Updated Winter 2017-2018 Forecast
Welcome to (Meteorological) Winter! When I issued the Winter Forecast about a month ago I said I would do a full update on December 1 and so here we are.
The themes of the original forecast were:
- Colder than the last couple of winters but still near or perhaps even slightly warmer than average.
- Near-average snowfall.
While presenting the forecast on TV, online and during speaking engagements I mentioned that I was "daring" the atmosphere to be cold. What I meant by that: there has been a fairly remarkable stretch of warm weather in our region since Autumn 2015. Colder-than-average months have been quite rare. Until the atmosphere "proves" it can get cold (relative to average) the smart money is on warmth, right? So my original forecast was not that cold, despite some data suggesting a cold winter was coming.The atmosphere looks like it is going to take me up on that dare.
What Do We Know Now That We Didn't A Month Ago??
I'll start with La Nina. The premise of this being a winter featuring a "weak" La Nina was certainly known a month ago but the "configuration" of the La Nina has certainly become more obvious recently. What does that mean? Well not all La Ninas are created equally. The orientation of the coldest water (relative to average) is very important. When the coldest water is close to the coast of South America ("east-based") the atmospheric response tends to be one that favors cold weather in the eastern United States. The cold air tends to be centered farther west in North America when the coldest water in the Pacific is farther west. Here's a look at the current water temperature anomalies (the important region is circled): 
Notice the change in the water temperatures over the last week, which shows cooling of the water in the easternmost region: 
I think this ups the odds of cold weather in our region this winter.What else has happened in the month since the original forecast was issued? COLD weather in western and central Canada...especially when compared to last November. Check out the difference. 2016: 
2017: 
This has resulted in a good snowpack across that region and that can help "refrigerate" arctic air masses coming southward across that snowpack.Remember that QBO thing I mentioned in my original forecast?[wpvideo kMeHfAXz]We have another month of QBO data under our belt now and it's firmly in the "sweet spot" for cold weather in the East, especially when paired with a weak, east-based La Nina.
Ok So What's The Forecast
Let's look at this month-by-month.Old December forecast: 
New December forecast (this is the biggest change in the forecast. December will likely be the coldest since 2010 here.): 
Old January: 
New January: 
Old February: 
New February: 
Old Winter (December-February) Forecast: 
New Winter Forecast: 
I have NOT changed the snowfall forecast. This winter may be colder than I originally thought but that does not necessarily mean snowier.
Forecast confidence has gone up since a month ago. I had temperatures in the "low" category then and for good reason.
The bottom line: I am now expecting a significantly colder winter than the last two and this winter can be more like the rather harsh seasons we had in 2013-2014 and 2014-2015. That is not to say it won't occasionally get mild. It will! A "January Thaw" is a distinct possibility.
Thanks for reading! Look for a video version of this forecast this evening!