Chicago Discussion
Posted by JAC on 6/18/2009, 8:44 am
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
719 AM CDT THU JUN 18 2009

.DISCUSSION...
433 AM CDT

OBVIOUS THAT NEXT 48 HRS TO BE QUITE ACTIVE CONVECTION-WISE AS
MULTIPLE STRONG SHORT WAVES CONTINUE TO EJECT OUT OF WESTERN NOAM
UPPER TROF. VERY STRONG UPPER JET FOR TIME OF YEAR RE-CARVES MEAN
UPPER TROF BACK OVER THE PAC COAST BY SAT MORNING...WHICH ALLOWS
UPPER RIDGE TO REBUILD BACK RIDGE OVER THE PLAINS.

DETAILED ANALYSIS OF SEVERE WX THREAT AVAILABLE IN SPC PRODUCTS
BUT BOTTOM LINE IS THAT CONVERGENCE POINT OF WHERE LOW...MID AND
UPPER LEVEL PARAMETERS COMING TOGETHER CURRENTLY SHIFTING THE
BULLSEYE OF MAX SEVERE WX THREAT EASTWARD OVER AND IN THE
IMMEDIATE VICINITY OF THE LOCAL FORECAST AREA FOR TODAY AND FRI.
VERY WARM AND MOIST AIRMASS CONTINUES TO CREEP NORTHWARD INTO
THE AREA THOUGH ACTUAL SFC BOUNDARY STILL ACROSS NORTHERN MO AND
SOUTHERN IL WHERE DIFFERENTIATED BY WIND DIRECTION CHANGE FROM SE
TO S AND DEW POINTS IN MID-UPPER 60S N OF FRONT AND LOWER 70S S OF
IT. BOUNDARY EXPECTED TO LIFT INTO NORTHERN IA...NW IL...W CENTRAL
IN DURING THE AFTERNOON WITH CAPE VALUES CLIMBING IN EXCESS OF 4000
J/KG ALONG AND S OF THE WARM FRONT. EVEN WITH THE WARM FRONT S F
THE CWA MOST IF NOT ALL THRU THIS AFTERNOON...SFC BASED LIFTED
INDICES ALL THE WAY N FROM THE UPPER MS VALLEY E ACROSS WI AND
NORTHERN IL INTO NW IN CURRENTLY IN THE -1 TO -2 RANGE AND
SUPPORTING SVR WX JUST UPSTREAM AS STRONG SHORT WAVE THAT LIFTED
NE ACROSS WESTERN NE EARLY LAST EVE AND CURRENTLY OVER CENTRAL IA.
THIS SHORT WAVE JUST STARTING TO TURN ESE AS IT TOPS THE UPPER
RIDGE AXIS. THIS TO BRING PERIOD OF STRONG TO POTENTIALLY SVR
STORMS ACROSS MAINLY SW AND FAR SOUTHERN PORTION OF FA THIS
MORNING WHERE NEAR SFC INSTABILITY GREATEST. LESS INTENSE
CONVECTION TO SPREAD ACROSS NORTHERN PORTION OF FA THIS MORNING.
8
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Possible Severe Weather this Weekend for Great-Lakes & Ontario - JAC, 6/15/2009, 7:29 am
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