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Severe Weather Threat 4/27-4/28

Storm mode (what a surprise, right?) is still the biggest question mark for me for Monday. The Synoptics are there, we seem locked in on the areas in play, but that “quick upscale growth” would really dampen the ceiling here.

If that EML plume in reality is close to what’s being modeled, I don’t think any morning or remnant convection from Sunday will be able to linger and train over the region.
 
ColdFront said:
Storm mode (what a surprise, right?) is still the biggest question mark for me for Monday. The Synoptics are there, we seem locked in on the areas in play, but that “quick upscale growth” would really dampen the ceiling here.

If that EML plume in reality is close to what’s being modeled, I don’t think any morning or remnant convection from Sunday will be able to linger and train over the region.
Click to expand...
I think we could see some duration for storm mode before the more congealed portion. Reminds me of 5/16 a bunch here, although we are not going that far East with extent
 
General placement, timing and structure/intensity of 500mb/sfc features for Monday reminds me a lot of a particular day when a messy storm mode was also considered a potential limiting factor for the northern end. It produced the tornado that was my profile avatar for two years, before the one that currently is, for those of you who know what I mean.

ILX AFD for Monday. I was a bit surprised/amused by how much they referenced the RRFS, including its simref output:

Area Forecast Discussion
National Weather Service Lincoln IL
844 AM CDT Sat Apr 25 2026

.KEY MESSAGES...

- An Enhanced Risk (level 3 of 5) for severe weather exists on
Monday. All severe hazards will be possible Monday afternoon
and evening as a potent storm system lifts through the region.

&&

.UPDATE...
Issued at 835 AM CDT Sat Apr 25 2026

Subsidence associated with high pressure building into the
region this morning has compressed boundary layer moisture
associated with the Lake Michigan marine layer, which has made
it as far south as a Kewanee to Paris line at 840am. This has
primarily manifest in the form of a stratus deck around 200-500
ft, but sharply reduced visibilities to 1/4 mile along the
leading edge also occurred. Given the transient nature of these
troublesome visibilities and the improvement noted at surface
observation sites over the past 30 minutes, we elected to hold
off on issuing a Dense Fog Advisory. However, the forecast
through the next hour now mentions patchy dense fog for the
impacted areas.

&&

.DISCUSSION...
Issued at 316 AM CDT Sat Apr 25 2026

*** Severe Weather on Monday ***

A vigorous short-wave trough evident on 0730z/230am water vapor
imagery well off the coast of southern California will come
onshore later today, then lift northeastward into the Upper
Midwest by Monday. As the negatively tiled wave approaches,
surface cyclogenesis will take place in the lee of the Rockies
across southeast Colorado on Sunday...with the low deepening to
around 992mb by the time it tracks into northern Wisconsin
by Monday evening.

The airmass ahead of the approaching storm system will initially
be stable thanks to E/SE boundary layer flow around high
pressure over the Great Lakes. As WAA begins, elevated
instability will increase late Sunday night into Monday morning
when the first round of convection is anticipated. Based on 00z
Apr 25 model consensus, it appears the initial storms will
focus along/west of the I-55 corridor with a marginally severe
hail/gusty wind risk.

As the low lifts further north, it will gradually pull a warm
front northward into central Illinois by Monday afternoon.
Morning convection and a continued easterly component to the
wind will keep the boundary layer stable until late afternoon
when richer moisture arrives. While mesoscale details are
impossible to properly resolve at this time range, the 00z RRFS
offers the first glimpse into the potential severe weather
scenario...showing MLCAPE values of 2000-2500J/kg along/south of
a Macomb to Champaign line by late afternoon/early evening.
Deep-layer shear will be more than sufficient at 45-55kt and
0-1km SRH increases to 300-400m2/s2 west of the Illinois River
by 21z. If this solutions pans out, the initial supercells will
most likely form across southeast Iowa, northeast Missouri, and
western Illinois late Monday afternoon where the greatest
tornado and very large hail risk may be maximized. The RRFS then
suggests the storms will congeal into a line and track E/SE
across the remainder of the KILX CWA Monday evening. While
daytime instability will wane somewhat after dark, strong shear
will support a continued risk for damaging wind gusts and
tornadoes as the storms sweep eastward into Indiana by around
midnight.

The other higher-resolution model that currently covers the
event is the 12km NAM, and it shows a similar flavor to the RRFS
albeit with initial storm development perhaps a bit further
W/NW into Iowa and northern Missouri. Even if this solution
verifies, central Illinois would still be in line for a volatile
Monday evening with an attendant damaging wind and tornado
threat. While it is still too early to pinpoint exact details
and timing, confidence is growing for a significant severe
weather episode. Stay tuned to later forecasts for more details.

&&
Click to expand...
 
CheeselandSkies said:
General placement, timing and structure/intensity of 500mb/sfc features for Monday reminds me a lot of a particular day when a messy storm mode was also considered a potential limiting factor for the northern end. It produced the tornado that was my profile avatar for two years, before the one that currently is, for those of you who know what I mean.

