Allright everyone, it’s the end of November which can only
mean one thing (at least for me): It’s Winter Weather Outlook time!
This upcoming season is one that probably won’t rank amongst Bowling Green’s harshest ever, but I think it will produce some smiles on the faces of snow lovers before it’s all said and done. “Meteorological Winter” starts Tuesday, Dec. 1st, and runs through February 28th, so it’s this time period that will be the focus of my forecast. First, let’s get this out of the way:
The thoughts in this blog represent those of the writer. This is NOT an official First Alert Storm Team forecast.
Now, let’s cut to the chase. Here are this winter’s main players:
1. El Nino-Southern Oscillation (ENSO): If you read my Winter Weather Outlook a year ago, you may vaguely recall we were heading into a season that would be “ENSO Neutral” with just a slight lean toward a La Nina. The previous winter season (2007-’08) featured a strong La Nina. La Nina refers to the significant cooling of the equatorial waters of the central Pacific Ocean. Well, this year things have changed. This will undoubtedly be an El Nino winter, one where waters in the central Pacific have warmed some. This will be our first El Nino winter since 2006-07. The strength of the El Nino, however, has a BIG bearing on winter seasons for the lower 48. For example, winters that featured a strong El Nino (where sea-surface temperatures in the cent. Pacific were 2 or more degrees Celsius above normal) yielded mild winters for South-Central KY (1972-73, 1982-83, 1991-92 and 1997-98 fall into that category). However, seasons with weak or low-end moderate El Ninos have given the Blue Grass state some of its snowiest winters on record (1976-77 and 1977-78 come to mind). More recently was the El Nino winter of 2002-03. This is the only season since 1995-96 in which Bowling Green picked up more than 10” of snowfall. In many ways, I think this upcoming season will mirror the ’02-’03 season. Think of it as a cousin to that winter, if you will. NOAA’s Climate Prediction Center always produces its “official” outlook for each winter season. This year’s forecast is based on the current El Nino conditions. To see their call for both temps and precip, check out this link: http://www.cpc.noaa.gov/products/predictions/long_range/seasonal.php?lead=1 There is some indication that this El Nino may weaken/collapse late season. That is up for debate amongst forecasters, but at least this episode does not look to fall under the “strong” category. For the lower Ohio Valley, that does make a difference!
2. North-Atlantic Oscillation/Arctic Oscillation: One could argue these two players have just as much say in KY’s winter trends as El Nino vs. La Nina. When the two are in “positive phase”, the weather is generally mild and quiet for the Eastern U.S. However, when the two are the “negative phase”, the pattern tends to be colder and stormier in our part of the world (to find out more about NAO/AO, check this link: http://www.cpc.noaa.gov/data/teledoc/nao.shtml
3. Atlantic Multidecadal Oscillation: Without getting too technical, this is basically a cyclical pattern involving changes in Atlantic sea-surface water temperatures and the semi-permanent pressure systems over them. Since the early 1980s, the AMO has been “positive”, something that I strongly believe to be a big reason why recent South-Central KY winters have been mild overall. To learn more about the AMO, take a look at this interesting article (note the maps that compare Atlantic sea surface temps in Summer 2005 to those of Spring 2009): http://wattsupwiththat.com/2009/07/14/the-atlantic-multidecadal-oscillation-not-quite-cool-yet/ While we remain in a “positive” phase here, the latest AMO indices are their lowest since the mid 1990s.
4. Sunspot/Volcanic Activity: The jury is still out on how much impact sunspot activity has on Earth’s winters, but for what it’s worth sunspot activity has been light this past year. Evidence seems to suggest that years with more sunspot activity produce warmer winter seasons than other years. As for volcanoes, this past year has been quite active (Russia’s Sarychev Peak comes to mind), and more dust/ash in the earth’s stratosphere generally translates to slight cooling down here in the troposphere.
Other factors such as snow pack over the arctic regions of the northern hemisphere, along with mid-autumn temperatures in Siberia were also considered when composing this forecast.
