November 11th-12th storm system

[ClicheVortex2014]

Dr. Forbes is calling it an outbreak already

 

http://www.weather.com/forecast/national/news/severe-storms-tropical-development-snow-flooding-winds

A vigorous southward dip in the jet stream is expected to swing into the Plains and Midwest by Wednesday where it will help spawn the development of a surface low pressure system. That area of low pressure will then intensify as it tracks towards the Great Lakes while intercepting moisture returning north from the Gulf of Mexico.

In short, the combination of those ingredients could lead to a severe weather outbreak, including possible tornadoes, in parts of the Midwest, Plains and mid-South Wednesday into Wednesday night. This includes locations from eastern Nebraska, eastern Kansas, eastern Oklahoma and northeast Texas to northern Louisiana, Arkansas, Missouri, Iowa, extreme southern Wisconsin, Illinois, extreme western Indiana, northern Mississippi, western Tennessee and western Kentucky.

As is always the case several days in advance, there remains uncertainty with the exact details such as the magnitude of this severe weather threat and the exact states where the risk will be the greatest.

Click the link below to see our story which contains the full details and the latest updates on this potential severe weather outbreak.

 

 

WEDNESDAY
There is some uncertainty in the forecast, because instability is predicted to be low but winds and dynamics strong. Severe thunderstorm and tornado threat in the morning and afternoon, then possibly diminishing in the evening as the system heads east into more stable air. Severe thunderstorms in extreme east parts of NE, KS, and OK, extreme northeast TX, north LA, northwest and west-central MS, AR, MO, south and central IA, IL, west KY, west TN, possibly extreme south WI. TORCON - 4 extreme east NE, south and central IA, north MO; 3 - rest of MO; 2 to 3 rest of area

[HillsdaleMIWeather]

I can see the wind line making it to central Ohio, it seems everyone feels the GFS has too little instability.

 

It's also a metric ton more windy.

[Indystorm]

Of course it's the NAM at 84 hrs this A.M. but STP is 5-7 from Quincy over to Springfield IL at 00zThursday.

[Hoosier]

12z ECMWF looks similiar in strength to previous runs, though wind fields seem a little stronger.  I could be wrong...

[HillsdaleMIWeather]

12z ECMWF looks similiar in strength to previous runs, though wind fields seem a little stronger.  I could be wrong...

 

Just checked Eurowx, you would be correct. This Euro run also has more instability.

[Hoosier]

Friday is looking pretty windy too...maybe bumping up near advisory criteria depending on location.

[Hoosier]

Looks like there's an arc of about 500-800 J/kg CAPE in IA/IL at 3z Thursday on the 12z ECMWF.  Something I've noticed though on the models in general is that it seems like the better instability starts to trail the precip to some extent.

[IllinoisWedges]

Just to give a bit more insight, even though we shouldn't rely on analogs. This is the 12z set. 

 

Yes, that is 11/17/13 in there. 

 

Link: http://www.eas.slu.edu/CIPS/ANALOG/DFHR.php?reg=MV&fhr=F096&rundt=2015110812

[Hoosier]

Just to give a bit more insight, even though we shouldn't rely on analogs. This is the 12z set. 

 

Yes, that is 11/17/13 in there. 

 

 

Looking at that map, I knew 11/17/13 was on there. 

[Chambana]

Wow. Heavy hitters in that analog package.

[ClicheVortex2014]

Yeah GFS was a bit conservative with the instability for the event on the 5th. With the extremely strong/veering winds... I'd imagine 1000 j/kg is approximately the threshold for a more serious tornado threat... as was the case in 11/17/13 and 3/2/12

 

Maybe even less than that if I actually knew what happened with 10/26/10. Not sure why tornadic supercells were expected with 250-500 CAPE at best (apparently).

[OHweather]

Yeah GFS was a bit conservative with the instability for the event on the 5th. With the extremely strong/veering winds... I'd imagine 1000 j/kg is approximately the threshold for a more serious tornado threat... as was the case in 11/17/13 and 3/2/12

Maybe even less than that if I actually knew what happened with 10/26/10. Not sure why tornadic supercells were expected with 250-500 CAPE at best (apparently).

