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2021 Short/Medium Range Severe Thread


Hoosier
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The HRRR late-CI bias is in full effect today given TS in the QC already. Its coverage is probably too low given the lake breeze boundary and strong MCV moving in during peak heating, but it overall seems to have the right idea for IL/IN this eve. Probably some pulse severe wind but mainly heavy rain given the weak shear and slow storm motions. 

Definitely some uncertainty tomorrow on the best overlap of shear and CAPE - SPC seems to be playing the farther S scenario for now which make sense if the effective front is shoved south by TS tonight. On the other hand, the 18Z HRRR is definitely showing a D-word scenario up into SE MN. IMO the training/flood setup tomorrow night has a pretty high ceiling in parts of the region. 

1905767147_ScreenShot2021-08-25at2_34_34PM.png.47dad4007b5af7a9fa4ab6595abf16e3.png

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BULLETIN - EAS ACTIVATION REQUESTED  
TORNADO WARNING  
NATIONAL WEATHER SERVICE QUAD CITIES IA/IL  
343 PM CDT WED AUG 25 2021  
  
THE NATIONAL WEATHER SERVICE IN THE QUAD CITIES HAS ISSUED A  
  
* TORNADO WARNING FOR...  
  CENTRAL HENRY COUNTY IN NORTHWESTERN ILLINOIS...  
  
* UNTIL 400 PM CDT.  
  
* AT 343 PM CDT, A CONFIRMED TORNADO WAS LOCATED NEAR GENESEO, OR 7  
  MILES NORTH OF CAMBRIDGE, MOVING EAST AT 20 MPH.  
  
  HAZARD...DAMAGING TORNADO.  
  
  SOURCE...LAW ENFORCEMENT CONFIRMED TORNADO.  
  
  IMPACT...FLYING DEBRIS WILL BE DANGEROUS TO THOSE CAUGHT WITHOUT   
           SHELTER. MOBILE HOMES WILL BE DAMAGED OR DESTROYED.   
           DAMAGE TO ROOFS, WINDOWS, AND VEHICLES WILL OCCUR.  TREE   
           DAMAGE IS LIKELY.  
  
* THE TORNADO WILL BE NEAR...  
  GENESEO AROUND 350 PM CDT.

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ED AUG 25 2021  
  
ILC073-252115-  
/O.CON.KDVN.SV.W.0097.000000T0000Z-210825T2115Z/  
HENRY IL-  
403 PM CDT WED AUG 25 2021  
  
...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 415 PM CDT  
FOR SOUTHERN HENRY COUNTY...  
  
AT 402 PM CDT, A SEVERE THUNDERSTORM WAS LOCATED NEAR WOODHULL, OR  
NEAR CAMBRIDGE, MOVING EAST AT 20 MPH.  
  
THIS IS A DESTRUCTIVE STORM FOR ULAH...BISHOP HILL...NEKOMA AND   
GALVA.  
  
HAZARD...BASEBALL SIZE HAIL AND 60 MPH WIND GUSTS.  
  
SOURCE...RADAR INDICATED.  
  
IMPACT...PEOPLE AND ANIMALS OUTDOORS WILL BE SEVERELY INJURED.   
         EXPECT SHATTERED WINDOWS, EXTENSIVE DAMAGE TO ROOFS,   
         SIDING, AND VEHICLES.  
  
LOCATIONS IMPACTED INCLUDE...  
KEWANEE, CAMBRIDGE, GALVA, WOODHULL, ALPHA, ANDOVER, LYNN CENTER,  
BISHOP HILL, OPHIEM, NEKOMA, KEWANEE MUNICIPAL AIRPORT AND ULAH.  
  

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mesoanalysis indicates 2000-3000 J/kg of MLCAPE is present
   across much of Illinois owing to strong heating and surface
   dewpoints in the 70s F. As the cluster of storms east of Davenport
   continues south and east, strong buoyancy will continue to support
   vigorous updrafts with occasional hail or damaging gust potential.
   CAM guidance is not overly bullish with any organization of the
   ongoing convection. However, hints at a weak cold pool developing
   suggest some clustering may occur as storms move southeastward.

   Across far western Indiana and eastern Illinois, a westward
   propagating cluster of storms may also pose an isolated risk for
   downbursts this evening. Little vertical shear is in place with
   multicell storms exhibiting pulse characteristics. However, as
   additional development takes place, collapsing storms may produce a
   few strong wind gusts into this evening.

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At least Ricky is using observations rather than relying on CAMS

 

As had noted in earlier update, the MCV slowly pushing east from
the Quad Cities area will be the trigger mechanism for convection
the rest of this afternoon into the evening. A small cluster
initiated right over the Quad Cities within the past hour. Aside
from near the new CI, the cumulus over most of the area isn`t all
that impressive with the exception of a more congested look near
the lake breeze convergence. Possible that the Quad Cities
activity just pushes east with CI near it or the ascent from the
MCV gradually triggers widely scattered convection through the
late afternoon.

Had noted a modest wind response from 850 mb up to 500 mb on the
DVN VWP, so deep layer shear as the MCV transits the area could
sneak up to as much as 20-25 kt. The CAMs have once again no help
in the forecast, so utilizing observational trends for the most
part. The anticipated scattered convection that develops should
gradually building/spreading southeast through the evening. Main
threat from the tallest cores will be localized wind gusts strong
enough to down tree limbs (level 1 severe threat). PWATs up in
the 1.7-1.9" range will certainly yield efficient rainfall rates,
so a localized flooding threat is there as well.

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7 hours ago, purduewx80 said:

The HRRR late-CI bias is in full effect today given TS in the QC already. Its coverage is probably too low given the lake breeze boundary and strong MCV moving in during peak heating, but it overall seems to have the right idea for IL/IN this eve. Probably some pulse severe wind but mainly heavy rain given the weak shear and slow storm motions. 

Definitely some uncertainty tomorrow on the best overlap of shear and CAPE - SPC seems to be playing the farther S scenario for now which make sense if the effective front is shoved south by TS tonight. On the other hand, the 18Z HRRR is definitely showing a D-word scenario up into SE MN. IMO the training/flood setup tomorrow night has a pretty high ceiling in parts of the region. 

 

Tonight's 00z convection-allowing models show a general consensus for storms to develop in southern Minnesota and possibly continue eastward quickly. A derecho seems possible. Some severe weather could affect the Twin Cities. Some storms could even develop with 50 kt of deep layer shear, certainly rare in August.

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