It seems like I posted a winter outlook only a week ago! But sure enough, here we are in late autumn 2017. Some years, we’re still waiting for those first flakes of the season by this date. Sometimes we’ll go well into December or even January before seeing wintry precipitation. This year is different. Bowling Green has ALREADY recorded its first snowflakes of the season (a trace on Oct. 29th) over a full month before the start of “meteorological winter” (the period from Dec . 1st through the end of February). Combine that with our recent cold shots and we’re reminded it’s time: Time to peer ahead at what the upcoming winter has in store for South-Central Kentucky.
A LOOK BACK: Before I look ahead, I do want to take a look back at Winter 2016-’17. I will forever call this “The Winter That Wasn’t”. The numbers tell the story.
Here were some highlights (and “low” lights, if you’re a fan of snow):
December 2016: Due in large part to a cold mid-month, our average temperature last December was actually near normal (39°). But I think the month will be best remembered for the INCREDIBLE warmth we experienced on Christmas Day! In fact, it was our warmest Dec. 25th ever (high: 72°). The day after Christmas was even warmer (high: 75°, also a record). We saw no measurable snowfall last December (only a trace/flurries).
January 2017: Winter showed itself for just a few days early in the month. A weak system on the 5th produced minor snow accumulations across South-Central KY, with Bowling Green picking up 0.7”. That would be our ONLY accumulating snowfall for the entire season. After a low of 9° on 1/8, the rest of the month was mild, if not warm. BG wound up with our 7th warmest January all-time (avg temp: 44.2°).
February 2017: For all intents and purposes, Old Man Winter, like Elvis, had left the building. The month was remarkably warm…so warm it would go down as our 2nd warmest Feb ever in Bowling Green (avg. temp: 48.5°). This was punctuated by an unusually long stretch of 70°+ days, including an 81° record high on 2/24. That’s just insane for February. Not one flake of snow fell this month…a far cry from what occurred in Feb 2016 (9.2” of snow) and that really cold and snowy Feb of 2015 (12.6” of snow).
When all was said and done, those three months comprised what turned out to be our 2nd WARMEST WINTER EVER in Bowling Green, with an average temperature of 43.9°. That is just INSANE.
I know, I know…hindsight is always 20/20. But it’s important that as forecasters we understand why certain patterns result in certain outcomes.
So why was winter practically non-existent last year?
One reason can be traced to the general lack of blocking in the North Pacific. When high pressure resides in this area, we tend to see the polar jet stream dive southward into the Eastern U.S. more often, especially if other indices over on the Atlantic side come into play. That rarely happened last season. This resulted in what we as forecasters commonly refer to as “blow torch” conditions, with south to southwest winds resulting in long periods of unseasonably warm weather.
Lack of snow cover in the upper latitudes going into last season also proved to be a tell-tale sign of things to come. When a snow pack is laid down over a large area, it tends to chill the air mass around it (“refrigeration effect”), and it often forces storm systems to track more southerly where there is no snow. But if that snow pack isn’t so expansive, storms tend to track farther north, pulling warmer air northward with them.
Here is the map of snow/ice cover in North America from mid-November 2016. Compare that to the map below from November 2014, just before Bowling Green experienced one of its harshest winters since the late ‘70s. A BIG difference, indeed.
So that was last year. If you like warm winters with hardly any snow and lower utility and gas bills, you were probably in heaven. But each season is different, and it’s time to jump into this one.
***THIS IS WHERE THE TALK GETS TECHNICAL AS I DIVE INTO THE ATMOSPHERIC PLAYERS FOR THIS SEASON. IF YOU WISH TO SKIP THIS PORTION, SCROLL DOWN TO “THE WINTER FORECAST”***
1.) EL NINO/LA NINA (EL NINO-SOUTHERN OSCILLATION)
You’ve probably heard the terms “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.
Although it won’t be strong, La Niña conditions are what we’re looking at for this season. This season’s La Niña looks weak to perhaps low-end moderate in strength.
