Last winter began early in the Mid-Atlantic region with significant accumulating snow in many spots before Thanksgiving Day and November turned out to be a colder-than-normal month. The rest of the winter season, however, was fairly mild with temperatures averaging slightly above-normal in the I-95 corridor and snowfall was generally near normal-to-slightly below-normal. In Philly, for example, the coldest month relative-to-normal was November (2018) with monthly average temperatures 3.9 degrees below the normal. The warmest month relative-to-normal turned out to be December (2018) with +2.8 degrees departure from normal. As has been the case in recent years, winter was hard to shake off at the end of the season as there were more cold air outbreaks and even accumulating snow as late as the middle of March.
Numerous factors have been examined for this year’s “Winter Outlook” including sea surface temperature anomalies, solar activity, teleconnection indices, and a comparison with analogous years that featured somewhat similar oceanic conditions. The all-important Pacific Ocean looks like it will feature a large pool of warmer-than-normal water this winter in the northeastern part of the ocean and a weak (slightly positive) El Nino in the equatorial region.
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The sun continues to be very quiet and it has been without sunspots on 200 days during 2019 or 72% of the time which is the highest percentage since 2009. We have entered into a solar minimum phase of the solar cycle and sunspot counts suggest this could turn out to be the deepest of the past century. Low solar activity has been well correlated with an atmospheric phenomenon known as “high-latitude blocking” and this could play an important role in the upcoming winter season; especially, across the eastern US. In addition, one of the natural impacts of decreasing solar activity is the weakening of the ambient solar wind and its magnetic field which, in turn, allows more cosmic rays to penetrate the solar system. The intensification of cosmic rays can have important consequences on such things as Earth’s cloud cover and climate, the safety of air travelers, and as a possible trigger mechanism for lightning.
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The overall numbers are likely to be slightly below-normal this year in terms of the number of tropical storms and hurricanes in the Atlantic Basin (includes the Caribbean Sea and Gulf of Mexico) with around 11 named tropical systems, 5 hurricanes and 2 majors. In a normal Atlantic Basin tropical season, there are about 12 named storms with 6 reaching hurricane status and 3 actually reaching major status (i.e., category 3, 4 or 5 on the Saffir-Simpson Hurricane Wind Scale).
The major factors involved with this year’s tropical outlook include the likely continuation of El Nino in the equatorial Pacific Ocean. In addition, the Atlantic Ocean is sending mixed signals in terms of the prospects for tropical activity this season with some sections featuring (unfavorable) colder-than-normal sea surface temperatures and others featuring (favorable) warmer-than-normal waters. The sea surface temperature pattern in the Caribbean Sea, Gulf of Mexico and western Atlantic Ocean (i.e., warmer-than-normal) makes the southern and eastern US somewhat vulnerable to what I call “home-grown” tropical hits during this upcoming tropical season.
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Key Factors
Several key factors listed below have been examined for the “2018-2019 Winter Outlook” and they suggest to me that this will be a colder-than-normal and snowier-than-normal winter in much of the eastern and southern US:
1. Weak-to-moderate “centrally-based” El Nino in the tropical Pacific
2. Warmer-than-normal water in the northern Pacific
3. Low solar activity
4. High-latitude blocking
5. Northern Hemisphere snowpack
6. Analog years
7. Soil moisture
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