Winter 2017-18 Outlook

After a disappointing winter season last year, all who love winter and all that comes with it are certainly hoping for a rebound. Last year, Washington DC recorded 3.4″ of snowfall, and Baltimore only 3.0″ for the entire year. Washington had it’s third warmest winter on record, and Baltimore ranked within the top 10. But, it’s a new year, and things are slightly different, so… without further ado…here is my forecast for this upcoming winter.

As always, I like to include a discussion showing what makes up my forecast. Below the discussion will be the forecast graphics for temperature & snowfall, if you want to skip the discussion or want to read the discussion after. And if you’ve never read one my posts, I do my best to keep things as simple as possible, so don’t worry, you don’t need to know thermodynamics or calculus to understand anything. 🙂

Discussion

So how do we actually forecast 3-4 months ahead? We do this by looking at various atmospheric patterns, or teleconnections, as they are right now, and attempt to find years in the past that are similar.  The idea is that if conditions are similar, the result will be similar too. But no too winters are alike, so this gives us a guideline. It’s up to meteorologists to use their forecasting experience to come up with the final result.

This year, was extremely difficult. Through my research, there really were no ‘good’ years to compare this fall/winter too. So instead, I had to look at things independently, and try to match the resulting patterns to get my answer. Fortunately, some interesting things popped out of this.

The El Nino-Southern Oscillation

You’ve probably at least heard of the El Nino-Southern Oscillation, or more colloquially known just as El Nino/La Nina. It refers to a coupling between the ocean water temperatures in the equatorial pacific and the atmosphere. El Nino results when warmer than normal waters exist in the equatorial pacific, and La Nina when the waters are colder than normal.

Weak La Nina. Blue = Colder than normal waters, orange = warmer than normal

Currently, we have a weakish La Nina. Uncertainty remains in how long this La Nina event will last, with some models suggesting it dies during the winter, and some not until late winter/early spring. There is also something unique about this event. If you look on the image above, notice the colder water temperatures (dark blue) are located along South America, and not in the middle of the ocean. This is a classification of La Nina, called an East Pacific La Nina. If we look back at the East Pacific La Nina winter in the past, we notice a few things. First, they contributed to rather cold eastern US winter, particularly over the Mid-West. Second, they were very favorable for high latitude blocking, particularly around Greenland.

High latitude blocking is just an upper level area of high pressure, that redirects the jetstream and any storms around an area. If you think of the jetstream as a highway, a block would just be an area they closed for roadwork. You’d have to take a detour to get around the block. The effect is that this helps bring cold air into the eastern US, as well as provides a more favorable storm track for any lows that come up the coast (it prevents them from moving too quickly, or going too far east). If you want snow & cold, you want blocking around Greenland.

So, this looks promising so far…

The Quasi-Biennial Oscillation (QBO)

Don’t let the words scare you. Quasi means almost, biennial means every two years, and oscillation means it goes back and forth, simply put. This is a very important teleconnection and deals with the wind direction wayyyyy up in the atmosphere (about 60,000-70,000) feet. It gets its name from the fact it goes back and forth over a 26 month time period (or almost two years). The positive phase is west to east winds, and the negative phase is east to west winds. Each phase, and how strong each phase is, has different implications. It’s a complicated link, but there is a connection to the lower atmosphere, where our weather exists. Last year, the QBO was extremely positive, which partially contributed to what we experienced last winter.

We began transitioning into the negative phase over the summer, which is the more optimal phase for ‘good’ east coast US winters, so long as the QBO doesn’t get too strong. Right now, things look good, but if the QBO were to get too strong, it will begin to work against us again.

Why is this important? If the QBO remains in its optimal range of the negative phase, a favorable pattern emerges. We also see high latitude blocking is more likely, again specifically around Greenland. So now we have two indices that point say we have an increased probability of seeing favorable upper level features appearing during the winter.

