OVERVIEW: A combination of the dynamics of a tropical system and the building instability with the heating of the day brings the potential for a few tornadoes on Saturday, especially during the afternoon and early evening hours. NWS Birmingham is really starting to push the word out that we will really need to focus on a higher tornado threat across Central Alabama as the latest model runs are showing that to be the case with the heating of the day. Due to this developing situation, NWS Birmingham is in discussion to upgrade parts of the area into a level 2 Slight Risk for severe storms. Right now, all of Central Alabama is in a level 1 Marginal Risk. We are using the 12z NAM-3k model run as this is the best view of what we will be discussing.
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7:00 AM SATURDAY: At this point, we see a pretty hefty rain band from Delta beginning to move into the extreme western portions of Central Alabama. While the threat is rather small for any tornadoes with this band at this early of the morning, we will still have to watch as the tornado chance is not 0%, especially over the southwestern portions of the area (Marengo and Sumter counties). The line will be moving slightly east of due north at this point.
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1:00 PM SATURDAY: We are starting to see the leading band has developed further and become a little more intense, and as we are getting to the main heating of the day, the instability has increased and continues to build as we go through the afternoon hours. You’ll notice that the line is getting a little more ragged. That is because the band has started transitioning into more of a line of cellular thunderstorms. This is when we will really need to start watching for tornado development. Remember, we already will have plenty of shear in place with Delta’s wind field over the area, so it won’t take much for a few spin ups to develop quickly.
QUICK NOTE: If any tornadoes do develop with this system as it moves across Central Alabama, they will more than likely be your smaller EF-0 to EF-1 tornadoes; but, with the banding turning into cellular storms, the potential for a stronger EF-2 tornado is there. We cannot let our guard down one bit just because we hear that Delta is weakening as it moves through the area. That weakening only tells us about the maximum sustained winds, not the ongoing storms occurring in the associated rain bands.
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7:00 PM SATURDAY: As you can see with the band, the storms within the band have turned mostly into cellular structures… almost like a supercell look. As we start to lose instability due to the sun setting, these storms will begin to lose their punch. At this point, these storms will be close to the highest potential to perform. Instability values will be in the 1000-1200 J/kg range and plenty of helicity (potential for rotating updrafts) in place, this will probably be the time that we would be at our highest risk throughout the day of seeing a tornado or two. The threat will continue on for a few more hours, more than likely ending around 11:00 pm.
We’ll also have to watch any other bands that enter into the western portions of Central Alabama at this time as well. Even though they will be working through air that as already been worked over, there could be some recovery in the instability according to the time in-between the first band moving through to this point.
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1:00 AM SUNDAY: By this time, just about all of the instability that built up during the daytime hours should have dissipated and the severe threat should be over with. We’ll be left with a little bit of a breeze and some showers. There may be a few rumbles of thunder, but the main action for the day will be over.
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QUICK SUMMARY: Don’t be surprised if portions of Central Alabama go under a Tornado Watch for a good bit of your Saturday. The main window for the potential of stronger to severe storms within the rain bands will be from 1:00 pm to 11:00 pm Saturday. If any tornadoes do develop, they will mainly be smaller EF-0s and EF-1s; but, the potential is there for one or two stronger tornadoes. Maximum wind gusts outside of storms are expected to be in the 20-30 MPH range, below Wind Advisory criteria. Damaging winds up to 60 MPH are possible in any storm that goes severe. We’ll keep you posted throughout the event.
Central Alabama Weather 