Weather Blog: Snow TALK! Christmas Edition

Merry Christmas Everyone!

I hope you all had a great holiday with friends/family.

Obviously, it was a warm one this year with a high of 54. While many of you were wanting snow today, there is some to talk about ...at least in that data we have right now.

We have a southern storm that is forecast to "phase" the northern and southern branches of the jetstream Monday/Tuesday. If you saw the blog post last Thursday, I talked about how this is what we needed to watch out for. GFS was out to lunch on the idea...EURO was on it. This evening, they are both are on the idea including the shorter range NAM. Which I will use for this update as well since it does pretty decent on short term events.

The low is forecast to move from N TX tonight into TN by tomorrow night/early Tuesday. It will then pass to our east Tuesday evening and out of our range during Tuesday overnight.

The speed and track of this low will be crucial on how this all turns out. So with us still more than 48 hours away, expect changes to the forecast.

Here is how it looks right now.

Near Sunrise on Monday...the rain shield arrives. Keep in mind, the blue 0 degree line on these maps is the "typical" rain/snow line. However, in this type of setup...that will not be exact. But gives us a good idea of the temperature profile of the low regardless.

GFS NAM

By midday Tuesday, the GFS keeps the colder air (snow risk) north of the Ohio River. The NAM is more more pronounced with the cold air wrapping around the backside. It also looks wetter.

GFS NAM

Tuesday afternoon, the GFS and NAM both show the changeover to snow across most of the region. NAM even suggesting some "banding" that may take place on the radar. I will explain that in just a bit.

GFS NAM

Tuesday evening, GFS/NAM begin to taper the snow off to flurries and push the moisture to the east.

GFS NAM

So how much are we talking about here?

Well, if you take the current speed of the system, the NAM Bufkit (a tool we use to help with snow forecasting) is showing about 1.1" of snow for Louisville out of this.

It gives Lexington about .5" Bowling Green 1.5" and Madison, IN about 1.0".

Overall, not a huge event based on those numbers of course.

The models suggest most of the snow will fall in the afternoon into early evening. That would mean less of an impact on roads and will keep any snow accumulations on grassy areas. Generally 1" or less.

If the banding on the radar does develop as the NAM suggest, we could see snow rates heavier than shown on the model. That would be enough to produce some accumulations on side roads and certainly on the grass...and would increase snow totals in spots under those bands.

And the last obvious factor for more snow than shown, would be if the system slows down in timing enough that we make it to nightfall. We would have a better chance to see accumulations at that point.

I hate to talk in "iffs" right now but those are pretty much the questions we have to still figure out with this system, and that is why we are not giving out official snow totals on this just yet.

I have noticed the trend in the last couple of runs to try to slow this system down...and make it wetter. So it will be interesting to see what the 00z runs of the models (due out after 10pm) look like this evening to see if that trends continues or holds.

Here is the NAM snowmap. You can see how accumulations would be spotty.

So in summary, we are facing about 1/4 to 1/2" of rainfall late Monday into early Tuesday. By Tuesday afternoon, the rain could change to a period of snow that will taper off Tuesday evening. Some light accumulations are possible on grassy areas during this time. There are still uncertainities on the speed/track so totals and timing of changeover to snow may still have to be adjusted.

One thing I should note is that lows are forecast to dip to around 30 Wednesday morning, so slick spots will be a concern at that time with everyone warming above freezing by mid morning Wednesday.

No need to panic or run for bread/milk :) This looks to be a minor event and more so..."festive" when it comes to the holiday decorations still up in many spots. So hopefully those of you that are starving for at least something on the ground...will get it this week.

Stay tuned for more updates!!