Snow in Siberia/Eurasia & in North America

Yellow = Snow covered areas
Notice almost all of Canada & much of Russia/Eurasia/Siberia are all covered

Recent work by a guy named Judah Cohen, has found a link between increased snowfall during the month of October in Eurasia/Siberia and colder eastern US winters. This year, the snowfall the snow cover in Siberia is above average, but not record high.  I will note, Cohen’s research doesn’t always work out (last year, for example), but it can be an indicator, especially if other indices can support it.

Snow cover in North America, specifically over western Canada, is very important because this is the source of cold air for the United States. Snow cover over North America is well above normal and much greater than last year. The cold air source exists, the question is, can we get it to transport southward?

The Pacific Ocean

Normally, I consider something called the Pacific Decadal Oscillation. This refers to a pattern of Sea Surface Temperatures in the North Pacific.

The Pacific Decadal Oscilation Phases. Yellow/Red = Warmer than normal water, green/blue = cooler than normal water

The positive, or warm phase, is more favorable for eastern US winters, and features a cold north central pacific, and warm  Gulf of Alaska and along the west coast.

If we look at temperatures right now in the Pacific, there really is no clear indication of what the PDO is doing. So, I had to leave this out of my outlook. However, this could lead to more variability in the jetstream over the pacific (as other mechanisms take control), meaning there could be stretches where it becomes favorable for winter weather (cold/snow) in the eastern US, followed by unfavorable.

Other Indicators

While the above are my ‘rocks’ so to speak for winter forecasting, there are other things that can be considered. There is a theory that low solar activity can lead to increased chances of blocking, and a weakening of the Polar Vortex (means arctic air can spill southward). Though, this theory isn’t definitive. We’ve been in a solar activity minimum for a couple years now, and this hasn’t worked out too well the past couple winters.

Some also look at the Atlantic Hurricane Season as a measure. Remember, weather exists to balance out temperature differences to keep the equator from getting infinitely hot, and the poles from getting infinitely cold. Hurricanes transport A LOT of heat northward. The more active the hurricane season, the more heat that gets transported. An argument could be made that this would reduce the ‘work load’ during the winter months, indicating fewer storms. We had a very active hurricane season in the Atlantic this year. However, the pacific Hurricane & Typhoon season, was a little quieter.

Also, the earth has been running warm. You can chalk it up to whatever explanation you want, but the fact of the matter is that most spots on earth are running warmer than normal. And this has to be accounted for when making a long-range forecast like this.

So, let’s get to the forecast then…

The Forecast

I expect an average winter this year. It will be colder than last year, but not frigid. Though, I do think we may see some spells of arctic air. I also expect near average snowfall. I think this comes from numerous small storms, many of which will feature rain, sleet, snow, and possibly freezing rain. I don’t expect any patterns to lock in for extended periods of time, in general, so I think the temperature roller coaster will continue. I also wouldn’t be surprised to see some wild temperature swings at times. It can never be ruled out, but the odds of a big snowstorm this year are very low.

I think December will feature some cold, and probably a little snow, but it will also have some warmer periods. Overall, the month should end about average. I expect January to be the coldest month, where arctic outbreaks may be common. The cold would be favorable for snow, but too cold means less moisture, and less total snow. February I expect will be slightly below average, and will still be favorable for snow. Winter should end quickly this year, and I expect March will be above average, with little snowfall.

This first map is NOT a forecast, it show an approximation of average snowfall for the region. 

The map below is my snowfall forecast. Again, I’m expecting near average snowfall for the winter.

What could go wrong?

  1. If the La Nina holds steady or strengthens, it would likely lead to a warmer & less snowy pattern in the eastern US
  2. If the QBO becomes too strong, it will lessen the likelihood of blocking, and makes the pattern less favorable overall
  3. If the jet stream over the Pacific configures itself in an unfavorable way, it will make the pattern over the eastern US more unfavorable

 

So there you go! My Winter Forecast for 2017-18. There aren’t a lot of winters past that were worse than last year, so you could say the odds are in your favor, if you like snow.

-Andrew