March 26-28 Severe Threat

[Sydney Claridge]

6 minutes ago, janetjanet998 said:

The current OK stuff is the crapvection..the northern edge precip/clouds will be over IL by midday

Makes sense.  I guess on the bright side a lot of worries about strong, long-tracked tornadoes could be alleviated, provided that this convection holds together.  That said, it looks like the risk for severe thunderstorms might have increased along the I-70 corridor in Indiana, Ohio, and SW Pennsylvania.  Cities like Indianapolis, Dayton, Columbus, and Pittsburgh could now be in the line of fire, and what's crazy is that 08z HRRR outputs PDS soundings at 18z near Pittsburgh.  Several HRRR and RAP runs, for about the last day or so (though on-and-off to an extent as I recall), have shown an area of increased parameters in E OH and SW PA.

[Sydney Claridge]

Some of those storms in OK may be trying to drop in intensity, especially north of OKC.  I’m starting to see more yellows and a little less of reds and oranges on the radar (with radar returns around the stronger cores), although I am not sure if this is the start of a weakening trend.  Perhaps some cloud/anvil debris is interfering with storms to the north of OKC?

[RobertSul]

House-rattling thunder and bright lightning going on here. Pretty impressive given it’s in the low 40s out. 

[janetjanet998]

09z HRRR continues its trend of midday convection over iL with a minor lead wave or something

this splits the threat into two

1) high instability but LLJ afternoon min over SE IL into IND (midday-mid afternoon action)

2) main spoke of supercells over IA but moving into less instability over IL because of #1 (late afternoon/early evening which was supposed to be the big bang)

This is just a model but this happens often in real time

compare warm sector Hel swaths from yesterday afternoon for N IL  and compare to current runs and you can see what the trend is

 

[A-L-E-K]

Was nice to experience some loud boomers again last night. Today not looking nearly as fun as it yesterday, surprise surprise 

[Sydney Claridge]

10z HRRR still has high EHI and STP values around the IA/IL/MO border region, and now brings those values further east into NW IL, although I am not sure if this is the start of a trend.  We'll see what happens with the "crapvection" and precipitation shield in NE OK and SE KS as it moves northeast, but I do not want to rule out a localized tornado outbreak just yet, though that MDT risk should be trimmed back away from the Chicago metro area.  The warm front from central Illinois into southwest Pennsylvania may also need to be watched closely as well, and I would not be surprised to see a higher risk category added along that boundary.

EDIT: I definitely spoke too soon earlier about that convection in OK weakening, although that severe-warned storm near Tulsa appears to be weakening as it does not look as well organized as it was earlier.  EDIT 2: severe t-storm warning dropped, and now that line is developing down into central Texas.  Looks like I may get some thunder soon.

[bdgwx]

3Z SREF suggests only modest tornado potential in western/northern IL. Verbatim the higher tornado probabilities are in AR/MO/TN/KY/IL border area. If I were to go off only the latest HRRR and SREF runs I think I'd be considering a downgrade right now. But...it's a big low with an impressive kinematic environment so maybe they'll decide to keep the 15% sig-tor area on the 13Z update and wait and see what the morning convection does before making big adjustments. I will say that the 10Z HRRR still has a pretty good parameter space in IL just on a more localized scale now.

[jpeters3]

FWIW, the 10 UTC HRRR is backing off a bit on junkvection and moving back toward a volatile environment in NW IL and NE IA.  So those of you who think this needs to be backed down to a MRGL risk with 2 % tornado probabilities should settle down a bit...

[Indystorm]

8 minutes ago, jpeters3 said:

FWIW, the 10 UTC HRRR is backing off a bit on junkvection and moving back toward a volatile environment in NW IL and NE IA.  So those of you who think this needs to be backed down to a MRGL risk with 2 % tornado probabilities should settle down a bit...

Fully agree as I will continue to watch successive HRRR runs and real time observations like a hawk today.

[Baum]

will there be a dry window in the central chicago metro where we can actually get out and enjoy some 60 degree dews before any action from the cold front invades?

[Indystorm]

11z RAP also developing a secondary area of concern late afternoon/evening in se MO and southern IL.

[Quincy]

Beware early day convection... I was a bit bullish last night. Not going high risk was the right call.

Convection over the Ozarks is on a trajectory to move into central/northern IL by late morning and midday.

The area most consistently progged to have the best environment may actually be southeastern to east-central Iowa. The area is aided by limited convective overturning and some dry slotting as the surface low winds up in the Missouri Valley. 

I could still see multiple scenarios yielding some tornado potential in northern Illinois:

1. Mixed/messy storm mode, but still a threat for embedded supercells. The tornado threat here would probably be more short-lived as the instability field is fragmented and/or storms interact with each other.

