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andyhb

April 26th-30th, 2014 Major Tornado Outbreak

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Another intense vort max rotating around the base of the trough at 144, with secondary surface low development, Monday/Tuesday is going to be a bad deal if that happens.

 

Looks like a classic, major Dixie Alley setup between 144 and 168 judging by the surface low track and how the vort rotates right through that area.

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Glad to see a thread up on this. I am traveling today but read the outlook and was looking over model data early this morning.

This is an impressive system. The environment looks reasonably consistent amongst the models and it is a bit troublesome that OKC area could again get hammered.

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Top 3 CIPS analogs for 12z GFS at 108 hrs...

 

6z -> 5/4/03

6z -> 4/26/91

6z -> 5/8/03

 

Also 5/3/99 is there and a host of others.

 

SPC MARS for Sunday...

 

9LJdbHJ.png

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f144.gif

 

 

Just thought I'd post the 12z Euro. Looks like a lot of the same areas that got hit in the 2011 outbreak would get hit again on the 3rd anniversary.

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Top 3 CIPS analogs for 12z GFS at 108 hrs...

 

6z -> 5/4/03

6z -> 4/26/91

6z -> 5/8/03

 

Also 5/3/99 is there and a host of others.

 

SPC MARS for Sunday...

 

9LJdbHJ.png

 

1999 May 3rd-6th is close, but it was further west. Hard to find another setup with an amplifying ridge over Utah and a strong block north of the Great lakes.

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The 18Z GFS has taken more steps toward the ECMWF, showing a much deeper low late Saturday into Sunday. By 12Z Sunday, the track of the low has also shifted a bit farther south and east than on the 12Z run. However, occlusion starts by 00Z Sunday evening, which could negatively impact the winds near the dry line and cause veering. Also, deep-layer shear is less perpendicular to the dryline on this run. Off the dryline in wrn AR / swrn MO, conditions look much better for tornado potential. Overall, however, the best upper-level dynamics are shifting north of the best thermodynamics, and the model is showing less of a secondary low center over OK / KS Sunday evening. If this trend continues, then the tornado threat will be significantly hampered.

 

(Maybe I'm wrong about the occlusion, so feel free to correct me. I'm learning from the explanations--I have not yet taken introductory or higher-level courses in meteorology, but am interested in potentially exploring a career in atmospheric science.)

 

The latest GFS also shows a secondary low trying to develop as the vorticity maximum over the MS Valley rotates around the trough base. That could provide a spark for substantial low-level shear/enlarged hodograph given the potent thermodynamics in place over Dixie Alley. Movement still remains stubbornly faster than on the ECMWF.

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What are the thoughts on the apparent meager moisture the NAM is depicting? It has consistently underdone moisture all Spring but it is worlds apart from the GFS and Euro currently. Not really concerned as this range sucks for the NAM but it adds a bit of uncertainty.

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I think the only argument really needed is that it's the NAM lol.

 

Also it is way far south with the s/w that the Euro has in the OV.

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It looked to me like the 12z Euro sped up the system. Wundermap showed the euro with storms firing west of I-35 Saturday evening and pushing into the I-35 corridor around 03Z from north Texas up through Oklahoma. Sunday around 18Z or so it looks as though dryline is past the I-35 corridor and best chance is far eastern sections into Ozarks for storms. 18z GFS just seemed to follow suit.

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Also, deep-layer shear is less perpendicular to the dryline on this run. Off the dryline in wrn AR / swrn MO, conditions look much better for tornado potential.

 

You don't need deep layer shear vectors to be completely normal to the dryline/boundary for sustained supercells, even in the Plains. In fact the further east you go, it's more of an angle ~60˚ to the boundary that tends to result in longer lasting supercell modes.

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I am saving this for posterity, wow. So think of any significant Plains/vicinity outbreak over the past 25 years at roughly this time of year...it's probably on there.

