Saturday, December 6, 2014

Flash Weather: So You're Dreaming of a White Christmas?

Thought it would be fitting to post a brief weather update on the day of my 10th prime birthday...
I'm going to be honest: the weather outside doesn't feel anything like December...which is rather anticlimactic and depressing; however, we did have the 7th coldest November on record here in Nashville, so a reverse/seesaw pattern isn't too surprising. 
Around this time every year, I get asked if we'll see a 'white Christmas'. The last two times it's happened here in Nashville was 2010 and 1993...and climatologically speaking, we see one in Nashville every 14-15 years. Thus, I wouldn't invest in the idea of one this year, especially if you buy into the law of averages. 
However, the main reason I doubt it will happen this year is due to the current positive AO/NAO, which is bottling up the colder air in Canada and causing the northern snowpack to diminish. If you check out the first map (valid on 12/14), you'll see a classic ridging setup over the eastern half of the US, with above average temperatures tied to above average heights. But even though this may look like a blowtorch forecast with highs in 60's/70's, I believe we'll only see slightly above average with high temps holding mainly in the mid-upper 50's through the middle of the month (given the Pacific zonal flow's tendency to buckle every now and then).
The end of the forecast period looks tricky as we approach Christmas. There's some evidence that our next pattern change (to a colder regime) will take place just in time for Christmas (see second map valid on 12/22), which would up the odds of a wintry conclusion to 2014. While the devil is in the details this far out (primarily in how far the AO/NAO will decrease in week 3/4), point is: it shouldn't be mild all month long. So for those dreaming of a white Christmas, don't stop dreaming; keep on believing. Several big weather minds agree with me in thinking the first month of 2015 will be quite cold...getting a head start around Christmas. 
At any rate, if you're a warm or cold weather fan, the pattern should oscillate back and forth all winter like it has been the past month...so there should be something for everybody...which I'd consider good news. 
Have a great day, everyone.
Cam out.


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