It's that time of year again...the leaves are changing, the football season is heating up and it's also WeatherWorks Winter Forecast time! Let's begin by taking a brief look at ENSO, or the El Niño Southern Oscillation. Last winter, the focus of our forecast was El Niño (anomalous warmth in equatorial Pacific Ocean waters), which was among the strongest in recorded history. That gave us high confidence in a fairly mild winter with the potential for one or two bigger storms. For the most part, that's pretty much what happened.
This year, the picture is not as clear. We're fairly certain that we won't have have a moderate or strong El Niño or La Niña event, but something closer to a "neutral" (neither El Niño or La Niña) season. This is actually something of a change from the late spring and early summer when a La Niña episode seemed likely. Right now, we favor what we'll term a "cool-neutral" ENSO...meaning that while overall neutral conditions are likely, there should be some La Niña traits present. In addition, another key teleconnection, the PDO (Pacific Decadal Oscillation) may exert its influences. Without getting into too many details, there's an area of warm ocean water south of Alaska, which may actually pull both the ridge and trough a little west and focus the cold air over the north-central US with the most likely storm track over the eastern Great Lakes (see map above).
However, our analysis didn't stop there, we also investigated snow and ice cover in the Arctic and Siberia. Over the last 2-4 weeks, there has been a marked increase in both Arctic sea ice and Siberian snow cover, which gives us confidence in the availability of cold air during the winter season. Just because cold air is available, however, does not necessarily mean that it can be tapped. The Arctic Oscillation (AO) can help us predict these cold outbreaks, but it is typically difficult to predict beyond 2 - 4 weeks in advance. However, based on October trends, we're starting to gain some confidence that the AO will be favorable for Arctic air to be unleashed (especially early and late season) into the central and eastern US.
So with that in mind...let's get into the forecast. We're expecting a good amount of cold air (on the average) to be present for a large portion of the central and eastern US. Particularly frigid conditions are anticipated in the Upper Plains/Upper Great Lakes. Despite the shadings shown in the maps, there are some indications that fluctuations are in store during the season, and temperatures (at least compared to normal) may be seasonable, if not mild compared to normal...especially in January. The lone part of the country that is likely to be consistently mild is California and the Desert Southwest.
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From a precipitation standpoint, an active pattern is likely along the jet stream, though the placement of the ridges and troughs referenced above will be absolutely critical to the amount of snowfall that a particular area will see. That said, snow events are favored to be quite numerous for the northeastern quarter of the nation...even if they don't happen to be powerhouse storms or nor'easters. As to be expected, the mid-Atlantic and southern Appalachians will be favored for several mixed precipitation events as the likelihood of cold air diminishes to the south and east.
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Elsewhere, the Rockies will likely experience typical mountain snowfall, but temperatures won't be particularly cold. Further south, an overall dry pattern will limit wintry weather from the mountains of southern California eastward into the Southern Plains and southern Mississippi Valley...though marginally cold air at times could still contribute to a handful of events (likely minor) along the way. The remainder of the West Coast will be subject to some degree of variability, in terms of both temperature and precipitation. But the mountainous areas of the Northwest may be able to squeak out normal to above normal snowfall if the timing of cold air is favorable.
While we may have a some long range themed blogs at times during the season, if you are looking for updates to this forecast in the mid-Atlantic or New England, the best source for is our one of a kind Winter Risk product, where our meteorologists constantly are monitoring patterns and tweaking the forecast. It's really a must have for decision makers in the snow and ice industry as we talk about storms in the not too distant future as well as weekly and monthly trends!
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