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April 12 Severe Event


joshwx2003
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2 minutes ago, jpeters3 said:

FWIW, 18 UTC NAM nest is a similar story.  Warm sector is devoid of convection closer to the cold front, and a bunch of junkvection further east....

 

Interested to see what CAMs do tomorrow.

What if I told you there were insane parameters in place, but no discrete supercells came? Would be something if things actually play out this way.

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7 minutes ago, Upper Level LOL said:

Good thread by good follow Tony Lyza on questions about the latest NAM run not initiating isolated supercellular convection. The start of the thread is here:

 

 

Goes back to what the Birmingham NWS Met posted earlier as well. 

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The afternoon AFDs and HWOs from JAN, HUN, BMX, and FFC are pretty bleak and highlighting long track strong tornadoes and other attendant hazards. Including what could be a flash flood event in addition to the rest of the severe. Chasing would be almost impossible given projected storm motion speeds. Would be more of a storm intercept situation. 

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One thing to take note of with this event is that the big 3 global models are all robust with thermodynamic and kinematic environment even with the low levels.

4 consecutive SREF runs show a 90 contour surrounded by an expansive 75 contour on the tornado ingredients product even though the event is more than 48 hours away.

CIPS analog guidance has 3 high risk days in the list including 2007-03-01, 2010-04-24,  and yes 2011-04-27 is there too.

 

 

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1 hour ago, Quincy said:

At first it was the global models shifting west and the NAM lagging behind. Maybe it’s just now catching up. 

The potential outbreak area is now much bigger than it was a couple days ago due to the west trend.   TX all the way to VA could potentially see Tornados from this. Even if most of the main areas is a bust there's still plenty of potential around the edges .

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Almost impossible not to imagine numerous discrete/semi-discrete supercells in the open warm sector on Sunday across Mississippi and Alabama with a 140-170kt 250mb jet core nosing in between 18-21z with 70 degree dewpoints at the surface.

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Hard to get a much better signal in the QPF fields of a global model for supercells than this from the 12z Euro... Perhaps the more interesting part is that it maintains QPF streaks like those below WELL into the night. 

qpf_006h.us_se.png

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I'm in Birmingham this week and next for work, not a big SVR guy,  prefer heavy snow, but somewhat concerned and at he same time a little pumped for what may be my 2nd time ever in a Day 1 High risk.  The Boran model posted earlier is a private model from my understanding, based on the WRF and around a 2km res through 60hrs.  The precip plots from the ECMWF strongly indicates discrete and long tracked cells. 

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00z NAM continued the slower, westward trend. Continues to depict a high-end environment across eastern Texas, all of Louisiana, southern/eastern Arkansas, all of Mississippi, southern Tennessee, and western Alabama. QPF/vertical velocity fields appear to show several rounds of supercells across the warm sector in a high-end parameter space. 

Appears to keep stuff cellular well into the night, much like the Euro, which is very concerning.

Interested to see what the 00z hi-res CAMs will have to say given that 7pm Sunday will be the last frame of their runs; what they end up showing will likely determine if we see a 06z Day 2 High Risk or not.

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Just now, jpeters3 said:

NAM nest remains stubbornly devoid of convection through much of the warm sector.  However, there do appear more discrete cells close to the triple point than in previous runs.

Would that clearing in MS between 21 and 00z be where discrete cells form? Maybe it's just not picking it up, it's happened before.

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3 minutes ago, jpeters3 said:

NAM nest remains stubbornly devoid of convection through much of the warm sector.  However, there do appear more discrete cells close to the triple point than in previous runs.

Seems to show a lot of junkvection/blobs of precip especially across Mississippi through early afternoon. Which would seem to me to be a huge damper on any higher-end threat. NAM NEST shows significant recovery beyond that junk it’s showing, but I’m not sure I buy THAT much atmospheric recovery happening, especially that quickly.

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Showing quite a bit of UH swaths over northern AL and into TN Sunday night though... Even if the daytime warm sector doesn't go of (and i'm not sold on that solution yet), it seems like there will be a substantial overnight event further east and north

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Yea 3km nam goes to show you a possible scenario if the warm sector doesn't clear quickly. A messy storm mode and not as high end threat. 12km nam on the other hand really lifts morning convection quickly north and has confluent bands of supercells. I think that was similar to the euro evolution. Really this comes down to morning convection and warm sector quality. Even if the lower end solutions pan out, the threat for significant tornadoes is still there given the wind fields. That Baron 3k run would be a worse case scenario for the South. If I were SPC I would hold off on high risk till day of to see how morning storms evolve. 