*Imagery courtesy of NOAA
Last year, most models/ensembles forecast a weak to moderate La Niña lasting through winter. That didn’t materialize, however, and we wound up with a “neutral” season. One could argue the lack of signal might have been another reason for last season being so mild, although some trace it back to the “leftovers” from the previous season’s strong El Niño. At any rate, it appears we should hang on to La Niña conditions for awhile, although a trend to more neutral conditions seems likely toward the end of winter.
Notice in the La Niña pattern depiction above where the word “wet” is placed: right smack dab over the Ohio Valley. The Pacific jet should be plenty active. I do believe based largely on past history with La Niña events that we will experience above normal precipitation this upcoming season.
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. 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 in the blue though much of the 1960s and ‘70s, many of those years featured harsh winters for South-Central KY):
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 (1917-’18). 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.
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 very erratic. There’s VERY little skill — even for the most experienced meteorologists — in forecasting how the AO and NAO might behave beyond just a couple of weeks out.
There are two phases of the AO and NAO: Positive and Negative. When each is in a negative phase, the polar jet often dives into the eastern U.S., sometimes sending cold, arctic air our way. A positive phase of each of those indices generally means the eastern U.S. (including our region) is mild to warm. The two indices stayed positive often last season.
4.) OTHER PLAYERS
It’s possible that solar flares and their cycles play a role on winter weather. To what extent that role is remains uncertain. Some speculate that more solar flares/activity leads to milder conditions. Another factor to consider is snow/ice cover across North America. Here’s how it stands over North America as of November 15th.
Image courtesy: NOAA
To better predict the future, we often must look at the past. While no two El Niño or La Niña seasons pan out exactly the same, there is at least *some* correlation among many of them. For example, many of our snowiest and coldest seasons (1977-’78, 2009-’10, 2014-’15) have featured weak to moderate El Niños. That’s NOT to say La Niña seasons can’t be big snow producers for us (1978-’79 and 2010-’11 come to mind), but more times than not, we wind up with snowfall at or below seasonal average for us (roughly 9”).
These are the seasons that were given the most weight as “analogs. By analogs, I mean seasons with central Pacific Ocean sea surface temps along with other indices most similar to the one upcoming:
Some notes/nuggets about these seasons:
*Winter ’67-’68 started mild with BG enjoying a 70° day just before Christmas before the pattern went crazy just after Dec. 25th. Some 10” of snow fell in a four-day span, with a blockbuster storm dumping 7” on New Year’s Eve
*The rest of Winter ’67-’68 was fairly tame beyond a bitter cold start to January, minus a very rare late March snow event
*Much of Winter ’74-’75 was mild (70s in late Jan ’75) before cold and snow returned in late Feb into mid-March
*Much of Winter ’07-’08 was also mild before cold/snow returned late season
*Winter ’07-’08 featured the deadly “Super Tuesday” tornado outbreak (happened late 2/5/08 into early morning 2/6/08)
*All three of the above seasons featured accumulating snows after “meteorological winter” in March. Bowling Green picked up 5” of snow on March 7-8, 2008 and a whopping 11” of wet snow on March 22, 1968!
Also given some consideration for this forecast were these seasons:
Both those winters featured severe weather outbreaks in January (early Jan ‘06/late Jan ’13) and return of cold late in the season.
THE WINTER FORECAST
My focus is on the three months that make up “meteorological winter” December, January, and February. I should also stress this is NOT an official First Alert Storm Team forecast! It’s simply my own take on how things may play out.
DECEMBER: I feel this is where I’m rolling the dice a bit. We’ve been downright spoiled by balmy December temperatures the past few years. However, this year is shaping up to be different. Many models and ensembles – including the often reliable European model – have been indicating some shots of very cold air diving into the Ohio Valley during the mid to late part of December. This *could* provide us with our coldest December since 2010.
Hmmm…2010. That was the start of another La Niña season. Bowling Green experienced one its snowiest Decembers on record that year (8.3”), along with…a White Christmas. Not saying, just saying. By the way, our last “White Christmas” was in 2010, also a La Niña season.
