DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 211614
SWODY1
SPC AC 211612

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1112 AM CDT FRI SEP 21 2012

VALID 211630Z - 221200Z

...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON AND EVENING
ACROSS PARTS OF IL AND IND...

...SYNOPSIS...

AN AMPLIFIED...FULL-LATITUDE TROUGH WILL BE MAINTAINED E OF THE
ROCKIES THROUGH THE D1 PERIOD. WITHIN THIS BROAD-SCALE REGIME...MID
AND UPPER-LEVEL JET STREAKS FROM THE CANADIAN PRAIRIE PROVINCES INTO
THE NRN PLAINS WILL PROPAGATE SEWD INTO THE OH VALLEY IN CONJUNCTION
WITH A SERIES OF VORTICITY MAXIMA. IN THE LOW LEVELS...A SURFACE
CYCLONE OVER WRN IA WILL DEEPEN WHILE DEVELOPING SEWD INTO CNTRL IL
BY 22/00Z...BEFORE WEAKENING AND EVENTUALLY REFORMING OVER SWRN
ONTARIO AT 22/12Z. AN ASSOCIATED WARM FRONT CURRENTLY ANALYZED
ALONG THE OH RIVER WILL ADVANCE NWD AHEAD OF THE MIGRATORY LOW WHILE
A TRAILING COLD FRONT SETTLES SWD/SEWD THROUGH THE OZARK PLATEAU AND
MID SOUTH.

...IL/IND THIS AFTERNOON AND EVENING...

THE 12Z SGF SOUNDING AND SATELLITE-DERIVED PW IMAGERY INDICATE A
CORRIDOR OF HIGHER MOISTURE CONTENT /I.E. PW VALUES AROUND AN INCH/
OVER THE OZARK PLATEAU WHICH WILL BE ADVECTED INTO THE REGION TODAY
ALONG A STRENGTHENING SWLY LLJ. THIS MOISTURE WILL ALIGN WITH
500-MB TEMPERATURES OF -16 TO -18C AND DAYTIME HEATING TO YIELD
AFTERNOON MLCAPE VALUES APPROACHING 1000 J/KG WITHIN SURFACE WARM
SECTOR.

AN ENHANCED ZONE OF LOW-LEVEL CONVERGENCE INVOF THE SURFACE LOW WILL
COMBINE WITH A COUPLED UPPER-LEVEL JET STRUCTURE TO FOSTER WIDELY
SCATTERED TSTM DEVELOPMENT BY MID-LATE AFTERNOON OVER CNTRL/ERN IL.
THE COLLOCATION OF 50-60 KT WLY MID-LEVEL FLOW AND A 30-40 KT LLJ
WILL RESULT IN A FAVORABLE WIND PROFILE FOR SUPERCELLS CAPABLE OF
HAIL...DAMAGING WINDS...AND PERHAPS A COUPLE TORNADOES. SEVERE
WEATHER POTENTIAL SHOULD BEGIN TO DIMINISH BY LATE EVENING AS THE
BOUNDARY LAYER COOLS AND STABILIZES.

...CNTRL NY THIS AFTERNOON...

CONVERGENCE ALONG A WEAK SURFACE FRONT/TROUGH WILL BE AUGMENTED BY
DCVA AHEAD OF A SHEARED VORTICITY MAXIMUM MOVING ACROSS THE REGION
TO SUPPORT WIDELY SCATTERED TSTMS THIS AFTERNOON INTO EVENING.
MODIFICATION OF THE 12Z BUF SOUNDING FOR ANTICIPATED AFTERNOON
CONDITIONS IN THE BOUNDARY LAYER YIELDS A WEAK UNSTABLE AIR MASS IN
THE PRESENCE OF RATHER STRONG DEEP-LAYER SHEAR. CURRENT THINKING IS
THAT STORM VIGOR AND RESULTANT SEVERE WEATHER POTENTIAL WILL BE
LIMITED BY THE MARGINAL INSTABILITY.

..MEAD/MOSIER.. 09/21/2012

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
To unsubscribe from WX-STORM send e-mail to LISTSERV@LISTSERV.ILLINOIS.EDU with
"unsub wx-storm" in the body of your message. For more information write cnovy@cox.net.