15 November 2016
This is a guest post from my weather intern Andrew McCormick (Senior at Salisbury University here in Maryland). We’ve been looking at what the winter may bring for a month or so now, and Andrew has a good track record of past winter forecasts. This is a good summary of the techniques we use to make long range forecasts, and in case you’re wondering, I see nothing to disagree with below…
Before we begin, let us reminisce at our past few winters. In the winter of 2013-2014, the term Polar Vortex entered everyday vocabulary and sent meteorologists scrambling to try to corral the hype train stirred up by the media. In January, parts of the region saw temperatures dip below 0°F (including the Salisbury Airport), and just about everyone saw wind chills dip below 0°F. The winter featured above average snowfall. In 2014-2015, it was yet another frigid year, and yet again temperatures and/or wind chills in parts of the area dipped below 0°F. The winter featured above average snow, but not as much as the previous winter. And I don’t think I have to remind you of 2015-2016, when we saw one of the largest snowstorms to ever impact our region – shutting areas west of the Chesapeake Bay down for days after the snow finished falling. The winter had above normal temperatures, and December 2015, ranked as the warmest December ever on record for the lower 48 states. Reagan National (Washington DC) averaged 11.5° above normal for the month, and BWI (Baltimore) 12.3° above normal. Here on Delmarva, Salisbury and Dover both averaged 12.8° above normal for December. In January, it turned much colder, and we did experience some bitter cold. Of course the blizzard of 2016 struck January 22-24. After that, the winter wasn’t too bad.
Now, what do ALL of these winters feature? Above normal snowfall and at least periods of bitter cold with temperatures and/or wind chills dropping into the single digits or below zero. And I think that will continue into this upcoming winter!
Alright, here we go with the forecast in 5…4…3…2…1…
Making the Forecast
One of the things I always like to do is to provide an explanation into any major forecast I make, and the same applies to the winter forecast. I do this because it offers a little more transparency into how I arrived at my forecast – and if anyone wants to challenge it, I have data backing up my case. Plus, you may learn something new, and that’s always a good thing!
As meteorologists, we often tell you forecasts beyond about five days are volatile and should be used with caution – so why is a winter forecast possible? Simply put, in doing a winter forecast, we simply are identifying the overall theme of the winter, as opposed to more specifics like highs/lows/precipitation, which you would see on a much shorter range forecast. The way we come up with a long-range forecast, such as a seasonal outlook, is by using a method called Analog Forecasting. Analog Forecasting involves looking back at previous years to identify years which featured a similar pattern to the current one. The idea is if you find a similar pattern, you should expect a similar result. This method does not tell you specifics, but does give an idea of what to expect. So let’s dive into how we arrive at our analog years for this upcoming winter…
El Nino / Southern Oscillation (ENSO)
One thing you will almost always hear about in a winter forecast is El Nino or La Nina, or sometimes just called ENSO. El Nino is warmer than normal waters in the equatorial Pacific Ocean, and La Nina is cooler than normal waters in the equatorial Pacific Ocean. The explanation for why ENSO affects the weather is much too long, and complicated, to include in this blog post, but the important thing to take away is that ENSO affects our weather, and the strongest impacts are felt during the winter.
This year, we currently have a weak La Nina. Normally, weak La Nina’s bring a milder and wetter winter to our region – though wetter does not necessarily mean snowier. The correlation between weak La Nina’s and snowfall isn’t very good. The forecast models expect the weak La Nina to eventually weaken and return to neutral by spring – which I agree with. Therefore, ENSO will play an impact in the winter, but I don’t think it will be the primary force.
Northeastern Pacific Waters and the Pacific Decadal Oscillation (PDO)
Just as the waters in the equatorial pacific have an influence on the weather, so do the waters in the northeastern Pacific, from the Gulf of Alaska and along the west coast. And that brings us to the Pacific Decadal Oscillation, or the PDO. If the waters over this region are warmer than normal, it’s associated with a positive phase of the PDO, if they are colder, it is a negative phase. And right now, we are, and have been in a positive phase. The positive phase is also very evident by a horseshoe shape of warmer than normal waters in the eastern Pacific. The PDO is weaker than it has been in the past few months, but I think it will stay positive through the winter.
Why is this important? During a positive PDO, the warmer than normal waters over the Gulf of Alaska and west coast help buckle the jetstream. A ridge (warmer, drier weather) sets up over the west coast, and a trough (colder, stormier) sets up over the east.
