DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 141951
SWODY1
SPC AC 141949

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0249 PM CDT SUN OCT 14 2012

VALID 142000Z - 151200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM THE SRN UPPER GREAT LAKES
REGION INTO THE LOWER/MID OH VALLEY...

...SRN UPPER GREAT LAKES INTO THE LOWER AND MID OH VALLEY REGION...
THE ONGOING FORECAST REMAINS GENERALLY ON TRACK...WITH MAIN CHANGES
THIS FORECAST TO BE A CONTINUATION OF THE TREND TO DOWNGRADE SRN
PORTIONS OF THE OUTLOOK -- I.E. AREAS FROM ROUGHLY THE OH RIVER SWD
ACROSS THE TN VALLEY. WITHIN THIS AREA...CLOUD COVER HAS HINDERED
APPRECIABLE DESTABILIZATION...SUGGESTING ONLY A LOW-END THREAT FOR
LOCALLY GUSTY WINDS WITH A FEW STRONGER CONVECTIVE CELLS.

FARTHER N...MORE VIGOROUS CONVECTION IS ONGOING INVOF SRN LK MI AND
ADJACENT AREAS...NEAR THE UPPER CIRCULATION CENTER. WITH AROUND 500
J/KG MIXED-LAYER CAPE ACROSS THIS AREA AND STRONG FLOW
ALOFT...LOCALLY DAMAGING WIND GUSTS REMAIN POSSIBLE WITH THE
STRONGEST CELLS -- ALONG WITH POTENTIAL FOR AN ISOLATED/BRIEF/WEAK
TORNADO. THIS THREAT -- BEING AIDED BY PEAK DIURNAL HEATING --
SHOULD BEGIN TO DIMINISH IN THE NEXT 2-3 HOURS.

..GOSS.. 10/14/2012

.PREV DISCUSSION... /ISSUED 1130 AM CDT SUN OCT 14 2012/

...OH/TN VALLEY REGION THROUGH THIS EVENING ...
A PRONOUNCED MIDLEVEL SHORTWAVE TROUGH OVER MO/IL WILL EJECT NEWD TO
LOWER MI THIS EVENING...AS A WEAKER UPSTREAM WAVE DIGS SEWD FROM THE
NRN PLAINS. AT THE SURFACE...A 997 MB LOW NEAR THE IA/IL/WI BORDER
INTERSECTION WILL LIKEWISE MOVE ENEWD TOWARD LAKE HURON AND DEEPEN
SOME BY TONIGHT. SE OF THE SURFACE LOW...A BROAD WARM SECTOR IS IN
PLACE ACROSS THE LOWER-MID MS VALLEY AND THE LOWER OH VALLEY. THE
SOMEWHAT ILL-DEFINED SURFACE COLD FRONT/PRESSURE TROUGH IS FORECAST
TO SHARPEN SOME TODAY...THOUGH THE THERMAL GRADIENT WILL REMAIN
RATHER MODEST. FARTHER E...A PRE-FRONTAL TROUGH FROM THE IL/INDIANA
BORDER SWD TO NRN MS WILL LIKELY BECOME MORE DIFFUSE THROUGH THE
DAY.

A BAND OF WEAK CONVECTION PERSISTS AS OF 16Z ALONG THE PRE-FRONTAL
TROUGH FROM CENTRAL MS INTO MIDDLE TN...THOUGH THIS BAND HAS
WEAKENED SOME SINCE EARLIER THIS MORNING. CLOUDS ASSOCIATED WITH
THE CONVECTION EXTEND NNEWD OVER THE OH VALLEY...AND IT APPEARS
LIKELY THAT THESE CLOUDS WILL CONTINUE TO INHIBIT SURFACE HEATING
THIS AFTERNOON FROM NRN MS/NW AL NWD ACROSS TN/KY TO INDIANA AND WRN
OH. MEANWHILE...EVEN THOUGH BOUNDARY LAYER DEWPOINTS WILL REACH THE
LOW-MID 60S...12Z REGIONAL SOUNDINGS SHOWED POOR LAPSE RATES.
THUS...MLCAPE IS UNLIKELY TO EXCEED 250-500 J/KG ACROSS MUCH OF THE
TN/OH VALLEY REGION THROUGH THIS EVENING...THOUGH SOMEWHAT GREATER
BUOYANCY IS EXPECTED CLOSER TO THE MIDLEVEL TROUGH ACROSS IL THIS
AFTERNOON.

TWO CONVECTIVE SCENARIOS APPEAR POSSIBLE TODAY -- 1/ NEW STORMS MAY
EMERGE FROM WITHIN THE WEAKENING PRE-FRONTAL CONVECTIVE BAND ACROSS
NRN MS/AL AND TN/KY...AND 2/ A SEPARATE BAND OF LOW-TOPPED STORMS
SHOULD FORM ALONG THE COLD FRONT THIS AFTERNOON IN IL AND MOVE EWD
ACROSS INDIANA/OH THROUGH EARLY TONIGHT. THE VERY MARGINAL
THERMODYNAMIC NATURE OF THE PRE-FRONTAL WARM SECTOR AND LINGERING
CLOUDS ACROSS TN/KY ALL CAST DOUBT ON THE CONVECTIVE
INTENSITY/EVOLUTION THIS AFTERNOON. FARTHER N...A LITTLE STRONGER
SURFACE HEATING WILL BOOST LAPSE RATES SOME IN IL THIS
AFTERNOON...BUT THIS WILL BE IN THE AREA OF WEAKER VERTICAL SHEAR
CLOSER TO THE MIDLEVEL TROUGH. ALSO...CONVECTIVE MODE SIGNALS ARE
MIXED ACROSS IL/INDIANA IN THE SECOND SCENARIO...WITH SUBSTANTIAL
CROSS-FRONTAL SHEAR VECTORS...MODEST LINEAR FORCING FOR ASCENT...AND
STORM MOTIONS THAT WILL SOMEWHAT MATCH EWD FRONTAL MOTION. THE NET
RESULT IS AN ENVIRONMENT THAT MIGHT FAVOR A BROKEN BAND OF
LOW-TOPPED SUPERCELLS THIS AFTERNOON/EVENING SPREADING FROM ERN IL
INTO INDIANA. HOWEVER...MARGINAL BUOYANCY AND A SOMEWHAT STRAIGHT
HODOGRAPH STRUCTURES DO NOT APPEAR PARTICULARLY FAVORABLE FOR
TORNADOES...AND THE LACK OF A SOLID LINE OF STORMS COULD REDUCE THE
DAMAGING WIND RISK.

WILL MAINTAIN A BROAD SLIGHT RISK AREA FOR THE POSSIBILITY OF A FEW
DAMAGING GUSTS GIVEN THE POTENTIAL FOR MOMENTUM TRANSFER OF 50 KT
FLOW TO THE SURFACE IN WEAK CONVECTIVE DOWNDRAFTS. THE TORNADO RISK
APPEARS TO BE SOMEWHAT MARGINAL/CONDITIONAL...WHILE THE POOR LAPSE
RATES WILL LIMIT THE POTENTIAL FOR LARGE HAIL.

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