Severe Weather Threat 4/27-4/28

[Justin Hindman]

All the storms are forming north of the boundary. Those should stay elevated, as we get any on the boundary or just south, look out

 

[DanLarsen34]

Surprised they didn't go with a PDS watch.

I was about to write the same thing. Even if they think the reasonable maximum intensity is EF-3, there's a reasonable likelihood that there will be more than a few of those within this watch to justify it being a PDS watch IMO. I also think a violent tornado or two on the table, which would ALSO justify a PDS.

If we are relegating PDS watches now to only high-risk days or CIG 3 intensity, I think that may be a mistake. I get that PDS has historically been used when they have high confidence in at least one violent tornado occuring, but I think this setup has that potential, right?

I also think we should have a discussion after this event regarding the discussion we saw a few days ago regarding the SPC really leaning on STP for the CIG level.

 

[UncleJuJu98]

W

Everytime I see it spotted out in the wild with one of these pics, It makes me think I'm looking at a horseshoe crab without a tail haha

 

[Brice W]

Today is probably the most complex severe weather setup we have had in a while - dare I say all year - which is troublesome when we are trying to differentiate between
what could be a high-end tornado outbreak and your more ordinary April event.

First things first, the overall synoptic is impressive with a large trough pushing through the Central US. Estimates on the translation speed vary but I would say are mostly above 40kts, the now well-known Chris Broyles' Omega value. The speed/vorticity maximum also appears to dig directly E after 00z (as opposed to moving off to the NE) which helps from a forcing point of view, and means the strong upper level flow is directly above the warm sector.

The second thing to note is that the tornado threat will be starting a bit earlier and further East than some may expect. Models suggest the axis of the current LLJ segment will be positioned from C IL down the Mississippi river. I think that the combination of WAA storms along what could be subtle confluence is likely to lead to the development of storms as early as 21/22z in a corridor from N MS (through W TN/KY, perhaps E AR) into S IL. The environment here will not be as favourable as areas further West, but HREF suggests still STP 2-4. As such I could see a couple tornadic supercells, with the risk for strong tornadoes (In terms of SPC outlooks this in my mind would be more in line with a CIG1 distribution).

In terms of the main MDT risk area - this is where major uncertainties lie. We have seen the current MCS continue to move East, leaving a remnant OFB which is oriented E-W across MO. This is now being modified North by the very strong low level flow and moisture advection. Even as the trailing thunderstorms decay, it seems very likely this boundary will be the focus for convective initiation. The environment along and just south of this boundary will be very potent, and a robust supercell would certainly have an intense tornado risk. That being said, given the orientation, it will be extremely easy for storms to grow upscale into clusters quickly, and any surface based updrafts to get cut off by outflow. A higher end tornado threat will depend on storms being to initiate just ahead of the boundary (as a few earlier HRRR runs showed) or develop an orientation relative to the other storms that allows it to ingest surface based parcels.

Later on, CAMS develop more storms along what seems to be a sort of cold front type feature. This feature is also pretty flow parallel, so we will see similar issues with storms growing upscale. That being said, I think we could see embedded supercell structures from this, especially as it moves further East into stronger low level shear.

The highest end potential is if we were to see any discrete supercells develop fully in the high STP OWS from N AR into SE MO and SW IL. In this scenario, I think we are looking at EF3+ tornadoes. The saving grace is, currently, I can't quite see an easy forcing mechanism for this to occur, given the confluence would probably be displaced East, the boundaries growing upscale, and the strongest synoptic forcing a tad to the north. That's not to say it won't happen though.

Those are some of my thoughts for now. Its annoying I can't upload any photos to visualise these points, but they can all be seen easily on model output. I think Moderate Risk is definitely a good call from the SPC - I don't think there is much basis to go higher. While I do think a tornado outbreak is probably on the cards - given the synoptic, large area of favourable parameters and multiple storm modes, some of the key components of proper higher end outbreaks aren't yet apparent to me personally (if we really want to differentiate). Will be a dangerous weather day regardless though, so worth keeping an eye on all radar and warnings closely.

I’m at work sadly, but here’s what I’ll say regarding this and today’s threat.


One thing that’s stood out with today’s runs is how the earlier clearing is probably going to change the recovery process compared to what guidance was showing yesterday. That boundary still looks like the primary focus, but it seems like it’s going to be modifying north a bit faster with a deeper unstable warm sector pushing in from the south. That at least raises the ceiling for anything that can stay surface based along or just south of it.