ILX AFD for Monday. I was a bit surprised/amused by how much they referenced the RRFS, including its simref output:
Click to expand...
There's similarities. Difference is it's a month later with better thermos. That can mean a lot
 
3K NAM has a big squall line (actually two of them) going through southern IL into Indiana and kind of suppressing things further north for Monday. Just looking at simref+UH, it fires apparent supercells over northern IL, but looking at the actual surface conditions they'd be elevated. However this model has a known tendency to blow up huge squall lines, so when it signals any discrete convection at all (assuming CI in that general area is supported by other CAMs), it's a bit of an alarm bell.
 
The Nino said:
What’s north Alabama looking like for this?
Click to expand...
A few days ago I would’ve said be on your toes. Now, it’s a pretty lower end severe threat for Monday. I watched Fred’s weekend update last night, and he also indicated the more severe weather will be to the north and west.

I think Dixie may just get a classic MCS for two days.
 
The QLCS Solution is beginning to look pess and less possible for me. You have solid eastward shear vectors and a slightly capped environment and decent 500 mb forcing that isn't ecxessive by anymeans. Even the NAM shows supercellular development and two rounds of it at that in MO/IL. The 3KMNAM is doing weird things though, with two big sqall lines inspide of being in an area with more subtle forcing and still slightly capped environment so I don't know what to think of it.
 
CheeselandSkies said:
3K NAM has a big squall line (actually two of them) going through southern IL into Indiana and kind of suppressing things further north for Monday. Just looking at simref+UH, it fires apparent supercells over northern IL, but looking at the actual surface conditions they'd be elevated.
Click to expand...
I really think we are going to have big storm mode issues here, NAM’s gross linear bias notwithstanding. I’m not saying we won’t have embedded supercells or a small window for some discrete supercells, but that jet is just a firehose of forcing right over that area. While the trough is negatively tilted, I’d still like to see more zonal flow geometry instead of that sharp-meridional flow right into the warm sector Monday.

It’s a freaking puzzle trying to figure out storm mode at this range though.

edit: Not downplaying this threat at all btw. I’m more speaking of factors that would cause this event not to reach an upper-end ceiling
 
Last edited:
ColdFront said:
A few days ago I would’ve said be on your toes. Now, it’s a pretty lower end severe threat for Monday. I watched Fred’s weekend update last night, and he also indicated the more severe weather will be to the north and west.

I think Dixie may just get a classic MCS for two days.
Click to expand...
Crazy how quiet it’s been around here Nader wise, not complaining but the rational probability part of my brain is saying we’re due. Keep waiting for it
 
ColdFront said:
I really think we are going to have big storm mode issues here, NAM’s gross linear bias notwithstanding. I’m not saying we won’t have embedded supercells or a small window for some discrete supercells, but that jet is just a firehose of forcing right over that area. While the trough is negatively tilted, I’d still like to see more zonal flow geometry instead of that sharp-meridional flow right into the warm sector Monday.

It’s a freaking puzzle trying to figure out storm mode at this range though.
Click to expand...

Which model(s)/run(s) are you looking at? Maybe I'm just interpreting it wrong but the flow doesn't look that meridional to me. Due southwesterly at most, but some areas with a greater westerly component.
 
ColdFront said:
A few days ago I would’ve said be on your toes. Now, it’s a pretty lower end severe threat for Monday. I watched Fred’s weekend update last night, and he also indicated the more severe weather will be to the north and west.

I think Dixie may just get a classic MCS for two days.
Click to expand...
100%. a lot depends on the evolution of a secondary LP and that doesn’t look likely. otherwise wind and rain. i would be on high alert from memphis back to OKC and points north.
 
ColdFront said:
I really think we are going to have big storm mode issues here, NAM’s gross linear bias notwithstanding. I’m not saying we won’t have embedded supercells or a small window for some discrete supercells, but that jet is just a firehose of forcing right over that area. While the trough is negatively tilted, I’d still like to see more zonal flow geometry instead of that sharp-meridional flow right into the warm sector Monday.

It’s a freaking puzzle trying to figure out storm mode at this range though.

edit: Not downplaying this threat at all btw. I’m more speaking of factors that would cause this event not to reach an upper-end ceiling
Click to expand...
I don't quite follow what you're saying here.
 
12Z HRW-FV3, while far from a perfect CAM (are any of them, really?) shows more of the higher-end scenario for Monday. Closely packed/possibly messy but still semi-discrete supercells crossing the MS River near the IA/IL/MO intersection, and a band of widely spaced, probably high-end supercells further south/east.

Would attach the screenshot, but, you know.
 
andyhb said:
I don't quite follow what you're saying here.
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I probably didn’t word that correctly, and unfortunately I can’t attach screenshots on what I’m referring to. Looking at the 3KNAM run from 12z, wouldn’t you want your main jet and enhanced flow to have a slightly more “east-west” component over the warm sector? I’m earnestly asking that.
 
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