Severe WX Severe Weather Event April 13-14, 2019 (4 Viewers)


KoD

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We're less than a week away now and guidance points to an event with severe potential. There's a lot of details that need to be sorted out as some operational runs are depicting scenarios less favorable than it's ensembles suggest. We can detail the progress here as the event moves closer and discuss our thoughts on this potential period for severe weather.
 

Taylor Campbell

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The GFS has noticeably trended towards a much more dangerous situation Saturday-Sunday.
 

Fred Gossage

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GFS, Canadian, GFS ensembles, ICON, even the FV3 have all shifted back northwest with the surface low track for late Saturday night into Sunday. FV3 is a feedback contaminated mess, but even it has shifted from a surface low track out of south central MS into central AL to one that tracks from TN/MS/AL to northeast TN. The others track something similar to Shreveport to Memphis to Louisville or just south.
 

akt1985

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I was originally going to go to Ruby Falls for my birthday on Sunday. Now that might not happen. What is the weather looking like Saturday afternoon/evening for Huntsville and Chattanooga? Should I try going Saturday or choose another weekend?
 

Fred Gossage

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I was originally going to go to Ruby Falls for my birthday on Sunday. Now that might not happen. What is the weather looking like Saturday afternoon/evening for Huntsville and Chattanooga? Should I try going Saturday or choose another weekend?
That's going to be tricky with warm frontal positioning and how that may mean some scattered showers and storms Saturday. However, I don't think Alabama is looking at anything severe until some time after midnight predawn Sunday.
 

Fred Gossage

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I can already tell the 6Z GFS is suffering from feedback and is causing the model to focus on that for the surface low placement. It magically jumps from southwest of Tuscaloosa, due northward to just west of Nashville, between 6z-12z Sunday. The GFS and FV3 were also a little weaker with the wave when it was out west than the 00Z runs.

Meanwhile, here were the individual members of the 00Z GFS ensembles:

https://www.tropicaltidbits.com/analysis/models/gfs-ens/2019040900/gfs-ememb_lowlocs_us_23.png

I'll take my chances with ensembles...
 

Fred Gossage

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Morning AFD snippets:

HUN:
Consensus guidance from the global models suggests that the
deepening surface low associated with the mid-level wave will lift
further northeastward into the lower OH Valley by 12Z Sunday and into
IN/OH by 00Z Monday. Conditions appear quite favorable for the
development of an intense QLCS along a surface trough/Pacific cold
front extending southward from the low late Saturday night, based on
orientation of bulk shear vectors w.r.t to the low-level boundary.
This system is expected to affect the local area in the 06-18Z
timeframe on Sunday, and has the potential to be a rather significant
and high-impact severe weather event for the TN Valley, as dewpoints
could rise well into the mid (perhaps upper) 60s beneath a 50-60
knot low-level jet. These parameters should easily support a higher-
end risk both damaging winds and tornadoes.

BMX:
The front will begin to lift back northward as a warm front on
Saturday ahead of another potent shortwave trough moving into the
Southern Plains, resulting in more potential for showers and
thunderstorms, with some stronger activity possible depending on
where the warm front is. This shortwave trough and associated cold
front will continue to move towards the area Saturday night into
Sunday. The overall synoptic setup has been very consistent for the
past 3-4 days for this potential severe weather event though some
model differences and timing differences remain. The latest trends
in the guidance are a bit quicker suggesting the threat could begin
during the overnight hours Saturday night and continuing into
Sunday. A deepening surface low lifting northeastward from Texas to
the Ohio Valley, mid to upper 60s dew points, presence of an EML,
and 40-50 kt southerlies at 850mb veering to 60-70kt southwesterlies
at 500mb are all supportive of a severe threat. Confidence in the
magnitude of the severe threat is somewhat low as the faster timing
does prevent more significant instability from developing, and
details such as convective mode and evolution of upstream convection
will certainly play a role. Still, expect continued fluctuations
in timing the next couple days and some runs have been slower and
more significant. Confidence is high enough to add a tornado
threat to the HWO, with further refinements likely in the coming
days.
 

Fred Gossage

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Looking at things carefully, despite feedback issues, the 6Z GFS is actually further north with the surface low at 12Z Sunday than the 00Z run was...

EDIT: It's also 5mb deeper...
 

Kory

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Wow a day 6 outlook already.

This also looks to be converging on a nocturnal threat for a lot of the Deep South (some guidance still keeps it during the day Sunday). That will NOT hamper the threat whatsoever. A very moisture rich and unstable atmosphere will be in place due to Thursday and Friday's system setting up return flow from the Deep Tropics. Evolution of the trough and placement of the SLP will be more important than timing.
 
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Canton, GA
Wow a day 6 outlook already.

This also looks to be converging on a nocturnal threat for a lot of the Deep South (some guidance still keeps it during the day Sunday). That will NOT hamper the threat whatsoever. A very moisture rich and unstable atmosphere will be in place due to Thursday and Friday's system setting up return flow from the Deep Tropics. Evolution of the trough and placement of the SLP will be more important than timing.
I was just looking at this as well. The Thursday system really primes the pump for the Sunday event.
 
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SPC has a 15% area to the west on Saturday 4/13, so that date should probably be added to the thread title.
Good note... each model run slowly positions the slp further north slightly west... trends keep up... southern Tennessee could come into play as well... especially a nice triple point factor edit .. it be a late Saturday nite threat for Tennessee ... least southern portions if trends hold...
 

NWMSGuy

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Senatobia, MS
Good note... each model run slowly positions the slp further north slightly west... trends keep up... southern Tennessee could come into play as well... especially a nice triple point factor edit .. it be a late Saturday nite threat for Tennessee ... least southern portions if trends hold...
Yeah, I’m still watching to see how much northwest Ms comes into play for this. Guess it’ll all depend on eventual low placement.
 

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