Storm mode still looks like the main issue. The orientation favors upscale growth pretty quickly, but some of the recent CAMs have hinted at initiation just ahead of the boundary rather than directly on it, which would be a more concerning scenario. Even a short window of semi-discrete storms in that environment would be enough given how strong the low-level field becomes later.

Also watching how the LLJ lines up into that AR/MO/IL corridor. If anything can interact with that zone before things congeal, that’s probably where the tornado potential gets maximized. Otherwise it probably trends more toward clusters with embedded structures as forcing increases.

Overall it still feels like one of those setups where the ingredients are clearly there, but how it’s realized is going to come down to small-scale details with boundaries and timing. The earlier clearing definitely doesn’t hurt the ceiling though at all and it’s gonna help the chance of this threat reach it’s potential.

 

[Kds86z]

I was about to write the same thing. Even if they think the reasonable maximum intensity is EF-3, there's a reasonable likelihood that there will be more than a few of those within this watch to justify it being a PDS watch IMO. I also think a violent tornado or two on the table, which would ALSO justify a PDS.

If we are relegating PDS watches now to only high-risk days or CIG 3 intensity, I think that may be a mistake. I get that PDS has historically been used when they have high confidence in at least one violent tornado occuring, but I think this setup has that potential, right?

I also think we should have a discussion after this event regarding the discussion we saw a few days ago regarding the SPC really leaning on STP for the CIG level.

Have we even had a Pds watch this year? Maybe one..

 

[Kds86z]

 

[Sharpy]

I know everyone is focused on today, but we do have the new D2 outlook and ENH has entered the chat.

 

[Clancy]

SPC has added an Enhanced Risk delineation for parts of the Lower Mississippi Valley for the Day 2 outlook. It's a wind/hail-driven Enhanced, but they've also significantly expanded the tornado risk area, and added a CIG1 hatch.

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1244 PM CDT Mon Apr 27 2026

Valid 281200Z - 291200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FOR
NORTH-CENTRAL/NORTHEAST TEXAS...SOUTHEAST
OKLAHOMA...CENTRAL/SOUTHERN ARKANSAS...NORTHERN LOUISIANA...NORTHERN
MISSISSIPPI...

...SUMMARY...
Scattered strong to severe thunderstorm development is probable
across parts of the southeastern Great Plains through the lower
Mississippi and Tennessee Valleys Tuesday afternoon and evening.
Large to very large hail, swaths of damaging wind, and a few
tornadoes are possible.

...Southeastern Great Plains into the Tennessee Valley...
Within broad southwesterly flow aloft, a mid/upper-level shortwave
trough is forecast to move from the south-central Rockies toward the
mid MS Valley on Tuesday. Other low-amplitude vorticity maxima may
move from TX toward the TN Valley and Southeast, to the south of the
primary shortwave trough. These features will impinge upon a
reservoir of strong instability extending from the southern Plains
into the lower MS Valley, resulting in a potentially active severe
weather episode Tuesday afternoon into Tuesday night.

Elevated convection will likely be ongoing across parts of the
region Tuesday morning, which could pose a threat for large hail and
locally gusty winds, especially within the more favorable lapse
rate/buoyancy environment across the southern Plains into the
ArkLaTex. Strong diurnal destabilization will be possible by Tuesday
afternoon, to the east of a dryline across TX, and along and to the
warm side of an outflow-influenced front extending from southeast OK
toward the mid MS Valley. Evolution of storm development remains
uncertain, but initiation will be possible along the dryline/front
and any other outflow boundaries in place by afternoon.

Strong buoyancy (MLCAPE of 3000-4000 J/kg across TX, and 2000 J/kg
as far east as the ArkLaMiss) and favorable deep-layer shear will
support supercell development, with an attendant threat of very
large hail initially. Modestly enhanced low-level flow from east TX
into the ArkLaMiss will also support some tornado potential, with
some conditional risk of a strong tornado with any sustained
supercell. An increase in storm coverage should lead to development
of storm clusters and potentially an MCS that would spread eastward
into the evening, with one or more swaths of damaging wind possible.
Storms should eventually weaken late in the period as they encounter
weaker instability with eastward extent, but the severe threat could
persist through much of the night with any organized storm
structures.

