Weather Headlines

1). A chance for light rain and mixed precipitation Sunday will become light snow by late Sunday into Monday. Any snow accumulations are expected to be light, mainly at upper elevations above 3000 feet (during 3-4 January).

Air is expected to turn colder Sunday into early Monday on W-NW flow (with minimal Great Lake connection).

Mixed rain and snow showers at lower elevations have been sticking at upper elevations, with some slick areas developing on northern slopes and crests. More widespread sticking will be possible around and after sunset across upper elevations (above 3000 feet). Limited sticking is expected at elevations below 3000 feet.

Caution is advised for those visiting High Knob Lookout and driving at high elevations.

2). Great Lake connected NW Flow snow will be likely Tuesday into early Wednesday (5-6 January 2021).

Snow accumulations of 1″ to 4″, with locally higher amounts, are expected in upslope flow along and NW of the Cumberland Front and along the windward side of the TN-NC border. Generally less than 1″ is expected in downslope areas.

A secondary surge of cold air will move southeast, with developing Great Lake connected NW flow, during Tuesday into Wednesday.

3). A snowstorm potential is being monitored for late this week (8-10 January period). More than one wave of significant snow will be possible.

Upper level waves (energy) moving through the jet stream flow are being monitored for amplification (intensification) as blocking strengthens across Greenland and southeastern Canada.

History Of Christmases Past
(1964-2019)

Reference White Christmas 2020 for a recap of the Christmas Holiday storm.

Winter Returns In January 2021

Important changes related to what appears to be a split in the stratospheric Polar Vortex upcoming during early January is now expected to alter the flow pattern across the Northern Hemisphere. Initially, these changes will favor warming across eastern North America and cooling across western North America.

The split on the European begins in the upper Stratosphere and works downward over time.

This update is being written on 30 December 2020.

A major Sudden Stratospheric Warming (SSW) event is now timed for the 6-7 January 2021 period.

Although produced from a UK (United Kingdom in western Europe) perspective, this video is excellent in its description of the Polar Vortex, its formation and break-down, and occasional major events known as Sudden Stratospheric Warmings.

Technically, a SSW requires reversal of winds at 60 degrees North latitude and 10 MB from westerly to easterly in direction (note this 10 day forecast).

A mild opening to January 2021 will begin to change during the 7-14 January period, with significant changes likely by mid-late month.

Strong warming will occur above high latitudes, and the North Pole, during the first week of January 2021 to result in a major SSW event.

This has also been highlighted by Dr. Judah Cohen in his weekly AO/PV Blog.

The current best analog pattern to what is being predicted is found during Winter 2009-10 (above).

While no two events, or seasons, are exactly the same it would be foolish not to recognize these correlations moving forward.

Major stratospheric warming events represent some of the most dramatic short-period (sudden) changes in the climate system, and occur within a typically stable setting (the stratosphere).

Impacts tend to propagate downward over time (after having been forced by wave activity propagating up from the troposphere) as coupling occurs.

It is also interesting to note, the SSW Event of January 1985 occurred during a weak La Nina winter with a E-W QBO (Quasi-biennial Oscillation) pattern.

While changes may begin to be seen toward the 5-10 January period, it will likely be mid-late January before full impacts are felt.

Given the difficulty in forecasting tropospheric weather conditions 24-48 hours away during winter, you may wonder why I would show a 16-day forecast chart? It just so happens, that once changes begin the enhanced stability (typically) of the stratosphere makes forecasts at least a little more dependable.

Getting to this point of a Major SSW can, indeed, be difficult for models to handle, but the confidence in this future stratospheric setting is now much greater than are details of how this event will actually impact local weather conditions within the troposphere (e.g., in the Mountain Empire).

What those impacts will be, in terms of details and intensity, remain to be resolved, but a major SSW climatologically tends to enhance the potential for severe winter conditions across middle latitudes.

Bitterly cold air and expansion of a deep snowpack has generated what may be a New Global Record for high barometric pressure, in Mongolia, related to persistent blocking in the region of the Ural Mountains and upward wave activity flux (WAF).

The Bottom Line…Despite a mild start, January 2021 is likely to generate dramatic weather changes as the hemispheric flow pattern across North America is changed by major stratospheric warming.