Shane Holinde’s Winter Weather Outlook 2020-2021
BOWLING GREEN, Ky. (WBKO) - Welp, here we are! We’re just one week away from December, meaning it’s also one week away from the start of “meteorological winter”, which runs through February 28th. With the season fast approaching, and colder air inevitably coming, it’s time to gaze into the crystal ball and see what might be expected for South-Central KY during Winter 2020-2021.
Perhaps you’ve heard Kermit the Frog sing “it’s not easy being green”. Such is also true for winter forecasting. As forecasters, we’re getting better at seeing the “overall” picture for a season (i.e. mild or cold). That said, there are SO many factors that come into play with temperature and precip forecasts. Those factors include the position and movement of multiple jet stream branches, snow/ice cover in the arctic and areas north of us, and other things. The jet stream plays an important role in how storm systems behave and where they track. Sometimes a winter storm tracking a few too many miles north or south of our region can be the difference between getting more rain vs. snow or missing out on winter weather altogether. In some seasons, we’ve scored some BIG hits (Winters of ’14-’15 and ’15-’16 come to mind). But we’ve also had some winter “duds” in the snowfall department. The past two seasons fall under that category. In fact, three out of the last four seasons were snowfall “duds”, with snowfall amounts not even close to normal.
Before the “non-winter” of 2016-’17, we had two back-to-back historic winter seasons in South-Central KY. Winter ’14-’15 was very memorable, especially the latter part of it. That season brought us nearly two feet of snow and a Top 5 cold February. Winter ’15-’16 was actually mild overall, but when cold came, so did the snow! Bowling Green picked up a a little over a foot of the white stuff on 1/22/16, and much of the area saw 4-7″ on Valentine’s Day that season. Those seasons, along with the three wicked winters of the late ’70s and the snowiest of ‘em all (Winter 1959-’60) are exceptions and NOT the rule for us!
Just for kicks, here are the snowiest AND least snowiest winter seasons all-time for Bowling Green:
Now, let’s talk about the players on the field for THIS season.
*NOTE: This is where the talk gets technical, so if you wish to skip ahead to the forecast, scroll down to “Winter 2020-2021 Outlook”.
1.) LA NINA (EL NINO-SOUTHERN OSCILLATION)
If you’ve read my posts over the years, then you’re probably already familiar with El Nino and La Nina. Basically, “El Nino” refers to an abnormal warming of the sea surface water in the Central Pacific ocean off the South American coast. La Nina, on the other hand, is a cooling of those same waters. If the water temperature at the sea surface is right at or very near normal, neither El Nino or La Nina is going on. That’s what we call an “ENSO Neutral” condition.
The upcoming Winter will feature a MODERATE La Nina. That’s important, because it means a couple of things are likely: 1.) Strong high pressure ridging over the Southeast U.S. that tends to keep the polar jet stream from diving south, and 2.) More rain than snow from storm systems that affect us. I can already hear the moans from you “snow birds”!
Below is a snapshot of how I believe the overall jet stream pattern will pan out through much of the coming season. It’s one that spells more rain than snow for our region:
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. Based on recent trends, it appears the PDO will be in a “warmer phase” this season given the mild sea-surface readings off the southern coast of Alaska (see the graph below). 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”. Since the 1980s, however, the AMO has been in a “warm phase”.
3.) NAO/AO (North Atlantic Oscillation/Arctic Oscillation)
These pressure systems are the “wild cards” when it comes to winter forecasting. That’s because 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. The AO/NAO stayed positive most of last winter, which was a major reason why the season was so mild.
4.) OTHER MINOR FACTORS
The jury is still out on solar cycles and how big a role they play in winter. Some speculate that more solar flares/activity leads to milder conditions. Another factor to consider is snow cover across polar regions and Canada leading into November.
There is much to consider when coming up with a winter forecast. The variability of the AO and the NAO makes it tougher. It helps to look back at previous winters to find those that saw atmospheric conditions and ocean temperatures similar to what is expected this go round. Those seasons are referred to as “analog” seasons. Here are the ones I found that seem to most closely resemble the kind of pattern I think shapes up this winter. You’ll note that didn’t have much to offer in the snowfall department:
With all that said, it’s time to get into what I’m sure you came here for and that’s the Winter Outlook. I will point out that stranger things have happened in these parts, including freak snows well into March and even April, although it’s VERY rare. (BG’s snowiest month of all-time was March 1960). However, my focus will be on the three months that make up “meteorological winter” December, January, and February.
First, here are the monthly temperature and snowfall averages for Bowling Green, based on 30 years of data. It’s important to keep those averages in perspective!
DECEMBER: I look for this December to feature a mix of cold and mild spells. In fact, it could even wind up being the chilliest of the winter months this go round. Typially, snow events in December are light. The last time we had a VERY snowy December was ten years ago, which by the way, was the last time Bowling Green saw a White Christmas (nearly 4″ fell on 12/24/2010 with an an additional inch on Christmas Day itself). The historical odds of Bowling Green seeing a White Christmas are about 1/10, so there’s that. Not saying this will be the year, as I believe most systems next month will bring us rain. Having said that, we may have at least a shot or two at accumulating snowfall.
JANUARY: This is normally the coldest of the winter months, although with such a pronounced La Nina taking shape, that may not be the case this time. The overall pattern points toward a strong high pressure planting itself over the Southeast U.S., one that may prove to be stubborn well into the season. That’s not to say we won’t have some cold shots – we will – but I think when the cold “hits”, it won’t stick around very long. South-Central KY will often be in the line of fire for an active subtropical jet that should bring frequent storm systems into the region. Most of which will likely bring rain. Don’t be surprised if the month brings us a severe threat or two. Of course, if moisture is available in what I believe will be rare times when it’s cold enough for it, some snow cannot be ruled out.
FEBRUARY: This is often the toughest month to make a prediction as there is more uncertainty about how the patterns will behave this far out. This is where I often rely a bit more on those analog seasons I mentioned above. In Winter 2007-’08, we did not really see much sustained cold until very late in the season (most of that season’s snow did not fall until March). It’s also worth noting that season gave us the infamous “Super Tuesday” Tornado Outbreak (late 2/5 into early 2/6/08). It’s also worth noting that two of our wettest Februarys have occurred in the past three years (2018 at #5, 2019 at #2 all-time). Just like in January, I expect the subtropical jet to stay quite active here. If La Nina breaks down late season, there could be more opportunity for arctic air to come into play. But keep in mind, average readings slowly warm the deeper we go into February
When it all shakes out, here is what I expect for the season as a whole:
Here are some more projections about the upcoming season:
SEASON’S COLDEST TEMP: 10 degrees (should happen in December)
There you have it. Basically, I think the recent trend of mild winters overall with below normal snowfall continues.
Could this forecast bust? Admittedly, the potential is always there. If the subtropical jet interacts with the polar jet more often that anticipated, then my snowfall forecast could wind up being too conservative. But I keep going back to those analog years where we didn’t even see 2″ of snow for the ENTIRE season. Not saying that happens this time, but that weighed heavy on my mind when comprising this forecast.
Overall, no matter what Mother Nature throws at us this winter season, be ready! Have a plan of safety should you ever need to use it. Whether an ice storm or a tornado, you should always be prepared. Ethan Emery, Jonathan Blake, and I will keep you informed!
Let’s see how it pans out.
Copyright 2020 WBKO. All rights reserved.