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Severe Weather Threat 4/27-4/28

kcyalater said:
i know it’s easy to dunk on the SPC, but there’s no world that exists in which you don’t make the same forecast 10/10 times.

the parameter space yesterday was ELITE, and you have to look at the ceiling for human impact, not the floor.

“people will stop paying attention to warnings.” that’s on them. it’s also a bad idea to play russian roulette, even though the vast majority of pulls have no round in the chamber. until they do.

it’s all about what could be, not what’s going to be.
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Not dunking on the SPC at all.
Im probably going to be off base with this but I can’t help but think that they really didn’t want to issue that moderate risk and were pressured into doing so by the model outputs. It’s obvious in their wording that they were never very confident.

Sure, the environment looked “elite” at face value but one look at the bulk of the forcing mechanism being too far north, stout inversion layer in the OWS, directional LLshear, widespread convective inhibition, and meager mid level shear velocities, it was staring us in the face the event would b#st.
It’s particularly the directional LLshear that completely negated the ability of supercells to develop any efficient inflow regions which caused them to either become outflow dominant or stay anemic. The meager mid level shear is the reason why all of the supercells yesterday looked deformed with shortened precip shields.
High parameters mean nothing when all of the limiting factors above are present.

I knew these were flys in the ointment leading to the event, but it didn’t become apparent to me that these would likely screw over the tornado threat until 3pm.
Looking at the undertones of the SPC forecasts, they were more than aware of this, obviously though they base their forecast off of what the modeled parameters and storms modes are, so they really didn’t have a choice but to issue the moderate.

Even though everyone was looking at the MCS system as the failure mode, apparently, it actually was the one thing that could’ve turned everything around with the outflow boundary it laid out, but ironically that boundary quickly got destroyed by the rapid air mass recovery so the supercells in the area had nothing to latch onto to counter act the poor streamwiseness.
 
ColdFront said:
Most likely a Combination of trough geometry, forcing and jet placement, capping, and dry air. Everytime there’s a bu$t and there’s a wildfire somewhere, that smoke theory gets shoehorned as the reason. I don’t buy it at all. Wildfire smoke has been present for many events, as you noted, 4/27 and 3/14. It seems like the 5/20/2019 bu$t really gave that “hypothesis” legs. I still haven’t seen any definitive literature that wildfire smoke plays any role in bu$ting weather events.
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I agree with you that given it's had opposite impacts in 4/27 vs. 5/20/19, there probably needs to be more research done into it before we really understand how it impacts (or doesn't!) an outbreak. IMO the jet was the failure mode here - it was significantly displaced from where the models predicted it to be, and as such the storms never had what they needed to truly get going in a juiced warm sector.
 
Wildfire smoke likely has some impact, but it entirely depends on when the wildfires actually initiate. And even if it is impacting the parameter space, like others have just stated, it’s not a guarantee that it tempers the threat - it could increase it, decrease it, may do nothing at all, maybe a mix of both… it’s really hard to say without a lot of researchers looking into it. I think it’s a reasonable hypothesis but it will remain a hypothesis until more work is done with it.

That being said, this event was very unlikely to be wildfire smoke that resulted in the outcome it did, and it was simply the trough geometry and location, 100%.
 
bckhd2 said:
I agree with you that given it's had opposite impacts in 4/27 vs. 5/20/19, there probably needs to be more research done into it before we really understand how it impacts (or doesn't!) an outbreak. IMO the jet was the failure mode here - it was significantly displaced from where the models predicted it to be, and as such the storms never had what they needed to truly get going in a juiced warm sector.
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I really don’t see how it simply was just the jet stream placement, which definitely wasn’t way off of what models predicted. It very much was ripping right over the moderate risk area.
It was the southern mode that was jet deprived, that’s where the models had made the error in terms of timing.
 
Yesterday wasn't a day with particularly major failure modes that were evident. Aside from one strong tornado in Arkansas, this didn't verify a significant day at much. And there will be the typical backlash on the SPC for this, but this really wasn't a setup that looked evident until later on with the more stout EML via ACARS soundings. Models didn't handle yesterday well and still initiated despite obvious 700mb temp issues, of course, this was due t models underselling this potential. It became evident your main regime of discrete cells in S AR was the main event.

Take it as a learning opportunity. I could've certainly been a bit more cautious with my wording, and maybe got ahead of myself regarding tornado intensity yesterday. It's funny this was the one setup people decided not to call off, but in the end, it still ended up severely underperforming unlike other events where people called off early and it ended up performing. Another late April event that severely underperformed nearly a day to the 4/28/25 bust. Stout EML played a huge part into this, and something was off regarding the S MO storms.
 
WW being considered across parts of MS/AL due to ongoing convection running across the middle of MS/AL/GA. Could also set up boundaries for later activity.
Mesoscale Discussion 0594
NWS Storm Prediction Center Norman OK
1050 AM CDT Tue Apr 28 2026

Areas affected...central parts of Mississippi and Alabama

Concerning...Severe potential...Watch possible

Valid 281550Z - 281745Z

Probability of Watch Issuance...40 percent

SUMMARY...The potential for damaging winds and large hail is
expected to increase across the area this afternoon. Convective
trends are being monitored for a possible Severe Thunderstorm Watch.

DISCUSSION...Thunderstorms have persisted through much of the
morning across the discussion area with that activity being driven
by modest low-level warm advection occurring along and to the north
of an outflow boundary extending from around Greenwood, MS to north
of Selma and Montgomery in Alabama. The 12z JAN sounding revealed
the eastern edge of the elevated-mixed layer has spread east into
the lower MS Valley, which when coupled with a moist boundary layer
is resulting in estimated MLCAPE of 2000-2500 J/kg as of 15z.

The 12z CAMs offer various scenarios with respect specific details
on thunderstorm evolution today. Some solutions suggest in situ
storm intensification/coalescence into smaller, forward propagating
complexes, while others indicate the primary severe weather threat
being associated with a complex of storms arriving from the ArkLaTex
later today. Regardless, the general notion is for a gradual
increase in surface-based storm coverage and intensity in the
vicinity of the outflow boundary this afternoon. Relatively strong,
mid/upper-level flow evident in the 12z JAN/BMX soundings will
support the potential for supercells and bowing structures capable
of large hail and damaging wind gusts. The tornado threat is
somewhat conditional and likely tied to any storms that can
favorably interact with the outflow boundary.

..Mead/Guyer.. 04/28/2026
Click to expand...

Storm Prediction Center Mesoscale Discussion 594

Severe weather, tornado, thunderstorm, fire weather, storm report, tornado watch, severe thunderstorm watch, mesoscale discussion, convective outlook products from the Storm Prediction Center.
www.spc.noaa.gov
 
CheeselandSkies said:
13Z outlook came out an hour early today.

1630Z outlook is 16 minutes late and counting.
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Looks like they are adding a small (likely hail-driven) moderate over the DFW area.

I can only imagine there was some animated in-house discussion about that, especially after yesterday.

@DanLarsen34 ninja'd me as I was typing.
 

..SOUTHERN PLAINS TO LOWER MISSISSIPPI VALLEY/SOUTHEAST

HAVE UPGRADED PORTIONS OF NORTH TEXAS TO A MODERATE RISK FOR WHAT IS
ANTICIPATED TO BE A SEMI-FOCUSED SUB-REGIONAL CORRIDOR OF SUPERCELLS
INCLUDING VERY LARGE HAIL POTENTIAL ALONG WITH SOME DAMAGING
WIND/TORNADO RISK CENTERED ON MID-AFTERNOON THROUGH
EARLY/MID-EVENING.
 
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