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May 15-20th Severe Weather Event


Chicago Storm

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I pray we have time to get notice out to the public..  Slow severe times I guess lends itself to questioning the pro's.  No different in winter when we disagree with winter watches and such.  The severe core is pretty tight and knowledgeable here so I get the questioning.

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6 minutes ago, UMB WX said:

I pray we have time to get notice out to the public..  Slow severe times I guess lends itself to questioning the pro's.  No different in winter when we disagree with winter watches and such.  The severe core is pretty tight and knowledgeable here so I get the questioning.

Yes, with risk outlook especially in the 2 day range, I would rather go too high and pull back later vs ratcheting up through the day of the event where people can get caught off guard. I do fully expect the new day 2 to at the very least be a slight risk but it could even be an enhanced risk, the potential is certainly there.

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May 3, 1999 in OK was the classic day of ratcheting up of svr probs during the day in successive outlooks and I think there may be some situations where it is just not possible to determine mesoscale influences on general parameters too far in advance.  Our knowledge and technology has increased since that classic day so I do agree with Stebo that the sooner we can get notice out to the public within a reasonable time the better.  I was also thinking of that high risk/PDS tor watch situation that busted in the southeast earlier this year.

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SEVERE WEATHER STATEMENT  
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN  
540 PM CDT TUE MAY 16 2017  
  
WIC005-162300-  
/O.CON.KMPX.TO.W.0007.000000T0000Z-170516T2300Z/  
BARRON WI-  
540 PM CDT TUE MAY 16 2017  
  
...A TORNADO WARNING REMAINS IN EFFECT UNTIL 600 PM CDT FOR EAST  
CENTRAL BARRON COUNTY...  
      
AT 539 PM CDT, A CONFIRMED TORNADO WAS LOCATED NEAR SUMNER, OR 11  
MILES SOUTHEAST OF RICE LAKE, MOVING EAST AT 30 MPH.  
  
HAZARD...DAMAGING TORNADO AND GOLF BALL SIZE HAIL.   
  
SOURCE...PUBLIC CONFIRMED TORNADO.

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SEVERE WEATHER STATEMENT  
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN  
552 PM CDT TUE MAY 16 2017  
  
WIC107-162315-  
/O.CON.KMPX.TO.W.0008.000000T0000Z-170516T2315Z/  
RUSK WI-  
552 PM CDT TUE MAY 16 2017  
  
...A TORNADO WARNING REMAINS IN EFFECT UNTIL 615 PM CDT FOR WESTERN  
RUSK COUNTY...  
      
AT 551 PM CDT, A CONFIRMED TORNADO WAS LOCATED OVER WEYERHAEUSER, OR  
15 MILES WEST OF LADYSMITH, MOVING EAST AT 30 MPH.  
  
HAZARD...DAMAGING TORNADO AND PING PONG BALL SIZE HAIL.   
  
SOURCE...PUBLIC CONFIRMED TORNADO.   
  

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12 minutes ago, JoJo said:

This thread is really threat, that supercell storm in Wisconsin has been dropping tornadoes consistently for the past 2 1/2 hours. Some very significant damage has occurred

severe weather crowd in the central/western forum

storm discussed there

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Tomorrow (5/17) I think eastern Iowa, northern Illinois, and all of Wisconsin will get some relatively fast-moving storms capable of severe weather. The 12 km NAM soundings have 2500 J/kg of CAPE, 150 m2/s2 of SRH and 63 kt of deep layer shear. All modes of severe weather are possible and an enhanced outlook could be issued tomorrow.

8wrwk95.png

 

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18 minutes ago, janetjanet998 said:

00z NAM nest TOR outbreak over IA Ito NW IL area later

may need Moderate risk if it pans out with 100kt mid Level jet streak and screaming LLJ

 

with arcs of storms spinning around the low

1st wave may start early over IA area

I would say if they were to do a moderate risk, it would very likely be for wind. With parameters like the ones in place tomorrow, wind is probably going to be the biggest threat. However, with 0-1km SRH values in the 200-300m2s2 range. Tornado potential is certainly there, and would be maximized if a discrete/semi-discrete storm mode becomes preferred.

