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2020-03-19 EVENT: IL/IA/MO/AR/TX

SPC Day 3 has the highest probabilities and Slight risk over the southern portion of this region; where models currently depict the most favorable parameter space. However, going off parameter space forecasting 3 days out I'd have picked 3/12 over 3/2-3 as the more likely significant tornado day, so...

I will focus on the northern end of the Marginal risk because that's all that will be in range for me after getting out of work at noon Thursday. NAM and now 3K NAM have looked somewhat more interesting than the GFS did a few days ago; with SBCAPE in the 500-1000 j/kg range and much steeper forecast lapse rates. It's also hard to ignore the 500mb chart with the left exit region of a powerful southwesterly jet progged over the area. However, the wind profile on the forecast soundings show some gnarly veer-back. It's hard to find one that turns steadily clockwise with height. Still, this isn't a traditional supercell parameter space event either way, so I'm not confident what impact that will have.
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Looking over things this morning, it seems the ceiling of this event has crept a bit higher, but the best action might be over western Iowa/northwest MO. It will sprint east/northeast and be near the MS river in just about three hours (going off the 06Z 3KM NAM here), but that'll be after dark. Also going by that model the boundary layer will be slow to decouple after dark (somewhat surprising for this part of the country this time of year) so the threat of nocturnal tornadoes might be legit (just what we need, again :rolleyes: ).
Keep an eye on southeast Iowa and northeast Missouri tomorrow evening. At the apex of the 500 mb exit region, and on the periphery of the stronger incoming H85 flow, the warm sector south of the surface warm front has ample MLCAPE values of 500-1000 J/KG coterminous with SRH values between 150-200 m2/s2, which is enough for rotating supercells that CAMS are showing as discrete for several runs.
Yeah, that is what I was looking at earlier this morning. Unfortunately, that area is poor terrain relative to just to the north, and you also have to contend with the MS river. Also further away for me vs. east-central IA or northern IL. Will probably sit this one out unless that changes.
One thing I’ve noticed in clicking around for soundings in various places in southern Iowa is the very large amounts of low level CAPE. I’m consistently seeing 250-350 numbers. I’m pleasantly optimistic for tomorrow. Either way will be nice to break the 6 month lull with a pretty close chase!
For STL area and 2-hour drive surrounding: Strong wind fields area wide with 0-1km SRH being 200+ pretty much everywhere is a good sign with that broad jet max arriving late afternoon, but lapse rates are pretty weak and there are some hints at VBV showing up. Like Jesse said, CAMs are showing discrete activity, but I'm worried about mushy updrafts struggling to balance outflow. Clouds and precip may also be an issue through noon, but I'm confident there will be sufficient breaks behind the early-day activity. With COVID-19 limiting me to a tank of gas's worth of a drive outside of STL, I do like the chances of a healthy supercell within that range, and if the sun comes out longer than expected, our low-level lapse rates will improve. Iowa looks much better with the proximity to the surface low and that low-level instability, but it could be a later show. It's outside of my home area and out of play though.
if I was in Iowa tomorrow I’d be out chasing. I’m not so I won’t be. The storms will be hauling butt tomorrow and might struggle to produce. Lapse rates are nothing special, cape is kind of blah but adequate. Most of the parameters are nothing special and the low will be weakening as the day wears on. The low level winds will be cranking though and they seem to be able to make up for a lot. I’m expecting a couple of vigorous tornadoes tomorrow and I’ll be bummed I didn’t go. I also think if I went I’d be wishing I didn’t while driving home tomorrow.
This only has to do with the Iowa target and not anywhere else...
Does look like a pretty good setup in Iowa being closest to the surface low. Decently curved hodograph leading to 250 m2/s2 of 0-1km SRH. As Jeremy mentioned, there a good cape profile near the ground, however it is skinny overall. But with all the shear that shouldn’t matter much. Looking at 40-45 kts of 0-3 km shear and 60-75 kts of bulk shear to organize the storms and aid the tornado/wind threat. Was checking the Euro and it forecasts pockets of 7 C/km lapse rates, so there will be some big hail.
Morning developments are not encouraging for the southern target (MO/IL/KY). I don't see much hope for appreciable breaks in cloud cover given upstream precipitation and the present visible satellite loop. CAMs insist that northward advection of higher theta-e air from NE AR ahead of the ongoing convection will focus discrete storms in southern IL, but current radar suggests that any supercells will end up being embedded in QLCS structures down in the bootheel and points south rather than the I-64/I-70 corridors. I have no plans to leave home yet.
I bet once the convection in OK/AR gets up your way, it may create a rain-cooled outflow boundary that becomes the focus for new storm development later. Unfortunately that looks to be southeast of STL. Probably a damaging wind situation with a couple rain-wrapped EF-1/2s in there maybe with the QLCS this afternoon/evening.

However, the HRRR is depicting a group of supercells initiating in far southern Illinois around 2/3:00 P.M. central time and tracking northeast into southern Indiana. And it keeps these out ahead of the main QLCS with eventual merging by late evening over southeast Indiana. This is within a combo of 1600-1800 J/kg MLCAPE and 0-1 km shear on the order of 40-50 kts. This will yield STPs around 3-4 per the HRRR. Also a decent veering of the winds from the surface to 850 mbs.

