Good evening! We’ve discussed for some time now the expected development (or should we say return) of anomalous cold across the Northern Hemisphere, more specifically the southward movement of this cold into Canada and the United States. In our post yesterday, we dove into the details of why we are so confident that this cold will occur, and how the seeds are already planted and growing for the change to occur.
However, while we look ahead to the cold’s development and entrance into Canada and the United States, it will become increasingly important for us to understand the timing of the pattern change – including where the cold will be most prevalent first, and how it is expected to move across the country. While pinning down these details is an inherently imperfect science at this range, we can utilize multiple long-range forecasting tools and analogs to find clues as to how things will behave.
One of the first things to note about the upcoming pattern is that it will be driven by the development of a large, anomalous and poleward reaching ridge in the Pacific Ocean. This ridge, which develops next week, will be responsive for perturbing both the troposphere and stratosphere in the arctic regions, and aiding in a realignment of the Pacific wave pattern. As a result, cold air will be dislodged southward into Canada and then towards the United States.
In addition, we can look to the tropical forcing evolution – namely, the MJO – to understand how things will evolve. Convection is expected to evolve through Phase 7 during the beginning of the month of February with notable amplitude (the GEFS and ECMWF EPS both agree on this) and then gradually towards Phase 8. But both of these phases feature very different historical analogs, and while ENSO forcing plays a role, it is important to pay attention to just how different the historical analogs for Phase 7 and Phase 8 amplified MJO’s are.
In the United States, at least, the combination of a La Nina MJO Phase 7 with an amplitude greater than 1 (what is being suggested by models) typically results in the presence of a Southeast US ridge anomaly. When one takes into account the ridging that is forecast to develop northwest of Alaska, and the resulting disruptions to the stratosphere, we can surmise that cold should then dump southward into the Plains states and North-Central USA as well as Canada. However, hypothetically, this cold air should encounter resistance upon its initial attempts to move east of the Mississippi River as some Southeast Ridge anomaly remains stout.
This would place the brunt of the most impressive/anomalous cold, through at least the first week of February, centered over the North-Central United States. This could be particularly anomalous across the Northern Plains and Canada (Montana, Dakotas, Minnesota). Meanwhile, cold will surge southeastward at times, but generally will not be as severe across the Eastern United States. A thermal gradient could exist between a Southeast Ridge anomaly (not a strong one, but one that is there) and the incoming cold – creating the potential for storms in the Ohio Valley.
Thereafter, forecast models suggest the development of an impressive, poleward-reaching ridge near British Columbia. As the MJO shifts towards Phase 8, tropical forcing should aid in this ridge developing closer to the PNA regions, extending northward into British Columbia. This will amplify the pattern and dislodge deep, arctic air further south — and East — into the United States. As a result, the idea is that anomalous cold will then shift eastward towards the Mississippi River, Ohio Valley, and then Eastern USA during Februaries second week. The resulting amplification in the pattern could result in multiple winter storm threats along the East Coast during Februaries second and third week.
This pattern progression suggests the most significant impacts to the market, in terms of heating demand and sensible weather, will begin in early February, and crescendo as the month goes on – likely peaking during the months second and third week. We will have to continue to analyze and detail the pattern as we move closer and guidance provides a closer look at how things are evolving and will shake down in the future.