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2017 Short/Medium Range Severe Thread


Hoosier

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10 minutes ago, Stebo said:

Yeah not much to decipher from the NAM at this point.  If anything the inverse NAM principle is in effect. :lmao:

Something I noticed is that even with the weaker surface low, the low level flow in the warm sector looks a hair less veered than the 18z GFS.

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2 minutes ago, Hoosier said:

Something I noticed is that even with the weaker surface low, the low level flow in the warm sector looks a hair less veered than the 18z GFS.

Not surprising since GFS is so notorious for veering the low level flow. The Euro is more backed as well too, which would lead to more credence that the GFS is struggling with low level winds.

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Caveat emptor as always at NAM at 84 but at least it didn't lose the storm.  Been rewatching videos of the Washington IL tornado of four years ago and waiting to see what future model runs say.  Right now I think any sig tornado activity might be best positioned in north central IL and IN closer to that warm front but things could change.  If a stronger southern low does materialize things could get quite interesting.  Both Skilling and Sebenste are raising heightened concerns at this time.

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The GFS for 3 runs in a row lights up the warm front in Michigan between 18 and 21z, the parameter space is very good there too and the surface  winds this run are a bit more backed enhancing the low level shear. Definitely something to monitor and see if it continues as a trend. 

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11 hours ago, Hoosier said:

Yeah it does look higher (as currently progged) farther east.  Illinois though had widespread 1000-2000+ J/kg that day, which is similar to what's being progged.   Bottom line, a high end CAPE day for this time of year with questions on evolution and shear (especially low level).  I'd rather have the instability in place and figure out the shear details later compared to the other way around.

IIRC the models were somewhat conservative with forecast instability until right before the event when some of the higher res models started to show the higher cape values you mentioned.

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9 minutes ago, cyclone77 said:

IIRC the models were somewhat conservative with forecast instability until right before the event when some of the higher res models started to show the higher cape values you mentioned.

I don't really remember to be honest.  The thing I do recall was that we were saying how that outbreak was going to get underway by late morning/noon (and models already had pretty good instability by that time) and that is what happened.

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20 minutes ago, Hoosier said:

I don't really remember to be honest.  The thing I do recall was that we were saying how that outbreak was going to get underway by late morning/noon (and models already had pretty good instability by that time) and that is what happened.

Blast from the past....thread from the 11/17/13 event..  

 

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I think Stebo is onto something about the warm front.  This would be roughly in a box including northern IL/northern IN/southern MI.  That looks like a potentially intriguing target for enhanced tornado chances if the instability is realized, though everybody in the threat area will have some tornado threat with the large low level hodos. 

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5 minutes ago, Hoosier said:

I think Stebo is onto something about the warm front.  This would be roughly in a box including northern IL/northern IN/southern MI.  That looks like a potentially intriguing target for enhanced tornado chances if the instability is realized, though everybody in the threat area will have some tornado threat with the large low level hodos. 

Yeah, also I wouldn't sleep on this lasting after sunset which would be an hour earlier too, the LLJ cranks up by 00z and the atmosphere should remain uncapped as well. It may gel into a QLCS by then though too. Still would have a tornado potential though.

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2 hours ago, cyclone77 said:

IIRC the models were somewhat conservative with forecast instability until right before the event when some of the higher res models started to show the higher cape values you mentioned.

2 hours ago, Hoosier said:

I don't really remember to be honest.  The thing I do recall was that we were saying how that outbreak was going to get underway by late morning/noon (and models already had pretty good instability by that time) and that is what happened.

Yup that is how it happened. The NAM/GFS also had quite a few issues with timing as well, with some of them quite a bit faster/less amplified with the shortwave than what ended up verifying.

The forecast instability (at least from the Euro) here is a tick higher than what we saw then tbh (which was a smaller pocket of ~2000 J/kg CAPE centered around PIA, and eventually utilized by the supercell that spawned the Washington tornado), at the expense of somewhat less impressive shear profiles warm sector wide, at least as it sits now.

