. Light snow is expected to develop especially from NYC and further north on Friday morning, which then changes over to rain or a wintry mix of rain/snow/sleet by the early-mid afternoon hours except for SE NY and southern Connecticut away from the coast, which continue to see light to moderate snow with light accumulations. Temperatures will cool down by the evening as the coastal low pressure makes its closest approach to the area, with rain gradually changing over to snow from west to east. Periods of moderate snow are likely, heavy in parts of Connecticut and Long Island, with the storm ending by Saturday morning. For more localized forecasts, please refer to the latest 5-day forecast.

There remains uncertainty regarding the exact accumulations, which depend on the development of the coastal low pressure, although at this time, preliminary potential amounts are at least 5 to 10 inches of snow from NYC and further west, with 6 to 14 inches in SE NY into parts of Long Island and over 10-20 inches in most of Connecticut with localized higher amounts possible. Keep in mind these are preliminary amounts, and especially considering confidence is not very high yet, are subject to change with the next forecast discussion on Thursday night. It is still possible that the low pressure ends up further east with less significant impacts in the area; the potential continues to exist for a stronger storm closer to the coast, however, in which case heavy snow and wind from the coastal low would directly affect the area, especially Long Island and Connecticut; should this be the case, snow totals could easily exceed 12 inches east of NYC. If the coastal low tracks close enough to the coast to include southern New England and Long Island under the deformation band, major accumulations as high as 18-24 inches may be possible along with strong winds. Stay tuned for more information over the next few days, with a mid-day update to be posted on Thursday afternoon followed by the next full length discussion in the evening.

Longer Range: Briefly Warmer, Then Colder Again

Cold temperatures will briefly return behind the storm, with low temperatures expected to drop into the 10s for most of the area on Saturday night, perhaps below 10 degrees for interior northern locations. This will be short lasting, however, as the progressive pattern continues and another low pressure heads towards the Great Lakes and southern Canada, bringing a short lived warmth surge along with it. Temperatures will surge back into the 30s and 40s for highs on Monday with light rain expected, possibly falling as snow for interior areas early in the event. The cold front is expected to move through overnight, with a colder air mass returning for the rest of next week as highs return into the 30s. Another storm could affect the region late next week, potentially with more wintry precipitation, although at this time it is too early to determine exactly what impacts this will have across the region.

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