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Just now, NWLinnCountyIA said:

I would say if they were to do a moderate risk, it would very likely be for wind. With parameters like the ones in place tomorrow, wind is probably going to be the biggest threat. However, with 0-1km SRH values in the 200-300m2s2 range. Tornado potential is certainly there, and would be maximized if a discrete/semi-discrete storm mode becomes preferred.

Discrete/semi-discrete is dominant on all of the current convective allowing guidance and it's not too hard to see why given the strength/orientation of the shear vectors to the pre-frontal trough.

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5 minutes ago, andyhb said:

Even the low res QPF/precip plots are suggesting a string of supercells moving right into that environment at that time.

Yep... convective mode can be tricky to pin down but I don't see a convincing argument against discrete convection or a semi discrete line of supercells.  Besides what you mentioned about shear vectors relative to the boundary, we don't really have massive height falls plowing across much of the warm sector.  

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This event sneaked up in a hurry. No matter what time storms develop during the afternoon, they will quickly acquire both mid-level and low-level rotation. Favorable deep-layer vectors indicate that supercell storm mode will be highly favored. Sufficient instability and moisture + rather prodigious deep-layer and low-level shear... Has all the makings of a significant severe episode across IA/MO/IL. Looks like we will see quite a dramatic uptick in severe probabilities, from no delineated area on the D3 to a marginal in the first day 2 to a slight on the 2nd D2, likely to at least an ENH if not a MDT on the D1 at some point. 

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29 minutes ago, homedis said:

What do you guys think of the eastern extent of the risk for severe tomorrow?

Depends on what you mean.  As far as the eastward extent of the better threat, I'd say perhaps into north central IL.  But some threat should exist farther eastward into Chicago metro.

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31 minutes ago, homedis said:

What do you guys think of the eastern extent of the risk for severe tomorrow?

I wouldn't be surprised if stuff makes it to Chicago tomorrow around midnight, at what capacity though remains to be seen.

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Thursday over an large area from Indiana eastward needs to be watched too. NAM and NAM hi-res has good parameters in place from Indiana into Ohio and Pennsylvania on Thursday. Some limiting factors but some decent parameters in place

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18 minutes ago, JoJo said:

Thursday over an large area from Indiana eastward needs to be watched too. NAM and NAM hi-res has good parameters in place from Indiana into Ohio and Pennsylvania on Thursday. Some limiting factors but some decent parameters in place

Large Day 2 marginal with small slight area.

If the threat ends up becoming bigger, they'll probably expand the slight. Right now lots of moving parts

 

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Might want to add Saturday (May 20) to this thread--SPC doesn't have anything outlined for Saturday yet but ILX begs to differ:

.LONG TERM...(Thursday night through Tuesday)
ISSUED AT 345 AM CDT Wed May 17 2017

Cold front to push south toward I-70 by midnight Thu night and and
south of CWA and into ohio river valley by Friday morning. Some
short wave energy interacting with frontal boundary overnight THu
night into Friday to increase chances of showers and thunderstorms
from sw to ne during that time. highs Friday range from mid to
upper 60s northern CWA to the upper 70s in southeast IL.

Main upper level low/trof ejects ne from sw into the Midwest on
Saturday along with deepening surface low pressure. This to lift
front back north across central IL late Fri night and Saturday
morning. Showers and thunderstorms look likely during overnight
Fri night into Sat and could be some strong to possibly severe
storms on Saturday as cold front moves in sat night. Warmer Sat
with highs in the low to mid 80s, expect upper 70s far north.
Models have trended quicker with bringing drier air east into
central IL on Sunday with qpf east of IL river Sunday morning and
near Wabash river valley Sunday afternoon, though GFS is slower
than ECWMF model with this trend. Weak 1020 mb surface high
pressure builds into areas overnight Sunday night into Monday
bringing dry and cooler weather. Highs Sunday mostly in the low to
mid 70s, then mostly lower 70s on Monday.

chances of showers and thunderstorms return to IL river valley
overnight Monday night and across area Tue into Wed with highest
pops (likely chances) Tue night and Wed. Highs 70-75F on Tue and
then mid to upper 60s on Wed with Lawrenceville around 70F as
strong upper level trof digs into IL by Wed.
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