When I issued my Winter forecast last year at this time, the idea was that we’d be seeing a fairly mild start to Winter with not too much snow into January before the back half of Winter would feature more snow. While that was what happened, my forecast was for nothing close to the magnitude of what we saw. I mentioned that we’d be counting the tenths of inches to see if Boston would go above normal in snowfall for the third consecutive Winter – something that had not been done since the Winter of 1975-1976 through 1977-1978. Little did I know that once the barrage began with a pattern change on January 24 leading to 4 major storms in February and several other significant events that we’d be counting tenths of inches to an all time snowfall record for Boston. I also missed on the magnitude of the cold, especially in February, which accompanied the relentless snow. A side irony of all of this is you’d think for one we’d not be in a drought situation after all of that snow, and that we’d have seen massive Spring flooding as the record snow pack melted. No, and no. A very large percentage of the 110+ inches of snow in the Boston area was very low water content, so it did not contain a very helpful amount of moisture for agriculture and water supply. Additionally, because of the lower water content combined with the cold and dry pattern that followed at the end of Winter well into the Spring, the snow was able to not only melt very slowly, but literally evaporate into the dry air – a process called sublimation. This made an already incredible and memorable Winter with record snow, ice dams, and roof collapses even more memorable in a way, as we were given the gift of skipping some of the additional post-season impacts.
So what can we expect this Winter? In studying the variety of atmospheric and oceanic indices and cycles that provide some guidance as to trying to predict the future, a couple of things stand out. The first is Siberian snow. The previous 2 Winter, Siberian snow cover increased at a much higher rate than normal in October and early November, an occurrence which very often leads to more frequent cold outbreaks in the US Northeast. This season, while the snow increased at a rate faster than the long term average, it was considerably slower than the previous two seasons. This may mean that its impact may be somewhat lesser than what we saw the last 2 seasons. In addition, an El Nino that was stubborn to get going and slow coming on, finally cranked up full force, and as of this post is at a level between that strong El Nino episodes of 1982 and 1997. In case you need a refresher, El Nino is part of the a normal cycle of water temperatures in the Equatorial Pacific off the western coast of South America, in which the water temperatures are above the long term average. You cannot have an El Nino this strong without some significant impact to the pattern in North America. But it’s not just about having a strong El Nino. It comes down to where the warmest water is centered relative to the west coast of South America, as well as El Nino’s interaction with other atmospheric indices. This particular El Nino has its warmest water displaced further west than the 1982 and 1997 events, however it is a fairly widespread area of warmth and there is still a significant positive departure right to the western coast of South America. The El Nino is forecast to strengthen a little further as we head into early and mid Winter, then begin a weakening trend later in the Winter. The most prominent impacts of El Nino include wet weather and sometimes flooding rain in the US Southwest, including California, which has been suffering a major drought, as well as above normal precipitation and below normal temperatures across much of the southern US. Additionally, El Nino winters often feature milder and drier than normal conditions across the northern US and southern Canada. For us here in New England, I expect that El Nino will be the biggest factor in determining the weather going through Winter. But we cannot ignore the above normal early season snow in Siberia and its tendency to want to result in cold in the Northeast. Though I think that El Nino’s force will be the dominant one, we will also feel the effects of the Siberian snow / cold Northeast correlation at times. If El Nino weakens as forecast later in the Winter, that is when its impact would obviously lessen, however the resultant weather would depend on the degree of weakening along with the other indices at that time. We cannot forget about the MJO (Madden-Julian Oscillation), which is often another significant determining factor in the overall weather pattern. Forecasting this index can be quite challenging, and we only have slight to moderate confidence in predicting this going forward though the Winter, though you can make some fairly reasonable assumptions of where this index might go over time. With this in mind, I offer this breakdown and then let time reveal its degree of accuracy…
DECEMBER
Breakdown: El Nino dominates the pattern which would result in milder and drier weather more often than not, though short-lived shots of cold to very cold air would occur with temporary reconfigurations of the polar (northern) jet stream with a flat ridge in the US northern Plains and Canadian Prairies provinces and a briefly deeper, progressive trough through the Great Lakes and US Northeast. As would be expected, the subtropical (southern) jet stream will become more active, resulting in the wetter/cooler weather for the southern US, but the interaction between the northern and southern streams would be limited, often occurring well offshore of the East Coast.
Temperature: Above normal.
Precipitation: Below normal.
Snow: Below normal.
JANUARY
Breakdown: El Nino will likely be the dominant player as it is peaking in intensity during the first half of the month, which will likely be similar to December. Watch for a more significant influence by the MJO at some point, which may result in some phasing of the northern and southern jet streams, with one point of phasing sending a couple storm systems through the Great Lakes (which are mild storms for New England), and another point of phasing, like December, being located well off the US East Coast, resulting in storms missing the area. Though we will still be prone to cold shots, the overall pattern should still be dominated by milder air. Something to watch for, despite a milder regime, the fact that cold air will be available can lead to cold being trapped at low levels while upper levels warm. If this coincides with precipitation, ice storms become a possibility. One saving grace would be the strong chance that overall events would be less frequent than average and precipitation would be below normal, limiting the chances.
Temperature: Above normal.
Precipitation: Near to below normal.
Snow: Below normal.
FEBRUARY
Breakdown: El Nino weakens but still remains a player. With less confidence based on not knowing how some of the other indices will behave, the cautious forecast will be for still a tendency for some mild weather but interrupted more frequently by shots of colder air. The southern jet stream may become a little less active, but still will have enough activity in it to produce some winter storm threats. There have been El Nino episodes before that have featured a significant snow event late in the season so this along with just straight climatology of February being a snowier month must be considered. Still, it will take just the right setup in this pattern to get a significant storm of any type. We will still have to watch for ice storm set ups if the cold surface/warm upper air pattern occurs and coincides, but if the pattern remains dry then these chances would be limited.
Temperature: Near to above normal.
Precipitation: Below normal.
Snow: Near to above normal.
MARCH
Breakdown: El Nino weakens further, but so does the southern jet stream though not completely. Northern jet stream remains dominant but will be able to deliver cold into the East a little more often than it had previously, but not nearly to the magnitude of last Winter. Though we’d likely be drier than average under this setup, there is always the chance of a late snowstorm, and many Winters coming out of El Nino have delivered late snow events. Obviously, this month being so far away means that confidence is lowest.
Temperature: Near to below normal.
Precipitation: Below normal.
Snow: Near normal.
WINTER SEASON OVERALL
Temperature: Above normal by 2 to 3 degrees F.
Precipitation: Below normal by 2 to 3 inches melted.
Snow: Below normal with the following ranges expected…
-Boston 25-35 inches
-Worcester 45-55 inches
-Providence 20-30 inches
-Hartford 35-45 inches