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00z CAMs were a mixed bag of results... Here is a run down, with some of my own thoughts on what each solution would result in.

HRW WRF-NSSL

Storms fire early in Eastern Texas, partially associated with a long-lived complex, they continue east-northeastward over the threat are with a mixed bag of storm modes, numerous UH tracks associated with this initially activity as it traverses Louisiana and Mississippi. Numerous other supercells fire in the main threat area. This solution likely yields a tornado outbreak of some extent.

HRW NMMB

Storms fire early in Eastern Texas, traverse Louisiana and into the main threat area... WAA activity explodes across the warm sector, still some hints of severe supercells embedded within this activity, but overall mutes most of the threat across Mississippi/Alabama... Meanwhile numerous discrete cells pop across Arkansas, possibly yielding a more localized tornado outbreak there. In relation to the WAA activity, from my own experience of using the NMMB, it does seem to frequently overconvect.

HRW WRF-ARW

Probably the scariest of the bunch... Storms fire early in Eastern Texas and remain mostly discrete/semi-discrete as they scream east-northeastward, numerous other discrete supercells fire in the open warm sector across large parts of Louisiana, Arkansas, Mississippi, and Alabama. This solution definitely produces a big-time tornado outbreak.

NAM NEST

Similar to every other solution, storms fire very early in the period over Eastern Texas and traverse Louisiana, essentially becoming a big blob by the time they reach Mississippi. Throughout the afternoon WAA convection is persistent across Mississippi and Alabama, with the chance for embedded supercells. By late afternoon several supercells are firing, embedded within clusters, in Arkansas with other cells trying to get going further down the front and in the open warm sector in Mississippi. Sunday night features what would likely be a dangerous QLCS over Tennessee. Unsure what this type of scenario would result in, but best guess is several tornadoes, and a ton of severe wind reports.

 

Imagine SPC will stick with a MDT risk for the 06z Day 2 SWO. 00z CAMs didn't do much to help squash the uncertainties that have been spoken about at length on twitter, this board, etc... If SPC takes credence in the idea of WAA convection persisting in the warm sector, we certainly will not get a high risk in a couple hours... If they do not put much faith in that solution, then we would probably see a high risk given the preponderance of evidence from every other model.

 

 

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I had to respectfully disagree with James Spann when he made the following post late yesterday afternoon:

 

Quote

have received many messages today from people asking "will Sunday be like April 27, 2011?". Long time readers know my response...

Bad question. The answer is no; it doesn't show up in any analog; those type events happen once every 40 years or so. Every severe weather threat needs to be taken seriously; if there is only one tornado in the entire state it becomes YOUR April 27 if it comes down your street.

Using the excellent CIPS analogs site, the top two analogs for Sunday are...

*March 1, 2007. This event did produce one strong/violent tornado that moved through Enterprise, in South Alabama, killing 9 people, including 8 at Enterprise High School

*April 24, 2010. On this day 8 tornadoes touched down across Central Alabama, including one EF-3 that hit Parrish in Walker County.

But, every severe weather event is different, and just understand all of Alabama has a significant threat Sunday afternoon and Sunday night. No need to be overly anxious, just be prepared and we will get through it together.

And to that, I'd say "Bad answer".

 

I responded with the following:

Quote

I respectfully disagree with some aspects of this post. April 27th, 2011, *has* shown up as an analog to this upcoming event. That doesn't mean the outcome will be the same, but the big atmospheric markers are pegged nearly off the charts in MS, just as they were in MS/AL on April 27, 2011.

Also, violent outbreaks don't know when the last outbreak happened. James Spann has said on numerous occasions something along the lines of "Outbreaks like this occur once every 40 years" which is just... well... nonsense. Sure, the last 3 horrible outbreaks were in 1932, 1973, and 2011. But the next "40 year outbreak" could come any time. The atmosphere is not operating on a calendar. We need thousands of years of data to really know how often these types of outbreaks can be expected to occur. Perhaps over the long run we expect to see an outbreak like this every 5 or every 10 years and we have been exceedingly lucky over the last century. Or perhaps these events "should" strike more like once ever 150 years and we have been very unlucky in "recent" memory. Or perhaps we will average about 1 outbreak of April 27th scale every 40 years.

Regardless, giving people the idea that this won't be as bad because it's only been 9 years since the last "40 year outbreak" has to make anyone who knows anything about data and statistics a little sick.

Thoughts?

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