An interesting day

Are you ready for a wild weather day? I’ve been up since 4:00 a.m. monitoring it all. At 4:00 a.m. the temperature in Nashville was 61 degrees. They are now in the low to mid 30s across the Nashville area. The front is now between Crossville and Nashville and slowly moving eastward. The front will arrive sometime around mid-morning but the 32-degree freezing line is lagging behind the cold front this morning. This was handled quite well by many of the models.

The precip is mixing across western Middle TN but it will take some time before it reaches us here on the Cumberland Plateau. The image below is one model’s forecast snowfall accumulation. This model does a good job at showing what many of us are thinking will happen.

One thing to keep in mind is that this is neither an ice or snow storm situation. But, we should pick up a little bit of both, which is more than enough to cause travel headaches, as we all know from Monday morning.

As with any winter weather forecast for the plateau, this one has some tricky points. We have a strong southerly flow aloft that will persist through the day. Meanwhile, this shallow, arctic air mass will be slipping underneath this southerly flow. This will create a wintry mix of precip. As we go through the day, the atmosphere will cool down sufficiently enough to support all snow. That will likely not happen until this evening though.

So, we have the moist, southerly flow aloft with cold air undercutting that flow. That is the perfect recipe for mixed precip. The rain falls through the warmer air and into much colder air near the surface. Eventually, the entire atmosphere cools down and everything switches to snow. But, the atmosphere is ever changing and complicated (ha). There may be times when you see sleet, then snow, then back to sleet, and even perhaps some light freezing rain. The precip changes could be a bit erratic as they transition to all snow.

There’s another fly in the ointment.

On the image below I’ve drawn arrows around the storm system to show you the direction it spins. This is an enhanced water vapor image that does a great job showing up pockets of dry air in the atmosphere. You’ll notice a dry pocket across Mississippi. That is swinging in our direction. Now, when I look at regular water vapor (without enhancements) I can still see that humidity levels are quite high at the surface. But aloft there is enough dry air that precip will be hindered. This could lead to several hours of no precip for us around noon to early afternoon. The area that I’ve circled in red would then swing through this evening. That area of cloud cover and precip is cold enough throughout the atmosphere to be all snow. That would give us our 1-2″ of snow.

The other caveat is that northwest winds will be really picking up as we go through the day and this evening. Overnight, those winds may continue to give us areas of light snow and flurries that could add additional light accumulation. The most favored areas for this are along the western edge of the plateau (ie. Mayland, Monterey, Jamestown).

Now, where is the 32-degree line right now? It has just moved through the Nashville area. The front just moved through Cookeville and their temp is now dropping. That means our temp will be dropping here shortly, probably before 9:00 a.m. The 32-degree line is lagging about 100 miles behind or so. That’s what I’ll be keeping an eye on today.

Here are the current advisories and position of the 32-degree line.

As always, I’ll be here watching this all day  and updating as needed. Our temperature right now is a very mild 57 degrees, after a morning low of 56.  The temperature in Cookeville has now dropped to 48 degrees (it has dropped 10 degrees in the past 10 minutes). You will notice a significant drop in temperature when the front moves through, followed by a much slower drop down to the freezing mark. I’ll let you all know as soon as that 32 degree line threatens. I still think we’ll be ok through at least noon.

Look for updates throughout the morning! And let me know if you have any questions! Again, keep in mind this is neither a snow or ice storm situation, but definitely one that has travel impacts. Pre-treatment of the roads was not possible this time due to the rain. I’ve seen some ugly comments on Facebook toward our road departments about this. You cannot pre-treat roads when rain will wash it off.

Finally, and on a side note for those of you who don’t follow me on Facebook…. I found out yesterday that I am one of only 20 members of the media invited to see the GOES-S satellite before it launches in March!!! I  leave for Cape Canaveral on Monday!! I will have much, much more on this after this weather has passed!

Meanwhile, stay safe and I’ll keep you posted on how things are looking!