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Major Severe Weather Outbreak November 17

Hoosier

By Hoosier,
in Weather Forecasting and Discussion

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Gilbertfly

Gilbertfly

Posted
Posted

Still the same NAM it was yesterday when we were tossing it, buds...

Sent from my HTCONE

 

FWIW....

 

 

MODEL DIAGNOSTIC DISCUSSION

NWS WEATHER PREDICTION CENTER COLLEGE PARK MD

136 PM EST FRI NOV 15 2013

VALID NOV 15/1200 UTC THRU NOV 19/0000 UTC

LONGWAVE TROUGH EVOLVING OVER THE WESTERN U.S. ON SAT...EJECTING

OUT ACROSS THE PLAINS/MS VALLEY AND THE GREAT LAKES THROUGH SUN/MON

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

PREFERENCE: NON 12Z NAM CONSENSUS

CONFIDENCE: AVERAGE

THE 12Z NAM IS QUICKER THAN THE REMAINING GUIDANCE AS THE UPPER

TROUGH EJECTS OUT INTO THE PLAINS AND THE NAM IS NEARLY OUTSIDE OF

THE ENSEMBLE SPREAD WITH ITS SURFACE LOW BY 00Z/18. WITH THE

REMAINING GUIDANCE TRENDING TOWARD ONE ANOTHER OVER THE PAST FEW

CYCLES...THE PREFERENCE IS TO GO TOWARD THE NON-NAM CONSENSUS.

 

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Chicago Storm

Chicago Storm

Posted
Posted

Still the same NAM it was yesterday when we were tossing it, buds...

Sent from my HTCONE

Yep.

 

Regarding frontal timing, the NAM and the GFS remain similar. The NAM obviously still has the SLP a bit further north though compared to other guidance. The 12z ECMWF was a tad more progressive yet again. Another run and it might be in the GFS/NAM camp.

 

As I said before, the NAM/GFS obivously still have a significant threat, but the previous ECMWF solutions were even more significant. Then add on that a more progressive solution cuts down on aerial coverage, and would take cities such as the QC, STL, MKE and possibly Chicago out of play.

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weatherwiz

weatherwiz

Posted
Posted

Saw this on twitter today. You don't need much CAPE when you have mad shear.

BZI4DtOCcAAC__m.png

That can be true but if shear is through the roof you need some sort of compensation or otherwise updrafts are just going to get shredded and they won't be able to grow talk enough to utilize Those stronger winds aloft. While you don't need a lot of cape you would at least want to see a to no forcing or jet support.

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Quincy

Quincy

Posted
Posted

I've been watching this potential for a while, but the 18z NAM almost caused me to fall out of my chair.

 

I pulled up the SPC Environmental Browser for central Indiana and it too shows that you don't need a lot of CAPE (MLCAPE). High (very high in this case) shear/low CAPE setups can certainly perform.

http://www.spc.noaa.gov/exper/envbrowser/

 

Note that for all tornadoes in the region, the mean MLCAPE value was 693 J/kg. That means that half of tornadoes in the area had less MLCAPE. The mean effective shear for those cases was 44kt.
envbw.gif

 

For significant tornadoes, MLCAPE did increase, but just to 997 J/kg for the mean. The range for most of the cases was 737 to 1222 J/kg.

 

The 18z NAM shows a large area of MUCAPE (and MLCAPE) >1000 J/kg during the peak heating, all the way up into Michican. Notice at 18z the most impressive parameters over the IN/IL border include MUCAPE of 1500 J/kg (MLCAPE of over 1000) and sfc-500mb bulk shear of about 60 knots. (Even if this is overdone, which it very well may be, wow.)
namUS_con_mucape_048.gif

 

Watch out if anything close to this forecast verifies. Also, I'm not sure it has been mentioned much, but we're looking at rather low LCL's too, which can enhance the tornado threat.

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Stebo

Stebo

Posted
Posted

timing is far from optimal for Chicagoland, we look to dodge this bullet.

I would be leery of this thought given the points Tony gave and the expectation that stuff will get going in IA and MO late tomorrow evening, stuff might be going during the morning and the parameters are more than ample to maintain stuff overnight tomorrow night. Sure it isn't the best time of day historically but things still would remain favorable.
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tornadotony

tornadotony

Posted
Posted

Folks seriously, I'm gonna harp on this until I'm blue in the face b/c timing isn't going to matter nearly as much in this case as in other cases.  How many cold season events in the GLOV region have started much earlier than what would normally be considered ideal (say, 15-19z)?  Let's think about it...

 

10/24/01

11/10/02

11/15/05

10/26/10

12/31/10

3/2/12

 

Anyone who thinks that the timing of this event, be it NAM/GFS or Euro, is going to all-out protect the I-55/I-57 corridors or the Chicago area, IMO, is doing a disservice to the discussion by ignoring the fact that the conditions on all three of the previously alluded to models would already be supportive of severe wx by 15z at the latest and all three models have convection going full blast by 18z (again, at the latest).  Again, this is going to be a dynamically-driven system with the dynamics driving the thermodynamics into being supportive of severe wx, whether or not there's sun, whether or not it's 15z or 18z or 21z or 00z or 03z.  We gotta keep that perspective into this discussion.

