Severe WX Severe Weather Threat April 27-30, 2021 (2 Viewers)

TH2002

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A large 15% risk area has been featured in the D4-8 outlook since D7 with the SPC mentioning a dryline supercell setup. Windy models are in good agreement that at least a few supercells will form along this dryline, primarly in the area stretching from west central TX to central OK, though some models have shown cells forming as far north as the Wichita, KS area. All hazards will be possible, including tornadoes. (SPC) Severe storms are likely to form on the 27th and persist through the 29th before they begin to weaken around the 30th.
 
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Tuesday evening has been within NAM range for a couple of runs now and it doesn't look too impressive...just a narrow axis of instability on the eastern fringe of SPC's outlined area. Actually, 12Z run just came in with a big increase in instability (although the east-west axis is still fairly narrow) but suggests most of it will remain capped. Greatest threat might end up being roughly in the same area where it was on Friday, although right now wind profiles don't look so hot.

Edit: 3K NAM is also within range of Tuesday evening as of this morning at 12Z, and manages to be even less impressive than its big brother.
 

TH2002

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I'm sure the storms are supposed to merely initiate on the 27th with most of the activity going on on the 28th. Any models besides Windy that have the 28th in range?
 

TH2002

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The D2 outlook has been updated with two 5% tornado probability zones and SIG SEVERE hail parameters roughly outlining the 5% tornado probabilites.
 
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On a somewhat related note: preliminary LSRs are below average for the month to date. When is the last time this has happened following a moderate wintertime Niña episode? A below-average April following a robust Niña seems almost shocking, even as a onetime occurrence. Moderate to strong Niñas typically guarantee an active April or at least May. Yet even weak tornadoes have proven harder to come by than usual this April. Seeing constant reversions to split flow regardless of ENSO state is certainly intriguing.
 
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On a somewhat related note: preliminary LSRs are below average for the month to date. When is the last time this has happened following a moderate wintertime Niña episode? A below-average April following a robust Niña seems almost shocking, even as a onetime occurrence. Moderate to strong Niñas typically guarantee an active April or at least May. Yet even weak tornadoes have proven harder to come by than usual this April. Seeing constant reversions to split flow regardless of ENSO state is certainly intriguing.

Maddening is the word I'd use.
 

pohnpei

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On a somewhat related note: preliminary LSRs are below average for the month to date. When is the last time this has happened following a moderate wintertime Niña episode? A below-average April following a robust Niña seems almost shocking, even as a onetime occurrence. Moderate to strong Niñas typically guarantee an active April or at least May. Yet even weak tornadoes have proven harder to come by than usual this April. Seeing constant reversions to split flow regardless of ENSO state is certainly intriguing.
Yes, with only 47 confirmed tornados this month. This April very likely end up as one of the most inactive April in modern history. It is still hard to predict whether May or June would follow last year's step.
 

warneagle

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Definitely wouldn't have expected 47(!) tornadoes through 26 days of April after having two fairly substantial events in the space of about a week in late March.
 

andyhb

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...or the active pattern happened in the second half of March this year instead of April...
 
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...or the active pattern happened in the second half of March this year instead of April...

I think more to the crux of the issue, though is the tendency for each spring to have a brief window for an "active pattern" (which more often than not skips over the Plains/Midwest and hammers Dixie) and be otherwise near-totally (as in, flirting with record-low activity) dead.

We'll see what happens with 2021 going forward. I remember some pretty frustrated posts from you on ST and American Wx last year regarding the abysmal state of the season in May and June, and I shared that frustration. Last Friday was a nice score for you (congrats btw) but this spring has been dead quiet in the upper Midwest so far, and there are no strong signs of that changing anytime soon. Maybe those long-range climate models you were posting about in February were right, after all.
 

JayF

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Kudos to @JayF for running our online memorial this year on Twitter. He started organizing and executing the plan over a month ago. Thanks Jay!

It was my humbling pleasure. To read about each one of these individuals and their families is very humbling. I did go through each one and read what al.com had written about each one and verified the links were correct. For those who didn't have an age or a hometown listed, I tried to find them and did find some. I think only one was I not able to find an age for.

Our thoughts and prayers still go out to these families as we remember the day that was April 27th, 2011.
 
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It was my humbling pleasure. To read about each one of these individuals and their families is very humbling. I did go through each one and read what al.com had written about each one and verified the links were correct. For those who didn't have an age or a hometown listed, I tried to find them and did find some. I think only one was I not able to find an age for.

Our thoughts and prayers still go out to these families as we remember the day that was April 27th, 2011.

This is the thread for this year's severe weather event.
 

TH2002

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The biggest potential for supercells now apears to be in the Marginal Risk area for tomorrow before a QLCS forms early in the morning of the 29th.
 

TH2002

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If we do see some action in the next few days, it will most likely be the result of a high shear low CAPE environment similar to 3/2/2020.
 

Austin Dawg

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San Antonio/Austin sounds like they are worried about our next two days but not confident enough to raise the alarm just yet. It's a lengthy discussion so I will pick a couple of spots. Linked if you want to read it. Definitely looks like a flash flood event which we have a lot in May.

Discussion

Instability (and PWATS, which will become more important to monitor
as we head into the long term) will only continue to increase on
Wednesday as S/SE BL flow continues and sunshine again looks
possible during the day especially out west. Additional severe
weather will be possible as the deep trough draws nearer and a cold
front approaches right at the end of the short term. This round of
storms is likely to develop in Mexico in the afternoon and impact
our western counties after 20Z, potentially reaching the Hill
Country before 00Z Thur as well. Again, large to very large hail and
damaging winds will be possible. Probably looking at a slightly
better tornado threat out west late Wednesday compared to tonight as
the cap finally erodes away completely and low level SRH remains
elevated. Locally heavy rainfall cannot be ruled out Wednesday
afternoon as well. The Coastal Plains will likely miss out on all of
the activity over the next 36 hours but most of the rest of the area
will see at least slight chances for some much needed rainfall.

Initially the storms are likely to be supercellular through the
southern Edwards Plateau and Rio Grande late Wednesday afternoon and
early Wednesday evening, then congealing into clusters and an
eventual broken line through the Hill Country and I-35 corridor.
Parameters are favorable for the discrete storms out west in the
early evening to be capable of producing all severe hazards,
including very large hail and isolated tornadoes. SPC has introduced
a Day 2 Slight Risk along and west of I-35, including a hatched area
for 2"+ diameter hail through the Rio Grande, southern Edwards
Plateau, and western Hill Country.
 

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