Fall is finally behaving…well, sort of like Fall. Many folks woke up to widespread frost and a hard freeze this past weekend. This means it’s that time again: Time to deliver my outlook for the upcoming Winter season! If you’ve lived in South-Central KY for awhile, you know darn good and well no two seasons are exactly alike for us. Take the last two winters, for example. The seasonal snow totals wound up being almost the same, yet the two seasons saw stark and DRAMATIC contrasts in temperature. Two winters ago, we encountered a brutally cold February with several subzero nights. At the opposite end of the spectrum was last December, one that felt like “Christmas in the Carribean”, to quote a song title from my favorite singer, Jimmy Buffett.
A LOOK BACK: Before I get into this season’s outlook, I want to glance back at what went right AND what went wrong with my Winter ’15-’16 Outlook. I mentioned it would be a “Jekyll and Hyde” kind of season with LOTS of ups and downs. Safe to say, it certainly had both. I thought December would wind up with above average temperatures, which was correct, although I underestimated HOW warm (record warmest December, in fact). I also felt the coldest part of winter would come later in the season, which was also correct (coldest reading happened in late January with another chilly stretch in mid-February). It was also wetter as a whole vs. the previous winter season.
What caught me by surprise…alright, I’ll just say it: STUNNED me…was how much snow our area saw from the VERY FEW times the air grew cold enough for a decent snow to happen.
How weird was last winter? Consider this: It was Bowling Green’s 2nd WARMEST IN THE LAST 50 YEARS (avg temp Dec. 1st through Feb. 28th: 42.1°), yet we wound up with over TWO FEET OF SNOW for the season! If you’d have told me last December when we were picking off one record high after another, I’d have cackled loudly. My forecast going into last season? 8.5-11.5” of snow. Um…yeah, that part didn’t go so well. But to my credit, I predicted most of that would come from two or three systems, and that much was true.
We had back-to-back systems in mid-January, with 2.5” falling on the 20th followed by that WHOPPER of a storm on the 22nd that dumped 12.2” on Bowling Green! Another blockbuster event took place on Valentine’s Day, with much of our area receiving 4-7” of the white stuff (5.5” fell in Bowling Green). Those totals went a long way toward sending us over the 20” mark for a second consecutive season. That’s more than many of our neighbors to the north experienced (Louisville, Lexington, and Evansville, among other cities had far less). Not to mention, we’re going into this winter with back-to-back 20”+ snow seasons for the first time since the late 1970s! Unreal.
By the way, here’s a picture from my house taken on January 22nd, in case anyone had forgotten how impactful that winter storm was.
If I had to grade last year’s outlook on just temperature and snowfall forecasts alone, I’d barely give it a passing grade, to be honest. But I did have SOME of the IDEAS right, and as mentioned here last year, just nailing down those ideas, especially months in advance, is half the battle with these seasonal forecasts. So, I’ll give myself a “C” for last year’s outlook.
Last season is ancient history, so let’s move on and discuss this season. I know the temptation will be to scroll down and find the actual forecast, but I do want to walk you through the various players that shape up our winters and how/why I come up with the kind of forecast I have. The talk will get technical at times, but I’ll do my best to explain things as I go.
1.) EL Niño/La Niña (EL NINO-SOUTHERN OSCILLATION)
Let’s first review “El Niño” and “La Niña”. Basically, El Niño is an abnormal warming of the sea surface water in the Central Pacific ocean off the South American coast. When those same waters cool, it’s a “La Niña” condition. If the water temperature at the sea surface is right at or close to normal, neither El Niño nor La Niña is present. That’s what we call an “ENSO Neutral” condition.
This season, we have a “weak” La Niña going in. However, it looks like that will trend more toward “Neutral” around mid to late winter.
*Imagery courtesy of NOAA
As mentioned, we had a stout El Niño in place last year, one of the strongest ever, in fact. That was a big reason why the lower 48 was often flooded with unusually warm temperatures (some of us weather-types call that the “blow torch” effect). However, on the rare occasions in which the polar jet stream (the northern branch of the jet) dropped southward and interacted with the subtropical jet stream (or “Pacific” jet, as depicted above), we got blitzed with some crippling snows! In “Neutral” seasons, however, the subtropical jet is USUALLY not as active as in seasons with a more-pronounced El Niño or La Niña. That’s one of the reasons why I think this season will be drier than last.