2. “Last minute” storms fire near sunset in a broken, arcing line. Models have gone back and forth with this, but it’s still a possibility.

With respect to Chicago... I wouldn’t completely call off a tornado threat, but the combination of convective overturning and their easterly displacement from the greater risk zone leads me to believe they’ll probably dodge a bullet here. 

[King James]

Tale as old as time

[Sydney Claridge]

That convection over western MO seems to be modeled (according to the 11z HRRR and the RAP shown on the SPC Mesoanalysis site) to make it to the Quad Cities in about 4 hours or so.  The setup is not looking as potent as it did yesterday, but there may be some time to destabilize after this line passes.

[Radtechwxman]

I think hrrr may be overconvecting imo. It was way off on extent of elevated storms last night. This complex is MO is definitely the fly in the ointment. If more storms don't blow up besides that, I think this could still be a big day. That remains to be seen

[DanLarsen34]

Murphy’s law has applied to these past couple of big on-paper set-ups. Things begin to look like they’re a go until we get to the day of. Not saying this set-up can’t still be potent today, but it looks a lot less certain that we’ll be seeing an significant outbreak than it did 24 hours ago. 

[jpeters3]

10 minutes ago, DanLarsen34 said:

Murphy’s law has applied to these past couple of big on-paper set-ups. Everything looks a go until we get to the day of. Not saying this set-up can’t still be potent today, but it looks a lot less certain that we’ll be seeing an significant outbreak than it did 24 hours ago. 

I don't think this is entirely true.  Both the GFS and the NAM/NAM nest, along with the euro intermittently showed solutions over the past few days akin to what the HRRR is showing today.  There were certainly uncertainties going into this event, and it was never a "slam dunk."  A lot of the hype originated from the HRRR runs before and at 00 UTC.

[WeatherMonger]

No High Risk yet

 

 

Quote

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0749 AM CDT Sat Mar 28 2020

   Valid 281300Z - 291200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
   EASTERN IOWA AND CENTRAL/NORTHERN ILLINOIS...

   ...SUMMARY...
   A severe-weather outbreak is expected for portions of the Midwest
   this afternoon and evening.  A few long-tracked, significant
   tornadoes are possible, along with large, damaging hail and severe
   gusts.

   ...Synopsis...
   A progressive mid/upper-level pattern will remain in place over the
   CONUS through the period, featuring a strong synoptic trough now
   extending from a 500-mb cyclone over the central High Plains
   south-southwestward over eastern NM to Chihuahua.  The cyclone aloft
   will strengthen and move northeastward to western IA by 00Z, with
   trough southwestward over west TX.  For the remainder of the period,
   the cyclone will become vertically stacked with its low-level
   circulation, moving northeastward to southern WI by 12Z tomorrow.

   At the surface, 11Z analysis showed the main surface low near HUT,
   with Pacific cold front arching across central OK, western
   north-central TX, the Edwards Plateau, and northern Coahuila.  The
   Pacific cold front superficially will exhibit some dryline
   characteristics, but with definitive baroclinicity, as it sweeps
   across the lower Missouri and mid Mississippi Valleys today into
   this evening.  By 00Z, the front should reach extreme eastern IA,
   western IL, eastern/southeastern MO, central AR, northern LA, and
   southeast TX.  By 12Z, the front should reach western OH, middle TN
   and near the central part of the LA coastline.  The warm front will
   move northward across eastern IA, northern parts of IL/IN/OH,  and
   parts of western PA by 00Z.  Further northeastward advance of this
   boundary over PA likely will be prevented until day 2, but by 12Z,
   it should reach the shore of Lake Erie in OH.

   ...Mid Mississippi Valley and vicinity...
   Scattered thunderstorms are expected to form in episodic arcs from
   midday through this evening across parts of central/eastern IA,
   eastern MO, IL, and IN, moving northward to northeastward generally
   at 45-60 kt.  This will include supercells with tornadoes (some
   long-tracked and significant at EF2+ damage levels), large and
   sometimes very large hail, and occasionally severe non-tornadic
   gusts.  Given the fast storm motions, any tornadoes that do form may
   persist for nearly as many miles as minutes of time -- at least,
   until supercells cross more than a short distance into what should
   be a very sharp warm-frontal zone.  