 

http://www.eas.slu.edu/CIPS/ANALOG/stats.php?reg=SP&model=GFS212&fhr=F132&case=2014042212_SP_132

 

LOL. It's absolutely incredible that this isn't Photoshopped by a weenie. There are considerable large-scale differences between a lot of those top events, so the implication that this one is straddling the space between all of them only lends more confidence to a high-impact outcome.

 

post-972-0-01956000-1398220249_thumb.png

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What are the thoughts on the apparent meager moisture the NAM is depicting? It has consistently underdone moisture all Spring but it is worlds apart from the GFS and Euro currently. Not really concerned as this range sucks for the NAM but it adds a bit of uncertainty.

Sent from my LG-LS980

 

And that is going out the window with a swift kick in the ass... :P

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I wasn't ever saying the earlier NAM solution was realistic. I am definitely aware of how terrible it is in the later hours. I was simply playing a bit of Devils Advocate and was curious as to what others thought. I am obviously very happy to see the 00z results swinging more in line.

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Nice post.  Saturday has a ton of potential, but I'm somewhat hesitant at this point myself given that the GFS is the fastest out of all the models.  Timing's going to be a big factor.

 

Words of wisdom. GFS just caved massively on the slower timing, making Saturday look shaky at best. Yeah, just one run, but it's simply snapping to all the other guidance. Really a shame from a chaser's perspective.

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Not a huge fan of the 00z GFS, but it seems to be falling more in line with the ECMWF.  The forcing is now worrying me for Saturday and Sunday is pretty terrible for good terrain.

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The sfc wind field response to the p-falls in nrn OK on Saturday between 21-0z is beyond impressive, as is the moisture advection westward into both southwest OK and the PTT area after 0z. Reminded me of the Greensburg moisture surge that evening.

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Not a huge fan of the 00z GFS, but it seems to be falling more in line with the ECMWF. The forcing is now worrying me for Saturday and Sunday is pretty terrible for good terrain.

Good point but I am worried about impacts a bit. The gfs still seems to indicate a significant event over eastern Oklahoma. And while East of I35 poses chase challenges it is none the less impactful for those of us living here.

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Not a huge fan of the 00z GFS, but it seems to be falling more in line with the ECMWF.  The forcing is now worrying me for Saturday and Sunday is pretty terrible for good terrain.

 

This run is pretty devastating if you take it literally (which I'm not). The way I see it, all the problems it depicts stem from the downstream ridge pumping just a bit more, which itself is likely modulated by the pain-in-the-ass New England cyclone. The result is that the energy takes a more curved, meridional path as it traverses the Rockies, which a) delays its eastward progression long enough to make Saturday look much less certain, and b] ultimately leads to the "pinched off low" Sunday that would make things very messy, possibly hindering tornado potential substantially. Again, for any nitpickers out there, this is all taking the 00z GFS literally. I'll wait to panic until seeing the ECMWF, which has been head and shoulders above everything else so far this spring.

Guess it's a necessary reminder to some (including me) that as incredible as guidance looked today, little is certain, and the "floor" tornado-wise is still kind of low. As I've been looking at analogs today, the close proximity of downstream ridging is the one thing for this weekend that makes me wonder, especially with eastward extent (Sun/Mon)... if it weren't for that, this would be a slam-dunk outbreak scenario for someone. It could still well be an outbreak, and any of the three days could still well be big... but unfortunately, the pattern is just blocky enough that relatively small changes could have large practical impacts.

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This run is pretty devastating if you take it literally (which I'm not). The way I see it, all the problems it depicts stem from the downstream ridge pumping just a bit more, which itself is likely modulated by the pain-in-the-ass New England cyclone. The result is that the energy takes a more curved, meridional path as it traverses the Rockies, which a) delays its eastward progression long enough to make Saturday look much less certain, and b] ultimately leads to the "pinched off low" Sunday that would make things very messy, possibly hindering tornado potential substantially. Again, for any nitpickers out there, this is all taking the 00z GFS literally. I'll wait to panic until seeing the ECMWF, which has been head and shoulders above everything else so far this spring.

