Potential Sever Weather Outbreak 4/27/2026

[pen_artist]

Large D4 30% contour for much of IL and parts of WI, IN, IA, MO, AR, TN and KY. Mention of strong tornadoes but not as strong of wording as I'd expect. Regardless, shaping up to be another all hazards possible event especially if things can remain more supercellular.

...DISCUSSION...
   Latest medium-range model output suggests that a significant short
   wave perturbation emerging from the Southwest will pivot northeast
   of the middle/lower Missouri Valley, into the upper Great Lakes
   region, Monday through Monday night.  It appears that the warm
   sector of an associated sub-1000 mb surface cyclone will become
   characterized by at least moderately large CAPE, ahead of the
   dryline/cold front overspreading much of the middle Mississippi
   Valley during the afternoon into evening.  In the presence of strong
   deep-layer shear, organized severe thunderstorm activity appears
   probable.  It remains a bit unclear the extent to which sustained
   supercell development will be maintained, as opposed to convection
   quickly growing upscale into one or more clusters/lines, but there
   appears at least some potential for a few strong tornadoes, in
   addition to large hail and potentially widespread strong to severe
   wind gusts.

[nvck]

Really, really rare to see this highest level contour on the CSU maps this far out

[sbnwx85]

Thinking another QLCS tornado threat this far east is best case scenario.

[A-L-E-K]

riding

 

[mob1]

Thanks for opening a thread for this, some of the soundings for Monday look pretty wild. Obviously every severe weather threat has many failure modes, but the potential is definitely there for a high-end event. 

[andyhb]

Quote

   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0228 AM CDT Sat Apr 25 2026

   Valid 271200Z - 281200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS MONDAY
   AFTERNOON AND EVENING ACROSS MUCH OF EASTERN IOWA...A PORTION OF
   SOUTHWESTERN WISCONSIN...MUCH OF EASTERN
   MISSOURI...ILLINOIS...WESTERN INDIANA...WESTERN KENTUCKY...WESTERN
   TENNESSEE...NORTHEASTERN ARKANSAS...

   ...SUMMARY...
   Widespread strong to severe thunderstorm development appears
   probable across the middle Mississippi into lower Ohio and Tennessee
   Valleys Monday afternoon and evening.  At least initially, this may
   include several evolving supercells potentially capable of producing
   strong tornadoes across parts of southeastern Iowa into central
   through southern Illinois and adjacent east central and southeast
   Missouri.

   ...Discussion...
   Models indicate that significant surface cyclogenesis will proceed
   across the Upper Midwest/adjacent Great Lakes region during this
   period, as a notable short wave perturbation and associated 50-70 kt
   cyclonic 500 mb jet streak progress northeast of the middle/lower
   Missouri Valley region.  Beneath a plume of warm/capping elevated
   mixed-layer air nosing northeastward across the middle Mississippi
   Valley, low-level warm sector moistening is generally forecast to
   contribute to moderate to strong potential instability.  Although
   the details of the potential convective evolution remain unclear,
   the environment appears likely to become supportive of organized
   severe thunderstorm development, including supercells.  Even if
   convection grows quickly upscale into one or more clusters/lines,
   embedded supercell structures will probably still pose potential for
   producing strong tornadoes.  If an initially discrete supercell mode
   is maintained for a sustained period, tornadic potential could
   maximize, with a few long track, particularly damaging tornadoes
   possible.

   At this time, it appears that strongest thunderstorm development may
   initially focus in forcing for ascent associated with
   lower/mid-tropospheric warm advection, near the nose of the
   initially capping elevated mixed-layer across parts of southeastern
   Iowa into central Illinois.  Enlarged, clockwise-curved low-level
   hodographs along this corridor, perhaps coinciding with a zone of
   stronger differential surface heating associated with a modifying
   outflow boundary, may become conducive to several strong tornadic
   supercells before convection tends to grow upscale while propagating
   southeastward into Monday evening.

   A dryline structure extending southwestward through portions of
   eastern Missouri may also support initially discrete supercell
   development, before activity tends to grow upscale ahead of an
   advancing cold front while spreading into the lower Ohio/Tennessee
   Valleys through Monday evening.

   ..Kerr.. 04/25/2026

Very strong wording in the latest D3 for Monday, got the feeling this ends up as a D2 MDT.

[A-L-E-K]

Looks rockin

[sbnwx85]

Jelly but will probably catch the very tail end of this late Monday 

[A-L-E-K]

Nice

[TheNiño]

Am I being a weenie thinking this has high risk potential around the STL to Springfield area? I know it’s still too early to tell but the models certainly aren’t backing down. 

[MidwestChaser]

2 hours ago, A-L-E-K said:

Nice

[Malacka11]

Pretty based that the timing actually looks okay for N IL to get a not nighttime show. Was tempering my expectations based on the SPC maps 

[cyclone77]

Lots of ongoing morning convection on the models over Iowa/northern MO and into northwest IL.  Likely to push the best chances for afternoon main show south and east of the DVN cwa.

[CheeselandSkies]

Seems like all the CAMs to come into range thus far (including 00Z HRRR) obliterate the warm sector north of about I-70 with incessant convection through midday. A couple days ago there was talk of an abnormally far east EML advection preventing this, what changed?

[Chicago Storm]

Seems like all the CAMs to come into range thus far (including 00Z HRRR) obliterate the warm sector north of about I-70 with incessant convection through midday. A couple days ago there was talk of an abnormally far east EML advection preventing this, what changed?

Nothing has really changed.

Globals have showed a messy look more often than not for days now.

[cyclone77]

Best bet for the northern IL play to work out is for the morning convection to blast through quickly/faster than current model forecasts, and then the rapidly overspreading mid-level lapse rate plume could recharge that area pretty quickly by mid-afternoon.  No question there's gonna be a large amount of morning convection, but if we can get it to blast out of the area by midday there may be enough time to recharge.

[Arishtat]

Looks like the morning convection absolutely tosses the environment two HRRR runs in a row.