Let’s get right to it: we’re still looking at the likelihood of at least SOME wintry weather across the Midstate this evening and tonight. Exactly how much and what kind of wintry weather will depend on your location, and on how this system decides to behave as it moves through.
These things haven’t changed:
1) Rain will change to freezing rain, sleet and snow, and the transition will happen faster to the northwest of Nashville
2) This is NOT going to be a big snow-maker for the Nashville Metro: the most likely forms of precipitation in Nashville will be ice (freezing rain and sleet)
3) Even without measurable snow in Nashville, roads could be icy/slick for the Monday morning commute
4) Best chance of measurable snow will be to the north and northwest of Nashville, especially in southern Kentucky
5) Areas farther south of I-40, especially closer to the Alabama state line, are likely to see just rain with this event, perhaps just a brief period of the sleet or snow as the precipitation ends early Monday morning
Two things have changed since the forecast in yesterday’s blog post:
1) The timing of the transition from rain to ice to snow. I was a little too aggressive in pushing back that timing yesterday, and I’ve corrected it in the graphic you’ll see a little down the line.
2) Our window for freezing rain looks like it will be slightly longer than initially thought. This brings in the possibility of some ice accumulations on elevated surfaces, including power lines, before the transition to sleet or snow occurs.
Overall, the computer models have been pretty consistent over the past 24 hours. There has been a little bit of wiggling from run to run, but in general the expected evolution of this system hasn’t changed a whole lot. Here’s the latest Futurecast time series from 6pm Sunday through 6am Monday. Still some differences between the two high-resolution models that we use, but they’re pretty close:
Interestingly, the two most prominent models from the National Centers for Environmental Prediction (NCEP — they run the models the NWS uses) are painting a similar scenario for the snowfall pattern, even if they have differences in the snowfall amounts:
(Once again, those are computer estimated amounts, so don’t get overly excited/worried. Those images are from wxcaster.com, a fantastic weather-nerd site.)
Here’s the tricky part about winter storms: the dividing line between all and nothing is very very narrow, on atmospheric scale. So while it’s great that most of the computer models are very close together with the “where, when, what, and how much”…the atmosphere is going to do what the atmosphere wants to do. I checked with a colleague in Oklahoma today (they’re getting sleet and snow with the system already) to see how the various models were performing with their forecasts. That information definitely factored into my version of the forecast for this evening and tonight.
That said, here is what I’m thinking in terms of how the system is going to play out. First of all, the timing. As I said above, I’ve adjusted this the most compared to yesterday’s forecast in the blog post. Areas northwest of Nashville will still see the earliest transition from rain to sleet to snow (in fact, it’s happening already), while areas farther south of I-40 may not see that transition at all. Here’s the radar image as of 2:30pm showing the mix to the northwest, and the map of expected transition times:
I’m optimistic that in the metro area at least, most people should be home from Super Bowl festivities before the transition from liquid to frozen precipitation occurs.
Now that you’ve looked at those maps, let me shout this from the rooftops: DO NOT MAKE THE MISTAKE OF THINKING “NO SNOW = NO PROBLEMS”. Sleet and freezing rain aren’t fun to drive in either, and of course we’ve seen recently that even less-than-measurable snow can cause problems.
Once again, I’ll emphasize that even a slight shift in the overall track of this very large storm system will mean a significant shift in the accumulation pattern. Winter storms are tricky, which means my inner child now looks like this:
I’ll be tweeting out radar updates and quick blurbs about how the forecast is shaping up throughout the Super Bowl this evening. Of course, Twitter is going to be deluged with Super Bowl-related tweets, so your best bet is to either go to my profile page within Twitter (@PaulHeggenWSMV), or search for the hashtag #4WARN.