Ehh 10/26/10 was more of a QLCS IIRC, but still managed to pull off 57 tornado reports.

[ClicheVortex2014]

Ehh 10/26/10 was more of a QLCS IIRC, but still managed to pull off 57 tornado reports.

It turned out that way, yeah... but SPC was expecting some supercells to pop ahead of the line. In retrospect, it didn't happen because there was too much CIN ahead of the squall.

 

MCD announcing the imminent tornado watch for the western half of the OV:

 

ARCING BAND OF STRONG/SEVERE STORMS CONTINUES MOVING RAPIDLY

EWD/ENEWD ACROSS THE MID AND UPPER MS VALLEY REGION AND

VICINITY...ALONG THE SURFACE COLD FRONT ASSOCIATED WITH A VERY

STRONG UPPER SYSTEM CENTERED OVER MN/IA/MO ATTM. A MOIST

PRE-FRONTAL BOUNDARY LAYER IS SUPPORTING MODEST INSTABILITY --

FUELING THE ONGOING STORMS...WHILE VERY STRONG FLOW FIELD THROUGH

THE ENTIRE TROPOSPHERE IS AIDING IN STORM ORGANIZATION/INTENSITY.

CONVECTION HAS REMAINED LARGELY CONFINED TO THE FRONTAL BAND -- AND

THUS MAIN SEVERE THREAT REMAINS DAMAGING WINDS. HOWEVER...WITH

SHEAR SUPPORTIVE OF UPDRAFT ROTATION...THREAT FOR ISOLATED TORNADOES

WILL PERSIST EARLY THIS MORNING -- AND MAY INCREASE THROUGH MIDDAY

AS POTENTIAL FOR MORE WIDESPREAD PRE-FRONTAL CELLULAR CONVECTION

INCREASES.

 

Then the actual tornado watch:

 

DISCUSSION...WRN IND/KY QLCS EXPECTED TO GRADUALLY STRENGTHEN AND

MOVE GENERALLY ENE AS WW REGION IS GLANCED BY IA/MO VORT LOBE

EJECTING NE TOWARD THE UPR GRT LKS. MODEST SFC WARMING...INCREASING

LOW LVL MOISTURE...AND INTENSE WIND FIELD TOGETHER SUGGEST

LIKELIHOOD FOR EMBEDDED SUPERCELLS/MESOVORTICES THAT WILL POSE A

THREAT FOR POTENTIALLY STRONG TORNADOES IN ADDITION TO BOWING

SEGMENTS WITH HIGH WIND. A LOW PROBABILITY ALSO WILL EXIST FOR THE

DEVELOPMENT OF A COUPLE ISOLD STORMS AHEAD OF QLCS IN ANY AREAS

WHERE LOW LVL CONFLUENCE IS SUFFICIENT TO OVERCOME EXISTING CINH.

ANY SUCH ACTIVITY WILL HAVE THE POTENTIAL TO YIELD A LONGER

LIVED...POSSIBLY STRONG TORNADO.

 

[Hoosier]

10/26/2010 definitely had activity tied to the front with nothing really out ahead.

 

 

[brohnhdon]

11/17/13 is only in the analogs because 500mb heights correlate well. Although the location and intensity of the system are comparable, 11/17/13 saw widespread 2000+ J/kg CAPE across Illinois. This system will be lucky to draw 750 J/kg. With helicity values approaching 1000 m2/s2 though, I wouldn't rule anything out...certainly a non-zero chance for a strong tornado or two, but not quite an outbreak I don't think.

[HillsdaleMIWeather]

For more insight from the CIPS with all analogs:

 

 

Hypothetical Worst Case Scenario has a High Risk:

 

 

^ Primarily for wind. 

[ClicheVortex2014]

11/17/13 is only in the analogs because 500mb heights correlate well. Although the location and intensity of the system are comparable, 11/17/13 saw widespread 2000+ J/kg CAPE across Illinois. This system will be lucky to draw 750 J/kg. With helicity values approaching 1000 m2/s2 though, I wouldn't rule anything out...certainly a non-zero chance for a strong tornado or two, but not quite an outbreak I don't think.

