Early signs are that that the PNA may begin the month a bit more favorable than expected.. There is also some support for perhaps some subtle disruptions of the PV during the month, which would be congruent with what was expected during the month of December. I do not expect the early month PNA to bare much if any fruit for the coast, as climo is relatively hostile and Canada is still largely void of cold. After about the 10th. cold reservoir be more replenished and climo will be less adversarial.
I like the chances for a white xmas across a lot of the region....especially pike points north and outside of rt 128.
December 2020 Outlook
The polar vortex is likely going to begin the season quite consolidated near the pole during the month of November. However, the polar domain should become slightly less hostile to the development of periodic higher heights during the month of December, which may bring the AO and NAO closer to neutral, as dictated by previously referenced la nina climatology. This is when the more canonical, eastern pacific la nina regime will try to flex its muscle. Note the Aleutian high displaced to the northwest, and protruding poleward. The greatest positive height anomalies will likely be biased over the Aleutians, and to the east of Greenland, perhaps similar to the Ural blocking of October. This does not mean to imply excessive blocking for the period, which is not constituted by higher Ural heights, but more likely at least some transient periods of positive heights at higher latitudes. Alaska should also predominately feature some higher heights, especially across the western portion. There should be continuous RNA, so there is warmer bust potential should the vortex remain more consolidated than forecast.
December Forecast H5 Composite:
December Forecast Temperature Composite:
There has only been one winter (DM) month, March 2018, that has averaged a negative NAO since February and March 2013. It is postulated that there is a high likelihood that we will add to that list this season. Most likely in December, but possibly March or even both. The month of December should average 1-2 degrees below normal for northern New England, near normal to a degree above normal for central southern New England, and 1-2 degrees above normal from north to south near New York City points southward into the mid atlantic. Cold will dump over the high plains and bleed eastward.
December Forecast Precipitation Composite:
It should be an active period marked by above average precipitation, especially for points north of Washington, DC. Primary modes of cyclogenesis include Alberta clippers, southwest flow events, and Miller B redevelopers, the latter of which especially prevalent during periods of negative NAO. New England should be favored for snowfall, especially central and northern parts of the region. The mid atlantic will need breaks in the RNA to coincide with negative NAO flex for significant snowfall, which is not exceedingly likely, but possible. A White Christmas is more probably than climatology would suggest this season. While the month is likely to average a negative NAO in the mean, this is not meant to imply that excessive blocking will reside for the entirety of the month.