2.) PDO/AMO (Pacific Decadal Oscillation/Atlantic Multi-decadal Oscillation)
The PDO refers to water temperatures in the North Pacific south of Alaska and off the coasts of western Canada and the U.S. Pacific Northwest. Much like last season, the waters in these regions have been running warmer than normal. That’s a key component to consider, because when waters off the southern shores of Alaska are warmer than average, we often see big ridges of high pressure become established over the Gulf of Alaska. If other indices and teleconnections are in place, such a pattern often force very cold air to ride up and over and then down into the lower 48. The chart below shows a history of PDO cycles (note the cold PDO though much of the 1960s and ‘70s, many of those years featured harsh winters for South-Central KY):
*Imagery courtesy of NOAA
The AMO refers to the overall water temperature in the Atlantic. The AMO typically runs in 30 year cycles. Throughout much of the late 1950s, 60s, and 70s, the AMO was in a “cold phase”. Some of you may remember the brutal winters we endured during that stretch (1959-’60 and the last three seasons of the ‘70s). The AMO was also in a cold phase back in the 1910s, a decade that featured one of the Ohio Valley’s most severe winters (1916-’17 and 1917-’18, respectively). Since the 1980s, however, the AMO has been in a “warm phase”. It remains in that mode now, although not as warm as in recent years.
*Imagery courtesy of NOAA
3.) NAO/AO (North Atlantic Oscillation/Arctic Oscillation
These pressure systems are the “wild cards” when it comes to winter forecasting. Unlike the indices mentioned above that deal more directly with sea surface temps, these refer to the movement (a.k.a. oscillations) of semi-permanent pressure systems in the North Atlantic and Arctic, respectively. Those movements can be erratic, and it’s difficult — even for the most experienced meteorologists — to forecast them beyond two to three weeks out.
*Imagery courtesy of NOAA
There are two phases of both the AO and NAO. When each is in a negative phase, the polar jet tends to dip down into the eastern U.S., sometimes sending cold, arctic air into our region. By the same token, a positive phase of each of those indices generally means the eastern U.S. (including our region) is mild to warm. During our extended period of cold air from mid-February to early March 2015, the AO and NAO tanked. Will such fluctuations occur again this season? They could, and when they do, our chances for wintry weather often increase.
4.) OTHER PLAYERS
There’s still a lot of uncertainty on the role solar flares and their cycles play on winter weather. Some speculate that more solar flares/activity leads to milder conditions. Solar activity has not been all that impressive of late.
Another factor to consider is snow/ice cover across North America. There are some similarities in this year vs. last:
*Imagery courtesy of NOAA
Above is last year around this time, below is our latest imagery. You do have to travel quite a distance north/northwest to find some snow in the ground. Also noteworthy has been the lack of snow in the Central Rockies so far this Fall.
*Imagery courtesy of NOAA
The polar and subtropical jet branches are key to how our storm systems move and what type of precipitation they bring. I have posted maps of three that are very common for our region during winter: The Southern Plains to Great Lakes track (aka “Lakes Cutter”), the fast-moving systems that dive southeast out of western Canada (aka “Alberta Clippers), and the southern-tracking systems that often pump moisture northward into the Ohio Valley (aka “Deep South/Piedmont” track).
Basically, if you really LOVE snow, the “Deep South/Piedmont” track is the one you want to see. I’d say eight times out of ten, our biggest snows have come from systems that track through central MS/AL/GA before heading NE into the Piedmont of North Carolina. Such a track is what brought us substantial snow totals in the storms of February 16, 2015 and January 22, 2016. Occasionally, a “Clipper” can bring us light snow accumulations, depending on the track. If you dislike snow altogether, then the “Lakes Cutter” is your track.
Each season is so different. While this upcoming season will NOT be an exact copy of any of the ones listed below, my thinking is that it will bear SOME resemblance to these winters based on similar ENSO patterns and teleconnections along with oceanic temperatures.
Some nuggets about the above winter seasons:
*Winter 1980-’81 followed a scorching summer (we’re coming off one this time, too). This season was mostly uneventful with the exception of one MAJOR storm that brought 6-10” of snow to South-Central KY at the end of January (7” fell in Bowling Green). That blockbuster snow was followed by flooding and rapid snowmelt just two days later.
*Winter 1983-’84 featured WICKED cold (though very little snow) on Christmas followed by some sub zero nights in January and early February along with above average snowfall those two months
*Winter 1995-’96 brought not one but TWO BIG snows to our area…the first in early January and the second on the first day of Spring (March 1996)
*Winter 2008-’09 featured below-average snowfall for Bowling Green, but most memorably, this was the season of that devastating ice storm in January 2009 that paralyzed many of our northern counties. I am NOT saying we will see a repeat this winter, but throwing the fact out there.
