With the start of “meteorological winter” (the period from Dec . 1st through the end of February) almost here, it’s time for me to make that annual stab at forecasting what’s to come for South-Central KY in the next three months. If you love snow, perhaps you’ve been awaiting this with baited breath. Then again, if you’re one of those that strongly dislikes snow and cold, perhaps you are NOT looking forward to this season after the way last winter concluded! But it’s important for all of us to remember that each season truly is its own animal. Some of the players on the field going into this Winter are obvious. Others…well, not so much. And it’s those variables – aka the “wild cards” – that can throw things for a loop. Think “Dr. Jekyll and Mr. Hyde”, as I believe that’s how changeable this upcoming season will be.
A LOOK BACK: Before I jump into what I expect for this season, I do want to take a look back at Winter 2014-’15 and grade how I performed. Last season did not present as many forecast challenges for us as the season before it (where we were seemingly “on the fence” between precip types in practically every event), but boy, did it ever end on a BRUTAL note! It’s easy to forget that going into mid-February, Bowling Green had less than 4” of snow for the season. In fact, very little school was missed through the first two-thirds of last winter. Then came that infamous week of Feb. 15th! Not one but TWO crippling snowstorms clobbered South-Central KY late season…one on Presidents’ Day (which was followed by more snow, record sub-zero cold, then ice and heavy rain) with the other coming on the eve of March 4th into the morning of March 5th. Both systems had parts of our area measuring the snow in FEET and not just inches.
Remember scenes like this? This pic from last season is NOT from Minnesota. It was taken right here in South-Central KY:
***MAKING THE GRADE: LAST YEAR:
2014-2015 Forecast snowfall for the season – 12-16” (about 3-7” above our seasonal average)
Actual seasonal total: 24.0”
GRADE: Obviously, my snowfall projection wound up well shy of the actual total for the season! BUT, I did have the IDEA right in that I believed we would wind up above normal in the snow department. So that much did verify. Getting the idea right is half the battle with these long-range outlooks. Heck, it’s tough enough just to nail snowfall accumulations within 8 hours of an event, much less over a three-month span.
***With that in mind, I’ll give this part of my forecast from last year a B-.***
2014-2015 Forecast temperatures :
–Dec. 2014: (1-2 degrees below normal) Actual monthly average: 41.7 (3 above normal)
–Jan. 2015: (1-2 degrees above normal) Actual monthly average: 34.6 (1 below normal)
–Feb. 2015: (0-2 degrees below normal) Actual monthly average: 29.3 (10 below normal and one of our coldest Februarys EVER!)
GRADE: December didn’t pan out so well for me, although January was called on the nose. As for February, again, the idea was right in that I believed it would be chillier than normal, but it turned out BITTERLY cold, especially in its second half. I also mentioned in last year’s post that I believed the season would be colder than normal overall, and that did come to pass.
***All things considered, I would score the temperature portion of last year’s outlook with a B- with the same average for the forecast overall***
To quote “The Monkees”, that was then, this is now. Let’s discuss this season and the factors taken into most consideration with this year’s forecast. The talk gets a little technical, or “weatherese” as I like to say, so hang in there with me.
1.) EL Niño/La Niña (EL NINO-SOUTHERN OSCILLATION)
You probably have heard the terms “El Niño” and “La Niña” at some point. 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. Without a doubt, El Niño is what we have going into this season, and it’s a stout one at that!
*Imagery courtesy of NOAA
Last year, we had only a weak to low-end moderate El Niño in place. That was important for us, as often times in such winters, while the subtropical jet stream may not be as active as it is in a Strong El Niño season, some of our coldest, snowiest winters tend to be those with weaker El Niño conditions. As mentioned, however, that’s not the case heading into this season. A strong El Niño means a very active Pacific jet…one that will send a lot of systems into the southern United States. Sometimes those weathermakers stay to our south and miss Kentucky altogether. But if the jet rides farther north, it can send a lot of moisture our way. Then it becomes a matter of how the Polar jet to the north interacts with that subtropical moisture. That can be the difference between rain and snow.
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. Heading into this season, the waters in these regions have been running a bit 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):
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 erratic, and it’s difficult — even for the most experienced meteorologists — to forecast them beyond two to three weeks out.
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 last season, the AO and NAO tanked. Will such fluctuations occur again this season? One can only speculate at this point.