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Indystorm

Indystorm

Posted
Posted

From IWX Fri. afternoon discussion

NAM/GFSGENERALLY DEPICT BETWEEN 300-800 J/KG OF SURFACE BASED CAPE LATEMORNING SUNDAY THROUGH SUNDAY EVENING. STRONG UPPER DVG ANDPREFRONTAL TROUGH DO LEND SOME CONCERN OF PREFRONTAL CONVECTIONDEVELOPING LATE MORNING/EARLY AFTERNOON FOLLOWED BY LIKELY MOREORGANIZED BAND WITH THE ACTUAL COLD FRONT FROM THE MID AFTERNOON TOEARLY EVENING HOURS. STRONG BACKGROUND FLOW LENDS CONCERN FORDAMAGING WIND GUSTS WITH LEADING FRONTAL BAND CONVECTION WHICH WILLLIKELY BE THE PRIMARY SEVERE WEATHER CONCERN. SHERBS3 PARAMETERVALUES FROM 12Z NAM STILL RANGE FROM 1.3 TO 1.5 AND 0-3 KM BULKSHEAR VALUES OF 40 TO 50 KNOTS ACROSS THE LOCAL AREA STILL SUGGESTPOTENTIAL FOR MESOVORT TYPE TORNADO SPIN UPS ALONG LEADING EDGE OFSHALLOW CONVECTIVE LINE.
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Memphis Weather

Memphis Weather

Posted
Posted

Yeah, folks should not get too caught up with the timing on this one. Sun is not a requirement for sufficient destabilization in the higher threat areas, because of the rush of mid-level cooling, aiding in steep lapse rates. It's actually across those southern areas again where sunshine is probably going to be a requirement in order to push destabilization and force convection, because those dynamics will be missing there.

 

That doesn't mean Chicago or other points further west/north of SPC's 30% risk will absolutely be at risk for a big tornado problem, but it may at least be higher than those on the eastern end, simply because of the convective evolution into a squall line by that time. It will all depend on how the radar looks Sunday morning. Dynamically driven events such as this one *do* typically have an earlier start time and the examples above should make that apparent.

 

Now with that said, the most concerning area remains across S & E Illinois into W & Central Indiana IMO. 

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chase_stormz

chase_stormz

Posted
Posted

The more I look at this, the more I see the highest potential for strong tornadoes to occur between 12-18z across the Northern half of Illinois into Indiana as the surface winds back ahead of the deepening surface low pressure. Don't let your guard down folks, while it's not the typical time for tornadoes, the parameters are there during this time frame. MUCape values >1000 combined with extreme wind shear spell something nasty.

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Jim Marusak

Jim Marusak

Posted
Posted

Saw this on twitter today. You don't need much CAPE when you have mad shear.

BZI4DtOCcAAC__m.png

 

that's part of that sliding scale I always remembered from my days as a student, where as long as the storms don't tear themselves apart, the biggest producers were high-cape low dynamics or low-cape-high-dynamics. And this case is looking a lot like the low-cape high-dynamics type.

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TimChgo9

TimChgo9

Posted
Posted

Folks seriously, I'm gonna harp on this until I'm blue in the face b/c timing isn't going to matter nearly as much in this case as in other cases.  How many cold season events in the GLOV region have started much earlier than what would normally be considered ideal (say, 15-19z)?  Let's think about it...

 

10/24/01

11/10/02

11/15/05

10/26/10

12/31/10

3/2/12

 

Anyone who thinks that the timing of this event, be it NAM/GFS or Euro, is going to all-out protect the I-55/I-57 corridors or the Chicago area, IMO, is doing a disservice to the discussion by ignoring the fact that the conditions on all three of the previously alluded to models would already be supportive of severe wx by 15z at the latest and all three models have convection going full blast by 18z (again, at the latest).  Again, this is going to be a dynamically-driven system with the dynamics driving the thermodynamics into being supportive of severe wx, whether or not there's sun, whether or not it's 15z or 18z or 21z or 00z or 03z.  We gotta keep that perspective into this discussion.

Makes sense to me.

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andyhb

andyhb

Posted
Posted

Uh oh...0z NAM coming in with even more instability by 15z Sunday morning, SBCAPE/MLCAPE values of 1500 j/kg now, only making STP go up even higher with southerly sfc winds.

 

attachicon.gifnamCGP_con_stp_039.gif

 

Equal sized area at 18z as well shifted east to focus on IN.

 

Also let's also note that the area is covered in H5 temperatures of -15 to -20˚C. It's kind of scary to see the NAM increasing the strength of the incoming 500 mb jet streak with every run, which is now at a whopping 110-120 kts at 42 hrs ripping through KS/MO. 60-75 kt LLJ to boot shifting eastward through the afternoon.

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