Christmas Snow Update

 Many of you know this has been a much hyped forecast given the possibility of a white Christmas, some folks have even been "forecasting" for tomorrow and Monday for over 2 weeks and I have been mentioning it for several days, so with that in mind I wanted to do another update to cover my thoughts on what you can expect over the next 48 hours or so. I will be the first to admit that this has certainly not been an easy forecast but we don't do this because it's easy. There have been adjustments along the way, I personally have changed my mind privately probably a half dozen times, but remember that the goal is to GET IT RIGHT. Also, make sure to follow along with your local NWS office and other authorities regarding instructions during hazardous weather. I will always post my forecasts with the intention of providing more in-depth glimpses at the process of weather forecasting than you get with an app or "7-day graphic" on the morning news, with a much more personal feel, and I put the utmost effort into what I do. Furthermore, every forecast I post is one that I stand behind 100%. That said, I am in no way a replacement for "official" information and do NOT want to be seen as someone who thinks I can do what they do better than them. Honestly, I'm working toward doing literally the exact things they do. Basically I want this blog to be a complementary tool in your weather info toolbox. 

  I just felt that I needed to say that. Back on track though. I'm sure you've heard about the possible snow in Kentucky for Christmas Eve and Christmas Day and I'm sure you've heard different people saying different things. Here's what we're looking at: 

Will It Snow At All?:

  Yes! I am pretty confident we will see snowfall across the most of the area beginning Sunday PM. Particularly areas along and North of the Western Kentucky Parkway with greater accumulations along/North of I-64. South of the WK Parkway will see snow in my opinion but I think that slightly warmer temps and a warm layer above the surface will delay the transition from rain to snow while locations North should see more consistent snowfall. This snow will move into Western Kentucky by early afternoon tracking Eastward throughout the day before exiting the region overnight.There may be lingering flurries early Christmas morning. 

  I also think we may see another shot of snow Monday night through Tuesday morning as an upper-level jet max passes over the region but this is more "low confidence" right now since I haven't seen any model data whatsoever suggesting accumulating snow during that time frame but it's worth mentioning since I see some analysis that suggests dynamics would support it. Obviously I'll address this more tomorrow. 

How Much Will "Stick"?:

  

  This has been an area of debate among many. The greatest snowfall accumulation is likely along and North of I-64 where about 1" is expected. I think we will see slightly more than that around that area as "convective snow squalls" seem to be a high possibility, locally enhancing snowfall totals. Any areas that see these heavier bands develop should see about 1"-2" of snow. I'm thinking areas in central Kentucky may very well see accumulating snow as well and I wouldn't be surprised to see up to 1" near/North of the WK Parkway where any "snow squalls" develop. Overall it looks like less than an inch in this area though. 

How Will It Affect My Day?: 

  While this certainly doesn't look like a huge snowstorm by any stretch (at least for Kentucky) and will provide nice optics for your Christmas spirit, that doesn't mean it should be ignored. There will be hazards associated with it. Gusty winds will spread across the region and could reach 20-30mph at times so anybody traveling and caught in wind-driven snow, especially if they're in one of the previously mentioned "snow squalls", would have reduced visibility and impaired driving conditions. Also, temperatures will drop quickly below freezing as cold air associated with a cA (Continental Arctic) air mass funnels into the area and we lose the help from daytime heating (diurnal heating). Naturally slick spots will develop throughout the night. 

  As I said, enjoy the fact that you may get holiday snow but use caution if you are out and about because you'd hate to ruin your Christmas over something you could have avoided (and I'd hate that for you because that wouldn't be cool). 

So What's Going On Up There, How Do I Know ANY of This?

  Now that we've hit the main points I thought we could briefly touch on a tiny bit of the processes at play driving this event. For starters, I don't necessarily know exactly what will happen, none of us really know. Weather forecasts are literally a prediction of the future, and more than that, they are a prediction of highly variable conditions that are governed by insanely intricate and nuanced processes. All is not lost however. Through attention to detail, careful and meticulous analysis, constant education, and with the help of sophisticated tools developed by crazy intelligent people we can anticipate many of these events with fairly good accuracy and regularity. 

  With that "disclaimer" out of the way here's a short-ish version of what's up. There's a shortwave trough, which is basically a wave in the atmosphere, over the central United States right now. This wave is tracking this way. At the surface Kentucky is located between a large area of high-pressure over the central U.S and a low-pressure system off to our Northeast. This is essentially funneling cold air into the region. As the shortwave continues this way while simultaneously pivoting around the base of the parent trough (the longwave, original I know) it should amplify and strengthen, as they often do when entering the base of a trough. This will both increase wind speeds aloft and should increase lift downstream from it (assuming different temperature processes don't negate it!). Given that there should be enough atmospheric moisture to support the development of precipitation across the region, and there should be enough lift to make it happen, it becomes a matter of assessing the temperature of the atmosphere layer by layer to determine whether there will be rain, snow, or some combination. Ultimately most of the area looks like it will support snow with the exception of a few hours that I mentioned in southern KY. You put all that together and determine the liquid ratio of the snow (wet or dry snow), how heavy it will be (rate), and how long it will last (duration), and you basically have the method used to develop this forecast. 

  I know that's a lot but I thought it would be useful to know a little bit about what can go into any given forecast as well as informative to know a little bit about the weather pattern that's determining what you're going to see on Christmas 2017.

I really hope you enjoyed this and more importantly I hope you have a safe and awesome Christmas. 

Later...

DKK