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April 26th-30th, 2014 Major Tornado Outbreak

andyhb

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brettjrob

brettjrob

Posted
Posted

Think I'm playing the cold core target Sunday.

Sent from my LG-LS980

 

Barring major changes, I think this has become the obvious chaser bullseye Sunday, and may end up with the most chaser convergence of any CC to date. It's obviously not your typical CC setup with 40s dews and hoping to squeeze out a spout-like tube; something more along the lines of Brady NE 2000 is probably on the table if things work out.

 

Oh, and one other thing re: Saturday. I agree with the Rozel (5/18/13) comparisons in some ways, but my excitement was really killed off when the GFS gave up on its faster and broader-based trough, which helped to draw moisture well back into the High Plains earlier in the day. In my experience, having that NW-SE arcing dryline (like we saw with Rozel) almost always results in a good day in W KS and the Panhandles region. Now that everything has slowed down, we're left with a crappy NNE-SSW oriented dryline, which I've only very rarely seen turn out well (Arnett/Greensburg being the main example I can think of). Just one of many factors to consider, of course.

 

I'd definitely hack off limbs for 65 Td Saturday and upper 60s Sunday... that don't mix out by 3pm like we've seen every day this year out there.

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Quincy

Quincy

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Posted

Saturday looks decent, but a late bloomer and not nearly as widespread/significant it could be if the upper level trough sped up even just three hours. It's not until close to 00z that the tornado threat seems to ramp up. At that point, the GFS shows increasing, but still not overly impressive shear. LCLs are about 1250-2000m just ahead of the dryline per GFS at 00z. Not great, but not nearly as high as they were yesterday. The other obvious advantage is more moisture to work with.
post-533-0-98390700-1398364650_thumb.png

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ZackH

ZackH

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Posted

Barring major changes, I think this has become the obvious chaser bullseye Sunday, and may end up with the most chaser convergence of any CC to date. It's obviously not your typical CC setup with 40s dews and hoping to squeeze out a spout-like tube; something more along the lines of Brady NE 2000 is probably on the table if things work out.

 

Oh, and one other thing re: Saturday. I agree with the Rozel (5/18/13) comparisons in some ways, but my excitement was really killed off when the GFS gave up on its faster and broader-based trough, which helped to draw moisture well back into the High Plains earlier in the day. In my experience, having that NW-SE arcing dryline (like we saw with Rozel) almost always results in a good day in W KS and the Panhandles region. Now that everything has slowed down, we're left with a crappy NNE-SSW oriented dryline, which I've only very rarely seen turn out well (Arnett/Greensburg being the main example I can think of). Just one of many factors to consider, of course.

 

I'd definitely hack off limbs for 65 Td Saturday and upper 60s Sunday... that don't mix out by 3pm like we've seen every day this year out there.

 

I would definitely take a Brady, NE event, lol... I just personally like the upper level support coming in by 00z via the 12z GFS... I think its promising.  Obviously, not a perfect setup but they rarely are.  Still think its the best chance of the year thus far, which is not saying much.

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Quincy

Quincy

Posted
Posted

The overall synopic evolution (based on GFS/Euro) is actually fairly similar to April 4-7, 2005, with just a few caveats. 

 

The 2005 setup was earlier in the season and just looking at the daily matchups, there was less moisture transport. The current Euro-based forecast is slightly further north and deeper system.

 

Daily matchups to (upcoming day):
April 4th (Saturday): No severe reports.
Differences: (The timing was about 3 hours slower with the upper level trough and dew-points ahead of the dryline were only in about the low 60s based off NARR)

April 5th (Sunday): A modest slight risk outbreak that went 25% hatched for hail in eastern TX/OK. 171 hail reports (mostly TX/OK/KS), 49 wind reports and 12 tornado reports. Most of the tornado reports were across Kansas.
Differences: Fairly good matchup, but greater moisture transport and higher dews this time around.

April 6th: (Monday): A moderate risk tornado outbreak across MS and adjacent LA. 43 tornado reports that day with a combined 183 reports overall.
Differences: Biggest thing I see is northward extend (vertically stacked over NE as opposed to OK/AR), as this time around could easier have great aerial coverage and an even more significant tornado threat.

April 7th: (Tuesday): A marginal slight risk event across the Southeast with just one tornado report.
Differences: The evolution diverges greater and there are not many similarities between 4/7/2005 and this upcoming Tuesday, which looks more impressive at this point than 2005.

 

The Saturday-Tuesday setup has greater moisture transport, especially with northward extent. Combine that with stronger kinematic support and I think the overall amount of reports we have for each day coming up could be potentially higher and placed further north. I am just a little wary about Saturday perhaps being underwhelming. Although the timing is slightly faster here, the 12z 4km NAM (FWIW) had virtually nothing on the dryline per forecast reflectivity.

(4/4-4/7/2005 had a total of 455 severe reports and 56 tornado reports)

 

Here's a look at matchups for Sunday and Tuesday between the two:
post-533-0-18268000-1398369680_thumb.png
post-533-0-87857300-1398369748_thumb.png

 

Edited for more clarity on the differences of the matchups.

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Quincy

Quincy

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Posted

Those two setups for the SE really don't look anything alike, just saying.

That's why I posted the images, the similarities diverge with time. I was trying to put the whole sequence into perspective to show why this setup is more impressive for each of those days. (Potentially especially Tuesday if some of the newer guidance is correct)

 

It's going to be awfully hard to find a four day "event" that matches up super close every single day. I edited the prior post for more clarity.

