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Severe WX April 12-15th, 2018 Severe Potential

rolltide_130 said:
Oh yeah I don't mean any disrespect to him at all, especially with all the health struggles that have been running through his family recently. I just found it somewhat of an interesting forecast on his part.
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Oh no, I didn't mean that. :) It's all good. Personally, I don't think any severe threat should be under-played because people are so complacent anyway, but that's just me. LOL
 
I think James Spann was tired this morning. He labeled this video April 11 2017.

 
JayF said:
I think James Spann was tired this morning. He labeled this video April 11 2017.

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That's today's date. I think the producers name the video based on the recorded date and not the outlook period.
 
KoD said:
That's today's date. I think the producers name the video based on the recorded date and not the outlook period.
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It's 2018 not 2017. I watch his videos daily.
 
amp1998 said:
James Spann's assessment for this weekend I think is good. Jason Simpson however is saying the GFS has been more consistent than the Euro in terms of dynamic support? Not sure why he believes the GFS over the Euro for Saturday. Jason is also dead set on convection over the Gulf Coast on Saturday.

James Spann's assessment: https://www.alabamawx.com/?p=157821

Jason Simpson's assessment: http://whnt.com/2018/04/11/stormy-setup-getting-ready-for-a-wet-stormy-weekend/
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To be honest, I don't see much difference between the Euro, NAM and GFS. The GFS is quickest and the NAM backs surface winds more, otherwise they look to be on the same page.
 
ARCC said:
To be honest, I don't see much difference between the Euro, NAM and GFS. The GFS is quickest and the NAM backs surface winds more, otherwise they look to be on the same page.
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EURO and the NAM are slower with the severe weather threat, which would bring a higher chance for severe storms on Saturday because it will give the atmosphere more time to destabilize and for the stronger dynamic support to catch up. The GFS would move everything into Alabama too soon potentially outrunning the better dynamic support and instability.
 
amp1998 said:
EURO and the NAM are slower with the severe weather threat, which would bring a higher chance for severe storms on Saturday because it will give the atmosphere more time to destabilize and for the stronger dynamic support to catch up. The GFS would move everything into Alabama too soon potentially outrunning the better dynamic support and instability.
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Not by much and it's really splitting hairs. The Euro is slower, but cape wise it's about the same as the GFS. The Euro has max capes before the squall line around 600-1000, the GFS about the same but about twelve hours faster and to no surprise the NAM is most bullish with 1000-1750 over a larger area.

Upper level wise they all are close except the GFS being faster with the whole system.
 
It's when that second vort max rounds the base of the initial occluded trough and the whole thing goes negative tilt, we'll see a secondary low pressure form. That will serve to really back the winds and ramp up the LLJ later Saturday. With the height falls associated with it, I wouldn't rule out some convection ahead of the main QLCS, which will probably be pretty rough.

Also of note, it appears the QLCS will slow down as it exits MS and enters AL as the whole trough is transitioning to a negative tilt. Probably a decent flooding threat as well where ever it slows down because these PWATs are 2-3 sigmas above normal.
 
Enhanced Risk now out for Saturday.
day3otlk_0730.gif
 
champal3003 said:
Enhanced Risk now out for Saturday.
day3otlk_0730.gif
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For a day 3 pretty impressive

From SPC

..Mid South/Tennessee Valley into the central Gulf Coast states...
Widespread showers and thunderstorms are forecast to be ongoing over
western fringes of the outlook area Saturday morning. The
associated cloud cover casts some uncertainty with respect to degree
of warm-sector destabilization which will be possible downstream.
Greatest CAPE will likely evolve from central Alabama south to the
central Gulf Coast, as southwest flow aloft should carry thicker
cloud debris across the Tennessee Valley region.

As the airmass destabilizes, expect reintensification of storms
near/ahead of the advancing front, with organization aided by strong
low- to mid-level flow likely to exceed 50 to 60 kt in the 850 to
500 mb layer over portions of the Alabama vicinity by late
afternoon. While somewhat unidirectional/southerly flow should
limit low-level shear to some degree, and roughly front-parallel
flow and linear frontal forcing suggests linear storm mode, damaging
winds can be expected with passage of the frontal storm band. Hail
-- and a tornado or two -- will also be possible, particularly with
southward extent. A gradual decrease in storm intensity/severe risk
should commence later in the evening, as convection reaches the
southern Appalachians and Florida Panhandle.



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One area to watch is right on the gulf coast. All models show the expected max in instability right there along with strong upper level divergence. These areas normally get nailed in these high amplitude neutral/negative tilt setups where messy storm mode doesn't matter as much due to the unhindered gulf moisture.
 
Outflow from the initial push of the QLCS will be key too. How far east does it make it before the second wave? That could clamp down on the threat for the Northern and Western portions of AL as indicated by some mesoscale guidance. Still quite far out for models to resolve this.
 
Starting to get a 4/15/11 feel from this system. The NAM is starting to shunt North AL out of the warm sector while setting the stage for a potential significant tornado outbreak further south.
 
Ironically, I'll be visiting my mom on the gulf coast this weekend. Was also doing so during Tropical Storm Cindy. Might apparently be decently close to the action!
 
rolltide_130 said:
Starting to get a 4/15/11 feel from this system. The NAM is starting to shunt North AL out of the warm sector while setting the stage for a potential significant tornado outbreak further south.
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I'm not so sure the storm mode would cooperate this time for something like that, but in terms of placement and the overall evolution of how the threat areas evolve, I'm starting to think this idea is 100% right. ALL of the CAMs are bringing the line into northwest Alabama before sunrise on Saturday, and while we shouldn't get too hung up on convective models and the exact evolution they depict, they do a much better job at handling cold pool propagation than models like the 12 km NAM or the Euro... which may STILL be right with the synoptic evolution, while the GFS might be the synoptic model that's right with the timing of the convection and actual impacts, but for the wrong reasons.
 
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