There has been a lot of talk the last couple of days about a major East Coast snowstorm during the first week of January. Two of the major models (the GFS and ECMWF) show a storm sometime during either the middle or latter part of the first week of January. While I do believe there will be a trough that swings through the eastern part of the country, the GFS and ECMWF are extremely over amplifying this feature.
NOTE: I will be writing this post assuming you already know what the AO, NAO, and PNA are, if you do not, you can refer to yesterday’s post that explains these indices.
As I mentioned yesterday, I do believe there will be periods of cold air and snow that will affect the eastern portion of the country starting during the first week of January. However, I do not believe that there will be a major east coast snowstorm such as the models are showing. Here is why:
- The AO is still extremely positive, and although it is forecast to become less positive over the next two weeks, it will not become negative. On top of that, the AO is more positive than any model has forecast, so I would expect the actual AO index to remain higher than the average of the forecasts. Below is the two week AO forecast, where the yellow shading shows the ensemble mean, while the upper and lower red lines show the range of the forecasted indices, respectively.
Two week AO forecast. Yellow shading = ensemble mean; redlines = upper and lower forecasted index.
- The NAO is positive, and just like the AO, it too is at the high (positive) end of every model forecast. While the NAO will likely approach neutral, or perhaps even turn slightly negative, it won’t be enough.
Two week NAO forecast. Yellow shading = ensemble mean; red lines - upper and lower forecasted index.
- To get a massive east coast snowstorm, you want both the AO and NAO to be negative, and the more negative the better. Also, you want the PNA to be positive, and it is forecast to be right around neutral, or perhaps even slightly negative.
Now this is not to say there will not be cold air and snow somewhere in the northeast U.S., or perhaps even the mid-Atlantic, during the mid or latter part of the first week of January. As I mentioned yesterday, with the AO and NAO forecast to become less positive, this will allow for cold (arctic) air to sink southward into the eastern U.S., especially the northeast U.S. The ingredients just do not appear that they will come together for a major east coast snowstorm during the first week of January.
