We're all dreaming about it, so what are the odds of a White Christmas THIS year?
It seems every since Bing Crosby's release of his chart topper from 1947, we've all been "dreaming of a White Christmas". So what exactly are the odds for us seeing one this year??
Before we look ahead, I think it's important to take a look back, historically, at the odds of a White Christmas. By definition, there must be at least one inch of snow on the ground on Christmas Day to be defined as a "White Christmas".
Historical Odds for White Christmas
The map below map shows the historic probability of there being at least 1 inch of snow on the ground in the Lower 48 states on December 25 based on the latest (1981-2010) U.S. Climate Normals from NOAA's National Centers for Environmental Information (NCEI).
Locally across Western New York, those chances historically aren't too bad. In fact, we are a "climatologically favored" area for that to occur. Depending on your exact location, you might expect somewhere between a 50 and 75% chance of that occuring any given year. Rochester has about a 60% of that occurring annually.. as measured over the last three decades.
A Fast Start to Winter and Current Snow Pack
With that being said, we also know that we have seen more than our share of snow so far this year. In fact, with 28+ inches of snow already being measured, Rochester has been one of the snowiest cities located in the United States to date. It seems like we've had a decent snowpack ever since that big winter storm back in early November... or almost a full month ago! As of today, approximately the northern one-third of the US plus the Rockies has a solid amount of ice and snow on the ground.
However, that is beginning to change with the recent warmth over the last couple of days. As of this writing, December 9th, there was only about four inches of snow on the ground at the airport in Rochester and we will see more warmth between now and next weekend... although we are also expecting another shot of some really cold stuff in between. More on that during tonight's 8:45 show..
My strategy for coming up with a White Christmas Forecast
While we are sitting still more than two weeks away from the big day, I like to break down the variables in the simplest terms. You see, while it's near impossible to figure out exact storm tracks over the next two plus weeks, we can lean into the models in terms of availability of cold air during that stretch. And all else being equal, cold air across Western New York this time of the year, whether in conjunction with a system snow and/or the lake effect variety, snow is usually the result. So let's look for some cold air!
What do the models say?
Keep in mind, we are only hunting cold air and not storm tracks or precipitation amounts. With that being said, the last couple of runs of the "Euro Weeklies" climate model are not looking too promising showing much of the Eastern US and Canada with above normal temps the week prior to Christmas. It also signals robust troughing out west which would also favor warming east.
Ok, that is a big bummer for me, b/c the Euro is typically our most reliable model at that range. With that being said, let's check in on the CFS or the Climate version of the US GFS forecast model. The last two runs of this model is keeping the really cold stuff locked north into Northern Canada and Alaska with "near normal" or "slightly above normal" temps across our area and into the East-Centeral US.
While that is not as dire as what the Euro is showing, it does favor a more melty solution and doesn't look all that favorable for a White Christmas either.
Ok, admittedly, just looking at the raw model data, I'm not very optomistic about our chances this year.
As the above models are hinting at, we could be looking at a stretch for some warmth heading into the Christmas Holiday. However, sometimes the devil is in the details.. There are other factors to be considered including climate signals.
North Atlantic Oscillation
Among a number of the climate signals or "climate teleconnections" that I look at in that two week range is something known as the North Atlantic Oscillation (NAO). When looking for cold air intrusions into the Eastern US, you would look for a "negative signal" in the NAO. While the operational run of the Euro shown as the black line below goes slightly positive in the 10 to 14 day range, most of the "ensemble members" represented by the blue boxes actually go negative.. below the zero line.
Ok for those who may not be a statistics freak, this simply means that the main model, the Euro, is not in agreement with the majority of it's prognostication counterparts and cold air, hence the possibility of snow before Christmas, is still on the table.
What do I think?
With all that being said, I'm still inclined to lean towards the Euro climate model and despite the fact that we've had snow on the ground for weeks, I'm only giving Rochester about a 40% for a White Christmas this year. I hope I'm wrong and my fingers will be crossed that the models come back around.
Lisa and I will be back with a full update on this week's lake snow and cold in tonight's WxLIVEat845. See you in then!