11:30AM UPDATE: The main line of storms has already moved through Nashville, and continues to progress eastward. It’s been very well-behaved so far — producing plenty of lightning and heavy downpours, but no wind gusts that have even approached severe criteria. The scenario I outlined in this morning’s initial post is pretty much what happened — the atmosphere didn’t have time to destabilize before the storms came through.
As the storms move eastward, a few could still be strong or even severe in southeastern Middle Tennessee this afternoon. That’s where the storms will arrive the latest, and thus it’s where the atmosphere will have the most time to “charge up.” Damaging winds are still the main threat, along with a fair amount of cloud-to-ground lightning.
The Storm Prediction Center has finally trimmed back the “Slight Risk” region, to include only the southeastern corner of the Midstate (but also still a significant portion of Mississippi, Alabama and Georgia):
For the rest of us, the weather won’t be dangerous, but it won’t be great either. Still rainy, turning colder, and breezy as well. Keep the umbrella handy the rest of the afternoon.
7:00AM POST: We’ll start with the easy part of today’s forecast: it’s going to rain. The more challenging part of the forecast is determining our severe weather threat level — we know it’s not going to be an ideal setup for severe thunderstorms, but the atmosphere doesn’t have be arranged perfectly…”good enough” is all that’s required.
Thunderstorms are approaching from the west as I type this — some spotty showers or storms will pop up ahead of the main line, but the main line will cross the Tennessee River by mid-morning and head west-to-east across the Midstate through mid-afternoon. This version of the Futurecast radar simulation (using the RPM model) is in good agreement with the other short-range model guidance in terms of the timing and strength of the storms:
The fast movement of the storms is good news for us — the atmosphere doesn’t have much time to become unstable. Temperatures this morning started in the 40s and 50s, with dew points in the 30s. For severe thunderstorms to become a reasonable possibility, the temperatures would have to warm up to the 60s, and dew points would have to climb into the 50s…there’s just very little time for that to happen!
The forecast sounding (the HRRR model-based simulation of weather balloon data) in advance of the storms is full of good news for Nashville:
Dew point in the upper 40s? Great.
CAPE (storm energy) values under 100? Super.
Cloud bases (“LCL”) more than a kilometer off the ground? Outstanding.
That said, there’s still enough wind energy in the atmosphere to support a threat of damaging straight-line wind gusts (60+mph):
The greatest threat is likely to develop east of I-65 — because the storms will arrive in that part of the Midstate later in the day, the atmosphere there will have had a bit more time to get its act together.
The most-likely scenario is that we all get rain, plenty of us hear some rumbles of thunder, but very few of experience the potential of damaging straight-line winds. That doesn’t mean you should let your guard down! The atmosphere is more than capable of surprising us though, and the Storm Prediction Center is sticking with a “Slight Risk” (level 2 of 5) for severe thunderstorms across the entire Midstate:
Again, my analysis of this scenario is that areas along and east of I-65 have the best chance of stronger storms from midday through this afternoon.
Once this system moves through, temperatures will drop rapidly — even cold enough for a few late-night/early-morning non-accumulating snow showers in the higher terrain of eastern Middle Tennessee. Cooler-than-normal temperatures will prevail the rest of the work week, with another good chance of rain showers on Thursday:
Clearing out on Friday, and warming up this weekend! In fact, it looks like above-average temperatures will prevail through most of next week.
Better late than never, here are today’s nerdy items of note…
- In advance of last week’s severe storms, some school districts in Louisiana and Alabama either let out early, or canceled for the day. Are “tornado days” for schools a good idea? (Count me in the “no they are not” crowd. Everyone thinks of the tragic deaths of students at an elementary in school in the 2013 Moore, Oklahoma tornado — but the fact is that schools are some of the most-sturdily built structures we have. They have to be strongly built, because they have to withstand…you know, kids. A tornado strong enough to do substantial damage to a school would almost certainly do even-worse damage to residences near the school. Keeping kids away from classes on potentially stormy days might make school administrators feel absolved of any sense of liability, but I don’t see how it does anything to contribute the most important thing, which is the students’ safety.)
- The national weather pattern will undergo a big shift beginning this weekend — that means warmer weather for us, and wetter weather for California…but not enough to break the drought.
- Tropical Cyclone Winston did almost a half-billion dollars worth of damage to Fiji — that represents 10% of the country’s GDP.
- A new solar wind model could improve space weather forecasts.
- To date, humanity’s longest exploration of the surface of Venus has been a few hours (the 800-degree-plus temperatures and crushing pressure make it a pretty hostile environment). But NASA is working on a probe that would explore Venus for about 50 days, within the next decade of so.
- A new photo from the Hubble Space Telescope shows a “blue bubble” in space.
- Where will our galaxy’s next supernova occur?
- It’s Super Tuesday — believe it or not, the location of your polling place (school, library, church, etc.) can subconsciously affect how you vote.
- Yesterday was “Leap Day” — is it time to re-invent the calendar?