We have the potential for strong to severe storms occurring on two separate occasions this week… one starting very late on Wednesday night and going through the entire morning on Thursday, and the next one taking place late on Friday and going through the morning hours on Saturday. Both long-range models show relatively good agreement with both systems, with timing and locations of the surface low only having minor differences. We’ll start with Wednesday night/Thursday morning event.
A deepening surface low will start off on Wednesday afternoon over the Oklahoma/Texas border and will move east-northeast throughout the remainder of the day and into the night. By midnight, it will be located over Central Arkansas, but rain and a few storms will begin moving into the western portions of Central Alabama out ahead of the low in the warm sector. By 7:00 am on Thursday morning, the low will be located near Memphis and storms will be ongoing across much of Central Alabama with the exception of the southeastern corner. By 1:00 pm Thursday, the low will be centered very close to Nashville with storms active across much of Central Alabama with activity starting to end over the western parts of the area. By 7:00 pm, almost all of the activity is out of the area and the low will be in the extreme southeastern parts of Kentucky.
There will be plenty of instability out ahead of the system as it moves across the area. Bulk wind shear will be high, but what might be our saving grace with this system is that helicity values will be below what we need for strong updrafts. At this point, I would say that damaging winds and hail would be the main threats on an isolated basis. A brief tornado is not out of the question, but it looks highly unlikely at this point.
We’ll also have to worry about the potential for more flash flooding issues as we are forecast to see totals ranging from 1.50 inches to as high as 2.75 inches by the time this system is finished. Don’t be surprised if you see even higher amounts if we have training of cells.
The picture will become clearer when the high-resolution, convection-allowing models start coming in which is roughly 60 hours out of the event. This forecast will change and let’s hope it is for the better.
The better news about the Friday night/Saturday morning system at this point is that the better dynamics will be farther off to our north as the low will move northeast toward the Great Lakes. A cold front will be moving through the southeast with rain and thunderstorms out ahead of it. It’s too early to get any good detailed model information, but both the GFS and European models are painting a decent amount of instability with this system.
The sounding for the Birmingham area valid at 7:00 pm Friday night shows instability values forecast at just over 700 J/kg. Helicity will be strong enough to support rotating updrafts at over 250 m2/s2. Shear will nearly be perfect close to 65 knots. Mid-level lapse rates will just be steep enough to support updrafts. What is really interesting in this sounding is that the winds will be backed out of the southeast at the surface. With all of these ingredients together, we’ll have a marginal tornado threat, along with damaging winds and maybe some small hail.
Once again, the forecast will change as we get closer to this event, especially when those high-resolution, convection-allowing models come into view.
Remember… this is not out of the ordinary for Central Alabama. We are still in the middle of our prime severe weather season, and we still have just over a month to go until it ends. I’ll have more throughout the week on both of these systems.