Confidence increasing in development of cold, active pattern in Eastern US

Good morning and happy Wednesday, everyone! Anomalous warmth has currently spread across a large majority of the United States, well forecast in is breadth and timing, but impressive nonetheless. Since the beginning of the week, much of the Midwestern United States has been blanketed by temperatures several degrees above normal averages for this time of year. The mid and upper level ridge in the atmosphere that is responsible for this warmth will continue its trek eastward over the next few days, allowing warmer temperatures to gradually move towards the Eastern United States.

As we speak, thousands of miles away, in the North Pacific Ocean, a major change to the hemispheric weather pattern is underway. This fundamental change will mark the end of the anomalous warmth across the aforementioned regions, working in tandem with several other global circulations to support the development of an anomalously cold pattern. In fact, by the middle of next week, temperatures will fall well below average across a large portion of the Mississippi River Valley and East Coast. This will obviously have a large impact on the markets, and Gas Weighted Heating Degree Days are expected to quickly jump above the 10 and 30 year averages. Lets break down why this is happening and how we can expect things to evolve.

ECMWF EPS showing a large ridge on the West Coast supporting cold air surging southward into the USA.

Earlier, we mentioned the Pacific Ocean – and the truth is that what is evolving there is tremendously important. A stagnant wave pattern across the Pacific Ocean is dramatically changing, with the rapid development of several waves and a restructure of the major ridges and troughs. By Days 4 to 6, a large ridge will develop on the USA’s West Coast, reaching northward into British Columbia by the middle part of next week. As this ridge builds poleward (i.e, towards the North Pole) it will disrupt the circulations in the arctic. This will dislodge cold air southward into Canada and towards the United States.

The movement of this cold air will be further aided by ridging that is developing near Greenland the Davis Strait on the Atlantic Side of Canada. This will allow additional cold air to surge southward into Central Canada and the United States, and ensure that the cold air isn’t simply “progressive”. Instead, the colder than normal air should remain consistent for several days, as polar atmospheric heights are dislodged over Southern Canada and parts of the Great Lakes. The low level flow of cold air will support colder than normal temperatures in the Ohio Valley, Eastern Plains, Southeast, and East Coast during this time frame, and some of the cold could be highly anomalous.

ECMWF EPS showing anomalously cold temperatures in the USA by Day 10.

The support for this pattern evolution continues beyond Week 2, with a 10-14 day period supporting colder than normal air over this region with the opportunity for storminess. Gas weighted heating degree days should average above the 10 and 30 year averages during this time frame, especially when population weighted given the spatial distribution of colder than normal temperatures. This pattern is expected to gradually moderate as December approaches its final week.

There is additional support for this pattern evolution emerging via the stratosphere. The stratospheric polar vortex is a major factor in the breadth and duration of cold outbreaks across the United States. A stronger, tighter, and less mobile polar vortex in the stratosphere can often mitigate cold, while a weaker and more perturbed polar vortex in the stratosphere can promote extended periods of high latitude blocking and cold air dislodging across both the United States and Europe. Observations currently suggest that the stratospheric polar vortex is disrupted, and GEFS and ECMWF data suggest additional disruptions and perturbations over the next 10 days.

In addition, the stratospheric high pressure locations can often offer clues as to where the most impressive ridges and troughs will develop in the atmosphere. A large stratospheric high pressure will develop in the Eastern Pacific towards British Columbia. This lends support to the idea that the ridging that develops into British Columbia during Weeks 2 and 3 could be quite impressive and anomalous, further exacerbating the degree of cold air surging into the United States during that 10 to 14 day period.

These changes, ideas, and progressions were reflected on our latest Long Range/Energy reports. Stay tuned for more information on the evolution of the weather pattern over the next few days!