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November 5th, 2017 Severe Weather Event


IllinoisWedges

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text...

Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0100 AM CDT Sat Nov 04 2017

   Valid 051200Z - 061200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   IL/IN AND NORTHWESTERN OH...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE MID MS VALLEY INTO THE OH VALLEY AND LOWER GREAT LAKES...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
   SLIGHT RISK...

   ...SUMMARY...
   Scattered severe thunderstorms capable of producing large hail,
   damaging winds, and a few tornadoes may occur across parts of the
   Lower Great Lakes, Midwest, and Ohio Valley regions on Sunday.

   ...Synopsis...
   A split flow pattern aloft will continue over much of the
   western/central CONUS on Sunday, with modest 500 mb height falls
   (around 30 dm per 12 hours) forecast to occur across the mid/upper
   MS Valley into the Great Lakes region. A strong southern-stream
   mid/upper-level jet will provide large-scale lift and should
   encourage convective development across parts of the lower Great
   Lakes, OH Valley, and mid MS Valley by Sunday afternoon. An elevated
   mixed layer with steep mid-level lapse rates (around 7-8 C/km in the
   700-500-mb layer) originating from the central/southern Plains will
   overspread these regions through Sunday evening.

   At the surface, a broad and moist warm sector will be in place
   across east TX into the lower MS Valley, extending northward into
   the mid MS Valley, OH Valley, and Lower Great Lakes to the south of
   a warm front. Surface dewpoints reaching into at least the low to
   mid 60s should be common throughout the warm sector Sunday
   afternoon. A weak surface low is forecast to develop northeastward
   along a warm/cold frontal triple point from the vicinity of eastern
   KS/western MO early Sunday to northern IN/southern lower MI by
   Sunday evening. A trailing cold front will progress southeastward
   parts of the mid MS and OH Valleys through the day, likely
   accelerating late in the period.

   ...Lower Great Lakes/Midwest into the OH and Mid MS Valleys...
   Strong effective shear of 40-55 kt associated with the
   southern-stream mid/upper-level jet will likely be present
   along/south of the front mentioned above. Supercell thunderstorms
   may be favored with initial development along the warm front or
   within the open warm sector to the east/northeast of the surface
   low. Given the steep mid-level lapse rates and moist low-level
   airmass that will be present, MLCAPE may increase to around
   1500-2000 J/kg by late Sunday afternoon, even with only modest
   diurnal heating forecast.

   Scattered large hail, some of which may be significant, could occur
   with initial supercell development, particularly across parts of
   central/eastern IL into western/central IN where buoyancy is
   expected to be greatest. The tornado potential should be maximized
   along the warm front through Sunday afternoon as long as the
   convective mode remains at least semi-discrete. Here, low-level
   winds should be backed to a more southerly direction, locally
   enhancing low-level helicity and updraft rotation. Eventual upscale
   growth into one or more bowing line segments may occur from late
   Sunday afternoon into the evening as the cold front begins to
   accelerate southeastward, and the primary severe threat should
   eventually transition to damaging winds. The accelerating cold front
   may tend to undercut ongoing convection by Sunday night, and with
   decreasing instability due to the loss of diurnal heating, the
   overall severe threat should gradually wane with eastward/southward
   extent late in the period.

   00Z GFS/NAM and 12Z ECMWF are in better agreement with the placement
   of the surface warm front Sunday afternoon, which increases
   confidence in the northern extent of appreciable surface-based
   thunderstorm potential and corresponding severe risk. The gradient
   of severe thunderstorm probabilities has therefore been tightened
   across far eastern IA/northern IL and southern/central Lower MI. The
   potential remains for early-day elevated convection across parts of
   IL/IN/OH owing to a strong southwesterly low-level jet. But this
   activity, if it develops, will likely remain isolated and should not
   substantially impact/delay destabilization of the warm sector across
   this region.

   ..Gleason.. 11/04/2017
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Latest HWO from ILX linked below.  ILX will also be having a conference call concerning tomorrow's severe threat at 2PM this afternoon (it seems like they do almost anytime there's a hatched and/or a Moderate risk anywhere in their CWA):

https://forecast.weather.gov/product.php?site=ilx&product=HWO&issuedby=ilx

 

 

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1 hour ago, Indystorm said:

12z NAM seems to be holding the WF farther south as it has previously done.  More of central and southern IL and IN now in play for severe.  Only 49 degrees here at 11am and cloudy.  Marion IL is 63/61.  The strength of the system will be paramount in deciding how far north that front goes on Sunday.

I would think the probabilities may be trimmed on the northern edge on the upcoming outlook.    

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3 minutes ago, Hoosier said:

I would think the probabilities may be trimmed on the northern edge on the upcoming outlook.    

Guarantee they are, I would pull them out of every MI county except Lenawee and Monroe Counties. Problem is now too many small ripples coming through so an initial small surface reflection comes through around 15z essentially closing the door to the north and not allowing the main low to lift the front. In other words this potential is finding anything and everything to limit it.

