Record breaking warmth will return Christmas week

I’m dreaming of a…Green Christmas? While there will certainly be no shortage of “White Christmas” puns in the weather headlines over the next week, the real story will be in the meteorological pattern evolving. The warmth we experienced over the past few days was impressive, and the warmth being advertised on medium range forecast models for the period around Christmas is arguably more impressive. Owing to a large trough in the West and Southwest United States, a large ridge is expected to build over the East Coast, pumping in much warmer than normal air once again next week.

Without any cold air source, or high latitude blocking, mild Pacific air can enter the region unabated. This is the same reason that record high temperatures were broken during the tail end of last week and this past weekend — southerly winds brought in mid and low level atmospheric temperatures that were highly anomalous. And it is likely the same reason that records will be broken in the period of time around Christmas.

Here’s how the pattern will shake down, and why:

El Nino and the Gulf of Alaska trough

Much has been made this Autumn and meteorological Winter in regards to the El Nino. Truth is, it’s quite strong — and has a tremendous influence on global atmospheric circulations. For our purposes, El Nino is producing much warmer than normal waters throughout the Equatorial Pacific Ocean. These waters are shifting all around the Pacific, actually, and eventually the warmer waters have an impact on the airmass above it as well. This air has a propensity to shift east/northeastward toward the United States.

Currently, the strong El Nino is working in tandem with what meteorologists refer to as a GOA Trough, or Gulf of Alaska trough. This is a large, notable feature which exists in the Gulf of Alaska, and extends southward to the Western Coast of Canada and the United States. Colder than normal temperatures occur throughout Alaska and along the West Coast. Most notably for our region, a trough there means the PNA (Pacific/North American Index) is in negative modality.

A negative PNA is almost always associated with a trough on the West Coast, and a ridge on the East Coast. Not surprisingly, the negative PNA and El Nino are working in tandem to produce a ridge on the East Coast — one that features extremely mild, anomalously warm air. This upcoming Christmas week will be no different; models show a large West Coast trough and a ridge on the East Coast.

Lack of high latitude blocking

To a certain extent, this ridging on the East Coast can be negated by high latitude blocking. High latitude blocking occurs when ridges of high pressure develop in the higher latitudes; most often Central Canada, Greenland, the Davis Straight, or the Northwestern Atlantic. These blocks can not only help dislodge cold air from the poles farther south, but they can also negate a large ridge on the East Coast, and change the pattern downstream.

This Autumn and meteorological Winter so far, there has been no high latitude blocking at all. In fact, the stratospheric polar vortex (way up there) is one of the strongest and most consolidated in recent memory. This may sound confusing, but think of it this way:

In order for polar air to be dislodged southward toward our area, or the United States, that stratospheric/atmospheric polar vortex needs to be disrupted — or sometimes even split. If it is strong and consolidated, as one large entity, it often doesn’t move much. This means that polar/arctic air stays consolidated near the poles, and doesn’t shift toward our area at all.

Wrapping it all up

The combination of the aforementioned features, all juxtaposed, helped to produce the record breaking warm temperatures we observed in our area this past week and weekend. The same combination will work to produce much above normal temperatures in the period of time around Christmas, as well.

Forecast models are in excellent agreement on much warmer than normal conditions and, in fact, in excellent agreement that record high temperatures will be challenged. Some forecast models are indicating the potential for temperatures 24 or more degrees above normal averages.

If you’re a winter or snow lover, stick with it. Your time will come several weeks down the road. More details on that in our next premium post.