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Severe Event March 25th 2021


Bob's Burgers
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2 minutes ago, jojo762 said:

00z HRRR is a touch more tame than the 18z run was... But still shows many discrete/semi-discrete supercells across AL and MS during the afternoon and evening -- toward evening it really starts to light up KY/TN with a broken line of what I would assume would be a mixed-bag of supercells and clusters, given the forecast parameter space across both these area i'm not exactly sure it is going to matter how "discrete" convection can stay.

I actually think it might make a huge difference.  The HRRR is blowing a big hole in the low-level instability beneath the region of widespread convection, which is going to put a tamper on discrete updrafts.  Furthermore, this sort of convective evolution will limit destabilization further north.  While I feel confident that there will be tornadoes somewhere, the 00 UTC HRRR scenario is a show stopper in terms of a historic outbreak.  Lets hope this pans out.

Given that this earlier convective blowup is consistent with the euro and some of the other CAMS, i'm inclined to believe it moreso than the crazy runs earlier today.  It's also (for the most part) more in line with how these events typically evolve in the SEUS.  

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4 minutes ago, jpeters3 said:

Given that this earlier convective blowup is consistent with the euro and some of the other CAMS, i'm inclined to believe it moreso than the crazy runs earlier today.  It's also (for the most part) more in line with how these events typically evolve in the SEUS.  

I mean that and what we saw last week generally + how rare big outbreaks with long track violent tornadoes are generally 

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7 minutes ago, jpeters3 said:

I actually think it might make a huge difference.  The HRRR is blowing a big hole in the low-level instability beneath the region of widespread convection, which is going to put a tamper on discrete updrafts.  Furthermore, this sort of convective evolution will limit destabilization further north.  While I feel confident that there will be tornadoes somewhere, the 00 UTC HRRR scenario is a show stopper in terms of a historic outbreak.  Lets hope this pans out.

Given that this earlier convective blowup is consistent with the euro and some of the other CAMS, i'm inclined to believe it moreso than the crazy runs earlier today.  It's also (for the most part) more in line with how these events typically evolve in the SEUS.  

Good news, honestly.

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While we wait for new model runs and a new SPC outlook. Always surreal to look back and read the 4/27/11 thread on here. All hell started breaking lose around page 19...

Not saying this will be anything like that event, but just in case anyone has some time to kill...

 

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Lol one slightly more tame run of the HRRR and the event ceiling gets mostly discounted immediately. Careful with that one folks. This still looks rock solid synoptically. 
 

As always, setup of the outflow boundaries and mesoscale details day of will determine magnitude, but this and last weeks setup are not the same. 

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Biggest difference to me seems to be the degree of instability that has built up by early afternoon. However, the HRRR still shows relatively similar levels of MLCAPE and 3CAPE at 22Z further north in KY/TN so (18Z v 00Z. run)... All of this is mostly a product of early-firing convection AND more messy/blobby storm modes.

 

18Z HRRR MLCAPE valid at 18z Thurs:

mlcape.us_ov.png

00Z HRRR MLCAPE valid at 18Z Thurs:

mlcape.us_ov.png

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Nam nest says "hold my beer."

Produces a warm sector with widespread 0-1 km SRH > 600 J/kg and 80-100 kt 0-6 km BWDs, but not one supercell or UH track over MS/AL.  Not much convection at all.  So much for CAMs making things clearer for the 06 UTC outlook.

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I'm going to go ahead and say what the NAM NEST shows of ZERO convection firing along the pre-frontal trough will not happen.. 

If every other CAM is showing plenty of pre-frontal convection, while the NAM NEST shows absolutely nothing because of some strong 700-800mb inversion , and the NAM NEST ends up being right..... If that happens I will eat a shoe.

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Just now, jpeters3 said:

Yeah, can we talk about where the hell these profiles came from??? Calling BS on this solution...

I wanted to be that aggressive with calling out how awful/suspect that thermo profile looked (from a forecast output perspective), but I couldn't.:lol:

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1 minute ago, jojo762 said:

I wanted to be that aggressive with calling out how awful/suspect that thermo profile looked (from a forecast output perspective), but I couldn't.:lol:

Fairly sure no observed sounding has ever looked like that

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The 00z 3km NAM is either scary af, clueless or both. I cherry picked some soundings with 700-500mb lapse rates over 9 C/km with Tds in the lower 70s. Even area averaged soundings show lapse rates around 8 C/km with a small capping inversion. Important note is that low level lapse rates in this environment are marginal, in some cases <6 C/km.

If the cold bias is correct, you’d have that tiny cap being obliterated. 

Is it overly simplified to say a HRRR/3km NAM blend is one of the scariest scenarios you could fathom? HRRR is messy with widespread convection, while the NAM is just a little bit too cool in the boundary layer, resulting in very little warm sector convective initiation. 

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2 minutes ago, Quincy said:

The 00z 3km NAM is either scary af, clueless or both. I cherry picked some soundings with 700-500mb lapse rates over 9 C/km with Tds in the lower 70s. Even area averaged soundings show lapse rates around 8 C/km with a small capping inversion. Important note is that low level lapse rates in this environment are marginal, in some cases <6 C/km.

If the cold bias is correct, you’d have that tiny cap being obliterated. 

Is it overly simplified to say a HRRR/3km NAM blend is one of the scariest scenarios you could fathom? HRRR is messy with widespread convection, while the NAM is just a little bit too cool in the boundary layer, resulting in very little warm sector convective initiation. 

It's like the ceiling got even higher, but the certainty lower.

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1 minute ago, Quincy said:

The 00z 3km NAM is either scary af, clueless or both. I cherry picked some soundings with 700-500mb lapse rates over 9 C/km with Tds in the lower 70s. Even area averaged soundings show lapse rates around 8 C/km with a small capping inversion. Important note is that low level lapse rates in this environment are marginal, in some cases <6 C/km.

If the cold bias is correct, you’d have that tiny cap being obliterated. 

Is it overly simplified to say a HRRR/3km NAM blend is one of the scariest scenarios you could fathom? HRRR is messy with widespread convection, while the NAM is just a little bit too cool in the boundary layer, resulting in very little warm sector convective initiation. 

IDK, let me consult COAMPS :wacko2:

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