Early Weather Event Not Seen Since 1968 May Bring Extreme December Temps

Headlines in energy markets news media have been circulating about a relatively normal winter approaching, however G&A has identified a particular pattern that could mean colder temperatures in December. What we are referring to is the recent looming “polar vortex” and talk of a major sudden stratospheric warming (SSW) later this month. A major SSW occurs when the usual westerly winds around the winter polar cap reverse to easterly at about 10 hPa and 60°N, accompanied by a sharp temperature jump in the polar stratosphere. This signifies a fundamental breakdown of the stratospheric polar vortex, not a routine wobble, and it is these major events that have the clearest track record of influencing winter surface weather.

Climatologically, major SSWs are very much a deep-winter phenomenon. More than 95% of onsets occur in December–February, with roughly half in January, according to recent reanalysis-based studies.The NOAA compendium of major mid-winter warmings shows only two events that have ever qualified as “major” in November (1958 and 1968), and none since. And since 1980, there have been about four major SSWs with December onset. Broadly speaking, early-season major events are rare, and November cases are exceptionally rare.

Multiple global models are flagging a strong warming of the polar stratosphere in the second half of November, with ensemble guidance suggesting a real possibility of a full wind reversal and thus a technically major SSW. The energy markets news media has been quick to connect the dots to winter energy prices. What is often left unsaid is the conditional nature of this signal: the event has not yet occurred, there is still spread across model ensembles regarding its magnitude, and the pathway from stratosphere to surface plays out over several weeks rather than days.

Historically, major warmings tilt the odds toward persistent high-latitude blocking patterns that can release cold Arctic air into the mid-latitudes. Some events, like 2018, were followed by extreme cold in parts of Europe; others produced more modest anomalies or shifted the cold elsewhere, and a few had surprisingly muted surface impacts despite clear stratospheric signatures. So while an SSW is a real regime-shift signal that increases the risk of extreme temperature and resultant demand, it’s not a deterministic forecast of extreme cold across the board. If a major SSW verifies later this month, history shows that the largest surface impacts should emerge one to three weeks later as the circulation anomalies descend through the troposphere. That points more toward early and mid-December as the first real window for change in day-to-day gas demand.

The other important variable is geography; while an SSW itself occurs across the Northern Hemisphere, the resulting surface response often differs by region. Extended-range outlooks currently show the clearest early-December cold signal over North America, with blocking near the pole/Greenland and a trough over Canada and the central–eastern US, favoring below-nor mal temperatures and active snowfall. Europe’s signal is weaker and more latitude-dependent: guidance leans toward near- to below-normal temperatures mainly in northern and north-western Europe, with much more uncertainty and milder conditions possible farther south. Asia is split: models consistently favor stronger cold anomalies over Siberia and parts of Northeast Asia, while impacts on more southerly gas-importing regions are less robust in the early-December window.

As of today we are looking at a legitimately rare early-season SSW risk which meaningfully increases temperature tail risk this December for the Lower 48. This can be seen in the data displayed above, which shows wind directions at the 60N latitude line at the 10 hPa elevation level in the atmo sphere. Current wind direction (Shown in green and red lines) now show significant variation from the mean (yellow line) in recent data, with forecasts approaching a potential wind direction reversal. G&A is keeping a closer watch on stratospheric diagnostics (zonal-mean winds, wave activity flux, indications of downward propagation) alongside the usual medium-range forecasts, because those diagnostics indicate whether the event is coupling into the troposphere or fizzling out. With that said, we note that the historical record includes cases of SSWs that did not deliver the kind of cold that some media coverage currently implies. Those cases are important for calibrating position size along with the blockbuster winters everyone remembers.