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Day 4 30%

Discussion below

Quote

ALTHOUGH MODEL TIMING DIFFERENCES EXIST, TRENDS CONTINUE TO POINT TO   SEVERE THUNDERSTORMS CAPABLE OF LARGE HAIL, DAMAGING WIND AND   ISOLATED TORNADOES ON SUN/D4, ROUGHLY FROM ILLINOIS INTO OHIO. A   BROAD AREA OF CYCLONIC FLOW ALOFT WITH DUAL/PARALLEL SHORTWAVE   TROUGHS WILL AFFECT THE UPPER AND MIDDLE MS VALLEYS, AND POINTS EAST   INCLUDING THE GREAT LAKES REGION. SOME EARLY DAY STORMS MAY EXIST   ACROSS THE REGION AS SOUTHERLY WINDS CREATE LIFT NEAR A WARM FRONT,   BUT THE MAIN SEVERE WEATHER THREAT WILL BE NEAR THE SURFACE LOW AND   COLD FRONT AS IT SWEEPS EASTWARD FROM SUNDAY AFTERNOON INTO MONDAY   MORNING. COLD TEMPERATURES ALOFT, A CAPPING INVERSION OVER THE WARM   SECTOR AND LONG HODOGRAPHS SUGGEST SUPERCELLS MAY BE THE DOMINANT   STORM MODE, CREATING DAMAGING HAIL AND WIND. A FEW TORNADOES WILL   ALSO BE POSSIBLE GIVEN A 50 KT LOW-LEVEL JET, AND MOST LIKELY WITH   ANY SUPERCELLS THAT CAN TRACK EASTWARD ALONG THE INTERSECTION OF THE   COLD FRONT AND WARM FRONT/OUTFLOW BOUNDARY.    

 

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  • 2 weeks later...

18z GFS continues with the impressive looking weekend system, though still faster than the Euro.  

Too early to get deep into details, but it should have at least some severe potential if it evolves anything like the models are suggesting (has a decent EML/steep lapse rates... not quite like the 11/5 system but the rapidly deepening surface low is obviously a big difference this time).  

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1 hour ago, Hoosier said:

18z GFS continues with the impressive looking weekend system, though still faster than the Euro.  

Too early to get deep into details, but it should have at least some severe potential if it evolves anything like the models are suggesting (has a decent EML/steep lapse rates... not quite like the 11/5 system but the rapidly deepening surface low is obviously a big difference this time).  

Naturally the Euro has it coming through on November 17th...

Did have enough CAPE in IL to cause some issues (60˚F Tds to PIA) given the degree of shear as well, although I'd like to see some colder temps aloft and sfc temps are also on the cool side, only 60-65˚F.

Heh, merge this system with the amount of instability/moisture there was last week and you have yourself a whopper of course.

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25 minutes ago, andyhb said:

Naturally the Euro has it coming through on November 17th...

Did have enough CAPE in IL to cause some issues (60˚F Tds to PIA) given the degree of shear as well, although I'd like to see some colder temps aloft and sfc temps are also on the cool side, only 60-65˚F.

Heh, merge this system with the amount of instability/moisture there was last week and you have yourself a whopper of course.

Bigly trouble, lol

If nothing else, a squall line/wind threat would be in play with even just a bit of CAPE, given the progged dynamics/deepening surface low.  

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2 minutes ago, Hoosier said:

Bigly trouble, lol

If nothing else, a squall line/wind threat would be in play with even just a bit of CAPE, given the progged dynamics/deepening surface low.  

Yeah a squall line threat looks pretty likely with this set up at current capacity.

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15 minutes ago, CheeselandSkies said:

Would like to see the timing change a little bit on the GFS for severe, it has the cold front coming through between 06-12z.

Daylight timing would be nice, though a dynamically driven setup of this magnitude would likely have a severe threat extending after dark. 

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13 hours ago, Hoosier said:

18z GFS continues with the impressive looking weekend system, though still faster than the Euro.  

Too early to get deep into details, but it should have at least some severe potential if it evolves anything like the models are suggesting (has a decent EML/steep lapse rates... not quite like the 11/5 system but the rapidly deepening surface low is obviously a big difference this time).  

Lol at Megan Dodson at IWX in describing the Euro/GFS differences:

"A big upper level low is forecast to develop over the Great Lakes, though the placement and strength of the low at this point is up in the air-no pun intended. The consensus blend lost it's mind with 80 percent pops in the Thursday night into Friday evening forecast. This may certainly pan out if we get the upper low, but at this point given significant discrepancies opted to cut them to more reasonable levels-like 30-55%."

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