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Strong El Nino conditions continue and are expected in most models to remain strong into early winter. Most models suggest the strength of El Nino will begin to wane during the winter which would gradually change its impact. In general strong El Ninos usually produce higher probabilities of warmer than average temperatures across most of the northern US (including our region), and cooler, wetter conditions across the southern US. There should also be an increased prevalence for strong Pacific storms to strike southern & central CA, bringing some relief for the terrible 4+ year drought, but also increasing the risk of mudslides, landslides, and flash flooding. We have not had an El Nino of this magnitude since the historical 1997-98 event, so the supply of sample strong El Nino years is limited…and no two El Ninos are identical.
As of now, El Nino is a dominant influence in much of the global mid and tropical latitudes. There are, though, other variables which could play an increasing role in what patterns set up later in the autumn and early winter. There are oscillating sea/air patterns such as the Arctic Oscillation and the Northern Atlantic Oscillation (AO & NAO, respectively) which can vary in strength. For example, if the NAO took on its negative/cold phase, that is associated with colder and sometimes stormier weather over the middle Atlantic, NE, and Great Lakes. Usually, the NAO becomes negative less frequently during strong el ninos. The AO, when it becomes negative, has often been linked to east coast storminess (less snow in our region). It usually is less negative during strong El Ninos. However, Dr. Judah Cohen (formerly of MIT, now a private sector seasonal forecaster near Boston) has still inconclusive but suggestive evidence that above average snowfall in Siberia during October has been linked with a more frequently negative AO. Most meteorologists and climate scientists feel the NAO and AO can only be well forecast out to 2 weeks in advance. Cohen had real success in several years during 2000-2011. It’s a little too complex to explain this relationship, but the winters of 2009-2010 (“Snowmageddon ” in Baltimore, Washington and Phila) and 2010-2011 showed a strong correlation between the October excessive snow in Siberia and the polar jet stream more frequently dipping south over parts of the midwest and NE. There have been a number of years in which Cohen’s winter outlook was relatively successful and the NWS Climate Prediction Ctr’s winter outlook suffered from poor verification. As of October 19, snowfall has been accumulating at an above average rate in a large part of Siberia, but not as rapidly as during the last 2 Octobers.
There are also other longer lasting oscillations such as the Eastern Pacific Oscillation and the Northern Pacific Oscillation which have an impact on the alignment of the polar jet, as well as something called the Madden-Julian Oscillation. The latter is probably the most complex of all these oscillations–so don’t ask!
At this early, early point in the season, I expect autumn to continue to be milder than average more often than not. There will be ups and downs, and some occasional cold shots but, in the mean, lengthy outbreaks of wintry weather–particularly temperatures–are less likely this late autumn than in the last 2 years. However, the great unknown is what will happen when the currently strong El Nino begins to lose its strength during the winter? If El Nino actually becomes weak by late February or March, that could spell an “interesting” late winter with more nor’easters and more cold outbreaks in the Great Lakes and NE. Weaker El Ninos are not associated with milder than average temperatures in our region. A lot will depend on the pace of the weakening which is not highly predictable. Remember that even a strong El Nino does not preclude occasional briefer breakdowns in a mild pattern which could allow polar intrusions and storminess. And, if El Nino does weaken more rapidly, my thought at this point is that the nature of the winter beast may change in late or even mid-winter. I’ll do my best to keep you updated.