****Very cold and active pattern to set up in early January with staying power…may feature some extreme cold and multiple snow threats…next week looks particularly interesting****

Numerous teleconnection indices are falling into place for a “high-latitude blocking” pattern across Canada during much of January which would be quite favorable for the transport of very cold air masses from northern Canada into the central and eastern US.

Overview

A much colder-than-normal weather pattern will set up for the central and eastern US during early January and it looks like it’ll be one with some staying power. In fact, this upcoming cold stretch for much of the nation may feature some extreme cold and very cold conditions may penetrate all the way into the Deep South from Texas-to-Florida. In addition, there are likely to be multiple snow threats in this developing weather pattern that can impact much of the central and eastern US to go along with the expected much colder-than-normal temperatures. Next week (1/5 to 1/12) looks particularly interesting in a period that may feature multiple snow and ice threats and potentially some extremely cold air. Numerous teleconnection indices support the notion of a much colder-than-normal weather pattern, and an unfolding stratospheric warming event enhances the idea that the much colder-than-normal temperature pattern can be sustained well into the month of January.

The North Atlantic Oscillation (NAO, top) and Arctic Oscillation (AO, bottom) index values drop into “negative” territory (forecasts shown in red, observed data in black) during the first half of January. Plots courtesy NOAA

Pattern change begins to unfold at mid-week

The last couple of days in December will feature warmer-than-normal conditions across a wide part of the nation, but the unfolding pattern change begins at mid-week with the movement of low pressure from the Midwest to the northeastern states and the passage of a trailing cold front. It turns moderately cold on the back side of the front for Thursday and Friday and then another cold front will usher in even colder air for the weekend in the eastern US.

The time period from January 5th to January 10th looks particularly interesting with snow threats and extreme cold on the table for much of the central and eastern US. This time period should feature strong high-latitude blocking (shown in orange) across Canada and a deep upper-level trough of low pressure centered over the eastern US (shown in blue, purple). Map courtesy ECMWF, Weather Bell Analytics

Teleconnection index trends (EPO, PNA, AO, NAO)

Looking ahead, numerous teleconnection indices point to the formation of high-latitude blocking in coming days across Canada (-AO, -NAO) and at the same time a deep trough of low pressure will form over the eastern US. In addition, strong high pressure ridging is likely to form over the eastern Pacific Ocean and the far western parts of the US and Canada (+PNA, -EPO). Specifically, the AO, NAO, and EPO teleconnection indices will slide into “negative” territory in early January and the PNA index moves into “positive” territory…all of these trends favor the idea that atmospheric conditions will be quite favorable for the transport of very cold air masses from northern Canada into the central and eastern US.

A stratospheric warming event will bring the stratospheric polar vortex to the North American side of the North Pole by the second week of January. Stratospheric temperatures will be at their lowest across Canada and the northern US (shown in purple) by January 8th or so as depicted here by this Euro model forecast map of 10 millibar temperatures. Map courtesy ECMWF, Weather Bell Analytics

Stratospheric warming, QBO

In addition to analyzing the North American continent (e.g., Pacific Ocean, Canada) for some clues about the upcoming weather pattern, it is worthwhile to monitor the top of the atmosphere known as the stratosphere for ongoing changes as well happenings across the global tropics.

An atmospheric phenomenon known as the “quasi-biennial oscillation” (QBO) is a changing wind anomaly in the tropical lower stratosphere. It has been found that strong stratospheric winds along an equatorial belt tend to completely change direction about every 14 months or so and this oscillation appears to play a crucial role in seasonal weather patterns as it can impact the polar vortex and the overall jet stream. Specifically, the tropical lower stratosphere winds flip from west-to-east or east-to-west every 14 months or so, an average period of about 28 months to return to the starting state. Recent upper air observations from NASA radiosondes suggest the QBO is now in a west-to-east phase or what is known as a “negative” (easterly) phase.

Recent upper air observations from NASA radiosondes suggest the QBO is now in a west-to-east phase or what is known as a “negative” (easterly) phase and this has been shown to be more favorable for stratospheric warming events to take place in the northern hemisphere. Data courtesy NASA

When the QBO is in an “easterly” phase, past observations have found that the chance for a weaker Atlantic Ocean jet stream can increase, and the chance of a stratospheric warming event can also increase in the northern hemisphere. This, in turn, raises the chance for cold air outbreaks into the middle latitudes of the US and Europe from the polar region. Indeed, a stratospheric warming event is underway and this is likely to result in a “disruption” or a “stretching” of the polar vortex onto the North American side of the pole in coming weeks. Indeed, one key to the sustainability of a cold stretch of weather is to move the stratospheric polar vortex towards North America to ensure a consistent supply of cold air down the road…multiple computer forecast models do just that including the Euro and GFS.

The MJO is forecasted to push through “phases” 8 and 1 in coming days which are typically associated with colder-than-normal weather this time of year across the central and eastern US. Map courtesy NOAA

Madden-Julian Oscillation (MJO)

Meteorologists track an oceanic-atmospheric phenomenon known as the Madden-Julian Oscillation or MJO which affects weather patterns across the globe. Unlike El Nino or La Nina which are stationary features in the equatorial Pacific Ocean, the MJO is an eastward moving disturbance of clouds, rainfall, winds and pressures that traverses the planet in the tropics and returns to its initial starting point in 30 to 60 days, on average. The MJO was first discovered in the early 1970s by Dr. Roland Madden and Dr. Paul Julian when they were studying tropical wind and pressure patterns. 

The MJO consists of two parts or phases with one being the enhanced rainfall (convective) phase and the other being the suppressed rainfall phase. The location of the convective phases is often grouped into geographically based stages that are numbered 1-8 by scientists. The location or phase of the MJO can be tied to specific weather patterns in different parts of the world depending on the time of year. During the winter season, “phases” 8 and 1 are typically correlated with colder-than-normal weather for much of the central and eastern US. These particular locations or “phases” of the MJO indeed appear to be on the table in coming days.

This upcoming cold stretch of weather might feature some extreme and potentially historic cold. These forecast maps of 2-meter actual temperatures (left) and 2-meter temperature anomalies (right) suggest just such an extreme cold event may take place around Friday, January 10th. Maps courtesy ECMWF, Weather Bell Analytics

The potential of next week (January 5th to January 12th)

While still many days away, the longer-range look ahead to next week – the 5th to the 12th – show the possibility of interesting weather to say the least in much of the country. This is a time period that could feature multiple snow threats for the central and eastern states and some extreme cold can mix into the picture. Furthermore, there can be some very cold air that penetrates as far south as the Texas-to-Florida region during this particular time period. And, as described earlier, the cold pattern may stay fully in tact right into the second half of the month.

Final Thoughts

Get ready…January might just be a wild month.

Meteorologist Paul Dorian
Arcfield
arcfieldweather.com

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