A RETURN TO FORM OR ANOTHER WINTER DUD?

Welcome to the 2020-2021 winter forecast for the WFMJ-TV viewing area, namely far eastern Ohio and western PA. This is the “written” version of the forecast; if interested, be sure to check out the video version as well.

FIRST, LET’S BE CLEAR, WINTER FORECASTS LAST YEAR STUNK.

Cruise around the internet and you can find a lot of seasonal forecasts, some by reputable TV meteorologists, some by NOAA’s Climate Prediction Center, some by forecasters with private firms and some by hobbyists. With few exceptions, the outlooks for winter 2019-2020 were a bust. My forecast belongs in this category as well although I will say that I did not have AS cold of a forecast as many I saw. But it was still off the mark. Last winter was a “blow torch winter” with all three months (December-January-February) being warmer than average by fairly large margins:

How did this happen? I mean, we do know what we are doing? RIGHT?? Well yes, for the most part those who create these outlooks have a (varying) level of expertise. But the atmosphere is extraordinarily complex and long-held assumptions and beliefs about this complex system are being challenged more and more by climate change.

In addition to the rapidly changing climate, a rare event occurred all the way over the Indian Ocean last fall/early winter that I believe created a domino effect across the Pacific, North America and the Atlantic that loaded the dice in favor of warm weather. This is called the Indian Ocean Dipole (IOD) and it was very VERY “positive” a year ago.

This led to a terrible drought and wildfires in Australia but the IOD’s impacts likely extended much farther east. A very strong IOD can also impact air circulations much farther east, and, in the absence of a strong El Nino or La Nina in the Pacific, these circulations can become the “boss”, lining up all the right players for warm winter weather in eastern North America. Many forecasters have little/no experience with the IOD, let alone such a strong one. It’s quite possibly the chief reason for some many bad outlooks last year. The IOD is not expected to be much of a player this year.

RECENT WINTERS IN OUR AREA

After a couple of tough winters in the middle of last decade, we have now reeled off 5 straight balmy winters (with 2017-2018 being the closest to average).

While precipitation has ben plentiful, snowfall has NOT been over the last 2 winter seasons. 3 of the last 5 have been “dud”s.

SO AGAIN, CAN WE DO THIS???

Let’s get back the subject of the skill in these forecasts. Do they have as much skill as the standard 7-day forecast that you find on the StormTracker 21 app or on 21 News? No way. But here IS skill in this. It’s not “guessing” or throwing darts. But unlike the rising skill of short-term forecasts, it can be argued that we are in the middle of a difficult period where climate change is likely REDUCING the skill of these forecasts by some amount. Some years (last year) it will be more than others.

Why? Well a big part of the “secret sauce” of creating a seasonal forecast is “analogs”; years in the past with similar ingredients in the oceans and atmosphere to this year. Ocean water temperatures are a very big part of this and, simply put, the oceans are on fire. The amount of heat in the oceans is not something we have analogs for and this heat content is undoubtedly making the atmosphere do things that we do not understand well just yet. Look at the current water temperature anomalies across the globe. With the exception of a tongue of cold water in the Pacific associated with La Nina, it’s hard to find much blue.

In addition to analogs, we depend some on computer models and some on stuff that’s a little less science-y like gut feelings, experience, etc.

LA NINA: THIS YEAR’S MAIN INGRIDIENT

La Nina. It’s the cooling of the waters in the equatorial Pacific, especially the eastern Pacific. It’s the opposite of El Nino. We have a pretty strong one on our hands this year, probably the strongest Nina in a decade. Some models suggest that water temperature anomalies will get close to -2 degrees Celsius, which would be quite rare.

A “typical” La Nina results in a weaker subtropical jet stream and a stronger northern branch of the jet. In the US, this can lead to a dry winter in the southern parts of the country and more frequent precipitation in the northern tier of states.

But not very La Nina is created equal. Some weaker ones can be overwhelmed by other factors. A stronger one can exert it’s will and it’s impacts can become more predictable.

THE QUASI-BIENNIAL OSCILLATION

This is a much less well-known ingredient in the winter casserole. The “QBO” refers to a zone of very high altitude winds over the equator. How high? We are talking about the stratosphere here. This river of fast-moving air changes direction every 14-16 months. The QBO can impact large-scale circulations in the northern hemisphere winter. The polar vortex tends to get dislodged more frequently in “easterly” or “negative” phases of the QBO. A dislodged or perturbed vortex then can meander off the pole and if it meanders into the western hemisphere, we can get cold shots more frequently. The opposite is true of the “westerly” or “positive” phase of the QBO; odds of a meandering polar vortex are lowered.

We will see a “positive” QBO this winter.

THE SUN REMAINS “QUIET” BUT IS WAKING UP

We are emerging from a “solar minimum”, a period in which the sun is “quiet” with little sunspot activity. This is a cycle that repeats itself about every 11 years. So what? There is some research that shows a correlation between low sunspot activity and COLD winters in the eastern US, but honestly I think the relationship is shaky. If there are strong pattern drivers (last year’s IOD, strong El Nino’s, La Nina’s etc) I suspect the solar cycle is not particularly important. Worth a quick mention though.

THIS YEAR’S ANALOGS

Ok let’s start getting into the forecast. As mentioned above, analogs are becoming tricky, especially because of the significantly warmer oceans that we have now. Any years before the late 90s can almost just be thrown out at this point. Much more “weighting” should be placed on recent years that are a good match.