   Intense deep-layer winds and low-level shear will be present, with 
   60-80 kt effective-shear magnitudes, amidst 90-100 kt of 500 mb
   flow, under and near a 150-kt 250-mb jet.  Long, somewhat curved
   hodographs are forecast, yielding warm-sector effective SRH of
   200-400 J/kg, but higher along the immediate warm front where
   storm-residence time will be brief.  A zone of favorable
   destabilization -- narrowing with northwestward extent from IL and
   eastern MO into central IA -- is forecast following morning
   clouds/precip, as diurnal heating and steep midlevel lapse rates
   overspread a plume of moist/warm advection just ahead of the Pacific
   front.  Additional supercells may form in the warm sector over IL
   and move into IN, also offering potential for significant
   tornadoes/hail and damaging wind before this part of the event wind
   down in the evening.

   Given that some uncertainties remain regarding the duration and
   width of destabilization across this region with respect to forecast
   rapid supercell motion across the warm sector, and regarding
   coverage of supercells, we are holding the probabilities to those
   supporting a categorical "moderate" threat at this time.  This does
   not preclude the potential for a tightly targeted area of higher
   probabilities during the day if mesoscale developments warrant.

   ...Central/east TX/Arklatex to Mid South/TN Valley...
   See SPC mesoscale discussion 246 for near-term coverage of a
   marginal severe threat with ongoing convection across portions of
   central/north-central TX, near the Pacific front.  

   Peripheral severe-outlook areas have been expanded southwestward
   into most of east TX to account for the increasing potential of
   development through afternoon along/ahead of the Pacific front, as
   well as more of southern MO and eastern OK on conditional potential
   for ongoing convection now in parts of central OK to produce
   isolated strong-severe hail and gusts into those regions in the next
   few hours.  This area will be characterized by weaker deep-layer
   wind fields and midlevel lapse rates than farther north up the
   Mississippi Valley, but still sufficient in a setting of rich
   low-level theta-e, with enough deep shear to support severe
   potential.  With mean-wind and deep-shear vectors oriented with a
   substantial component parallel to the axis of low-level convective
   forcing, mode should be messy, with a mixture of quasi-linear,
   multicell and supercell characteristics.  Tornadoes will be possible
   from supercells and QLCS-embedded vortices, particularly across
   parts of the Mid-South in closer proximity to the intense mid/upper
   winds.

   ..Edwards/Mosier.. 03/28/2020

 

[DanLarsen34]

4 minutes ago, jpeters3 said:

I don't think this is entirely true.  Both the GFS and the NAM/NAM nest, along with the euro intermittently showed solutions over the past few days akin to what the HRRR is showing today.  There were certainly uncertainties going into this event, and it was never a "slam dunk."  A lot of the hype originated from the HRRR runs before and at 00 UTC.

“Everything” was doing more work than I intended here. I’ll edit the post because I agree with this. 

[CoalCityWxMan]

Hrrr not handling current convection over MO too well

[A-L-E-K]

MO convection couldn't be in a worse spot for chicago proper

[Chicago Storm]

That activity across MO/AR/OK/TX is tied to a subtle wave that will rapidly push NE 15-18z.

I noticed the wave on the NAM last evening, but didn’t think much of it until runs of the HRRR caught on to it and started showing activity with it.

And here we sit now this morning with a large corridor of activity across the aforementioned areas, that will push across and near the main areas of interest through early afternoon.

This definitely is a failure mode, and will likely prevent today from being what it could have been.


.

[kevlon62]

MO convection couldn't be in a worse spot for chicago proper

Can we nuke the complex?

Sent from my SM-N960U using Tapatalk

[RyanDe680]

This was fun while it lasted

[bdgwx]

It may not be as focused or as certain as it appeared last night, but odds still favor a significant outbreak including tornadoes. The SPC is still pushing EF2+ tornadoes today afterall. 

[Indystorm]

I think that initial surge of moisture heading to northern IL may be diminishing somewhat and becoming more cellular in nature.  I never discount the power of warm fronts in the spring, particularly with kinematics as strong as what we have today.  Parts of se Missouri and Arkansas are clear.

[nwohweather]

I wouldn’t be too let down by current conditions. This atmosphere will recover extremely quickly

[UMB WX]

1 hour ago, Chicago Storm said:

That activity across MO/AR/OK/TX is tied to a subtle wave that will rapidly push NE 15-18z.

I noticed the wave on the NAM last evening, but didn’t think much of it until runs of the HRRR caught on to it and started showing activity with it.

And here we sit now this morning with a large corridor of activity across the aforementioned areas, that will push across the areas of interested through early afternoon.

This definitely is a failure mode, and will likely prevent today from being what it could have been.


.

Excellent if it comes to fruition.  Last thing communities need right now is more widespread devastation and body bags. 

[hawkeye_wx]

Northern Missouri appears to be clearing out fairly well behind the morning convection.

[crossbowftw3]

This threat is still very much in play. That complex is weakening and clearing is happening behind it.