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2017 Short/Medium Range Severe Thread


Hoosier

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18z GFS today has a 990 system over Chi town at 18z next Friday.  Maybe the antecedent system on this coming Wed. might serve as an appetizer and moisten things up a bit for the main entree.   Interesting weather ahead as systems normally speed up and deepen as we get into the late fall season. Terrific 130 knot 300 mb jet over St, Louis punching into central IL at that hour. 377 surface CAPE around Champaign/Urbana at this early stage in the game.  Low topped squall line most probable at this time frame.

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Not saying to not look at CAPE progs, but I'm paying more attention to this at this point

 

lr75.us_mw.thumb.png.25955a721b09f7d5a5b95ff2d168868e.png

lr75.us_mw-1.thumb.png.e1c50b8d00d8281685e5470f0239ea6d.png

 

Just get decent to good mid level lapse rates into the warm sector and you take your chances.  Low level warm/moist advection should be pretty stout in this type of setup, and we may need to heavily rely on that as sun may be hard to come by (obviously that would increase the threat)

The twitter hype should be a joy if this thing actually falls on the anniversary of 11/17/13.

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In the next few days, you may want to take a look at Euro CAPE maps, which now can be viewed for free.  Last night's 00z Euro had some CAPE of about 1000 J/kg near Memphis for this storm. That's why I am thinking this may be a severe event farther south than most of the members of this sub-forum.

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imo, but wouldn't be surprised to see SPC outlook a risk area in the next day or two, provided we have relative model/ensemble agreement.

Yes, the thermodynamics don't jump off the page (as is often the case at this time of year), but there's something to be said for synoptically evident severe wx setups.  And I think we're close enough on the thermodynamics that some relatively small tweaks would make things look quite a bit more threatening in the presence of these dynamics.  

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18z GFS for today outlooks the Keokuk IA area on eastward as the place to be for possible svr Friday afternoon with good lapse rates, helicity, and suface CAPE of 577.  Of course this will change as we get closer with a slower EURO but at least there is the possibility with a deepening low pressure moving into the Midwest.

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Large day 5 15% area has been added.

 

Quote

 Day 4-8 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0355 AM CST Mon Nov 13 2017

   Valid 161200Z - 211200Z

   ...DISCUSSION...
   Latest runs of the GFS and ECMWF appear very internally consistent,
   with respect to runs from 24 hours ago.  However, they remain
   similarly inconsistent each other with respect to timing as was the
   case yesterday.  As the developing surface cold front crosses the
   central U.S. late Day 4 (Thursday 11-16) and then Day 5 (Friday
   11-17), and finally across the eastern U.S. Day 6 (Saturday 11-18),
   a 9 to 12 hour timing difference persists between the two models.

   With that said, the overall pattern continues to suggest a linear
   band of frontal convection, occurring within a pre-frontal
   environment featuring modest CAPE but very strong flow from the
   lower troposphere to upper levels.  As such, damaging winds would be
   the main severe potential, with degree of risk at least partially
   modulated by the degree of CAPE and associated intensity of the
   convection.  Given this potential, a 15% risk area is being
   introduced at this time, from the Midwest to the Arklatex vicinity. 
   Partially due to timing differences between the models, a rather
   large area is being included in the risk, with fine-tuning of the
   lines left for later outlooks as evolution becomes more certain. 

   At this time, an outlook area will not be included for Day 6 over
   the eastern U.S., as the GFS shows the front moving offshore during
   the first few hours of the period, while the ECMWF depicts the front
   still lying west of the Appalachians through midday.  Depending upon
   the actual evolution, a risk area may be required in later
   forecasts.

   ..Goss.. 11/13/2017

 

day5prob.gif

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25 minutes ago, Chicago Storm said:

It really wasn't going to be worth a D5 outlined risk anyway. They were way too optimistic too far in advance, just like the last event.

Probably will see a low end slight somewhere come Friday.

They were too far north last time, but it's not like that event fell apart (2 dozen tornadoes and a decent number of wind/hail reports).

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This really comes down to the evolution.  If we get an outcome with a rapidly deepening low into the 980s or lower as it's moving through the lakes, then I think we could get a respectable severe event (at least wind; for a recent such example of a lot of wind reports with very little instability, look at 10/31/13).  If the flatter/weaker solution pans out, then I'd agree with lower end.

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I'm not digging this trend of systems to look so potent in the long range and get weaker as we get closer. It needs to be the other way around. Ha. But based on what I'm seeing I totally agree with you guys. If we see a weaker low and more neutral to positive tilt then I see a marginal to low end slight. If we get the bomb that gfs had before with a potent neg tilt then I say an enhanced is not out of the question. Hopefully sampling in a day or so will help models come to a better consensus 

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44 minutes ago, StormChaser4Life said:

I'm not digging this trend of systems to look so potent in the long range and get weaker as we get closer. It needs to be the other way around. Ha.

I know, right? It seems to have been particularly bad this year, ever since all these model "upgrades." I think I've seen more potentially high-end/high-impact systems fizzle on the GFS in the 84-120 hour range than ever before.

One of these years, the atmosphere is going to produce a real big dog over the central CONUS again. The question is, will the weather enterprise see it coming in time to introduce enhanced wording in the medium range, or will they have become gun-shy after all these "false alarms"? Even the mighty EURO has had issues at times with modeling patterns a lot more ominous/hazardous than they turned out to be.

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2 hours ago, CheeselandSkies said:

I know, right? It seems to have been particularly bad this year, ever since all these model "upgrades." I think I've seen more potentially high-end/high-impact systems fizzle on the GFS in the 84-120 hour range than ever before.

One of these years, the atmosphere is going to produce a real big dog over the central CONUS again. The question is, will the weather enterprise see it coming in time to introduce enhanced wording in the medium range, or will they have become gun-shy after all these "false alarms"? Even the mighty EURO has had issues at times with modeling patterns a lot more ominous/hazardous than they turned out to be.

Yea it does seems like models are struggling more. Esp the GFS. It is way over amped far out. It did the same thing with the Nov 5th storm system. I would love another Groundhogs Day Blizzard like in 2011. It's been a while since we had a solid 1ft+ snowstorm in my area. But regarding severe I think with the strong wind fields we could see a low topped squall but if this trough ends up more positive tilt we can see more of an anafrontal event with more forcing behind the front. That would kill severe potential 

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7 minutes ago, Hoosier said:

Can I trot out the ol argument about RAOB sampling?  Seemed like we had pretty good agreement on a deeper system when the upper level wave was in the Alaska area, say, on Sunday.  :weenie:

Hail Mary pass :lmao: Honestly I think it is safe to say we can sack this one.

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9 minutes ago, Stebo said:

Hail Mary pass :lmao: Honestly I think it is safe to say we can sack this one.

It's true though that we started seeing those weaker solutions after it moved offshore. I'm not necessarily saying it's because of that, as there could simply be something that changed in this setup to lead to the recent weaker runs. 

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25 minutes ago, Hoosier said:

It's true though that we started seeing those weaker solutions after it moved offshore. I'm not necessarily saying it's because of that, as there could simply be something that changed in this setup to lead to the recent weaker runs. 

Oh I know, I think the key though is the phasing, the Northern stream sped up since then too. Thus the fractured attempt at phasing instead of previous runs.

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No surprises there. Every and I mean EVERY storm system has trended south and weaker this year. Very foul pattern we're in that will no doubt carry into winter and spring. Can't even remember that last time I've seen an actual bow echo.

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