Based on the intensity of La Nina and the other factors discussed above, here are my analogs for this winter. #1 is 2016-2017. It’s a recent year with similar heat content in the oceans. But it’s far from perfect as the La Nina that winter was a fair amount weaker than this time.

The 2016-2017 winter was quite warm but snowfall was actually a little above average. Here’s a look at the national temperature map that winter:

2010-2011 is actually a pretty good match for La Nina strength, the QBO phase and low solar activity. It was quite a bit different though! Very cold and actually our snowiest winter on record(!). BUT looking at the oceans globally, while it is a good match in the LA Nina zone, there was much more cool water elsewhere, most importantly in the northern Pacific. Also important is the very warm water in late 2010 near Greenland and the lack of significant warmth of the East Coast of the US. So while we have to keep this analog year in mind, I think the chance of a repeat of 2010-2011 this year is pretty low.

When you throw all the analogs in the hopper, with particular emphasis on 2016-2017, you get a composite map that looks like this:

Precipitation:

THE COMPUTER MODELS

Meteorologists have access to a treasure trove of computer models these days. Some only predict the state of the atmosphere 12 hours out in time, some a week and some on a seasonal time scale. Of course, the accuracy and reliability of seasonal models is less than the short-term ones but they still have value. It’s another tool in our tool belt. Just like a hammer is not going to build a deck for you (YOU have the USE the hammer correctly!), the models do not build the forecast.

So that being said, one word describes the look of the seasonal models at this point: WARM. All of them are factoring in the strong La Nina and suggesting it will be quite balmy in the eastern 2/3 of the country. For example, the European model seasonal outlook for winter:

We have to be careful with the European, as it has a hard time “seeing” cold on the seasonal scale. I very much doubt the winter is warmer than average across the ENTIRE lower 48 states. The Euro precipitation outlook is pretty classic La Nina stuff:

THE FORECAST

“Don’t bore us, get to the chorus!”.

Ok, after all that, let’s talk about the actual forecast. Given all that I have said so far, it would be pretty shocking if my forecast was cold and snowy, right? Well, don’t worry it is not. I expect this winter to be another relatively “easy” one by Ohio/PA standards. BUT! That does not mean we won’t have bouts of cold and snow. And I do think odds favor at least 1-2 “BIG” storms this season even though snow events may be quite infrequent.

I’ll break down the temperature outlook by likelihood.

THE MOST LIKELY OUTCOME: A WARM WINTER OVERALL IN MUCH OF THE COUNTRY; LOCALLY A SIMILAR FLAVOR TO THE LAST 5 YEARS.

THE NEXT MOST LIKELY OUTCOME (ALTHOUGH WITH SIGNIFICANTLY LOWER ODDS): A VERY WARM WINTER, LOCALLY PERHAPS EVEN WARMER THAN LAST YEAR. A TOP-5 WARMEST WINTER ON RECORD FOR US.

OUTCOME THAT CANNOT BE RULED OUT: A WINTER THAT IS NOT SIGNIFICANTLY COLD BUT CLOSER TO AVERAGE THAT MOST OF THE LAST 5 WINTERS.

I would be pretty shocked if the national temperature map ended up any colder than this, especially for our area. A wager on a cold winter locally would be very very risky at this point.

Precipitation forecast:

It does seem like it will be pretty wet winter. Because above-average precipitation is expected, when things DO come together just right, a SIGNIFICANT snowstorm will be a possibility at times this year. The odds of a couple of “big ticket” storms may even be higher than the last couple of years, despite the warm forecast overall. The FREQUENCY of snow events may be rather low, however.

THE SNOW FORECAST:

FORECAST CONFIDENCE

As shown above, we think there’s is about a 60% chance of the kind of winter that has been common in recent years; warmer than average. Beyond that, a 1 in 4 chance of it being VERY mild…to the point that it can be one of the warmest on record. We are confident that a colder-than-average winter will not occur. Overall, we have high confidence in the drivers of the pattern….the moderate/strong La Nina, the positive QBO, etc. Confidence is reasonably high that it will be an unsettled winter with plentiful precipitation. Where confidence is not that high….the snow. This may end up being a season with snow totals within shouting distance of average but it may be PERCIEVED as pretty snowless because of the long intervals between snow events. Expect a lot of cold rains, snow changing to rain situations and maybe even some rare wintertime thunderstorms when the pattern gets real warm.

WHAT COULD GO WRONG?

All forecasts carry inherent risk; this is tricky business. Where is the bust potential this year? The forecast is likely to be not-warm-enough at this stage rather than too warm. But how could this end up being a colder and snowier winter?

1) The unusual temperature patterns across the oceans produces outcomes that have low predictability.

2) The polar vortex has unexpected weakening episodes and decides it wants to take a stroll on this side of the world rather than staying parked over the pole.

3) The Great Lakes remain unfrozen/unusually warm and we get enough cold shots, especially early in the season, that sizeable lake-effect snow events occur, driving up snow amounts (especially in areas north of I-80).

THIS WINTER VS. LAST WINTER

Compared to last winter, this winter is most likely to be pretty similar temperature-wise but somewhat snowier, thanks to a higher chance for “big ticket” events. Caveat: The number of days in which it snows? Likely below average.

THE BOTTOM LINE

The Winter 2020-2021 Forecast