Sooo…just what does all of the above mean for you and me? Well, to me it means we should have a winter that will contain some cold spells, perhaps getting bitterly cold on occasion. But will this season be another “underachiever” as far as snow is concerned? That is the question that I have wrangled with heavily over the past few weeks. Here is my monthly breakdown (complete with comparisons to average):
DECEMBER: I see us transitioning into a more winter-like pattern by the end of this month’s first full week, with cold temperatures likely to rule through at least mid-month. I think we’ll see the cold relax a bit as we head into the latter part of the month and close out 2009, but overall speaking this will be a chilly month! In most past moderate El-Nino winters (1969-70, 2002-03), Bowling Green has experienced at least one significant snowfall (at least 2”) during this month. I believe such will be the case this month. Oh, by the way, that significant Dec. 1969 snow just so happened to fall on Christmas Day…not saying, just saying. :) While I think overall precip will fall shy of normal, a more active sub-tropical jet (a hallmark of many El Nino winters) should make things interesting for us (and challenging for us weather forecasters!).
Forecast Dec. ’09 mean temperature: 35 degrees (3 below 30-year normal)
Forecast Dec. ’09 Snowfall: 3 inches (2” above normal)
JANUARY: This is normally our coldest month, and this one should live up to the billing. I believe this month may start mild before the coldest readings of the season descend upon us by mid-month. I also expect the sub-tropical jet to stay pretty active, though my “fear” (and I say that for fans of the white stuff) is that the storm track may often be suppressed too far to our south many times to give our area much snowfall. That being said, I think we do cash in on at least a couple of winter weather opportunities during the month.
Forecast Jan. 2010 Mean Temp: 32 Degrees (2 below normal)
Forecast Jan. 2010 Snowfall: 4.5 inches (near normal)
FEBRUARY: Now here is the month that presents the biggest challenge for me, especially given the uncertainty of this El Nino and whether or not it breaks down late season. If this season behaves like some moderate El Nino winters in the past (a la 1970), then this is the month we could see a major pattern “flip” from being cold overall to being mild overall. I should point out that even some of Bowling Green’s roughest winters (1918 and 1977) included a complete pattern reversal from wild to mild in February after several weeks of brutal cold and storminess in January. However, no two El Ninos are exactly the same. For instance, in 2003, much of the central/northern portions of the Blue Grass state were bombarded with an epic winter storm…one that spared Bowling Green but dumped several inches of sleet on Louisville and produced major icing in Lexington. For now, I am leaning more to “mild” for this month, and that’s loosely based on the unusually cool summer we just had. Now you may ask, “What would the past summer have anything to do with February?” This is where a little thing called “thermal lag” comes into play. One of the reasons I think the first half of the winter will be colder than the second half is because the ground over the region already has a bit of a head start in the cooling process thanks to the cool, wet summer and early fall. Therefore, I believe it takes until February this season for El Nino to “catch up” with the cooler soils. The opposite was true two seasons ago (2007-08) when we came off that very hot, dry summer. We really had no winter to speak of until late February/early March ‘08 when colder air supported some snow. That being said, I think this will be the wettest of the three winter months, and if temperatures are cold with the added moisture in place, the potential for fun and games grows exponentially.
Forecast Feb. 2010 Mean Temp: 40 Degrees (1 above normal)
Forecast Feb. 2010 Snowfall: 2.5 inches (1.5” below normal)
Some of my other winter forecasts within the forecast:
--Forecast seasonal snowfall: 12” (2” above normal, this includes what I think will be a late season surprise in March)
--Chances for “off-season/cold-season” severe storms: Less than 10%
--Chances for significant icing of ¼” or more: 60%
--Chances of a snowfall of 4” or more (single storm): 60%
-- Chances of a snowfall of 6” or more (single storm): 25%
--Forecast for coldest low temperature: -3 in mid-January (would be first sub-zero for BG since Jan. 2003)
So there you have it. Basically, I think when it all shakes out this winter features slightly below normal temps and slightly above normal snowfall overall. Do I think it comes anywhere close to the epic seasons of 1959-60 (total snowfall 48”) and 1977-78 (31”) in terms of snowfall? No, not even close (although BG is WAY overdue a 20"+ season). But one must keep things in perspective, and a double-digit seasonal snowfall for South-Central KY is not too shabby if you enjoy seeing the flakes fall. One more thing: I do NOT think our area sees a repeat of the disastrous ice storm that occurred late last January. While there still exists a threat for some “overrunning” (warmer air along with moisture riding up and over colder surface air, conditions responsible for the heavy icing), the odds of a storm of that magnitude happening two consecutive seasons are extremely slim.
Let the winter games begin!! Thanks for logging on.