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June 28-July 1 Severe Threat


Thundersnow12

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With that bow in the NE/IA area, we're in the early stages of what could be a very impressive damaging wind event imo.  No reason it shouldn't maintain itself for many hours and by the time it heads toward the Chicago metro area, it may begin to take advantage of the nocturnally strengthening low level jet.

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Definitely quite a few debris clouds over the Racine area. Currently 80°/70°.

 

 

recovery when it happens should be rapid...flow is going to strengthen out ahead of the low and organizing MCS

 

that pesky cell in C. IL finally died so we should start to burn off this debris as well

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...CENTRAL PLAINS TO MID/UPPER MS VALLEY AND LOWER MI...

REF SPC WWS 371-372 AND RELATED MESOSCALE DISCUSSIONS FOR LATEST

NEAR-TERM INFO ON CONVECTION FROM WRN NEB TO CENTRAL IA.

EARLIER TSTMS OVER NRN/ERN IA HAVE PRODUCED PRONOUNCED OUTFLOW

BOUNDARY THAT APPEARS TO FOCUS SVR POTENTIAL MORE TIGHTLY OVER

IA...FOR MIDDAY THROUGH AFTN WITHIN MDT RISK AREA...AND WHICH ALSO

INCREASES RISK OF SIGNIFICANT TORNADOES. VERY LARGE/DAMAGING HAIL

STILL IS LIKELY FROM ANY SUSTAINED SUPERCELLS.

OUTFLOW BOUNDARY HAS BECOME ALIGNED CLOSE TO OR JUST RIGHTWARD OF

MEAN FLOW...AND MAY BE REINFORCED LOCALLY BY CONVECTION NOW MOVING

EWD OUT OF ERN NEB. ANY RELATIVELY DISCRETE SUPERCELL ALONG OR JUST

N OF THAT BOUNDARY MAY HAVE SUSTAINED ACCESS TO VORTICITY-RICH AND

DIABATICALLY DESTABILIZED AIR WITH SFC DEW POINTS LOW-MID 70S

F...CONTRIBUTING TO MLCAPE 4000-5000 J/KG. SIMILARLY RICH

MOISTURE/BUOYANCY WILL EXTEND SWD INTO PRECONVECTIVE WARM

SECTOR...SUPPORTING RAPID GROWTH OF ANY FRONTAL CONVECTION.

GREATEST JUXTAPOSITION OF STG BUOYANCY AND DEEP SHEAR THIS AFTN

SHOULD BE OVER IA...ESPECIALLY WHEN CONSIDERING ENHANCEMENT TO

LOW-LEVEL SHEAR/SRH RELATED TO OUTFLOW BOUNDARY.

FARTHER E...AIR MASS WILL TAKE LONGER TO RECOVER FROM MORNING

CONVECTION/OUTFLOW OVER SRN WI/NRN IL/SWRN LOWER MI AND VICINITY.

HOWEVER...SUSTAINED LOW-LEVEL WAA AND AREAS OF AFTN HEATING SHOULD

ENABLE THAT PROCESS...WITH WAA CONTINUING IN PRECONVECTIVE REGIME

AFTER 00Z. AS SUCH...DAMAGING-WIND THREAT WILL EXTEND INTO THESE

REGIONS DURING EVENING INTO TONIGHT...EXCEPT FOR RELATIVE MIN OVER

COLD NEAR-SFC MARINE LAYER OF LM. POTENTIAL EXISTS FOR NEB/IA

CONVECTION TO EVOLVE UPSCALE AND PRODUCE SWATH OF SIGNIFICANT WIND

DAMAGE -- PERHAPS WITH ENOUGH LATERAL/AREAL EXTENT TO CLASSIFY AS

PROGRESSIVE DERECHO -- EWD AS FAR AS SWRN SHORES OF LM.

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Latest outlook mentions derecho more than once. Pending organizational trends the rest of the afternoon, I wouldn't be surprised to see a high risk area/60% hatched wind later.

Starting to clear out here. Would expect pink on the cat map down I80 across IA, IL, and NWI at 20z.
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Me either (assuming storm surveys count and the gust not needing to be measured).

Yeah good point, I was leaning more on surveys, I mean you might get a mesonet report that high but most of the triple digit reports from derechos come after surveying.

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12z SPC WRF has this...

 

attachicon.gifrefd_1000m_f09.gif

 

attachicon.gifrefd_1000m_f10.gif

 

attachicon.gifrefd_1000m_f11.gif

 

attachicon.gifrefd_1000m_f12.gif

 

...and then it does that weaken/turn southeast thing again (for IL/IN purposes). But as noted by those in the know, it hasn't been the best lately.

 

 

Monster updraft helicity with that thing.  One of the more impressive runs I can recall in that regard.

 

 

post-14-0-92193500-1404148101_thumb.gif

 

 

post-14-0-16203200-1404148109_thumb.gif

 

 

post-14-0-11672500-1404148116_thumb.gif

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