WINTER OUTLOOK: 2017-2018
Since the end of summer, we've been asked (especially in schools) what our thoughts would be for this upcoming winter. It took a little bit of time, but we feel that we have our ducks in a row. Before we get to the actual forecast, there are some limitations with long-range forecasting.
1. Despite the many advances in meteorology, there still isn't as much skill in long-range forecasting as there is in day-to-day forecasting. A lot of what we do is look at the past to help predict the future.
2. Because we look at the past, the sample size is fairly small.
Regardless of limitations, we're eager to try our hand at this year's winter forecast. So, let's get to it!
TRAIN OF THOUGHT:
Our train of thought this year revolves around three key ingredients. 1) The chance of a La Niña, 2) This very active tropical season and 3) Warm Atlantic waters over a long period of time (referred to as the Atlantic Multidecadal Oscillation).
WHAT IS A LA NIÑA?
A La Niña refers to cooler than average ocean waters in the eastern Equatorial Pacific (off the coast of Peru). These ocean currents can alter the jet stream patterns in the continental US, and therefore provide implications on what kind of long-term weather we can expect.
What this traditionally means is a less active storm track in the southeastern US, which almost puts us in a questionable battle zone. The jet stream will dip from time to time, which would infer colder air and perhaps a chance of storm systems moving through. That exact location, though, can't be pegged down months in advance.
Given this tricky nature, we decided to look back at past weak La Niña years to see what they meant for us, snow-wise and temperature-wise. Temperature-wise, 6 of the 11 weak La Niña years on record yielded above-average temperatures for the winter.
8 of those same 11 years, though, yielded below-average snowfall in the Tri-Cities. (The average amount of snow per year in the Tri-Cities since 1938 is 14.7" and much higher in places like Wise and Boone.)
Now, if we were to take weak La Niña years, where the tropics were very active and the Atlantic was in a long-term warm state - we'd be left with the years 1954, 2000, 2005, 2008, and 2011. In those five years, four of them featured below average snowfall.
THE TROPICS INFLUENCE
Why do the tropics matter? Oftentimes, we talk about the atmosphere trying to stay in balance. So just going off the notion, we could infer that a more active tropical season would lead to a less active winter in the the eastern US. (Tropical systems transport heat to the poles, so the more heat that's transferred in the tropical season - the less that would have to be in the winter.) Inferring isn't necessarily responsible science, though, so we looked at past active tropical seasons.
The average 'Accumulated Cyclone Energy' for a given tropical season is 111. This year, that number is twice the average! Again, this would infer that the atmosphere has less ground to make up.
What we can show, though, is that there have been 16 years since 1970 in which the 'Accumulated Cyclone Energy' or 'ACE' is higher than that average of 111. In 16 of those following winters, 14 of them featured below average snowfall in the Tri-Cities.
THE FINAL VERDICT:
Being that there isn't as high level of skill in long-range forecasting, we had to resort to past instances that are similar to the current state of the atmosphere. In doing that, we have come up with our prediction for the winter.
Since the weak La Niña pattern puts us in somewhat of a battleground, we are not fully confident in the temperature forecast. Only 6 of 11 weak La Niña winters featured above average warmth, which doesn't give us a clear sign to go with.
Given this recipe of a weak La Niña, an active tropical season and a warm long-term period in the Atlantic (as well as a clearer sign in the past data), we predict that there will be less chances of snow this winter. Does that mean we won't see snow at all? That's highly unlikely. The less active storm track, however, lends us to think that there will be less overall chances.
We know that we've delved into a lot of information here, but we believe 100% in being transparent with you all. If you have any questions for us, please feel free to message/comment on our respective Facebook pages.