After such a cold November, the Arctic air has taken a break so far for the month of December. Temperatures have been slightly above the average for the month, with nothing too warm, and nothing too cold. We will be seeing some slightly cooler and drier air being directed back into New England to end the week with increasing sunshine and temps mostly in the 30's for highs with building high pressure. This should take us right through the weekend with cool and fair weather.
We have been talking about Sunday for the potential of a burst of rain and snow. The potential still exists for a light mix to develop, but now it appears Monday and Tuesday may be more problematic with the low will tracking south of New England in a progressive, fast flow. A significant system will not be able to gather close to us to create any big problems, but the weather will come with some rain and the potential for snow in higher elevations.
While the weather will not be ideal to start next week, we are also keeping a close eye around the Christmas Eve day-night as it looks like a storm is in the works for the Northeast. There has been a parade of storms lined up in the Pacific Ocean and these storms continue to pile into the nation and keep the weather pattern active. The strongest storm will pile into Washington and Oregon Thursday with 4-8" of rain. This low will dig into the Great Lakes next week along with a push of colder from Canada. A deep trough will form and direct moisture from the Gulf of Mexico right into the Northeast Wednesday (Christmas Eve Day). A warning to last minute shoppers: don't wait for this day, since it could be miserable with heavy rain! Upper level winds will direct warmer air up the east coast with this blast rain and gusty winds. Temperatures will surge into the 50s with the potential for a few embedded thunderstorms in any downpours. So at this point, the chances of a white Christmas appear low, unless you are in the mountains of Vermont, New Hampshire, and Maine.
Luckily, this front will push through quickly so that Christmas Day is simply looking breezy and cooler. This storm will be a powerhouse as it lifts north over the Great Lakes Christmas morning. It will likely become one of a few triggers sparking a wholesale pattern change in the weather.
The end of December and much of January we can expect much colder and stormier weather to develop. We see signs and triggers which will bring about this change. First, we see the North Atlantic Oscillation taking a dive around Christmas. This means pressures are expected rising over Greenland, which can create blocking in the jet stream and allow cold air from Canada to be directed into the Northeast. The buckling, high amplitude flow of the jet stream also becomes more favorable for storms to form and be directed up the Northeast coast.
While the cold has been lacking in the overall pattern, you can see how by Dec. 26-27, the Arctic air is returning back into the U.S. and will eventually shift east. The contrast between the Arctic cold air and milder air will become another focus for storms to generate.
Forecast ensembles and guidance are showing a clear cold signal heading into the month of January. The cold will keep the jet stream active, so I would expect a couple a good snow storms in January along with more Arctic blasts of air. No surprise there. It's very typical for this time of year, but definitely a change from this December weather, which has been welcome break. Saddle up: it's time to go for a ride!