I agree in general... but I agree with the idea of calling this a "possible" outbreak at this time. I'm not talking about a tornado outbreak though; that's much less likely IMO.

 

There was certainly a decent area of 2000 CAPE on 11/17... but most of the tornadoes in Illinois happened in ~1000 CAPE. Then all the tornadoes in Indiana, extreme south Illinois, Ohio, and Kentucky occurred with less than 1000 CAPE. Of course these were much weaker than the ones in central Illinois... but this is where a good portion of the tornadoes occurrred

 

[OHweather]

It turned out that way, yeah... but SPC was expecting some supercells to pop ahead of the line. In retrospect, it didn't happen because there was too much CIN ahead of the squall.

 

MCD announcing the imminent tornado watch for the western half of the OV:

 

 

Then the actual tornado watch:

Yeah, all activity that day was tied to strong forcing along the front with nothing ahead. I guess it's a little curious why the SPC expected supercells ahead of the squall line...the point being though that it was still a decent tornado producer.

[ClicheVortex2014]

Yeah, all activity that day was tied to strong forcing along the front with nothing ahead. I guess it's a little curious why the SPC expected supercells ahead of the squall line...the point being though that it was still a decent tornado producer.

Agreed. Not only because of the lack of forcing ahead of the squall... but I wouldn't expect long-lived tornadic supercells to form in the <500 CAPE that was ahead of the line. I guess this is only because I'm not aware of a time where that amount of instability has fostered a long-lived tornadic supercell.

[OHweather]

Agreed. Not only because of the lack of forcing ahead of the squall... but I wouldn't expect long-lived tornadic supercells to form in the <500 CAPE that was ahead of the line. I guess this is only because I'm not aware of a time where that amount of instability has fostered a long-lived tornadic supercell.

One of the 3/2/12 supercells tracked into an area with very low instability in WV while still producing a strong tornado, but it developed in an area of higher CAPE initially.

[brohnhdon]

I agree in general... but I agree with the idea of calling this a "possible" outbreak at this time. I'm not talking about a tornado outbreak though; that's much less likely IMO.

 

There was certainly a decent area of 2000 CAPE on 11/17... but most of the tornadoes in Illinois happened in ~1000 CAPE. Then all the tornadoes in Indiana, extreme south Illinois, Ohio, and Kentucky occurred with less than 1000 CAPE. Of course these were much weaker than the ones in central Illinois... but this is where a good portion of the tornadoes occurrred

Well, we haven't seen a year with no high-risk days since 2000 and only 3 have been issued since then in November or December. Wishful thinking   . In seriousness though, I do think this system will progress somewhat like 11/17/13. More of a tornado threat in the Western-sub before (in my opinion) a fairly widespread wind damage threat further east. Lapse rates across the northern portion of the line in Indiana and Ohio aren't too bad...I've hand calculated some SHERB values for Wednesday in Ohio and they're very respectable in the 0.9 - 1.3 range (1 is the sig-severe threshold).

[ClicheVortex2014]

Does anyone remember the forecasted CAPE values leading up to the 11/17 event? This event happened when I was very new at this kind of stuff... so I wasn't looking at the CAPE/shear/etc.

 

But I remember I saved an image of NAM that was about 60 hours out that showed a large, obviously continuous squall line near the Indiana/Illinois border. That's why I remember I was extremely surprised to wake up on that day and, not only see that there's a high risk for tornadoes, but that I was included in it. So I get the impression that something changed pretty close to the event, and I wonder what that was.

[Hoosier]

Obviously getting 1000+ CAPE would really up the ante, but we shouldn't need it in this case.  imo, anything north of ~500 J/kg could lead to a fairly robust tornado threat.  If you asked me what the floor is for this event, I'd say a decent damaging wind producer with embedded brief tornadoes.  The ceiling would be a lot higher. 

