12:30 PM (Tuesday) | ***The overall weather pattern becomes stormy and colder for the central and eastern US as we flip the calendar to December***

Teleconnection indices known as the PNA, AO and NAO are trending in a direction that favors colder and stormier weather for the central and eastern US. Plots courtesy NOAA (black:observed; red:forecasted)

Overview

The weather pattern will get pretty interesting in much of the US as we transition to the month of December and it is likely to include some significant temperature and height anomalies for this time of year.  High pressure ridging in the upper part of the atmosphere will intensify dramatically next week across Canada at the same time colder-than-normal air sets up across the central and eastern US and there will be plenty of strong energy aloft. The transition to this colder and stormy weather pattern in the central and eastern US (and warm weather pattern across Canada) could begin with a major storm system in the Monday/Tuesday time period (i.e., last day of November and first day of December). A second storm could threaten the east coast at the end of next week and that system should have more in the way of cold air to work with in the eastern states.

Colder-than-normal air is likely to push into the central and eastern US as we transition into the early part of December. Map courtesy NOAA, tropicaltidbits.com

Details

High pressure ridging will likely intensify significantly next week across Canada - possibly extending from coast-to-coast - and this type of upper air pattern can potentially produce some interesting winter-like weather conditions across the central and eastern US this time of year.  Many computer model forecasts in recent days have been consistent in building strong high pressure across Canada next week virtually wrapping over the entire top of the US and colder-than-normal air likely in much of the central and eastern states associated with deepening low pressure aloft.  In addition to the cold air, it looks like there will be lots of energy aloft to closely monitor next week which will be forced to move generally in a west-to-east fashion across the nation as a result of the strong (blocking ) ridging to the north.  While the US can become cold and stormy in this type of pattern in early December, it may become quite a bit warmer-than-normal across Canada.  There is, however, a pretty extensive snow pack across Canada and this could limit the warm-up next week across the Canadian provinces to our north.

Strong high pressure ridging is likely to form next week across Canada and the North Atlantic. Map courtesy NOAA, tropicaltidbits.com

In addition to the computer forecast models, there is also some support for the formation of a colder and stormier weather pattern in the central and eastern states by “teleconnection indices” including the Pacific-North American (PNA), Arctic Oscillation (AO), and North Atlantic Oscillation (NAO).  When the PNA goes “positive” this time of year and the NAO/AO go into “negative” territory, the result is often a colder and stormier weather pattern for the central and eastern states. Furthermore, there is some correlation between a highly active October and November with respect to tropical activity in the Atlantic Basin and a colder-than-normal month of December in the central and eastern US.  An average temperature anomaly for the month of December is shown below for five years with high tropical activity in the fall depicting colder-than-normal conditions in the eastern half of the nation (Credit Joe Bastardi, Weather Bell Analytics).

There is a correlation between highly active fall seasons (October/November) in terms of Atlantic Basin tropical activity and cold Decembers in the central and eastern US. This composite map of December temperature anomalies is for five different years that featured lots of fall season tropical activity in the Atlantic Basin. Credit Joe Bastardi, Weather Bell Analytics, NOAA

The transition to a colder and stormy weather pattern may very well begin with a major storm system early next week with heavy rain in much of the eastern US and accumulating snow in the Ohio Valley. As a strong cold front drops south and east into the eastern states, low pressure is likely to form and intensify in the frontal boundary zone and result in a significant precipitation event. After that initial storm, the overall pattern may very well remain on the stormy side and colder-than-normal given the blocking pattern that is likely to set up to the north of the US. In fact, a second storm could threaten the east coast at the end of next week and that system should have more in the way of cold air to work with in the eastern states.

A major storm may form in the eastern states early next week as we transition to a colder pattern and as we transition from the month of November to December (i.e., the Monday/Tuesday time frame). Map courtesy NOAA, tropicaltidbits.com

Stay tuned…the first couple of weeks of December could be pretty interesting.

Meteorologist Paul Dorian
Perspecta, Inc.
perspectaweather.com

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