Two November Storm Systems

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Late October, November, and early December are the “peak” of the secondary severe weather season in the Tennessee Valley. As you probably know, things work a little differently here in Dixie Alley compared to the traditional “Tornado Alley” in the Plains and Midwestern States; for us, that means we have to be on our toes anytime a storm system moves this direction.

At this point, we are craning our necks to look at the potential for some heavy rain and thunderstorms on Monday. This is a suspicious-looking system with strong dynamics and strong wind shear; however, there may not be enough fuel to fire up a major severe weather outbreak. Storms need at least some marginal instability to become intense, and this particular system will have a tough time pulling in enough warm, humid Gulf of Mexico air to fuel widespread severe weather. It is not impossible, but as of now, the threat is marginal. If I had to put a percentage chance on severe storms, I’d give it a 20% with the idea that there is a chance it could go higher if we get a more substantial push of warm, humid air. Basically, if dewpoints can rise to or above 60ยบ, the risk of severe storms will rise quite a bit.

CAPE (convective available potential energy) is forecast to only peak at around 100 J/kg. That’s not a lot at all, but remember this: Dixie Alley’s storms can be much different than the more famous ones in the traditional Tornado Alley. We don’t always have to have high CAPE to get severe storms and tornadoes. One case in recent history that proves this was the tornado that came right through Downtown Huntsville on January 21, 2010.

Rain is a much different story! We are all but guaranteed at least a good 0.25 to 0.50″ of rain with this next cold front. The ensemble probability for Huntsville getting more than a half inch of rain in a 24-hour period peaks at 6 AM Tuesday, November 13th. That means there is a 52% chance (based on model ensemble data) of Huntsville picking up more than a half inch of rain in the 24 hours preceding that time. So, from 6 AM Monday to 6 AM Tuesday, there is a 52% chance of heavy rain. I believe we can narrow that down to mainly Monday afternoon and Monday evening, but exact timing is difficult days in advance!

Notice that other peak in the probability of more than a half inch of rain? That comes with another suspicious-looking storm system that will move through here toward the end of next week. Most guidance brings it in on Friday; however, we are still nine days away from that one, so the margin of error is very large with respect to timing and intensity.

The only reason to even begin talking about a second system is for long-term planning. If I can give you a heads up over a week in advance, that gives you time to read, listen or watch as much as you need to as we narrow down the forecast through the course of a few days. If you have plans next Friday, Friday night or even Saturday, check back with us from time to time. We will post information here on the blog as well as a small blurb about it on WHNT.com/Weather in the main forecast section every day through next week.

THE BOTTOM LINE:

Enjoy a warming trend for the next few days; it’s going to be very nice this weekend! This information is here simply to help you understand what you see on our Seven Day Forecast. There will be changes, adjustments, and clarifications here and on the main forecast page, so if you are only interested in the finished product, check out WHNT.com/Weather. There is no immediate threat of severe weather, so don’t start worrying about it just yet. We can’t know for sure this far away, but we’d rather let you know that we’ve got our eyes on something a long way off instead of letting it sneak up on us!

-Jason
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