..Dean.. 04/27/2026

 

[speedbump305]

Have we even had a Pds watch this year? Maybe one..

I’m quite shocked that it isn’t a PDS watch given the wording on the outlooks. Maybe they’ll re issue another one?

 

[Sharpy]

I know everyone is focused on today, but we do have the new D2 outlook and ENH has entered the chat.

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1244 PM CDT Mon Apr 27 2026

Valid 281200Z - 291200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FOR
NORTH-CENTRAL/NORTHEAST TEXAS...SOUTHEAST
OKLAHOMA...CENTRAL/SOUTHERN ARKANSAS...NORTHERN LOUISIANA...NORTHERN
MISSISSIPPI...

...SUMMARY...
Scattered strong to severe thunderstorm development is probable
across parts of the southeastern Great Plains through the lower
Mississippi and Tennessee Valleys Tuesday afternoon and evening.
Large to very large hail, swaths of damaging wind, and a few
tornadoes are possible.

...Southeastern Great Plains into the Tennessee Valley...
Within broad southwesterly flow aloft, a mid/upper-level shortwave
trough is forecast to move from the south-central Rockies toward the
mid MS Valley on Tuesday. Other low-amplitude vorticity maxima may
move from TX toward the TN Valley and Southeast, to the south of the
primary shortwave trough. These features will impinge upon a
reservoir of strong instability extending from the southern Plains
into the lower MS Valley, resulting in a potentially active severe
weather episode Tuesday afternoon into Tuesday night.

Elevated convection will likely be ongoing across parts of the
region Tuesday morning, which could pose a threat for large hail and
locally gusty winds, especially within the more favorable lapse
rate/buoyancy environment across the southern Plains into the
ArkLaTex. Strong diurnal destabilization will be possible by Tuesday
afternoon, to the east of a dryline across TX, and along and to the
warm side of an outflow-influenced front extending from southeast OK
toward the mid MS Valley. Evolution of storm development remains
uncertain, but initiation will be possible along the dryline/front
and any other outflow boundaries in place by afternoon.

Strong buoyancy (MLCAPE of 3000-4000 J/kg across TX, and 2000 J/kg
as far east as the ArkLaMiss) and favorable deep-layer shear will
support supercell development, with an attendant threat of very
large hail initially. Modestly enhanced low-level flow from east TX
into the ArkLaMiss will also support some tornado potential, with
some conditional risk of a strong tornado with any sustained
supercell. An increase in storm coverage should lead to development
of storm clusters and potentially an MCS that would spread eastward
into the evening, with one or more swaths of damaging wind possible.
Storms should eventually weaken late in the period as they encounter
weaker instability with eastward extent, but the severe threat could
persist through much of the night with any organized storm
structures.

..Dean.. 04/27/2026

 

[Kds86z]

I’m quite shocked that it isn’t a PDS watch given the wording on the outlooks. Maybe they’ll re issue another one?

I’d almost like to ask them why not.

 

[Ledian]

Gonna be an active period for many, including North MS. I wonder if those storms that are developing east of Grenada will give me something to keep an eye on much earlier than i would like to.

 

[Kds86z]

 

[Clancy]

Something to note - HRRR has been very persistent in depicting a supercell with a strong UH streak making its way across parts of northern Mississippi into northwestern Alabama this evening. That area is a relatively notorious corridor for significant tornadoes, and with highly-favorable kinematics at this time frame in the region, this is a possibility that should definitely be watched closely.

 

[Kds86z]

W
Everytime I see it spotted out in the wild with one of these pics, It makes me think I'm looking at a horseshoe crab without a tail haha

 

[The Nino]

HRRR really increasing the threat for N MS and NW AL it seems like.

 

[Tennie]

The cloud base on Nick Gorman's stream looks rather low to me.

 

[Kds86z]

 

[Tennie]

There's a fairly large Severe Thunderstorm Warning for western St. Louis.

 

[VultureDirge89]

I'd like to throw it in that even if the maximum intensity expected is EF3, if you're expecting several of them then that would still probably warrant a PDS watch (case in point 4/15/2011 or 5/6/2015).

W
Everytime I see it spotted out in the wild with one of these pics, It makes me think I'm looking at a horseshoe crab without a tail haha

Thanks, now I can't unsee it lol.