Severe Thunderstorm Watch #829 Briefing

This briefing features discussions produced by the SPC and NWS weather forecast offices (WFO).
From SPC:
DISCUSSION...LARGE-SCALE ASCENT SPREADING AHEAD OF BOTH A

   SUB-SYNOPTIC WAVE OVER THE CORN BELT AND A PRIMARY MID-LVL WAVE
   SPREADING ACROSS THE UPR GRTLKS REGION WILL RESULT IN UPSCALE GROWTH
   OF TSTMS ACROSS THE REGION LATE THIS AFTN/EVE.  STORMS WILL LIKELY
   FAVOR A CORRIDOR VCNTY OLD OUTFLOW BOUNDARY FROM SERN LWR MI SWWD
   INTO NRN IL.  HERE...SRN FRINGE OF LARGELY UNIDIRECTIONAL 30-40 KTS
   OF MID-LVL FLOW WILL RESULT IN KINEMATIC ENVIRONMENT CONDUCIVE FOR
   BOWS AND BRIEF SUPERCELL STRUCTURES...ESPECIALLY GIVEN 2500-3000 

J/KG OF MLCAPE. DMGG WIND GUSTS AND LARGE HAIL WILL BE LIKELY.


From NWS Chicago:

AREA OF ELEVATED CONVECTION HAS BEEN STRUGGLING AS IT IS MOVING INTO
THE NORTHWESTERN PORTIONS OF THE FORECAST AREA EARLY THIS AFTERNOON.
THIS COULD CHANGE OVER NEXT COUPLE HOURS AS ENVIRONMENT OUT
AHEAD IS STRONGLY UNSTABLE...AND WEAKLY CAPPED. LATEST RUC INDICATES
CAP ERODING 18-19Z AS H5 VORT ENHANCES LIFT ACROSS THE REGION. ONCE
PARCELS BECOME ROOTED IN THE BOUNDARY LAYER...EXPECT EXPLOSIVE
DEVELOPMENT AS 2500 TO 3000 J/KG MLCAPE IS TAPPED. DEEP LAYER SHEAR
ON THE ORDER OF 35-40KTS ACROSS ALONG THE WI/IL STATELINE IS DUE TO
A UNIDIRECTIONAL WIND FIELD...AND WOULD SUPPORT EVOLUTION INTO
BOWING SEGMENTS WITH SEVERE WINDS THE MAIN THREAT. SEVERAL OUTFLOW
BOUNDARIES ARE EVIDENT ON RADAR/SATELLITE IMAGERY AND SHOULD BE
FOCUS FOR DEVELOPMENT...WITH MAIN AREA OF CONCERN FOR INITIATION
RUNNING FROM LAKE COUNTY ILLINOIS SOUTHWEST TOWARDS BUREAU COUNTY.