With the discreteness of the storms in a ripe warm sector, makes me concerned for potential for a strong, long-track tornado this afternoon and evening in that area. Someone may want to hop on that.
This VERY LONG continuous formation was observed in the morning hours of 2020-03-19, first seen near the Stanton, TX and continuing on the north side of I-20 to and beyond Colorado City, TX area, leading toward a residual ongoing minor rain complex near the Red River [from the previous evening's storms in W/Central Texas]



Looks like I haven't missed much after deciding to sit today out. The cell approaching Knoxville, IA probably looks pretty cool, but it's not even tornado-warned as darkness rapidly approaches. Not worth the five-hour drive on the heels of a 3AM-noon work shift what with everything else going on.

EDIT: Looks like what I previously thought might happen in Iowa is happening in Arkansas, with three small supercells all tornado warned. The northern one (near the MO border, too low-topped and far from LZK or SGF to really get a good bead on) is now "confirmed" with a public report.
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Those discrete supercells originally shown by the HRRR in southern Illinois/Indiana this afternoon were a bust and that severe QLCS just raced across that region. Also was more of a hail event in Nebraska/Iowa.

Essentially, if you weren’t in an enhanced risk today, you didn’t get severe weather (except some hail in southern Nebraska and far southern Texas). Considering that the CAMs were originally showing little/no convection in the slight risk between the 2 enhanced areas this morning, a marginal risk or even a general thunder would’ve been much more apropriate. But, I think the kinematics were just too good-looking today to narrow down.
This one was yet another example of when the atmosphere is all cluttered from a number of messy early day storm systems in the target area that result in a lack of significant widespread convection. Isn't this around the 4th enhanced to flop thus far in 2020, be it because of rain-cooled air, lack of shear, or other?
I have no plans to leave home yet.

^ This right here. This was the winning move yesterday, IMO.

I was itching to go back for a do-over after getting Broyled last week in western KY. I packed some food and water, grabbed some sanitizing wipes, hermetically sealed myself in my truck, and made the trek back to about the same area as 3/12, but stayed north of the Ohio river this time, targeting extreme SW IN (IA was outside of my range for the day). And just like before, despite decent parameters, a supportive wind profile, a few brief breaks in the cloud cover, and continuous SPC agreement, all that occurred in the target area were a few sporadic wind gusts. There were a pair of tornado warnings for a mesovortex circulation embedded in a fast-moving linear segment, but the area of interest was shrouded in rain. As far as I know, no tornadoes were confirmed from that storm. That was about the peak of the excitement. Tail-end Charlie produced an isolated storm with a small hook-shaped appendage near Mount Vernon, but with no clearly defined mesocyclone, I didn't have high hopes. It fell apart right around sunset. No photos worth sharing.

One of these days I'll learn to dial it back a bit on these March setups. But I figured this may have been the last shot I get for a while, until the Covid-19 situation stabilizes.

Total chase time: 18.5 hrs. Total miles driven: approx. 950.
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Based on yesterday’s storm reports in the tornado watches, today’s wind event across Ohio and especially upstate NY should’ve warranted a severe thunderstorm watch. There was more concentrated severe reports across upstate NY today than any region yesterday, though the hail event in IA/NE might be a similar concentration.

Not to rip on the SPC, but I think they need to be more aware when it comes to severe events with little instability. Based on yesterday’s enhanced risk (max CAPE ~ 1500 J/kg) compared to today’s marginal risk (max CAPE ~ 400 J/kg), I think their awareness of potential severe weather increases with instability values. That is a very unscientific statement, but I’m just trying to get my point across.

They issued 2 MCDs today, each acknowledging potential for isolated severe wind gusts because of strong low-level winds. But when you have 55 kt winds at 1km, shouldn’t that be of more concern than a marginal risk? In my opinion, yes. To their credit, they did say, “even minor momentum transfer from the ongoing line of shallow showers will likely result in near severe wind gusts where the boundary layer is not overly stable.”

But I think when there’s little instability available, our minds as weather enthusiasts/meteorologists want to write off an event with great kinematics as a bust. But to clarify, if you aren’t looking for this type of event, you will probably miss it.

Coming from Michigan, I’ve learned to stop myself from doing this because we usually only see appreciable instability from May-September (sometimes a bit earlier/later) In fact, I get excited when I see these super high shear/very low CAPE setups because you can really get freak storms out of them. I experienced one in late November of last year: no warning (not even a special weather statement), 65-70 MPH gusts, wind-driven small hail (very surprising), extensive tree damage, and widespread power outages in my area.

Not only that, but look what happened in MD/DE/NJ/southeast PA in early February. They had the biggest tornado outbreak there EVER there in the month of February, alongside widespread damaging winds. There wasn’t even a thunder category until after the first severe warnings were issued, but it was too late once the marginal risk was issued. Even if you have almost no instability, but you see 60-70 kt flow at 1 km and a rapidly deepening low immediately north of that, shouldn’t you have more concern than only expecting some isolated severe gusts?

This doesn’t all apply to yesterday’s events, but I felt the comparison to today was appropriate to bring up alongside other examples.
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