Archive March 18-20th, 2018 Severe Weather

[CheeselandSkies]

Yikes, "PDS TOR" soundings in abundance across AL on the 06Z GFS at hour 90. Moreover, the wind profile and analog lists back it up.

 

[Kory]

The NAM is outbreak level stuff for Monday. Just bad.

Models are trending worse.

 

[rolltide_130]

Re: Recovery. I'm seeing a lot of similarities to 4/5/17 last year, so it's why I'm still a little iffy on this system and I haven't been posting much about it. The GFS, while it has improved some, still has that nasty lead wave in the morning that I am highly concerned could throw a wrench in the wind fields. Also, the Euro has a nonexistent LLJ in the afternoon and the 0z run in general was still a total mess.. I need to see more from this system before getting legitimately concerned about it. There have been improvements but I've been burned too much the last year by jumping on board more than about 48 hours out..

 

[warneagle]

Forecast soundings on the 06z GFS keep triggering Super Tuesday as an analog...

Edit: 06z, whoops

 

[MichelleH]

Forecast soundings on the 06z GFS keep triggering Super Tuesday as an analog...

Edit: 06z, whoops

Oh peachy...my birthday outbreak. Nope, we don't need that. LOL

 

[warneagle]

Re: Recovery. I'm seeing a lot of similarities to 4/5/17 last year, so it's why I'm still a little iffy on this system and I haven't been posting much about it. The GFS, while it has improved some, still has that nasty lead wave in the morning that I am highly concerned could throw a wrench in the wind fields. Also, the Euro has a nonexistent LLJ in the afternoon and the 0z run in general was still a total mess.. I need to see more from this system before getting legitimately concerned about it. There have been improvements but I've been burned too much the last year by jumping on board more than about 48 hours out..

Yeah, that's a good point about the LLJ, especially earlier in the day back in MS.

I missed most of the 5 April event last year because I was traveling back from Michigan, what went wrong that day?

 

[NorthGaWeather]

It appears the 12z NAM came in a little more impressive thermodynamics wise.

 

[CheeselandSkies]

First sounding I looked at on the 84H 12ZNAM valid for 0Z Tuesday from N AL is a PDS TOR with an insane shear profile...and yet has no quality matches on the supercell analog list. That is another red flag that I noticed leading up to last 4/5.

 

[Taylor Campbell]

The NAM is outbreak level stuff for Monday. Just bad.

Models are trending worse.

I just looked at the 12z NAM.

 

[Argus]

Analogy to 4/5/17? Better alert Delta!

 

[SilentShadow87]

Analogy to 4/5/17? Better alert Delta!

4/5/17 was nothing to scoff at. At least two of the officially-rated EF2 tornadoes were likely at EF3+ strength over rural areas.

 

[warneagle]

Yeah. Something doesn't seem right with the 12z NAM. Just look at it compared with the 12z GFS. There are areas where the NAM has 500+ SRH and the GFS is only in the 200s. Did the NAM goof up the track of the surface low or something like that? There's a big discrepancy between it and the GFS in that respect.

 

[Kory]

Yeah. Something doesn't seem right with the 12z NAM. Just look at it compared with the 12z GFS. There are areas where the NAM has 500+ SRH and the GFS is only in the 200s. Did the NAM goof up the track of the surface low or something like that? There's a big discrepancy between it and the GFS in that respect.

The NAM has a stronger LLJ.

 

[KoD]

It's hard to look at the NAM @ H84 and not raise an eyebrow. Good dews, helicity, CAPE and lapse rates.

Randomly sampled Madison county (although after reviewing supercell composite realized this is close to the highest region, this is not a good indication of the larger area):

Looks impressive to say the least.
Important to keep in mind that the NAM has shown this type of thing many times before and is more often wrong than right. I can recall a couple events where NAM nailed it, and I can recall dozens of times the NAM burned nearly everyone.
My thoughts yesterday & before was that this system has potential to underperform or overperform. Now that NAM seems to have gone nearly all-in, underperforming and verifying are about the only two things left. Let's see if we get run-run consistency now that we're getting close to the medium & short range ballpark.

Here's a sample from GFS for ~Madison county at roughly the same time

Much more moderate, but still eyebrow raising.
Regardless, we know what can happen with this type of setup. There's definite potential. Stay tuned to this one!

 

[rolltide_130]

Yeah, that's a good point about the LLJ, especially earlier in the day back in MS.

I missed most of the 5 April event last year because I was traveling back from Michigan, what went wrong that day?

Morning crap rained on the parade (literally), and we had the wind fields get ruined which caused a chain reaction (SRH plummeted, hardly any moisture to work with, dryline mixed out). Not saying that will happen again here, but I have some reservations..

 

[Richardjacks]

While it might be too early to be this specific, I am not seeing much of a cap during the morning or early afternoon, there may be a lot of junk convection.

 

[warneagle]

The NAM has a stronger LLJ.

Oh okay. I see that now. Significantly so. Let's hope it's wrong, that's nasty.

 

[MattW]

I'll be more interested in what the NAM is saying at 60 hours out instead of 80+. I'm always leery of end-of-range data from these things.

 

[Fred Gossage]

I'll be more interested in what the NAM is saying at 60 hours out instead of 80+. I'm always leery of end-of-range data from these things.

While I feel the same way as a general rule, the GFS isn't too far from the NAM depiction once you remember that it usually underdoes shear because it can't handle processes associated with pressure falls and height falls well (a long-standing issue)... and that it often doesn't handle thermos too well either, and has been way off with systems so far this year (even the NAM has underdone thermos, when in years past, it would usually be too unstable or too moist). Then, a big important thing to remember is that the upper system started getting sampled by our balloon network this morning in time for the 12Z observed soundings... and that data was ingested into the 12Z models.

 

[Richardjacks]

While I feel the same way as a general rule, the GFS isn't too far from the NAM depiction once you remember that it usually underdoes shear because it can't handle processes associated with pressure falls and height falls well (a long-standing issue)... and that it often doesn't handle thermos too well either, and has been way off with systems so far this year (even the NAM has underdone thermos, when in years past, it would usually be too unstable or too moist). Then, a big important thing to remember is that the upper system started getting sampled by our balloon network this morning in time for the 12Z observed soundings... and that data was ingested into the 12Z models.

This is also after the EURO has been sounding the alarm. Quite the agreement this far out.