4/17-4/18 Severe Storms Threat

[sbnwx85]

Could be another big day with an expansive Enhanced Risk. Locally, the NAM likes the idea of keeping severe wind gusts going into Michiana late into the evening.

Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1241 PM CDT Thu Apr 16 2026

   Valid 171200Z - 181200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS EXTENDING FROM
   WISCONSIN SOUTHWESTWARD INTO OKLAHOMA...

   ...SUMMARY...
   Widespread severe thunderstorms are expected from parts of the
   southern Plains to the Middle and Upper Mississippi Valley vicinity
   Friday into Friday night. Tornadoes, possibly strong, very large
   hail, and swaths of damaging winds will be possible.

   ...Synopsis...
   An upper trough will move into the central and northern Plains
   during the day, strengthening through Friday night as it moves into
   upper MS Valley. Continuous height falls will occur across the
   entire central to northern Plains region, where mid and upper level
   temperatures will already be relatively cool.

   During the afternoon, low pressure will develop across IA and WI,
   with a cold front extending southwestward into southern KS and
   northwest OK. A warm front will also lift across IA and into WI
   during the day, with an influx of mid 60s F dewpoints. Given the
   cool temperatures aloft, this will create a highly unstable air mass
   ahead of the cold front. This front will accelerate during the
   evening as storms become numerous, and should extend roughly from
   Lower MI into central TX by 12Z Saturday.

   The combination of steep lapse rates aloft, ample shear, and ample
   moisture will support corridors of significant severe storms,
   including all modes of severe. 

   ...From IA into WI and northwest IL...
   Strong tornado potential is evident Friday afternoon into early
   evening, especially from IA into southern WI and northwest IL. While
   convective evolution is a bit uncertain, there is good agreement in
   a very unstable environment with midlevel lapse rates to 8.5 C/km,
   along with 200-300 m2/s2 effective SRH ahead of the surface low and
   near the warm front. While an eventual squall line may take shape
   late in the day, scattered supercells appear likely after about 19Z
   ahead of the developing low and as dewpoints rise rapidly. As such,
   conditional tornado probabilities have been increased further to
   indicate stronger tornado potential.

   Cells should eventually consolidate as the front pushed east, with
   damaging bowing structures expected, possibly as far east as Lake
   MI. The severe risk is expected to persist as far east as IN and
   lower MI late evening/overnight as the southerly low-level jet
   brings moisture northward. Damaging winds appear possible.

   ...OK/KS/MO...
   A volatile environment will develop near and ahead of the cold front
   Friday afternoon, with significant severe hail, wind, and several
   tornadoes expected. An impressive combination of deep-layer
   shear/wind fields and steep lapse rates aloft will exist, and while
   the forcing mechanism will be linear, shear vector orientation and
   likely rightward-propagation of the stronger supercells will support
   tornadoes and very large damaging hail initially. All this activity
   is expected to merge into a linear MCS, with corridors of
   destructive winds and continued large hail risk expected over much
   of MO and into northern OK through the evening.

   ..Jewell.. 04/16/2026

[Chinook]

The 12z/00z convection-allowing models have a ton of activity in this time frame tomorrow (20z-00z), with these helicity tracks shown. The 12z HRRR shows many strong helicity tracks in Wisconsin.

[andyhb]

18z HRRR and 12z MPAS variants are bordering on a tornado outbreak in WI tomorrow. The former would be a huge problem for the I-94 corridor.

[pen_artist]

@andyhb What are your thoughts on QLCS tor threat in Chicago area?

[andyhb]

17 minutes ago, pen_artist said:

@andyhb What are your thoughts on QLCS tor threat in Chicago area?

I'm not so certain there won't be a few supercells further south into N IL, although things may be a bit more mixed out down there so the tornado threat is less. Haven't looked much into the QLCS threat yet, but I'd imagine with strong shear and strong instability that it is certainly elevated.

Oh and the 18z NAM is not just bordering on a tornado outbreak in WI, it is one.

[Chicago916]

16 minutes ago, andyhb said:

I'm not so certain there won't be a few supercells further south into N IL, although things may be a bit more mixed out down there so the tornado threat is less. Haven't looked much into the QLCS threat yet, but I'd imagine with strong shear and strong instability that it is certainly elevated.

Oh and the 18z NAM is not just bordering on a tornado outbreak in WI, it is one.

Any prefrontal cells that pop ahead of the front that aren't undercut and are in the better parameter space. Yikes. 

[BuffaloWeather]

57 minutes ago, andyhb said:

18z HRRR and 12z MPAS variants are bordering on a tornado outbreak in WI tomorrow. The former would be a huge problem for the I-94 corridor.

Im off tomorrow and thinking of making the journey to chase this, worth it you thinking or wait for tonights outlook before leaving? 

[luckyweather]

2 hours ago, BuffaloWeather said:

Im off tomorrow and thinking of making the journey to chase this, worth it you thinking or wait for tonights outlook before leaving? 

as of now if you target S. WI seems like platteville -> msn -> west bend is where I’d set up shop. probably platteville and watch development from there. 