THE WINTER FORECAST
As always, the focus is on the three months that make up “meteorological winter” December, January, and February. Here comes the obligatory disclaimer: This is NOT an official First Alert Storm Team forecast! It’s simply my own take on how I think the season may go.
DECEMBER: While I do NOT think it will go down as one of our coldest ever, I do have reason to believe it will not be as warm as December 2015. For one thing, last December was anomalously balmy, and two, there are signs that some high-latitude blocking (that negative NAO I mentioned earlier) might show itself on occasion. This should allow for the polar jet to dive into the lower 48 on occasion. For those wanting a White Christmas, something we haven’t experienced since 2010, such a scenario COULD provide you with some hope. Of course, moisture has to be present when cold air is to bring us significant snowfall. With the subtropical jet looking less active this go round, that combination could be hard to come by. Never say never, though! I will go out on a bit of limb here and say we have a good chance at seeing our most snowfall in December since 2010 (we’ve seen no more than 0.1” in any December since). We’re overdue in that regard.
DECEMBER TEMPERATURES: 1-3 degrees above normal (Avg. temp for the month is 38.6)
DECEMBER PRECIP: Slightly below normal
DECEMBER SNOWFALL: 0.5”-1.5” (just above normal)
JANUARY: I expect some stretches of mild weather with cold shots coming from time to time. The coldest air probably shows up later in the month. While the subtropical jet does not appear too active through mid-season, I still expect several “chances” at significant snowfall, with our area likely cashing in on at least one or two of those. Watch for an ice threat this month.
JANUARY TEMPERATURES: 1-3 degrees above normal (avg. temp for the month is 35.7)
JANUARY PRECIP: Below normal
JANUARY SNOWFALL: 2-4” (2” Below normal to near normal)
FEBRUARY: This is the month that could feature some of our coldest temperatures and best chances for snow. This is because it appears ENSO indices will be most “neutral” this month, allowing for more cold shots to come our way. The subtropical jet also tends to be more active in February than in January. I highly doubt it will be as cold as February 2015, though.
FEBRUARY TEMPS: 1 degree below normal to 1 degree above normal (avg. temp for the month: 39.8)
FEBRUARY PRECIP: Slightly above normal
FEBRUARY SNOWFALL: 4-6” (Above normal)
Here’s a general view of what I anticipate:
TEMPERATURES: Near to slightly above normal overall
PRECIPITATION: Below normal overall
TOTAL SNOWFALL: (8-12” – near to 3” above normal, factoring in possibility of slushy late-season snow in March)
CHANCES OF SEEING AT LEAST ONE STORM SYSTEM BRINGING US AT LEAST 4” OF SNOW: 60%
CHANCES OF SEEING AT LEAST ONE STORM SYSTEM BRINGING US AT LEAST 6” OF SNOW: 30%
CHANCES OF SEEING A WHITE CHRISTMAS: 10%
CHANCES OF SEEING AT LEAST ONE ICING EVENT OF A TENTH OF AN INCH OR GREATER: 60%
CHANCES OF SEEING AT LEAST ONE SIGNIFICANT SEVERE WEATHER EVENT BETWEEN DEC. 1ST AND FEB. 28TH: 30% (low chance due to weaker subtropical jet but can never rule out one or two episodes…we always have to be ready!)
SEASON’S COLDEST TEMPS: Around 5 degrees (should happen in early February)
Other key points here:
**This should NOT rank among our coldest or snowiest seasons ever, but we WILL encounter wintry conditions on occasion
**Bowling Green has not seen three straight winters with more than 20” of snow since the late 1970s. Odds are HIGHLY against that feat being matched this season, but just so you know it has happened in the past!
**I like ONE GOOD SHOT at a snowstorm potentially bringing us 4” or more, with most other events being minor (less than 3”)
**It’s possible we could have one last accumulating snow event in March this year
**I think a significant icing episode (one bringing us ¼” of ice or more) is a greater risk this season based partly on past history of “neutral” years
**Our ongoing drought could be tough to shake given the weak ENSO signal shaping up for this season. Don’t be surprised if drought conditions persist for awhile
As always THERE IS BUST POTENTIAL WITH ANY FORECAST, especially one that goes several months out! The snowfall portion holds the biggest bust potential. If the subtropical jet stays suppressed to the south and/or the polar jet stays locked up into Canada, then we could wind up with less snow than forecast. But if the two jets line up and “phase”, look out.
My thanks to Dr. Greg Goodrich, professor of meteorology at WKU, for his input while I comprised this outlook.
And now…we watch. And wait.
Thanks for reading.