Guess it's a necessary reminder to some (including me) that as incredible as guidance looked today, little is certain, and the "floor" tornado-wise is still kind of low. As I've been looking at analogs today, the close proximity of downstream ridging is the one thing for this weekend that makes me wonder, especially with eastward extent (Sun/Mon)... if it weren't for that, this would be a slam-dunk outbreak scenario for someone. It could still well be an outbreak, and any of the three days could still well be big... but unfortunately, the pattern is just blocky enough that relatively small changes could have large practical impacts.

It's part that and I think it partly also the convective feedback issues this GFS run is having in wrn OK.  To me, the synoptic scale doesn't look too different from previous runs, but the conv feedback is really playing havoc with the upper-level wind fields.

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The Sunday low is ugly, ugly, ugly. I wouldn't call it a disaster though. Wrn OK & KS would still look decent on Saturday, maybe not as amazing as before but at least there's still something. Sunday might be out of the picture taking the run literally though.

 

The bad news is the Euro has trended towards a faster closing off of the low, which means messier Sunday, more occlusion, further east dryline. Not surprising to see the GFS fall into the Euro camp.

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The Sunday low is ugly, ugly, ugly. I wouldn't call it a disaster though. Wrn OK & KS would still look decent on Saturday, maybe not as amazing as before but at least there's still something. Sunday might be out of the picture taking the run literally though.

 

The bad news is the Euro has trended towards a faster closing off of the low, which means messier Sunday, more occlusion, further east dryline. Not surprising to see the GFS fall into the Euro camp.

The big days on the 12z Euro were definitely Saturday and Monday.  Ought to be interesting to see what the 00z Euro does.

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It's part that and I think it partly also the convective feedback issues this GFS run is having in wrn OK.  To me, the synoptic scale doesn't look too different from previous runs, but the conv feedback is really playing havoc with the upper-level wind fields.

 

That's a good observation. The feedback at 00z Sun from that convection is ridiculous.

 

Unfortunately, the 00z CMC is very similar, with a stacked low sitting over SW KS. The atmosphere is amazing; a wiggle in the downstream waveform takes us from the analog list above to that.

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That's a good observation. The feedback at 00z Sun from that convection is ridiculous.

 

Unfortunately, the 00z CMC is very similar, with a stacked low sitting over SW KS. The atmosphere is amazing; a wiggle in the downstream waveform takes us from the analog list above to that.

It looks to me like the conv feedback on this run really plays havoc in the whole evolution of this system.  The feedback initially appears Sat evening, which then causes height rises in the warm sector, amplifies the trough, makes flow more meridional in the warm sector, which leads to more upscale conv growth, and the process builds and repeats.  I'd be very wary, even if there is some CMC support, of using the 00z GFS.  I'd even go as far as to basically throw it out (at least for Sunday-Monday) if the Euro comes in like the wrecking ball that the 12z was.

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In addition to that, I think this trough needs to actually come onshore before some of these wild swings tighten up, as always

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It looks to me like the conv feedback on this run really plays havoc in the whole evolution of this system.  The feedback initially appears Sat evening, which then causes height rises in the warm sector, amplifies the trough, makes flow more meridional in the warm sector, which leads to more upscale conv growth, and the process builds and repeats.  I'd be very wary, even if there is some CMC support, of using the 00z GFS.  I'd even go as far as to basically throw it out (at least for Sunday-Monday) if the Euro comes in like the wrecking ball that the 12z was.

 

The trough is already notably slower by Friday night though. Vorticity within the trough is a little more strung out on the upstream side early on Friday, so the trough is at a little larger wavelength and thus moving slower. The timeline for vorticity collecting in the base of the trough is maybe like 6 hours slower,

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00z Euro through 72, the lead s/w that drops through the GL into the Northeast is weaker and further north than last night. Antecedent ridge axis through the Rockies appears further east as well.

 

And...Sunday looks messy and Monday lights up Dixie Alley.

 

Saturday still looks threatening as well, obviously given initiation.

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