[HillsdaleMIWeather]

Does anyone remember the forecasted CAPE values leading up to the 11/17 event? This event happened when I was very new at this kind of stuff... so I wasn't looking at the CAPE/shear/etc.

 

But I remember I saved an image of NAM that was about 60 hours out that showed a large, obviously continuous squall line near the Indiana/Illinois border. That's why I remember I was extremely surprised to wake up on that day and, not only see that there's a high risk for tornadoes, but that I was included in it. So I get the impression that something changed pretty close to the event, and I wonder what that was.

 

I remember:

 

GFS had widespread 1000 j/kg to Chicago, 500 k/jg to Detroit, with a very small 2000 area.

 

NAM had the large area of 2000 that verified, with 1000 arching into Michigan to near Three Rivers.

[Hoosier]

Does anyone remember the forecasted CAPE values leading up to the 11/17 event? This event happened when I was very new at this kind of stuff... so I wasn't looking at the CAPE/shear/etc.

 

But I remember I saved an image of NAM that was about 60 hours out that showed a large, obviously continuous squall line near the Indiana/Illinois border. That's why I remember I was extremely surprised to wake up on that day and, not only see that there's a high risk for tornadoes, but that I was included in it. So I get the impression that something changed pretty close to the event, and I wonder what that was.

 

 

There were models hinting at 1000-2000 J/kg CAPE in the leadup. 

[brohnhdon]

Does anyone remember the forecasted CAPE values leading up to the 11/17 event? This event happened when I was very new at this kind of stuff... so I wasn't looking at the CAPE/shear/etc.

 

But I remember I saved an image of NAM that was about 60 hours out that showed a large, obviously continuous squall line near the Indiana/Illinois border. That's why I remember I was extremely surprised to wake up on that day and, not only see that there's a high risk for tornadoes, but that I was included in it. So I get the impression that something changed pretty close to the event, and I wonder what that was.

I'm actually in the process of my own case-study type project of model performance in the 7-10 day range leading up to that outbreak. When its finished - I hardly know when at this point - I'll post my findings somewhere and let you know. Hopefully it will be interesting.

 

Also IIRC, the 11/17/13 outbreak was originally forecast to be exactly where the current D4 (Mississippi valley) is on its D5. Later outlooks then shifted the outlook area. Maybe a similar shift with this system once we get land observations?

[Thundersnow12]

I agree in general... but I agree with the idea of calling this a "possible" outbreak at this time. I'm not talking about a tornado outbreak though; that's much less likely IMO.

 

There was certainly a decent area of 2000 CAPE on 11/17... but most of the tornadoes in Illinois happened in ~1000 CAPE. Then all the tornadoes in Indiana, extreme south Illinois, Ohio, and Kentucky occurred with less than 1000 CAPE. Of course these were much weaker than the ones in central Illinois... but this is where a good portion of the tornadoes occurrred

 

 

Eh false. I believe the ILX sounding at 16z had 1,900 j/kg of CAPE

[Hoosier]

Eh false. I believe the ILX sounding at 16z had 1,900 j/kg of CAPE

 

 

[ClicheVortex2014]

I'm actually in the process of my own case-study type project of model performance in the 7-10 day range leading up to that outbreak. When its finished - I hardly know when at this point - I'll post my findings somewhere and let you know. Hopefully it will be interesting.

 

Also IIRC, the 11/17/13 outbreak was originally forecast to be exactly where the current D4 (Mississippi valley) is on its D5. Later outlooks then shifted the outlook area. Maybe a similar shift with this system once we get land observations?

Day 5 had a similar position, but it shifted when we got to day 4

 

 

Eh false. I believe the ILX sounding at 16z had 1,900 j/kg of CAPE

You're right... my mistake. A bunch of tornadoes happened there, but there was also a decent amount of tornadoes that happened elsewhere in the state (i.e., south), which was in ~1000 CAPE

[brohnhdon]

If we could get a little more dry air into the middle levels along the line, momentum transfer could be pretty efficient at drawing down 60-70 kt. winds along the squall line. Decent lapse rates wouldn't hurt either.

 

Sounding for central Ohio: