Jan 4: Update on Friday Storm

Verification for Sunday: I expected snow showers in the afternoon, with high temperatures in the low 20s north and west of NYC and in the mid 20s for NYC and closer to the coast. This forecast mainly verified, though some places towards Passaic, NJ and Orange, NY counties had highs in the upper 10s.

Verification for Sunday Night: I expected low temperatures in the mid to upper 10s north and west of NYC, and in the low 20s for NYC and closer to the coast. This forecast verified.

Tonight: Partly Cloudy. Low temperatures will be in the mid to upper 10s north and west of NYC, and in the upper 10s to lower 20s for NYC and closer to the coast.

Tomorrow: Partly Cloudy. High temperatures will be in the mid to upper 20s north and west of NYC, and in the upper 20s to lower 30s for NYC and closer to the coast.

Tomorrow Night: Mostly Cloudy. A few snow showers possible. Low temperatures will be in the upper 10s to lower 20s north and west of NYC, and in the lower to mid 20s for NYC and closer to the coast.

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No big snowstorm?

In this time range of about 4 days before a storm comes, the forecast models usually begin to agree on a solution. From starting out with a solution that showed what had the potential to become a major snowstorm for a lot of people, the forecast has changed to a not so snowy solution. What changed on the weather models that is causing this solution to be shown?

One thing that was always an issue for this storm is too much cold air. We have a widespread arctic air mass across the United States, which would prevent any coastal low from moving inland. Then, the long range GFS model showed a storm dropping out of the Northwest into the Gulf of Mexico, filling up with moisture, and moving up the East Coast, producing a widespread snow event. However, as the other, more accurate short range models came into this time range, they have showed a solution more different that the GFS. Instead of the low dropping into the Gulf of Mexico, it is unable to do that, and what we get is a weak storm racing through the Ohio Valley into the Mid Atlantic. That type of storm is called an Alberta Clipper, typically due to its origin from Alberta, Canada, and a clipper due to this type of storm being fast moving. Then we have a weak storm that forms in the Southeast, however due to the amount of cold it is unable to move along the coast, and moves out to sea harmlessly. Below is what the NAM model shows for this time period:

Image source: http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/nam/18/images/nam_pcp_084m.gif

For those who do not know how to read this map, this would show a weak storm moving through the Ohio Valley, with light snow in the light green areas, which in this case would be from Illinois to New Jersey/Maryland.

If we were to take the current storm solution, the result would be the clipper moving through the Ohio Valley, producing light snow of 2 to 4 inches, however as it reaches Pennsylvania, the Appalachian Mountains act as a barrier and prevent most of the snow from advancing east. While the clipper would continue moving east and probably start intensifying as it moves offshore, it would not be able to produce too much snow for the area, and we would end up with light snow, with generally light accumulations no more than 2 inches. Also while the forecast models had trouble with forecasting coastal storms this year, they did not have much trouble with forecasting storms that tracked inland, which leads me to believe that we will likely not be seeing a significant trend away from this solution. We will still see some changes, though I am thinking that we are starting to close in on a weak, fast moving storm solution. I will probably make my first scenario map tomorrow.

After this storm though, it will be turning much colder. High temperatures will return into the 20s, and in the case that it ends up being colder than currently expected, interior areas further away from NYC might even see highs in the 10s.

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