****Very cold and active pattern setting up with staying power...extreme cold on the table...snow threats begin this weekend/early next week...big impact coming to the southern states****

The trend is down for 2-meter temperatures across the central and eastern US in coming days with below-normal conditions extending all the way into the middle of January as depicted here in this loop of temperature anomaly forecasts maps. Maps courtesy ECMWF, tropicaltidbits.com

Overview

A much colder-than-normal weather pattern is about to commence for the central and eastern US 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 southern states 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 looks particularly interesting in a period that may feature some extremely cold air and multiple threats of snow including one in the Sunday/Monday/Tuesday time frame for the Midwest and at least portions of the Mid-Atlantic.  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 probability of “greater than an inch of snow” by mid-January extends all the way down into northern Florida. This upcoming weather pattern is indeed one that can produce some snow across the Deep South as cold air penetration seems destined for that part of the country. Map courtesy NOAA (GFS), Weather Bell Analytics

Pattern change begins to unfold later this week and weekend

Low pressure will bring rain to the Mid-Atlantic region later today and tonight and it can include some thunderstorm activity with mild conditions still in place across the region. The passage of a cold front will usher in cooler air for Wednesday, New Year’s Day, and winds can gust past 40 mph on the backside of departing low pressure. It turns progressively colder later this week and weekend as the pattern change to much colder-than-normal kicks into full gear. There will also be the chance for snow shower activity during this transition to colder weather with the best chance likely coming on Friday in the Mid-Atlantic region as another cold front moves through the area.

06Z Euro forecast map for early Monday, January 6th, with snow (in blue) depicted across the Midwest and southern Mid-Atlantic region and ice (purple), rain (green) to the south of there. Map courtesy ECMWF, Weather Bell Analytics

Snow threat(s), widespread Arctic cold next week

By the latter part of the weekend, low pressure will begin to organize over the middle of the nation and it’ll have quite a bit of cold air to work with resulting in plenty of snow on its north side. This system will slide east on Sunday night likely producing quite a decent and widespread snowfall across much of the Midwest. By Monday or thereabouts, there is a good chance for accumulating snow to make its way into at least portions of the Mid-Atlantic with the southern half of the region likely having the highest probabilities (e.g., DC, Baltimore). However, this “highest probability” zone for accumulating snow can certainly shift or expand in coming days, for example, to the north and into the Philly metro area. The low pressure system should then slide off the east coast by Tuesday or so of next week and Arctic air will encompass a wide part of the nation in its wake.

A widespread area of colder-than-normal 2-meter temperatures is depicted here by the ensemble run of the Euro model for the 10-day period from 04 January to 14 January. Map courtesy ECMWF, Weather Bell Analytics

Later next week, a second storm system is likely to form way down to the south in the south-central part of the nation. Cold air will have penetrated deep into the southern US by then and this system will have the potential of producing snow in unusual areas from Texas-to-Florida somewhere in the Friday/Saturday/Sunday time frame...something to closely monitor next week. After a likely push across the southern US, it is unclear if this low pressure system will stay “suppressed” to the south or try to take a turn up along the eastern seaboard...too early for any details on that possibility, but certainly another facet of this upcoming wintry pattern that will need to be monitored closely next week.

The Pacific-North America (PNA, top), North Atlantic Oscillation (NAO, middle) and Arctic Oscillation (AO, bottom) index value trends for the first half of January favor the transport of cold air masses from northern Canada into the central and eastern US. Plots courtesy NOAA (forecasts shown in red, observed data in black)

Supporting data for the upcoming major pattern change

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

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 southern Canada (shown in purple) by January 8th or so as depicted here by this GFS model forecast map of 10 millibar temperatures. Map courtesy NOAA

2)     Polar region and “Stratospheric Warming”

In addition to the analysis of temperature and pressure patterns across places like Canada and the Pacific Ocean, it is worthwhile to monitor what is taking place at the top of the atmosphere known as the stratosphere over the northern hemisphere polar region. Indeed, a stratospheric warming event is taking place and it is one that will bring about a “disruption” or “displacement” of the stratospheric polar vortex to the North America side of the North Pole. In fact, in about a week to ten days from now, the stratospheric polar vortex will be “stretched” out positioning itself over southern Canada and the northern US. 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, 1 and 2 in coming weeks which are typically associated with colder-than-normal weather this time of year across the central and eastern US. Map courtesy NOAA

3)     Tropical region and the “Madden-Julian Oscillation (MJO)”

Yet another area of interest with respect to the forecast of coming trends in the atmosphere is the tropical region all around the world. Meteorologists track an oceanic-atmospheric phenomenon known as the Madden-Julian Oscillation or MJO which affects temperature and pressure 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. 

“Phases” 8, 1 and 2 (boxed regions) of the Madden-Julian Oscillation (MJO) are typically colder-than-normal across much of the central and eastern US during the winter season. Data courtesy NOAA

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, 1 and 2 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 weeks.

Final Thoughts

Get ready…January is looking like a wild month.

Meteorologist Paul Dorian
Arcfield
arcfieldweather.com

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