Thunderstorms possible this afternoon

Mesoscale update from the Chicago NWS regarding storm development this afternoon:

 

.MESOSCALE DISCUSSION...
1216 PM CDT

STRONG SUMMER TIME JET STREAM DIVING INTO THE UPPER MS VALLEY TODAY
WITH MORNING U/A ANALYSIS SHOWING NEARLY 100KT WINDS FROM BIS
SOUTHEAST TO MPX ALONG THE AXIS OF THIS JET. WEAK SURFACE FRONT
MOVED THROUGH THE REGION ALREADY BUT SECONDARY COLD FRONT WITH A
MORE PRONOUNCED PUNCH OF COOLER AND DRIER AIR STRETCHED FROM
NORTHERN WI SOUTH INTO EASTERN IOWA. NORTH/SOUTH AXIS OF DEWPOINTS
IN THE LOWER 70 DEWPOINTS OVER IL NORTH INTO SOUTHERN WISCONSIN IS
EXPECTED TO MIX OUT SOMEWHAT THIS AFTERNOON...BUT DEWPOINTS EXPECTED
TO REMAIN HIGH ENOUGH TO SUPPORT MLCAPE VALUES OF 2000+ J/KG WITH
LITTLE INHIBITION REMAINING BY MID AFTERNOON.

WINDS IN ADVANCE OF THE SECONDARY FRONT HAVE ALREADY SHIFTED TO WEST
AND NORTHWEST RESULTING IN VERY WEAK CONVERGENCE ALONG THE FRONT.
ACTUALLY...STRONGEST LOW LEVEL CONVERGENCE EXISTS ALONG THE WESTERN
SHORES OF LAKE MICHIGAN WHERE LAKE BREEZE HAS FORMED. OUTSIDE OF THE
LAKE BREEZE...TOUGH TO FIND ANY GOOD SURFACE FEATURES TO FOCUS LOW
LEVEL CONVERGENCE/ASCENT. ALOFT...ENCROACHING STREAM WILL RESULT IN
INCREASING ASCENT...WITH DEVELOPING ACCAS FIELD NOTED ON VSBL
SATELLITE IMAGERY OVER CENTRAL WISCONSIN LIKELY ALREADY AN
INDICATION OF THIS TAKING PLACE. VISIBLE SATELLITE IMAGERY ALSO
SHOWS AN AXIS OF CUMULUS BLOSSOMING ACROSS FAR EASTERN IL AND
WESTERN INDIANA.

OUTSIDE OF THE LAKE BREEZE...REALLY HARD TO FIND ANYTHING SPECIFIC
AT THIS POINT TO HANG MY HAT ON FOR PIN POINTING WHEN/WHERE
CONVECTION WILL DEVELOP THIS AFTERNOON. CONVECTIVE ALLOWING MODELS
CONTINUE TO BREAK OUT THUNDERSTORMS THIS AFTERNOON ACROSS THE REGION
AND GIVEN THE DESTABILIZATION THAT IS TAKING PLACE CAN'T DISPUTE
THIS. GIVEN THE ORIENTATION OF THE UPPER LEVEL JET THE BEST UPPER
LEVEL SUPPORT FOR CONVECTION WOULD APPEAR TO BE MORE SO OVER OUR
NORTHERN AND EASTERN CWA...BUT CERTAINLY THREAT DOES EXIST SOUTHWEST
CWA TOO.

RATHER NEBULOUS FORCING WOULD TEND TO FAVOR CONVECTION BEING MORE
CELLULAR/SCATTERED IN NATURE VS LINEAR. THE WOOD LAKE MN PROFILER
SHOWS 60-70KT FLOW AT 5-6KM WITH RAP SEEMINGLY HAVING A GOOD HANDLE
ON THIS SHOWING 50KT+ AT 5KM SPREADING SOUTHEAST ACROSS OUR CWA THIS
AFTERNOON RESULTING IN STRONG DEEP LAYER (0-6KM) SHEAR >40KT. THE
MODERATE INSTABILITY AND STRONG DEEP LAYER SHEAR ALONG WITH
ANTICIPATED CELLULAR NATURE OF THE CONVECTION WOULD LIKELY RESULT IN
SUPERCELLS. STRONG VEERED LOW LEVEL FLOW IS CERTAINLY NOT FAVORABLE
FOR TORNADOES...BUT THE STRONG SHEAR AND COOLING TEMPS ALOFT WITH
EXPECTED SUPERCELLULAR STORM MODE COULD RESULT IN LARGE
HAIL...POSSIBLY GREATER THAN 1.5 INCH DIAMETER. SOME THREAT WOULD
EXIST FOR DAMAGING WINDS AS WELL...THOUGH THE MORE PROMINENT THREAT
WOULD APPEAR TO BE LARGE HAIL.

WILL CONTINUE TO MONITOR FOR SIGNS OF CONVECTIVE INITIATION AND
PROVIDE UPDATES AS NEEDED.

 

 

 

Thunderstorms will be possible once again this afternoon as an upper level disturbance rolls through the Great Lakes.  Storms have been moving through southwest Iowa and into northern Missouri but those won't be a factor for us as they're moving more southeast.  Thunderstorms are likely to develop between 2pm and 3pm in Wisconsin and drift southeast into north-central Illinois after 3pm and begin to diminish as the sun begins to set.  Storms, should they develop, they could become strong as winds in the atmosphere favor hail and wind producing storms.  Because of this the Storm Prediction Center has northern Illinois southern Wisconsin under a slight risk for storms this afternoon.