Because I have a lot of friends who are weather fanatics, finding strange joy in the bitter cold and frozen precipitation that most of the civilized world finds miserable, I see plenty of gnashing of teeth and rending of garments on social media when winter isn’t going as hoped for … and winter 2019-2020 is obviously not going as hoped for. It might’ve seemed like it early, when teachers and students were enjoying a November snow day, before the last of the fall foliage had even turned loose, but things just never materialized from there.
In recent days I’ve seen a couple of well-meaning folks admonishing the complainers, reminding them that winter is only a couple of weeks old. In other words, don’t give up on it just yet.
It’s true that winter isn’t far along on the calendar. Officially, winter doesn’t begin until the winter solstice, which is December 21. But from a meteorological standpoint, winter begins on December 1, ends on February 28, and we’re in the climatological heart of winter. The sun is climbing higher in the sky each day, and the proof is in the setting sun each evening. Sunset today was at 5:38 p.m. Just a couple of weeks ago, as we were preparing to celebrate Christmas, the sun set at 5:25 p.m. As it climbs higher in the sky, our temperature increases and the window for snow — real snow; serious snow that lays around on the days and causes all the chaos that winter-lovers dream of — begins to close.
In Oneida, we reach the coldest part of the year on December 30. That’s when our average daily high temperature drops to 44 degrees. It stays there for a while, but rises to 45 degrees on January 18, and just keeps increasing after that. By January 31 it will be 46 degrees, and then the uphill climb to spring accelerates as the calendar flips to February. By just four days after Valentines Day, our average daily high in Oneida is 50 degrees. The higher sun angle does more than warm the atmosphere and lengthen the daylight hours. Its penetrating rays make it more difficult for snow to accumulate, and melt it more quickly, even behind thick cloud cover. February snowfalls have less staying power than January snowfalls.
That’s not to say that we can’t have significant snowstorms in February and even in March. Obviously we can, and history speaks for itself. February 1998 and March 1993, anyone? But in terms of probability, you wouldn’t want to bet the farm on accumulating late winter or early spring accumulating snows.
So we’re in the heart of winter, and so far Winter 2019-2020 has been a winter that wasn’t … again. There are a variety of reasons why, but it didn’t always look like this was going to be the case. Long-range forecasts in late summer and fall certainly pointed towards a cold and snowy winter. Even the Farmer’s Almanac projected misery. There was a pre-winter buildup of cold air in the arctics — which is our source of cold air in the northern hemisphere, like freon to an air conditioning unit. But conditions simply haven’t lined up for that cold air to spill into the southeastern U.S.
What’s gone wrong? Several things. But perhaps chief among them, the Pacific Ocean simply hasn’t cooperated. With a lack of ridging in the eastern Pacific to help steer the jet stream, modified Pacific air has flooded the continental U.S. The result has been an active storm pattern — hence, the reason it’s been so wet in Tennessee since the latter part of November — but an unfavorable storm track (in a nutshell, we only get snow in this part of the world if storms track to our south and place us in the cold sector; if the storm track is to our north, we’re in the warm sector and will see primarily rain) and lack of cold air has prevented snowstorms from forming. There has been a lack of atmospheric blocking in the northern Atlantic that can cause cold patterns to take hold in the eastern U.S., and the lack of ridging in the eastern Pacific has allowed the available cold air to pool in the western part of the country, leaving much of the eastern U.S. in a milder weather pattern.
It’s not quite that simple, of course, but that’s a broad overview of what has happened.
Back to the admonishers’ point, it is true that the season is young. Winter may have begun in meteorologists’ eyes back on December 1 — meaning we’re about halfway through already — but snowstorms are uncommon in Tennessee in December. Our time to shine, if you like wintry weather, is January and early February. From 1981 through 2010, the rolling 30-year period currently used by the National Weather Service, our average annual snowfall in Oneida was 7.1 inches (which, by the way, is much lower than the average annual snowfall when numbers from 1971 through 2000 were in use). Of that, only 1.3 inches, on average, has fallen by December 31, and 4.2 inches has fallen by January 31. By February 28, the average for the season jumps to 6.4 inches. So, the numbers aren’t difficult to break down: 1.3 inches of snowfall in December, 2.9 inches in January, 2.2 inches in February, and 0.7 inches in March.
However, there is something to keep in mind, and that is the ability of meteorologists and the computerized tools they rely on to project weather patterns beyond the next 3-7 days. The medium-range guidance models most often used by meteorologists, the American-made GFS and the European-made ECMWF, are 15-day operational models and both are quite adept at projecting patterns for up to two weeks at a time. Beyond 15 days, long-range forecasting begins to become more of a crapshoot.
Just before Christmas, when I pointed out in a Facebook post that the next two weeks looked somewhat mild and rainy, I said that if we got through that two-week period and there was no sign of the pattern breaking down, it might be time to start preparing to throw in the towel on Winter 2019-2020.