[Chinook]

Seems like still probably a pretty high threat for tornadoes in southern Wisconsin and possibly northern Illinois before the system becomes more of a squall line tomorrow night.

[MidwestChaser]

[A-L-E-K]

friday evening mood remnants, nothing wrong with that

[Jackstraw]

Wish I still had it in me to drive more than 50 miles to chase lol. Again, line will come through here overnight, probably just enough to scare the dog and wake me up. To be honest , there's a a good 250 mile stretch of that front that if any kind of updraft can get isolated there's a decent possibility of a long tracker. Yes more so in the N/IL S/C/WI areas, but there are more than enough shotgun/ semi automatic impressive pre-frontal hodo's on the models anyway. Guess my play was back in March with and 80mph downburst lol, may have to wait until June now. Regardless, agree with all, good chance of a long tracker here, and very well could be where one doesn't expect it with this setup. Good luck to all that dare the chase traffic jam and stay away from that one idiot that goes 100mph and runs stop signs. Thats what got Corbin Jaeger, Randy Yarnell and Kelley Williamson (I chased with him a lot many many years ago, great guy) killed. Be the fuck careful man 

[Malacka11]

Maybe I'm squinting at it too hard but it looks like the passage of the evening QLCS is bumping earlier instead of later, which I'd love to see it with even half a lux of sunlight left. Also:

.UPDATE...
Issued at 1015 AM CDT Fri Apr 17 2026

There is a trailing boundary extending south from ongoing
convection across the Minneapolis area.  This boundary may be
an initial source for forcing as it spreads towards northern
Illinois in the mid afternoon time frame. The airmass is still
stable per the extensive area of billow clouds across Iowa,
however we have noted a significant uptick in the dewpoints out
ahead of this feature. Instability progs would suggest by the
time this boundary arrives northern Illinois should destabilize,
and thus there at least some concerns for a leading round of
convection, which could be in the form of supercells with an all
hazard threat. Some questions still exists as to whether this
will just graze the local area or continue to push closer to the
Chicago metro area. There is a shortwave across Missouri that
also slide through the area ahead of the cold front which could
be a mechanism to keep convection farther east, so this will be
a mesoanalysis focus in the coming hours. Limiting factors for
this first round convection having a larger footprint would be
that the forcing is a bit more subtle, and we still have a
fairly deep dry layer ahead of this boundary.

Regardless of this, low level flow will reintensify ahead of
the cold front which should help to keep instability up into the
evening hours, where a damaging wind threat would be the
highest concern, along with a QLCS tornado threat. Thoughts from
the morning AFD still tell the story quite well.

KMD

[ILSNOW]

 

[Jackstraw]

38 minutes ago, Malacka11 said:

Maybe I'm squinting at it too hard but it looks like the passage of the evening QLCS is bumping earlier instead of later, which I'd love to see it with even half a lux of sunlight left. Also:

.UPDATE...
Issued at 1015 AM CDT Fri Apr 17 2026

There is a trailing boundary extending south from ongoing
convection across the Minneapolis area.  This boundary may be
an initial source for forcing as it spreads towards northern
Illinois in the mid afternoon time frame. The airmass is still
stable per the extensive area of billow clouds across Iowa,
however we have noted a significant uptick in the dewpoints out
ahead of this feature. Instability progs would suggest by the
time this boundary arrives northern Illinois should destabilize,
and thus there at least some concerns for a leading round of
convection, which could be in the form of supercells with an all
hazard threat. Some questions still exists as to whether this
will just graze the local area or continue to push closer to the
Chicago metro area. There is a shortwave across Missouri that
also slide through the area ahead of the cold front which could
be a mechanism to keep convection farther east, so this will be
a mesoanalysis focus in the coming hours. Limiting factors for
this first round convection having a larger footprint would be
that the forcing is a bit more subtle, and we still have a
fairly deep dry layer ahead of this boundary.

Regardless of this, low level flow will reintensify ahead of
the cold front which should help to keep instability up into the
evening hours, where a damaging wind threat would be the
highest concern, along with a QLCS tornado threat. Thoughts from
the morning AFD still tell the story quite well.

KMD

You can see what they're talking about on the SPC meso page in the 700mb and visible sat. I might add there's a very impressive dry line trying to out run the front in  W/NW Iowa SW MN. I think any SUPS in IA. IL, WS will seed there as this area tries to race E ahead of the front. It's pretty prominent and has upper level help coming in behind it.

[Chicago Storm]

i'd argue a solid moderate risk area will end up being needed/verifying for wind and qlcs tors.

sometimes the spc forgets that their forecasts are coverage based.

[ILSNOW]

[MidwestChaser]

Yet another watch that's just shy of the metro; getting almost comical at this point.

[cyclone77]

Got the lawn's first haircut done this afternoon.  Now let's do this.