Winter Outlook 2016-2017
When forecasting, I normally don’t put much effort beyond a 7-10 day forecast, seasonal forecasting is difficult at best. And while in the energy sector, it is a billion dollar business, for the TV viewer, I’m not sure a whole lot can be gleaned from a seasonal forecast. Yes, we know it will be dark….yes, we know beach/golf days are slim & none and most likely we will deal with cold & snow but beyond that, nailing down specifics is next to impossible. So….with full transparency out of the way here I go….
…Before looking ahead, let’s recap last winter. It was an El Nino winter, our strongest in 20 years, and El Nino winters usually mean warm winters for the United States. Check out the temperature anomalies (above/below normal temps) from last winter:
In the business, we call that a *blowtorch*. For Boston, it was our 2nd warmest winter on record and for Worcester, 3rd warmest. There will be no El Nino around this winter. In fact, the opposite is expected, La Nina. (quick recap..El Nino is a warming of the equatorial Pacific Ocean waters that naturally occurs every 3-7 years, affecting world weather patterns, while La Nina is the opposite, a cooling of equatorial Pacific Ocean waters).
Typically, this is what a La Nina will do to the North American winter jet stream:
Cool & wet across the northern tier and warm & dry across the south. Winter trips to FL likely favor sunny/warm weather–book now! ;o) For us in New England, the storm track is right over New England. This storm track is likely to waver so some storms would offer a messy mix (or just rain) while other storms would be mostly snow. That wavering storm track would mean our temps would waver…bouts of cold but also warm spells.
Unlike last winter’s El Nino, this winter’s La Nina isn’t expected to be very strong. This graphic shows the intensity/longevity of each & every El Nino/La Nina (also known as ENSO, or El Nino Southern Oscillation) dating back to 1950:
You can see that strong/very strong ENSO events are rare. What I’ve also done is circled two of the stronger El Nino events that were followed by weak La Nina’s. I’ve done this because one technique to seasonal forecasting is looking to the past for clues of the future–known as analog forecasting. I’ve Identified two winters that have a fairly close match to what this winter should be (a weak La Nina following a strong El Nino). The winter of ’66-67 and the winter ’83-84. For the winter of ’66-67, the temps across the United States looked like this:
No Blowtorch here…temps for the winter were slightly below normal. For the winter of ’83-84, here is what the nation dealt with:
Overall cold for the nation (quite cold in fact) but here in New England, temps pretty close to normal over the course of the winter. The message to take from this would be a colder winter than last winter for New England but overall, a winter with near normal temps. Snowfall…….the one thing that sends shivers down our spines OR ignites the meteorological flame inside some of us (like me). This is tougher to figure. I did go back and dig up four La Nina Winters (3 weak La Ninas and 1 strong La Nina). Here’s what happened in those winters:
You can see, for Boston, we have two winters with extremes (above and below normal snowfall) as well as two average snowfall winters. For Worcester, 3 of those 4 winters finished with above average snowfall.
Another factor for winter forecasting is what’s known as high latitude blocking (sometimes I drop the term Greenland Block on TV). While La Nina/El Nino play a role in our weather, strong High Latitude blocking (or no blocking) can also have a major effect on our winter weather. The North Atlantic
Oscillation (NAO) is one measure of just how blocked the atmosphere is over the North Atlantic. When the NAO is negative, we label the atmosphere *blocked.* A negative NAO usually means cold (stormy) weather for the Northeast:
While a positive NAO usually means warm (dry) weather for New England:
Some of our longe range computer guidance suggests that blocking could be a recurring theme in the North Atlantic this winter. In fact,
check out the jet stream chart across North Amerca recently:
(Graphic courtesy tropicaltidbits.com)
Those cool colors up near Greenland and the warm colors in New England and along the US/Canadian border are why we have had such a mild first
half of November (positive NAO).
Now look at a forecast jet stream chart for Thanksgiving Weekend:
(Graphic courtesy tropicaltidbits.com)
All sorts of warm colors up near Greenland…blocking(Negative NAO)! This type of pattern could eventually bring us some wintry weather down the road (in a few weeks).
There are several other variables that play a role in the atmosphere during winter (each one exerting its influence on weather patterns all at once….like a mom/dad grocery shopping and their 5 children along for the ride with each child vying for their parents attention) and I could continue on with those variables but I chose to focus on these two particular variables as they will most likely have the greatest effect on our winter.
So……If I had to sum it up in a few key points:
* Colder winter than last year–but overall an average winter in terms of temperatures.
* Near normal snowfall (perhaps above for central/western/northern New England)
* Likely a faster start to winter than the previous two winters—IE–plan on some snow & cold between Thanksgiving & New Years)
We’ll see how this turns out…if we have the warmest/driest winter on record…I’ll stick to 7-day forecasts. Promise.