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March 31st Severe Threat


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   SPC AC 301732

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1232 PM CDT Thu Mar 30 2023

   Valid 311200Z - 011200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS EASTERN
   IOWA INTO NORTHWEST ILLINOIS AND FAR NORTHEAST MISSOURI...AND ALSO
   ACROSS NORTHEAST ARKANSAS...THE MISSOURI BOOTHEEL...EXTREME WESTERN
   KENTUCKY...WESTERN TENNESSEE...AND FAR NORTHWEST MISSISSIPPI...

   ...SUMMARY...
   Intense and widespread severe thunderstorms are expected Friday
   afternoon into the overnight hours across portions of the Middle
   Mississippi Valley and Mid-South vicinity, eastward to the Lower
   Ohio and Tennessee Valleys. Intense, damaging gusts and several
   tornadoes (some strong and long-track) are expected.

   ...A regional outbreak of severe storms is expected on Friday across
   parts of the Mid-Mississippi Valley and also into the Mid-South...

   ...Synopsis...
   A deep mid/upper-level trough and attendant 100 kt midlevel jet will
   move quickly eastward from the central Plains into parts of the MS
   Valley and Midwest on Friday. A surface low will deepen as it moves
   across IA toward the Great Lakes region, as a cold front sweeps
   eastward through parts of the Great Plains into the mid-MS Valley.
   In advance of the cold front, low-level moisture will stream
   northward across a broad warm sector from the ArkLaTex region into
   parts of the lower/mid MS Valley and Midwest. 

   ...Mid-MS Valley vicinity into IN/lower MI...
   Rapid destabilization and increasing large-scale ascent will support
   thunderstorm development by early/mid afternoon across parts of IA
   into northern MO. Very strong deep-layer shear (effective shear in
   excess of 60 kt) and MLCAPE increasing to 1000-1500 J/kg (locally
   greater) will support organized convection, with initial supercell
   development expected somewhere over central IA into north-central
   MO. Very large hail will be the initial threat, given steep midlevel
   lapse rates and cold temperatures aloft. 

   Some uncertainty remains regarding the convective mode evolution
   with time, but a few semi-discrete supercells are expected to move
   into an environment with stronger low-level shear/SRH across eastern
   IA into northwest IL by late afternoon, posing a threat for a couple
   strong tornadoes. Evolution into small clusters or bowing segments
   is expected, resulting in an increasing threat of severe/damaging
   winds in addition to a continued threat of a few tornadoes and
   sporadic hail. 

   Organized convection will spread eastward into parts of IN/southern
   MI Friday night. Instability will weaken with eastward extent, but
   some threat for damaging wind and a couple of tornadoes will persist
   before a more definitive weakening trend occurs overnight into early
   Saturday morning. 

   ...ArkLaTex/Mid South vicinity into the TN/lower OH Valleys...
   A concerning scenario still appears possible across portions of the
   MO Bootheel, northeast AR, western TN/KY and far northwest MS
   vicinity during the afternoon/evening. At least mid-60s F dewpoints
   are expected beneath modest midlevel lapse rates. This will support
   1500-2000 J/kg MLCAPE amid intense vertical shear. Forecast
   soundings indicate 0-1 km SRH increasing to around 400 m2/s2 by
   early afternoon. Thunderstorms are expected to develop by early
   afternoon ahead of the cold front within a pre-frontal
   trough/low-level confluence zone. Storm motion near 50 kt with
   supercell wind profiles will support cells capable of significant
   and long-track tornadoes. With time, upscale growth into a QLCS is
   expected, and intense wind gusts will be possible in addition to
   mesovortex tornadoes. The threat for damaging gusts and a few
   line-embedded tornadoes will spread into parts of the TN and lower
   OH Valleys Friday night, with a gradual weakening trend eventually
   expected overnight as storms move into increasingly weak buoyancy
   with eastward extent.

   ..Dean.. 03/30/2023
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I want to give it a shot tomorrow but I'm having a tough time with storm motions in the 50-60 knot range. Driving 3-4 hours each way to hopefully watch a storm fly by just doesn't sound all that appealing. Throw in a snowstorm on the drive home and it really doesn't sound like it's worth it coming from MSP.

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Just don't feel good about the potential for north-central / northeast Illinois. Taking models verbatim, we have potentially widespread, potentially strong storms plowing through the area in the morning hours, almost totally overcast skies through the balance of the day, and yet somehow we still end up with over 1000 j/kg CAPE? I get the very impressive dynamics of the system, including similarly-impressive unstable air advection on northwards, but a daytime high in the area somewhere in the low/mid-60s with extensive cloud cover and substantial early-morning convection never feels very good.

