A happy Tuesday morning to you all! We hope you are having a great start to your week. The weather across the United States has moderated quite a bit over the past several days, as you may have noticed, and from an energy standpoint this has led to a fairly substantial decrease in heating demand country-wide. This marked a fairly significant change from the early part of the winter and first half of the month. This warmth is expected to continue for the next 10 to 14 days, with ECMWF EPS and GEFS in good agreement.
It is important to take a look at why this airmass is so much different than the one that brought deep, arctic cold to the United States just a few short weeks ago. When we take a look at the hemispheric weather pattern, there are a few significant pieces that are “driving” the weather pattern from a synoptic standpoint. First, we can look to the higher latitudes in Canada and the Arctic regions.
We often discuss these areas as being critically important to the weather in the United States, and with good reason, because the atmospheric circulations here have tremendous effects on the mid and upper level weather pattern in the United States as well. In the current and forecast weather pattern through the end of January, there are troughs and below-normal heights in the mid levels. This will aid in arctic air remaining, well, in the arctic. High latitude blocking, or ridges of high pressure, are what help to dislodge this air away from its typical residing location.
We can also look to the Pacific Ocean for clues as to how things are going to evolve down the road. In the current weather pattern, a large vortex spins in the Gulf of Alaska. Without much high latitude, or poleward reaching, ridging in the Pacific Ocean this vortex works to pump Pacific air into the United States. This brings warmer and modified air into the country and makes it much more difficult to obtain any arctic air source.
The result of this weather pattern, overall, is warmer than normal tendencies for the airmass across the country, but especially across the Eastern 1/3 where the Southeast US ridge can amplify without much resistance. The ECMWF EPS and GEFS are both indicating the presence of warmer than normal temperature anomalies throughout those critical heating demand regions essentially through the end of the month of January.
Seeds of change are already planted
If there is one thing we know about meteorology, it’s that things are always in motion. The same is true for the upcoming change to the weather pattern that we are forecasting in February. When we issued our winter forecast in November, our ideas were strongly suggesting the change back to a wintry and colder pattern in February based on tropical forcing analogs and stratospheric evolution. Those ideas have not changed, but the evolution is starting to come into focus as we draw closer.
Thousands (and thousands) of miles away from the USA, in the tropical Pacific and Indian oceans, we are monitoring the development of an MJO pulse and resulting affects on global circulations. The convection that develops in these critical areas affect the forcing on weather patterns throughout the globe. After a notable MJO pulse in the coming weeks, forecast models are suggesting the MJO will move into Phases 6, 7 and 8 with notable amplitude to begin February. This is obviously a very important factor in the weather forecast – not only because the MJO in Phase 8 historically produces colder air across the USA, but because this evolution is similar to many of the analog years we discussed in our Winter Forecast back in November.
Further exacerbating the issue over the next few weeks will be the state of the stratospheric polar vortex, and stratosphere as a whole, across the higher latitudes and arctic regions. Guidance has continually suggested the weakening of the stratospheric polar vortex over the next few weeks – and while this is climatologically favored anyway, it is an important factor to consider. An initial poleward-building Pacific ridge is forecast by the end of January to disrupt the vortex, and this could set the stage moving forward for the development of ridging in the high latitudes.
The ECMWF Weeklies are in agreement on the overall pattern evolution, with Pacific wave-breaking pattern undergoing significant changes as January comes to a close, and cold air filtering down into the USA by the end of the first week of February. While the exact details remain somewhat uncertain (where will the most impressive cold be, how expansive will it be, etc), confidence is increasing in the discussed ideas – we expect the weather pattern to turn colder and more wintry across a large majority of the country, particularly the Great Lakes, Ohio Valley, and Northeast from the first week of February onward.
Over the next week or two, details on exactly how the pattern will evolve should begin to come in to focus. Looking for things to monitor closely? Our suggestion is the above MJO and stratospheric evolution, but also the wave development in the Pacific Ocean. The orientation and alignment of poleward-reaching waves in the Pacific Ocean will have a major influence on the alignment of the pattern over the USA as February begins.
Stay tuned for further updates as the pattern change draws closer.
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