Evening look at storm potential for late Thursday night into Friday morning. Threat increasing?
I'm sitting here in the home edition of the Tennessee Valley Weather Center, looking over the early evening set of the latest high-resolution computer model data as it all comes in. We started noticing this trend in the data earlier this evening as Ben and I were wrapping up our weathercast recordings and getting ready to head home for the day while looking at some of the afternoon data that had come in. Some of the models had started hinting that more significant instability (thunderstorm fuel) would make its way northward during the morning hours on Friday, possibly setting the stage for the severe weather threat in our local area to increase just a bit. That's why I made sure to stress more than once in my evening weathercast that the forecast may change and you still need to stay in touch with the latest information, in case the threat may go up some. As we look over this evening's data, it still continues to have that look that suggests the threat may be increasing, at least a little bit.
Above is the latest set of our high-resolution Futurecast model that comes from Baron, the developer of our VIPIR and Lynx storm tracking and graphics system. This shows a band of strong storms that works across our viewing area during the morning hours on Friday, roughly after 3:00 or 4:00 am through about 11:00 am. With dewpoints up into the low to mid-60s and temperatures coming up into the mid and upper 60s during the morning hours as the warm front moves northward, the air will grow more unstable. And yes, it will warm like that during the morning, even before sunrise, because the strong south winds behind the warm front will pull the warm air from down to our south up into our area. This happens very often in our severe weather threats during the winter months.
What's interesting is that this band of storms is not a solid line, but rather a broken band of short line segments and individual cells. That concerns us because a setup with more individual cells has a little bit of an easier time when it comes to producing a tornado. Storms are more spaced and don't have to compete as much with nearby storms. This, along with other high-resolution models, suggests that the storms coming through the area on Friday morning may have a supercell mode to them. Often times, we hear the word "supercell" on big tornado days, and it is true that supercells are the type of storms that produce the big tornadoes. However, the ingredients for that kind of threat will not be in place.... but having the storms in a supercell mode somewhat increases the chance that one or two of them might be successful in producing a tornado or a damaging wind gust of 50-60 mph. The threat is still on the lower end of things, but it has ticked up a little higher than it previously was.
As we stated, the main timeframe for this to happen is roughly 3 am through 11 am or so on Friday morning. That means you are going to have to have a way to be able to hear warnings, even when you are asleep... and waiting to hear a siren outdoors at 3:00 in the morning with a raging storm ongoing just does not cut it. Again, this is a low threat, but the threat is not zero, and it's a touch higher than we had previously been thinking. It's still very much possible that we get through this without a single storm becoming severe, but if one or two storms do become severe, the main risks would be a damaging wind gust to 50-60 mph... and maybe one or two of the storms being capable of producing a tornado. We have attached a map that shows where this threat is, and it is areawide. This map is separate from the Level 1-5 risks from the Storm Prediction Center. However, we think that in future updates, those guys may put more of our area in a Level 1 risk, if not pull the Level 2 risk farther north as well. Regardless of whether or not that happens, we ask that you be in a position to receive warnings if they have to be issued Friday morning. We will be staffed in the Tennessee Valley Weather Center, ready to provide live coverage, if that happens.