 

Assuming model guidance is right and I'm dead-wrong (more likely than not), though, I'm super concerned about damaging winds in the Chicagoland area. Storm movement per LOT potentially over 60 MPH plus the aforementioned dynamics of this system lead to some eye-watering images like this ... maximum 4-hour swath 10m winds showing pretty large swaths of >80 knot (~92 MPH) winds with this line. Pretty much a worst-case scenario type of graphic, of course, but does give a sense of what mets & others here have discussed re: significant severe potential.

wspd_004hmax.spc_mw.f03800.png

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8 minutes ago, Kaner88 said:

Just don't feel good about the potential for north-central / northeast Illinois. Taking models verbatim, we have potentially widespread, potentially strong storms plowing through the area in the morning hours, almost totally overcast skies through the balance of the day, and yet somehow we still end up with over 1000 j/kg CAPE? I get the very impressive dynamics of the system, including similarly-impressive unstable air advection on northwards, but a daytime high in the area somewhere in the low/mid-60s with extensive cloud cover and substantial early-morning convection never feels very good.

 

Assuming model guidance is right and I'm dead-wrong (more likely than not), though, I'm super concerned about damaging winds in the Chicagoland area. Storm movement per LOT potentially over 60 MPH plus the aforementioned dynamics of this system lead to some eye-watering images like this ... maximum 4-hour swath 10m winds showing pretty large swaths of >80 knot (~92 MPH) winds with this line. Pretty much a worst-case scenario type of graphic, of course, but does give a sense of what mets & others here have discussed re: significant severe potential.

wspd_004hmax.spc_mw.f03800.png

Northeast IL/Chicagoland sure, north-central IL is definitely in a fairly high threat area though.

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36 minutes ago, CheeselandSkies said:

What a way for MKX to start their afternoon AFD...

 

LOT pounding it too. 
 

Concern for several tornadoes into the area,
including a noted risk for significant/long- track tornadoes,
continues to increase with the latest forecast guidance. This
guidance puts the low-level wind/thermo tornado parameter space
into the upper-echelon climatology of values for our area,
highlighted by significant 0-1km EHI and 0-3km CAPE that will be
realized by discrete supercells. At this point, the highest threat
area for tornadoes appears to be near/west of I-39. However, the
eastward extent of the highest supercell/tornado risk will be
determined by how quickly convection evolves toward a linear mode.
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44 minutes ago, Stebo said:

I am absolutely getting concerned about Chicago Metro on this one. Models have supercells all around and some have them moving into the suburbs around 22-02z.

I don’t chase … but if I did I’d sit myself near the 57 and 294 interchange. Looks primed for fireworks. 

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2 hours ago, Kaner88 said:

Just don't feel good about the potential for north-central / northeast Illinois. Taking models verbatim, we have potentially widespread, potentially strong storms plowing through the area in the morning hours, almost totally overcast skies through the balance of the day, and yet somehow we still end up with over 1000 j/kg CAPE? I get the very impressive dynamics of the system, including similarly-impressive unstable air advection on northwards, but a daytime high in the area somewhere in the low/mid-60s with extensive cloud cover and substantial early-morning convection never feels very good.

 

Assuming model guidance is right and I'm dead-wrong (more likely than not), though, I'm super concerned about damaging winds in the Chicagoland area. Storm movement per LOT potentially over 60 MPH plus the aforementioned dynamics of this system lead to some eye-watering images like this ... maximum 4-hour swath 10m winds showing pretty large swaths of >80 knot (~92 MPH) winds with this line. Pretty much a worst-case scenario type of graphic, of course, but does give a sense of what mets & others here have discussed re: significant severe potential.

wspd_004hmax.spc_mw.f03800.png

Dynamics can compensate for lack of instability (high shear/low cape outbreaks). In fact some of the higher end, more substantial outbreaks have featured such setups. Though I live in the Midatlantic (Virginia), I can testify that overcast and 60f temp means very little in the way of hindering the setup. I chased the 2/24/16 outbreak here in VA. There was an overcast all day and temps were bouncing between 50-70 all day. 2 devastating high-end EF3’s struck Appomattox and Essex. Also, our state record tornado that struck Petersburg on 8/6/93 was a high-end F4. That day also featured an overcast and thick cloud deck. 

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1 hour ago, Stebo said:

I am absolutely getting concerned about Chicago Metro on this one. Models have supercells all around and some have them moving into the suburbs around 22-02z.

Since I live in Griffith I will be monitoring this board and warnings all day Friday and am somewhat nervous hearing your concern  Fortunately I live in a basement apartment.

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40 minutes ago, StormChaser4Life said:

23z hrrr showing an mcs developing in ne MO at end of its run. Oh boy. Getting 3-28-20 vibes from that run. Hopefully won't get an early day wave that messes everything up. 

Its a bit soon to jump on this concern especially since no other model has it yet. If we see some consistency there would be concern of that screwing with the setup.

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41 minutes ago, StormChaser4Life said:

23z hrrr showing an mcs developing in ne MO at end of its run. Oh boy. Getting 3-28-20 vibes from that run. Hopefully won't get an early day wave that messes everything up. 

00Z has it too, but it then turns it into round 1 of potential supercells across IL, and fires another round behind that. Iowa looks a lot less impressive (at least purely in terms of simulated discrete convection with strong UH) this run compared to previous ones, though.

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Other model guidance suggesting an early wave now. 01z hrrr has an expansive precip shield at end of its run. Definitely something that will need to be watched. Certainly would shunt the threat south where destabilization could possibly happen on southern fringe. This is just giving me 3-28-20 vibes. This is about the time models went from outbreak scenario to a total mess. Only time will tell. 

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