It's going to be a long week here in the weather center, with a couple different threats of strong to severe storms expected. We have already been giving a cursory mention of both of these systems for the past couple of days, but this blog is going to be focused specifically on outlining the potential for each system.
The latest update from the Storm Prediction Center has expanded to Level 2 of 5 risk of severe weather for Wednesday/Wednesday night northward to now include portions of southern middle Tennessee. Areas as far north as Hohenwald, Mt. Pleasant, and Lewisburg in Tennessee are now in the Level 2/5, and then southward through the Highway 64 corridor and then through all of north Alabama and north Mississippi. North of there, a Level 1 of 5 risk goes all the way up past the Nashville area.
There is still some uncertainty with this threat, especially in relation to the magnitude of the tornado risk. However, there has been a trend for the low-level winds to look stronger and the low-level wind shear to be higher. This is making the tornado risk look more appreciable than we previously thought. The Storm Prediction Center mentioned in the outlook that should the trend for stronger wind fields continue, a more significant tornado risk may develop, and they may have to upgrade to risk to Level 3 of 5. As of right now, there still isn't enough confidence in that scenario, but it is one that is possible, and it is gaining credibility in the higher-resolution model guidance. For right now, we will move forward saying that "tornadoes are possible", and we will be working to fine tune the forecast to see whether or not limiting factors come into play or if we need to increase the tone of our wording.
The Wednesday threat is just coming into focus now on our in-house high-resolution Futurecast model from Baron, and it does look supportive already of the severe weather threat. Details will continue to be fine tuned, and the model run stops before the end of the threat, but this gives a good early look at how this may all evolve.
By daybreak on Wednesday, we have hints at a few isolated showers and maybe even a rumble of thunder over the area, but most folks look relatively quiet, with the more widespread rain off to our east over northeast Alabama, southeast Tennessee, and northwest Georgia. The main upper storm system is still off to the west during the morning; so, as of now, we don't expect any morning or midday activity to go severe. As we move from the midday into the afternoon hours, things begin to change. The main upper system starts approaching. This adds lift into the atmosphere, and it strengthens the wind profiles and increases the shear. As this happens, the atmosphere continues to destabilize as temperatures climb into the lower 70s and dewpoints are way up into the middle 60s. From the afternoon into the evening, this Futurecast model is already showing discrete severe storms that develop out in the open warm sector across the area ahead of a band of storms with embedded cellular elements. If these cellular storms are more dominant, that would increase the tornado risk. If the band of storms is more dominant, with the storms ahead of it struggling to really intensify, a tornado or two would still be possible, but the main threat would be damaging straight-line winds. The model doesn't yet go past 6PM, but the overall evolution suggests that things would continue east across middle Tennessee and north-central Alabama through the evening, likely ending by or before midnight.
Of the two systems mentioned at the beginning, the one that may end up being a greater magnitude threat for the area is the one timed for Saturday and Saturday night, possibly stretching into early Sunday morning. The Storm Prediction Center has already outlined a large area of severe weather possible for Saturday (the equivalent of a Level 2 of 5 risk, but they don't do the 1-5 levels this early) on their "Day 6" outlook. Today is considered "Day 1", tomorrow "Day 2", etc. Saturday is the Day 6 period. It is not frequent at all that a risk area gets outlined at the Day 6 timeframe. The Storm Prediction Center already also mentions that this is a situation where higher probabilities and risk levels may be needed as details become more clear. This is a situation where all threat types are possible, including tornadoes. It is too far out for exact details: exact timing, exact areas with the higher risk, the exact magnitude of the risk. However, it is a risk that includes the entire viewing area. Should conditions continue to align themselves as they are now and they have been, this could end up being a substantial threat to our area. It's just too soon for details and too soon to sound alarms, because it's Monday currently, and this is a risk for Saturday. There's plenty of time for changes.
What you can do now for BOTH threats, is to stay in touch with weather information as we get closer, and go ahead and go through your severe weather safety plans. I know we went through this a few weeks ago, but we noticed then that, despite us urging you multiple days ahead of time to go over your safety plans or formulate your plans if you don't already have one, when we got to the storms actually happening that night, there were a few people who had never tried to prepare all those days in advance, and then panicked trying to figure out what to do when the warnings were being issued. That is NOT the time to prepare for a severe weather threat. NOW is the time to prepare, while the weather is calm and quiet. Use the guidelines and tips above to formulate a shelter/safety plan for your home, your business, wherever you may be. Make sure you have MULTIPLE RELIABLE ways of hearing watches and warnings. Prepare while the weather is quiet. Have your plan formulated and thought out ahead of time, so that you can just react on second nature when storms actually threaten.
Be sure to stay in touch with weather information on a regular basis through the week as we continue to iron out the details of what to expect with both systems.