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Chinook

Chinook

Posted
Posted

Keep in mind all models are also breaking out dryline convection in between 00z-03z still also. I still like Saturday's potential from a chasing perspective. Rozel wasn't much different. Dews were higher but so were temps. If the GFS is right there will also be more upper level support.

Sent from my LG-LS980

The 12z NAM (reflectivity image) shows that all the precip is all south of OKC that at 00z-03z, Saturday. The north area appears to be capped.

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ZackH

ZackH

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The 12z NAM (reflectivity image) shows that all the precip is all south of OKC that at 00z-03z, Saturday. The north area appears to be capped.

 

Sorry, I should have been more specific.  Previous runs of the NAM had been showing precip breaking out.  And I'm personally not following the NAM at this stage.  Its the clear outlier and while the GFS is overdoing dews... the NAM is probably underestimating them slightly.  I also don't think the 700mb temps are realistic on the NAM.

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OKpowdah

OKpowdah

Posted
Posted

The 12z NAM (reflectivity image) shows that all the precip is all south of OKC that at 00z-03z, Saturday. The north area appears to be capped.

 

So Jake (locoako) and I were talking about that this morning. The NAM uses the BMJ convective scheme, which activates when CAPE > 0, and triggers deep convection (and precip) when the reference profile produces net warming and drying of the column. So the BMJ scheme doesn't directly care about capping, or forcing at all.

 

From KS northward, the mid levels are relatively dry which is why the NAM doesn't produce any precip there. It's also interesting to note, because as a result there's less latent heating downstream of the trough, thus lower heights, which is why the NAM progresses the trough to the east a little faster than the rest of the guidance.

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LocoAko

LocoAko

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Posted

So Jake (locoako) and I were talking about that this morning. The NAM uses the BMJ convective scheme, which activates when CAPE > 0, and triggers deep convection (and precip) when the reference profile produces net warming and drying of the column. So the BMJ scheme doesn't directly care about capping, or forcing at all.

 

From KS northward, the mid levels are relatively dry which is why the NAM doesn't produce any precip there. It's also interesting to note, because as a result there's less latent heating downstream of the trough, thus lower heights, which is why the NAM progresses the trough to the east a little faster than the rest of the guidance.

 

Yep -- good stuff and a classic example. It really is the presence of that EML (which produces a cap, but the temperature inversion itself is not responsible for the lack of convective-scheme activation, it is the dry air associated with the EML) that limits the precip breaking out. This conference abstract by John Kain actually discusses the opposite situation, in which the scheme activated erronenously due to moisture advection in the mid-levels, destroying the EML and eliminating CIN (https://ams.confex.com/ams/pdfpapers/23318.pdf-- section 3.2.2)

 

tl;dr: Don't trust the explicit NAM convective precipitation in situations like this. 

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OKpowdah

OKpowdah

Posted
Posted

Yep -- good stuff and a classic example. It really is the presence of that EML (which produces a cap, but the temperature inversion itself is not responsible for the lack of convective-scheme activation, it is the dry air associated with the EML) that limits the precip breaking out. This conference abstract by John Kain actually discusses the opposite situation, in which the scheme activated erronenously due to moisture advection in the mid-levels, destroying the EML and eliminating CIN (https://ams.confex.com/ams/pdfpapers/23318.pdf-- section 3.2.2)

 

tl;dr: Don't trust the explicit NAM convective precipitation in situations like this. 

 

tl;dr: Don't trust the NAM synoptic forecast in convective situations like this.

 

tl;dr: Don't trust the NAM beyond 48 hours.

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ZackH

ZackH

Posted
Posted

What am I missing about the dryline around Saturday evening that makes it look bad?  From what I can see, it seems like a pretty good setup near the Texas Oklahoma border?

 

I believe its been discussed pretty exhaustively.

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Radtechwxman

Radtechwxman

Posted
Posted

For giggles the 18Z 4-KM NAM develops discrete storms by 03Z Sunday near Chickasha, OK and moves them right up I-44 into OKC. As so many have said before me don't trust the NAM outside 48 hours (maybe 36 if it's really on kool-aid). 

just was looking at that. man if that were to happen that would be a scary situation. highly unstable and highly sheared environment. storms would be firing on the nose of the jet and on the edge of the highest moisture returning north. boundary layer should stay pretty coupled to. but like you said, cant trust nam this far out. but if it keeps showing it watch out

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NTXYankee

NTXYankee

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Posted

Well I am going to try and remain optimistic about the system and hang on to the hope that the dryline will remain west of I-35 here in north texas Sunday and not blow on through. After all it was supposed to do the same on April 4th and then became stationary just 1 or two counties west of DFW, which made all the difference.

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brettjrob

brettjrob

Posted
Posted

FWIW, 00Z NAM digs the trough a little more, keeping the support further behind the thermodynamics.

 

Yeah. Certainly a negative trend, and it's inside of 48 hrs now. Really starting to get the feeling that choosing the correct storm in a string of pearls across NE/N KS between 18-22z Sunday will determine whether a chaser has any real success this weekend. At least, that's becoming the most probable scenario. Saturday is likely to be one of those very frustrating exercises in knowing a daytime cap bust is more likely than not, but "having" to go out anyway.

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