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July 11-14 Severe Weather Event


Powerball

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more SW flow might be the kiss of good this time around, instead of all this really veered westerly low-level winds we are getting... Over C IL its much more SW'ly, but across northern and western Illinois its increasingly more of a westerly flow, which in turn makes the wind profile pretty unidirectional. VWP from DVN does a good job of showing this, and the HRRR also shows most of the flow veering to westerly across most of the area later on which could temper the tornado threat some.

post-7962-0-09239400-1436815988_thumb.gi

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more SW flow might be the kiss of good this time around, instead of all this really veered westerly low-level winds we are getting... Over C IL its much more SW'ly, but across northern and western Illinois its increasingly more of a westerly flow, which in turn makes the wind profile pretty unidirectional. VWP from DVN does a good job of showing this, and the HRRR also shows most of the flow veering to westerly across most of the area later on which could temper the tornado threat some.

Plainfield occurred in W-WNW sfc flow.  If you get a dominant supercell that turns right, all bets are off with this kind of atmosphere.

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Would have to imagine that if any discrete cell forms near this boundary, it could have an elevated tornado threat. Note that the environment throughout most of Illinois is favorable for tornadoes, so it's not to say a storm has to form in this region, but if one did, I'd be fairly concerned.

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IWX Afternoon Discussion:

 

   
SHORT TERM
 
(THIS EVENING THROUGH TUESDAY)  
ISSUED AT 316 PM EDT MON JUL 13 2015  
 
RAPID DESTABILIZATION HAS BEGUN ACROSS NORTHERN ILLINOIS AS EXPECTED  
AT 18Z THIS AFTERNOON. THIS DESTABILIZATION WILL CONTINUE TO ADVECT  
EASTWARD THROUGH THE AFTERNOON WITH THE WESTERN HALF OF OUR FORECAST  
AREA INTO THE WARM SECTOR BY EARLY EVENING. 18Z DVN SPECIAL SOUNDING  
SAMPLED NEARLY DRY ADIABATIC LAPSE RATES FROM H850 TO H500 AND  
NEARLY 100 KNOTS OF FLOW ABOVE 300MB. WITH SURFACE TEMPERATURES IN  
THE MID 80S AND DEWPOINTS IN THE UPPER 70S BENEATH THIS EML...EXPECT  
EXTREME INSTABILITY OF 4000 TO 6000 J/KG BY 22Z. THIS INSTABILITY  
COUPLED WITH DEEP LAYER SHEAR OF 55 TO 65 KNOTS WILL LEAD TO  
EXPLOSIVE STORM DEVELOPMENT AND ORGANIZATION LATER THIS EVENING. HP  
SUPERCELLS WILL BE THE PRIMARY STORM MODE FOR THE FIRST FEW HOURS  
BEFORE STORMS CONGEAL INTO A FORWARD PROPAGATING MCS.  
 
DURING THIS 22Z TO 02Z TIMEFRAME...SURFACE WINDS WILL REMAIN OUT OF  
THE SSW WITH A STRENGTHENING WESTERLY LOW LEVEL JET. EXTREMELY LOW  
LCLS COUPLED WITH THIS STRONG LOW LEVEL SHEAR WILL LEAD TO AN  
ENHANCED TORNADIC RISK DURING THIS TIMEFRAME. ADDITIONALLY...A  
STRONG TORNADO CANNOT BE RULED OUT...ESPECIALLY IF STRONGER 850 FLOW  
(35 TO 40 KNOTS) FROM THE LATEST HRRR VERIFIES.  
 
EACH RUN OF THE HRRR HAS ADVECTED THE WARM FRONT PROGRESSIVELY  
FURTHER EAST...SO CANNOT RULE OUT A GREATER THREAT FURTHER NORTHEAST  
THAN THE CURRENT AREA OF FOCUS WHICH IS ALONG AND SOUTH OF US 30 IN  
INDIANA.  
 
MOST OF THE CWA RECEIVED BETWEEN 1 AND 1.5 INCHES WITH THE ROUND OF  
RAIN THIS MORNING. FLASH FLOODING APPEARS INCREASINGLY LIKELY THIS  
EVENING WITH A VERY HIGH THETA E AIRMASS AND TRAINING STORMS  
POSSIBLE. THEREFORE...WILL KEEP THE FLASH FLOOD WATCH IN EFFECT  
THROUGH 06Z.  

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Would have to imagine that if any discrete cell forms near this boundary, it could have an elevated tornado threat. Note that the environment throughout most of Illinois is favorable for tornadoes, so it's not to say a storm has to form in this region, but if one did, I'd be fairly concerned.

attachicon.gifboundary.gif

 

 

18z HRRR lights up that area in the next few hours, in addition to development in MN/WI that drops toward Chicago later.

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Most of the current mdt is going to be capped.  The mdt needs to be shifted back to where it was in the 2nd day 2 yesterday.  Focus is going to be RFD-JOT-LAF for this event, the MKX/LOT/IWX/IND CWAs.

They've proven to be stubborn before on convective outlooks... especially  the 20Z update, that was more so my reasoning for that. But yes I agree that that is likely the highest threat area at this point, basically along the instability/theta-E gradient. 

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