The teleconnections just aren't in the favorable territory for a late December snowstorm for the Northeast. Among the most prevalent is the positive NAO and the raging positive AO.
The NAO has been on a mixed path this fall, up until about November 20th, when the NAO took a turn for the positive territory. Since then, the NAO has not managed to get into negative territory, which has hurt the Northeast's snow chances. As of right now, the NAO is entering a raging positive phase. This is typically hard to break, and even with a sudden change that would bring the NAO down to negative territory, this process would take at least 3 days. Because today is December 23, and the storm is supposedly on the 27th, I do not believe that the NAO will be able to dip into negative territory fast enough in time for a snow event in the Northeast.
A typical NAO features a high pressure over Greenland, leading to a dip in the jet stream over the Northeast, where storms would move around the Northeast region and produce snow for that area. The new 18z NAM is showing pretty much the opposite, with a ridge of high pressure affecting the Northeast and instead pushing the jet stream north. The 27th storm then dumps a few inches of snow on Illinois, Indiana, unable to get to the Northeast due to the high pressure. I am liking this solution, as the NAO should still be positive enough to influence these conditions.
The Arctic Oscillation (AO) involves a vortex (spinning) of air over the Northern parts of the NH (North Hemisphere). When this vortex is unusually weak or nonexistent, the AO is said to be negative. Cold air then flows south into the US. However, when this vortex is strong, the cold air is literally locked in that space where the vortex covers. Until that vortex weakens, the cold air is forced to stay north. As of right now, we see the AO moving into a strong positive phase. Like the NAO, this is hard to break. Because it will likely be still positive on the 27th, not enough cold air would be present, even if the storm managed to squeeze into the Northeast. I could see a rain event being the outcome.
It's just not a good combo of teleconnections right now for this storm. I am not supporting the idea of a Northeast snowstorm, but do feel that there is potential for the Great Lakes to get some snow rather than the Northeast.
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| Past NAO and AO indices. (Policlimate) |
A typical NAO features a high pressure over Greenland, leading to a dip in the jet stream over the Northeast, where storms would move around the Northeast region and produce snow for that area. The new 18z NAM is showing pretty much the opposite, with a ridge of high pressure affecting the Northeast and instead pushing the jet stream north. The 27th storm then dumps a few inches of snow on Illinois, Indiana, unable to get to the Northeast due to the high pressure. I am liking this solution, as the NAO should still be positive enough to influence these conditions.
The Arctic Oscillation (AO) involves a vortex (spinning) of air over the Northern parts of the NH (North Hemisphere). When this vortex is unusually weak or nonexistent, the AO is said to be negative. Cold air then flows south into the US. However, when this vortex is strong, the cold air is literally locked in that space where the vortex covers. Until that vortex weakens, the cold air is forced to stay north. As of right now, we see the AO moving into a strong positive phase. Like the NAO, this is hard to break. Because it will likely be still positive on the 27th, not enough cold air would be present, even if the storm managed to squeeze into the Northeast. I could see a rain event being the outcome.
It's just not a good combo of teleconnections right now for this storm. I am not supporting the idea of a Northeast snowstorm, but do feel that there is potential for the Great Lakes to get some snow rather than the Northeast.
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