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Being a Sunday I am too busy tomorrow to consider chasing.  I agree the Lafayette/Kokomo area looks good, but follow wherever that warm front sets up as you well know for greatest chance of backing winds and any tor potential.   Though I agree with Chambana that hail seems to be the biggest threat right now.

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Think I'm going to head over to Frankfort and work from there if everything pans out.  Most of the fields are in so should have good visibility.  The other half and I were going to Kokomo tomorrow anyway so I've talked her into going on her first chase with me.:P  I know some big hailers and lightning will scare her more than than any spin ups so it could get interesting for us..  My windshields still broke in my chaser beater from a chase back in the spring lol.  Hopefully my new camera mount won't fail me this time!

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Oh NAM, the things you do to us sometimes.

I should say I'm somewhat intrigued by how bullish the SREF has been with this. 15z run is popping a max of 75 on the STI around I-70 at 00z. I would like to see more support for pre-frontal convection though given the rather iffy shear vectors (forcing along/behind the front), and in general more support for the kind of shear profiles the 18z NAM is indicating, most other guidance isn't quite that impressive.

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4 minutes ago, Hoosier said:

Even with a pretty pathetic surface low and likely a limited tornado count, the CAPE/shear parameters and rich low level moisture would support the possibility of a strong tornado, particularly the longer that cellular mode can be maintained.

Very large hail is a big concern and a moderate risk for hail would not surprise me. Even the slightly less unstable HRRRX shows a CAPE/shear parameter space that would support very efficient hail growth. Very uncommon for this time of year. Some soundings I pulled showed 700-500mb lapse rates steeper than 8 C/km. 

IMG_5515.thumb.JPG.bddb226a9e3241230c8a148b1cddeac8.JPG

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1 minute ago, Quincy said:

Very large hail is a big concern and a moderate risk for hail would not surprise me. Even the slightly less unstable HRRRX shows a CAPE/shear parameter space that would support very efficient hail growth. Very uncommon for this time of year. Some soundings I pulled showed 700-500mb lapse rates steeper than 8 C/km. 

IMG_5515.thumb.JPG.bddb226a9e3241230c8a148b1cddeac8.JPG

Could the potential moderate risk stretch into Northwest Ohio as well tomorrow?

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The CWASP parameter off the 18z NAM on the CIPS model page is popping a value of 90 (very high) at 21z in a similar area to the SREF max.

CWASPnam212F027.png

Info on this parameter: http://www.spc.noaa.gov/exper/mesoanalysis/help/help_cwasp.html

Max value you can actually achieve on this is a 99 since it's an aggregate of 33 parameters on a scale from 0-3.

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Makes a potential chase tomorrow very iffy. Usually don't deal with the big hail in this part of this country.

I will say this, Quincy nailed it. Might not see a proliferation of twisters, but definitely wouldn't be shocked to see a couple strong ones and maybe 10. Happened like that last August, had a free day from work and liked the environment, didn't expect to be chasing a half mile wide tornado in NW Ohio

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35 minutes ago, nwohweather said:

Makes a potential chase tomorrow very iffy. Usually don't deal with the big hail in this part of this country.

I will say this, Quincy nailed it. Might not see a proliferation of twisters, but definitely wouldn't be shocked to see a couple strong ones and maybe 10. Happened like that last August, had a free day from work and liked the environment, didn't expect to be chasing a half mile wide tornado in NW Ohio

I know how you feel, I'm begrudgingly chasing tomorrow since I have to drive down near Fort Wayne to get something tomorrow. Hoping my windshield doesn't get busted.

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4 hours ago, Jackstraw said:

Think I'm going to head over to Frankfort and work from there if everything pans out.  Most of the fields are in so should have good visibility.  The other half and I were going to Kokomo tomorrow anyway so I've talked her into going on her first chase with me.:P  I know some big hailers and lightning will scare her more than than any spin ups so it could get interesting for us..  My windshields still broke in my chaser beater from a chase back in the spring lol.  Hopefully my new camera mount won't fail me this time!

Good luck on your chase tomorrow with your wife going along.  Sometimes fall rather than spring events can yield surprises.  I will be watching models and radar carefully.

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4 minutes ago, Indystorm said:

Good luck on your chase tomorrow with your wife going along.  Sometimes fall rather than spring events can yield surprises.  I will be watching models and radar carefully.

Thanks! The good 'ol in the fall you don't chase 'em , they chase you in Indiana  kinda surprises!  Still some sorting out as everyone's pointed out but if we get a mini outbreak, and we can get lucky, hopefully we can get some good pics and video...... if I can control the potential localized panic lol.

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Unfortunately, in my position with EMA, I won't be able to chase since there's still a slight possibility of severe hitting in the FWA and just south area. I would love to be able do a little chase. Good luck Jack and the others that are going out. I'll just be waiting for them to come to me here in Huntington County.

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