12/27/2019 – 3:32 AM
The Storm Prediction Center has placed all of the Shoals Weather coverage area in a Level 1 of 5 risk of severe weather for Sunday. The main timeframe to watch appears to be from roughly 10:00am through about 8:00pm.
The main question concerning this severe weather potential is whether there will be adequate instability for organized severe storms. Unlike the storm system back on December 16th, there is a disturbance from the subtropical regions that moves across the warm sector during the day on Sunday. This will likely mean that the mid and upper levels of the atmosphere won’t be quite as cold, which means that, even with temperatures climbing into the upper 60s and lower 70s and dewpoints into the mid 60s, there won’t be a significant amount of instability for storms to work with. That disturbance may also cause scattered showers and storms to try to hang around during the day, and if that happens, it may help to further limit the amount of daytime heating and destabilization.
Despite these questions about instability, it may still be adequate enough for trouble, especially in the face of other ingredients expected to come together. Another difference from the December 16th event is that the upper-level system will be taking on a “negative tilt” as it approaches Sunday afternoon. This means that there will be significant dynamic support in place. Often times, especially when instability is higher, that can mean that too many storms form at once at things get messy, but these enhanced dynamics may be just enough to overcome the lack of better instability on Sunday. When combining that with the strong wind profiles in place, there may indeed be an environment favorable enough for a few storms to grow severe.
The main threats with any of the stronger storms that will be possible are damaging winds of 50-60 mph and the potential for a few tornadoes. Storms may come both as a line along the approaching cold front by early evening and the potential for a few individual supercells out in the open warm sector ahead of the front from the late morning through the early evening. The magnitude of the tornado risk is very uncertain and will depend quite a lot on whether the amount of instability we see will be adequate enough to fuel storms. During the winter months, the balance between marginal instability and strong shear is often very delicate. If we do see “adequate” instability (and it doesn’t have to be high to be enough), the tornado risk may end up elevated. However, if clouds and rain keep the atmosphere relatively stable through the day, the tornado risk would still be there but wouldn’t be nearly as significant as some of the other ingredients may otherwise allow. Should we get more confidence in the idea that enough instability will be in place, it is very possible that our area may get an upgraded risk level (probably to a Level 2 risk) in future outlook updates from the Storm Prediction Center.
Take the time over the next couple of days, before the weather turns threatening, to think about your safety plans and review them, and make sure you have multiple reliable ways of hearing warnings. If you live in a mobile home or other manufactured housing and you don’t have a sturdy site-built shelter at the same location or 2-3 minutes away at most, make plans NOW on where you will go to seek shelter on Sunday if a warning is issued for your area. Another important thing to keep in mind is that you need reliable ways of hearing warnings if you will be in worship services on Sunday. If you are a church leader and are reading this, make plans now to dedicate someone in your congregation to monitoring weather conditions and listening for warnings to be issued on Sunday. Practice your severe weather plans, and make sure your congregation knows where to go and what to do in the event a tornado warning is issued for your area during services.
We will continue to go through the latest data as it becomes available and have updates to the forecast as details become more clear. We will also have the Shoals Weather StormTrack Center staffed and ready to provide live streaming coverage if any watches or warnings are issued in our area on Sunday.