Summary: The evolving extreme cold across the Central and East U.S. likely to last 7-10 days was not obviously caused by any particular climate diagnostic. However, looking at a non-conventional parameter such as solar activity offers a possible link. Solar activity is currently entering the 11-year minima about 1 year faster than forecast. The last solar minima which was unusually strong and of long duration produced cold to very cold mid-latitude winter seasons.
Discussion: The incoming arctic air temperature pattern will be extreme and of long duration as many locations from the Midwest to the Northeast Corridor are 15F-30F below normal for the next week (Fig. 1). Snow cover (Fig. 2) certainly helps the arctic air maintain intensity. The polar vortex ensures a cross-polar flow of arctic air well into next week. There remain questions on whether the upper flow can tilt more westerly and become sufficiently vigorous to push milder Pacific air across the U.S. in the extended-range. Without a strong Pacific push the widening snow cover will resist any warm-up although the extreme cold should ease in 1-2 weeks.
Of interest is understanding the potential catalyst for this expected impressive long duration cold. The standard mechanisms driving arctic air generation include Kelvin Waves driven pole ward from the tropics and into the stratosphere. This process ignited the polar vortex winters of 3 and 4 years ago. Solar flares can also cause stratospheric warming leading to contraction of the troposphere and arctic air generation. Stratospheric warming did occur to drive this event but the episode was not particularly intense given the depth and aerial coverage of intense cold that is forming. However, one possible contributor is the general influence on polar climate by a faster than expected descent of solar activity into the next solar minima (Fig. 3).
We’re in a potential similar solar activity pattern to the 1800-1830 Dalton Minimum when global temperatures cooled due to an inactive sun stretched over 3 solar cycles. Evidence of this potential appeared about 10 years ago when the last solar minima lasted longer and with stronger intensity than previously observed certainly within the past 100 years.
Further evidence that a Dalton Minimum-type solar signature was developing was observed when the 2012-14 solar maxima was about half as strong as normal. Continuing the streak of evidence supporting this unusually long period of an inactive sun is current solar activity which indicates we’re already in the next minima about 1 year ahead of forecast.
Influence of solar activity on global climate is not well understood. Attributing the current cold wave to an inactive sun is a hard to prove. However, the DEC/JAN/FEB (meteorological winter) 2008-09 and 2009-10 averaged colder than normal in the middle latitudes of the northern hemisphere including the U.S. and especially Russia (Fig. 4). The 2 winter seasons cited occurred during a prolonged period of an inactive sun. The second of the 2 winter seasons was much colder (Fig. 5) which may be an implication for winter 2018-19.
Conclusion: The evolving extreme cold pattern affecting the U.S. and particularly high population zones of the Midwest and East U.S. was not clearly driven by any particular climate diagnostic. One possible contributor is the early entry of solar minima based on solar sunspot progression analysis. The solar minima appears to be developing about 1 year ahead of forecast. The last solar minima which was unusually intense and long-lasting occurred nearly 10 years ago and correlated to colder than normal winter in the middle latitudes of the northern hemisphere. The second winter of the 2 occurring within the solar minima nearly 10 years ago was the most extreme cold. Whether solar activity is a direct contributor to the evolving cold in the U.S. now is uncertain. However, the most recent analog does support the tendency for cold to very cold middle latitude winter seasons in the northern hemisphere most intense with the last winter of the solar minima episode.
Fig. 1: Storm Vista WX Models depiction of the 7-day U.S. temperature anomaly forecast utilizing the European ensemble (model).
Fig. 2: U.S. snow cover has expanded across the northern U.S. (and advancing) helping to enhance the intensity of nearby generated arctic air.
Fig. 3: Solar cycle sunspot progression analysis this century and valid through November 2017 indicates the current activity has arrived at solar minima ahead of the NASA forecast (red line).
Fig. 4: The last unusually intense solar minima lasting for 2 winter seasons helped to produce cold meteorological winter in the U.S. and Russia plus Europe.
Fig. 5: The second winter of the solar minima occurring nearly 10 years ago was extremely cold in the middle latitudes.