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Severe WX April 1-2 (overnight) Severe Weather Event

AJS said:
ClapWell, catching up on everything this morning. Got 1st place at my open water championship so that’s a win. But those models for Wednesday continue to show a potential significant severe weather outbreak. Definitely some high parameters in place and the NAM is certainly showing that
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Nice @AJS
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I’ve always found it helpful to consider what the potential floor and ceiling is when it comes to these kind of events.

I think that can help with conceptualizing and communicating the potential range of outcomes that are in play, including helping us identify when something COULD be especially high-end.

This event certainly has the look right now of an incredibly high-ceiling event.
 
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Sounding pulled from Warsaw IN at 5 PM eastern time Wednesday. I mean the kinematics in this are crazy. Not going to take a whole lot of CAPE to make tornadoes happen. This proves it. Over 430 0-1km of Helicity.

IWX agrees as well. From their AFD:

"Given background synoptic fields, instability magnitudes will
not have to be that strong to result in a potential outbreak of
severe weather for the Mid MS Valley, southern Great Lakes, and
Ohio River Valley with all modes of severe weather possible.
More on this event will be forthcoming in the days ahead.
Otherwise, after below normal temps early week, sharp warm/moist
advection will take temps/dew points above climo normals
heading into Wednesday. Frontal boundary associated with this
system may tend to stall across the Ohio River Valley late work
week which will make local area prone to additional rounds of
showers and possibly some thunder with any additional frontal
waves."
 
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UK_EF4 said:
The setup next Wednesday continues to look pretty high-end, its not hard to see why the experts at the SPC have delineated a very large 30% area with the mention of 'several tornadoes'.

Very strong, broad-based trough overlapping a very large warm sector. I tried to draw the 60F DP line in black over the 500mb chart, and you can clearly see how the mid-level speed max is impinging on the northern half of the warm sector. While fairly basic, that alone is a fairly strong signal for a widespread severe weather risk

View attachment 37720

The one thing that could be viewed as somewhat of a limiter is the fact the strongest synoptic scale forcing will be limited to the Upper Midwest and Great Lakes region, further north than the warm sector. In fact, most regions in the SPC 30% area see very small or even zero height falls throughout the forecast period, especially 21z-03z. This is likely to make initiation, especially from S IN into TN much more dependent on surface factors.

That being said, surface factors at the moment do seem to favor at least a scattered storm mode. Most model soundings suggest capping will be fairly minimal, and there also seems to be support for a confluence zone (rough position denoted with green dashed line) running from NE Arkansas up to wards IN/OH. This does seem to set the stage for dangerous event Wednesday afternoon/evening.

I don't make this comparison in terms of saying this event will be the same, whatsoever. However, 1974 had a similar situation in that height falls were fairly minimal through the southern portion of the risk area but mesoscale features led to the development of a couple convective bands. Read more in this paper here:

journals.ametsoc.org

Revisiting the 3â4 April 1974 Super Outbreak of Tornadoes

Abstract The Super Outbreak of tornadoes over the central and eastern United States on 3â4 April 1974 remains the most outstanding severe convective weather episode on record in the continental United States. The outbreak far surpassed previous and succeeding events in severity, longevity, and...
journals.ametsoc.org journals.ametsoc.org

To stress again, I am not in anyway comparing the events other than noting a lack of strong upper level forcing doesn't necessarily mean there wont be widespread severe. I am sure there are better examples than this, but I trust this forum is not as weenie as other places (cough wxtwitter) to take comparisons like this out of context anyway.

Either way, models should be watched closely next few days.
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I lived through that night of April 3rd in Northern Jefferson County. My grandparents farm was struck by a weaker tornado that night near Bear Creek, Al., NE of Guin. I remember the one lady in Guin, AL. who had her own weather station and by 3:00 P.M. I believe she said, had a Td (dewpoint) of 80F. The air was so thick that day and the constant surface winds were very strong all day. The sky to our north looking out the window towards Cullman was "greenish" at 8:00 ish P.M. at night.

Hard to say yet about this setup at this point of coarse.
 
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New IWX AFD for Wednesday:

"Between Monday night and Tuesday, a low pressure system forms east
of the Rockies and ejects northeastward toward the western Great
Lakes Tuesday night and Wednesday. With warm advection continuing
Tuesday night, a warm front is pushed northward, but is expected to
move through by the early afternoon setting up the area in the warm
sector for thunderstorms Wednesday. Of course, one issue with this
is that convection may get in here after midnight and before sunrise
and we'll see what that does to the eventual placement of the front.
A 40 kt low level jet was modeled for storms on Sunday, but an even
stronger 45 to 55 kt low level jet is being modeled for storms on
Wednesday. Dew points reattain 60 degrees and highs reach 70 degrees
especially south of US-6. It looks like there may be some
instability available, as long as that warm front is able to move
north through the area and this event occurs around peak heating. As
long as that's the case and with the shear and helicity values being
modeled, this could be a potent severe weather event with all
hazards on the table. Gusty synoptic winds outside of storms will
also be possible. Flooding could be a hazard with this event given
antecedent conditions of recent rainfall, but we'll need to see how
the basins fair and how much runoff can occur to bring rivers back
into action stage or below. Storm motions may be quick through the
area, but training of storms may become an issue with a tendency for
the front to slow down."
 
Some very strong values coming off the 12Z GEFS. One of a handful of times I can recall where mean SCP values rose into the 7-10 range at this time frame and it wasn't due to weight bias from Atmospheric Anti-Climax ensemble members. The potential for a pretty serious event is very clear here for the Mississippi River Valley up into the Ohio River Valley and Midwest.

Edit: Addendum, also a huge flooding threat here with this system and the subsequent systems that will more or less stall over the same regions.
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