The latest update this morning from the NWS Storm Prediction Center has placed all of our region in a risk for potential severe storms for Tuesday, March 4th. Locally speaking here in the Tennessee Valley, the latest data suggests our threat will be during the late evening and overnight hours of Tuesday night into the early early morning hours of Wednesday before sunrise. While there aren’t a lot of exact details we know this far in advance, the basic pattern looks favorable for a line of thunderstorms with some degree of threat for both damaging straight-line winds and a tornado threat of some magnitude. As we will talk about in a minute, at least for our local area, the magnitude of that threat is what is in question. Farther to the west, the NWS SPC has already flagged areas from central Mississippi back to east-central Texas in an Elevated Risk of severe storms for Tuesday into Tuesday evening, and they mention they potential for a significant severe weather event with strong tornadoes in those areas. That is uncommon wording for this far in advance, and a major severe weather threat may be in store for those areas to the west on Tuesday. However, we do not have the same level of threat as those areas.
Models are coming into general agreement on a big storm system ejecting out of the Plains with a strong surface low tracking through Missouri Tuesday in association with a powerful upper-level system that goes into a negative tilt as it approaches and the strong upper-level jet stream fans out overtop the warm sector. Meanwhile, an intense low-level jet about 5,000 ft above the ground sets up over the Tennessee Valley by Tuesday night, providing northward transport of moisture and strong low-level wind shear. The upward lift and the wind shear are very favorable for a severe weather event. It is the degree of instability, or fuel for thunderstorms, that is in question.
Above are the dewpoint model forecasts from both the Euro and GFS models at the time they have the line of storms moving into our area Tuesday night. There are minor timing differences (for this far in advance, three hours is minor), but the basic idea is the same. Areas shaded in green have dewpoints of 60+ degrees, with the darker the color, the higher the dewpoint. Both models agree on a scenario where adequate-but-barely-so moisture returns to the area just immediately ahead of the line of storms right as it moves into the area. Typically, situations like this result in lower instability. If that is the case, there would still be the potential for severe storms, including a tornado threat, but it would be a lower-end type threat with only isolated damaging winds and maybe a spin-up tornado or two. However, we will be watching to see if there are trends in the moisture getting here faster as we get closer. That sometimes happens in the model data, and it happened in the last severe weather event we had a couple of Saturdays ago. Should higher dewpoints end up getting here sooner than currently shown, instability would trend up, and that would support a more elevated severe weather threat. We won’t have a good handle on that until probably the weekend, when we begin getting our threat timeline into higher-resolution model data and we see how far southward the weekend front will push moisture in the Gulf before it has a chance to come back northward.
The thing to do right now is to prepare. Even if this system didn’t exist and wasn’t on the board, we are just about to head into the primary part of our tornado season here in the Tennessee Valley (March and April), and it is important that you are ready ahead of time for threats like this. If your family doesn’t already have a safety plan, now is the time to be formulating that while the weather is quiet. Also, make sure you have multiple reliable ways of hearing warnings, including something that will wake you out of your sleep during the overnight hours. There’s no reason to be scared or worried or to panic. Just be prepared ahead of time, have your plan in place, and have multiple reliable ways of hearing warnings. We will be sorting through the data and making adjustments to the forecast over the coming days to nail down the details. Keep checking back for updates as we sort out those details!