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. Another factor to consider is snow/ice cover across North America. There’s a notable difference in how it looks this year vs last year at the same time. Here’s last year (at least 1” of snow on the ground where you see white – note the snow cover upstate along the Ohio River):
And here’s how it looks this year. You have to head quite a ways north to find some snow this go round. This is one reason why I think our seasonal snow tally will be lower this time:
*Imagery courtesy of NOAA
No two winters are exactly the same. What makes this season particularly challenging with my forecast is that I could not find a really good analog match in terms of past seasons with similar patterns and teleconnections. Previous Strong El Niño seasons have not been big snow producers for our area. In fact, the last three seasons that fit in the “strong” category (1972-’73, 1982-’83, and 1997-’98) all featured below-average snowfall for South-Central KY. Great if you like it mild, though not what you wanna hear if you want to break out the sleds again. But oceanic temperatures going into this season don’t exactly match those other strong El Niño years. So with that in mind, these are the seasons that were given some weight, aside from the three I just mentioned:
And yes, even 2014-’15, although El Niño is more pronounced this go round
THE WINTER FORECAST
With all that said, let’s get to the reason why you came here: The Winter Outlook. My focus is on the three months that make up “meteorological winter” December, January, and February. I’ll add, too, that this is NOT an official First Alert Storm Team forecast! It’s simply my own take on how things may play out.
DECEMBER: It’s a month that should set the tone for how the rest of the season goes…that being up and down. I think we could have a chilly start and finish to December with some mild periods in between. In many years, we don’t see much more than a trace of snow in December, with much of it holding off until January. It’s worth noting, however, that in December 1997 – right in the midst of a Strong El Niño – we had a decent snowfall to the tune of 2-4” regionwide just a few days after Christmas.
DECEMBER TEMPERATURES: 1-3 degrees above normal (Avg. temp for the month is 38.6)
DECEMBER PRECIP: Near normal
DECEMBER SNOWFALL: Less than 1” (Near to below normal)
JANUARY: Again, I expect some stretches of mild counterbalanced with some cold shots here, with the coldest air likely showing up later in the month as El Niño starts to collapse. A weakening El Niño usually allows for the Polar/Northern branch jet to make a move southward more frequently. Such interactions are key when it comes to snow/ice threats. We’ll have at least two or three of those threats this month.
JANUARY TEMPERATURES: 1 degree above to one degree below normal (avg. temp for the month is 35.7)
JANUARY PRECIP: Near normal
JANUARY SNOWFALL: 3-5” (Above normal)
FEBRUARY: While a carbon copy of last February’s brutal cold is NOT likely, this could be the month that brings us the most cold shots along with chances for wintry precipitation. El Niño’s predicted collapse should be in full swing during this period, although the subtropical jet should stay active late season. Don’t be surprised if we have to deal with severe weather during this time frame, too.
FEBRUARY TEMPS: 1-3 degrees below normal (avg. temp for the month: 39.8)
FEBRUARY PRECIP: Above normal
FEBRUARY SNOWFALL: 3-5” (Above normal)
Here’s a general view of what I anticipate:
TEMPERATURES: Near normal
PRECIPITATION: Slightly above normal
TOTAL SNOWFALL: (8.5-11.5” – near to slightly above normal)
CHANCES OF SEEING AT LEAST ONE STORM SYSTEM BRINGING US AT LEAST 4” OF SNOW: 70%
CHANCES OF SEEING A WHITE CHRISTMAS: 5%
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: 40% (lower chance than in La Nina winters but one or two severe episodes are possible)
SEASON’S COLDEST TEMPS: Between 5-10 degrees (should happen in late January)
Other key points here:
**The odds of a repeat of our brutal stretch of weather last February into early March are VERY slim. Having said that, there will be some snow, and we will encounter some cold air from time to time
**I think most of this season’s snow probably comes from two or three storm systems
**The odds of a repeat of last season’s lack of thunderstorm activity (no thunderstorms at all from late October through March) is also VERY slim. I would not be surprised to see a couple of severe weather threats for us over the next three months
**It’s possible we could have one last accumulating snow event in March again this year. I believe that since El Nino will be collapsing late in the season, which may allow for more cold shots then
As always THERE IS BUST POTENTIALWITH ANY FORECAST, especially one that goes several months out! The snowfall forecast, as always, holds the biggest bust potential. If the subtropical jet stays suppressed to the south and/or the polar jet stays locked up into Canada even more often than I expect, than we could wind up with less snow than forecast. But as we saw last season, if the stars line up correctly, we can see a blockbuster.
Sometimes we’ll see Dr. Jekyll, sometimes we’ll get a look at Mr. Hyde. We now sit back and see how this all plays out. Thanks for reading.