DECEMBER TEMPERATURES: 0-2 degrees below normal (Avg. temp for the month is 38.6)
DECEMBER PRECIP: Near normal
DECEMBER SNOWFALL: 2-4” (1-3” above normal)
JANUARY: This month could start out quite cold but we should see a “January thaw” by mid-month. In fact, we could see some extended stretches of mild temperatures develop toward month’s end (would not be shocked to see a 70° day or two). However, our pattern should remain active. Most systems will likely bring rain, but a little snow/ice can’t be ruled out.
JANUARY TEMPERATURES: 0-2 degrees above normal (avg. temp for the month is 35.7)
JANUARY PRECIP: Above normal
JANUARY SNOWFALL: 2-4” (2” below normal to near normal)
FEBRUARY: Often the toughest month to project, simply because it’s so far out. This is where I lean more heavily on past La Niña seasons along with the ensemble outlooks for the one upcoming. Many past La Niña “breakdowns” have resulted in cold air returning when we sometimes may not be crazy about seeing it again (a la tail end of Feb or even March). All the “analog” seasons I mentioned above saw just that, including some other La Niña seasons not mentioned (’64-’65 and ’73-’74). Of course, such an occurrence may be preceded by a threat or two of severe weather.
FEBRUARY TEMPS: 2-4 degrees above normal (avg. temp for the month: 39.8)
FEBRUARY PRECIP: Above normal
FEBRUARY SNOWFALL: Less than 2” (below normal)
Here’s a general overview of what I anticipate:
TEMPERATURES: Slightly above normal for the season (but a LOT of ups and downs getting there!! NOT as warm as last season, though)
PRECIPITATION: Above normal (pretty high confidence here)
And from the “just for ‘kicks and grins’/gut feelings” department:
TOTAL SNOWFALL: (7-10” – slightly below normal to near normal)
CHANCES OF SEEING A WHITE CHRISTMAS: 25% (on average BG has 1” of snow on the ground one out of every 10 Christmases…going with higher odds this time as all signs point to cold air around/close to Christmas time)
CHANCES OF SEEING AT LEAST ONE ICING EVENT OF A TENTH OF AN INCH OR GREATER: 40%
CHANCES OF SEEING AT LEAST ONE SIGNIFICANT SEVERE WEATHER EVENT BETWEEN DEC. 1ST AND FEB. 28TH: 70% (high probability given our history with La Niña winters – always be ready!)
SEASON’S COLDEST TEMPS: Between 5-10 degrees (should happen in late December)
Some other thoughts:
**I think the coldest part of this winter happens early this go round (mid-December through mid-January), although we may see another cold stretch very late February into early March as La Nina breaks down
**Don’t be surprised if we go from 70° one day to 7° a couple of days later. THAT is the kind of variability I think we’re dealing with this time!
**Cold shots will often be transient…in other words, they won’t often hold very long before temperatures rebound
**I think most of this season’s snow probably comes from a couple of systems
**I like our chances of getting in on at least one “big ticket item”/Winter Storm Warning criteria snow/ice event
**Don’t be surprised if we see accumulating snow in March as in many past La Niña winters
**We SHOULD see more snow than last season, although that’s not saying much since we didn’t even see 1” of snow last winter
**A repeat of the 20”+ snow seasons of ’14-’15 and ’15-’16 appears highly unlikely
**Odds of a “cold season” severe weather outbreak are higher than normal given what I think will be an active subtropical jet and wild temperature swings. Many of our “dead of winter” outbreaks struck late at night (the “Super Tuesday Outbreak of Feb ‘08” and another in late January 2013 come to mind – ALWAYS have multiple ways of receiving watches and warnings!!)
I’ll be the first to admit THERE IS BUST POTENTIAL WITH ANY FORECAST, especially one that projects several months out! The snowfall forecast holds the biggest potential for going awry, simply because of so many variables.
No matter what with the weather, you can count on the First Alert Storm Team – both on-air and on-line – to keep you informed of the changing conditions throughout this upcoming winter season! Download our WBKO App for your smartphone, and if you’re an Amazon user, you can stay up-to-date anytime on your Alexa device.
Thanks for reading.