Siberian / Eurasian Snowfall and Arctic Sea Ice
Another factor I consider is the amount of snowfall during the month of October over Siberia. The research by Judah Cohen, of the Atmospheric and Environmental Research (AER), has been shown to have a direct correlation to the weather during the winters in the eastern US. When there is an excessive build up of snow during October over Siberia, it tends to weaken the Polar Vortex – and a weak Polar Vortex allows the cold air to spill out of the arctic and move south. The explanation of this link gets too complicated for me to include here, so I will spare you the lesson in atmospheric dynamics/thermodynamics ( see, even that sounds complicated 🙂 ).
This year, the snow advance in Siberia was the third highest ever recorded!
Based on this Cohen runs a computer model to predict the December-February temperature anomalies. As you can see, his model is predicting a well below normal winter overall – and his model has shown significant skill.
And, if we take a look at arctic sea ice, it has been on a record slow recovery rate – meaning the amount of ice in the arctic is lower than it usually is by this time. As a result, the arctic is warmer than usual (by 36°F, as of Nov. 15), and that also helps weaken the polar vortex – again, bad if you don’t want the arctic cold!
The Analog Years
Those are the three primary things I look at, but there are a few more things that I’m not going to include here, really for simplicity’s sake.
Looking at all the variables, I have come up with four analog years, that match: 1966-1967, 1985-1986, 1995-1996, and 2013-2014. So what were these winter like?
Pretty cold, right?! And all but one featured above normal snowfall (1985-86 featured near normal snowfall).
So now you know what goes into the forecast, let’s dive into my 2016-2017 winter forecast!
Across the US, I expect much of the eastern US to experience below normal temperatures. The heart of the cold air will likely be centered over the upper Mid-west. If you’re looking for any warmth, the west/southwestern US will likely see above normal temperatures.
Locally, it will be a cold winter. I expect the cold will arrive earlier than it has in past years, but it will take some time to establish itself. I expect December will be near normal. The pattern we’ve seen so far in November, with the cold and warm alternating, will likely continue into most of December. By the end of the month, I think we’ll start settling into a winter pattern. I expect January and February will likely feature the heart of the COLD. We could see some brutal cold, and I think we will, once again, see temperatures and/or wind chills dip near or below 0°F. March will also be below average, so don’t expect spring to arrive early or on time this year!
In terms of snowfall, I expect a snowier than normal season overall. I am predicting 150% – 200% of normal (click here to view normal snowfall). December will be our least snowy month. By January, expect the pattern to ramp up, and that will last through February and even into March. The one thing we will have to watch is if we get any arctic cold, it could keep storms suppressed too far south to give us any decent snowfall. Most of the storms we see will be smaller events, generally less than 6/7″ widespread. The threat of another blizzard or significant snowstorm is very low this year. But, more frequent storms I think will help make up for that.
So, how about snow totals:
So just to recap, a snowier and colder than normal winter is expected. Don’t expect any crippling snowstorms, but snow lovers can still rejoice! Make sure you have your winter coat, because you will very likely need it this year. I do think because of the cold, the ice threat will be higher-than-normal this year, and that is much more dangerous than snow. Expect winter to want to hang on as we go into March, keeping Spring at bay as long as it possibly can. And something I like to do for fun, I’ll say 3-6 snow days this year.
What could go wrong
- If the La Nina remains weak in the weak phase, and doesn’t turn to neutral by the end of the season, it could influence the pattern enough we may not have enough cold air available for snowfall – resulting in either all rain, or mixed precipitation events.
- If the Pacific Jet (the part of the jet stream over the pacific ocean) remains strong through the winter, it will prevent the ridge over the west coast from forming. The result is a very progressive pattern, meaning alternating cold/warmth, fast moving storms, and likely little snowfall with a lack of cold air.
- If the PDO turns negative (NE Pacific Ocean waters turn colder than normal), it will also work against a west coast ridge – and may actually allow the ridge to form over the east coast – meaning warmer than normal conditions for the winter.
- If the Polar Vortex doesn’t stay weak through the winter, arctic air would be kept in the Arctic, and winter may not be as cold.
- Conversely, if any of these signals end up stronger than forecast (the La Nina breaks down quicker, PDO turns way positive, or the polar vortex remains very weak), the winter could be even colder and snowier than forecast ( and I already have an aggressive snowfall forecast )!
So…There you go, my 2015-2016 winter forecast. We’ll revisit this in the spring to see how it turns out.
I always encourage questions & comments. You can follow me on my Facebook page : facebook.com/weathermd
Have a great evening! -Andrew