And here we are. Two weeks have elapsed. We could be reasonably sure there wouldn’t be major winter storms in the Cumberland Plateau region during the Christmas and New Year holiday period, and there wasn’t. Some light snow on January 4 that didn’t amount to anything more than a light dusting in some areas was the extent of our wintry precipitation. So what does the pattern look like now, going forward? In a nutshell: More of the same.
For the next two weeks, the mild and wet pattern looks to persist. The upcoming weekend looks like a virtual washout for our region, and we’ll be talking more about the possibility of severe weather than wintry weather (chances of severe weather are relatively low on Saturday, but strong thunderstorms are possible). After that, there are signals of additional storm systems around January 14-15 and January 20-22. Combined, these next three storms could produce upwards of half a foot of rainfall for the already-saturated region, but virtually no snow. Temperatures are likely to push into or near the 60s with each of the storm systems.
If — and I stress “if” — we get through this next two-week period and a pattern change still isn’t on the horizon, we will be entering the final week of January and looking forward towards the middle of February. And if we get to Valentines Day and a pattern flip to cold and snowy weather still isn’t looking likely, it is almost certainly going to be time to declare the entirety of Winter 2019-2020 a big, fat bust.
So that’s why I say that this winter is dwindling. Chances for it to be a memorable winter in terms of snow and extreme weather are diminishing. With that said, there’s a major caveat that deserves to be highlighted: it only takes one significant snow storm to make any winter memorable. The Winter of 1992-1993 was quite bland before the Blizzard of ’93 that March, and the Winter of 1997-1998 was ho-hum before the devastating dynamic cooling storm that exceeded even the 1993 blizzard in terms of the havoc it created.
There are more recent examples, too. The Winter of 2014-2015 had featured zero — as in 0.0 inches — snow until February 17, three days after Valentines Day. Then we got slammed with a major pattern change, temperatures that bottomed out at -11 (an all-time record for the month of February, and the coldest temps that Oneida had recorded since January 1984), and a total of 7 inches of snowfall in the final two weeks of February. The cold pattern continued into March 2015 with record-low temperatures before spring finally arrived by the middle of that month.
So it’s certainly not time to declare winter over, not by any stretch of the imagination. And there are some signs that a pattern change could be on the horizon. For now, though, those signs continue to be delayed and I wouldn’t put much stock in the idea of a pattern change until it’s actually showing up with a little more consistency on long-range models.
For now, the North Atlantic Oscillation — which has been predominately positive this winter — looks to stay in positive territory through the middle of the month, though it does show signs of dropping back towards neutral territory as we get into the latter stages of January. The NAO is a measure of storminess in the northern Atlantic Ocean, and a negative NAO state is typically desirable for sustained cold and snow chances in the Mid-South. The Arctic Oscillation has spiked to extreme positive territory, and will stay there for the next several days before perhaps trending towards neutral by the latter part of the month. For now, models keep the AO in positive territory, however. The AO is a measure of storminess in the arctics, and a negative AO is generally preferred for cold air to be unleashed into the Lower 48, while a positive AO is viewed as a hindrance for serious wintry weather. Finally, the Pacific North American ridge index is trending into negative territory and will become sharply negative in the days ahead, before beginning to trend back towards neutral in the latter part of the month. For now, models keep the PNA for the foreseeable future. The PNA is a measure of ridging in the eastern Pacific. A lack of ridging, which places the PNA in a negative state, doesn’t force colder air into the eastern U.S. and often leads to a pattern where the West is generally colder than normal and the East is generally warmer than normal. A positive PNA is generally preferred for cold and wintry weather in the Mid-South.
Taken together, a +NAO, +AO and -PNA isn’t a death knell for wintry weather in Tennessee, but it’s definitely not an ideal setup. On top of this, the Madden-Julian Oscillation — a measure of omnipresent and eastward-moving storminess in the tropics — looks to remain in unfavorable position for the time being. The current forecast has the MJO progressing through Phases 4-6 for the next couple of weeks. Generally speaking, Phases 7, 8, 1 and 2 are where cold weather outbreaks occur in the eastern U.S., while Phases 5 and 6 tend to be where warm-weather extremes occur. Not surprisingly, with the MJO stuck in Phases 4-6, the next couple of weeks look mild.
If, over the next couple of weeks, the MJO begins to show signs of progressing into Phases 7 and 8, and if there are signs of increased ridging along the Pacific Coast, and if there are signs of the AO flipping to negative, those will be pretty good indicators that a pattern change is brewing. And I’ll add that brand-new guidance for February 2020 from the long-range CFSV2 model is showing cold air flooding much of the eastern half of the country in February. Previous guidance from this model was showing cold air only in the New England region for February. However, the model doesn’t have a good track record thus far this winter. It did not lock on to the mild January pattern in the eastern U.S. until late in the game.
The bottom line: It’s far too early to stick a fork in Winter 2019-2020, but we’re further along in the game than it might appear at first sight. For now, a mild and wet pattern is in command and will continue its death grip on the Mid-South region for at least the next 10 days or so. After that, it may be time to re-evaluate the broader atmospheric setup … and if there are no serious signs of pattern change, the ol’ fat lady may be starting to warm up her vocal cords.