DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 171947
SWODY1
SPC AC 171945

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0245 PM CDT WED OCT 17 2012

VALID 172000Z - 181200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE MIDDLE AND LOWER
MISSISSIPPI VALLEY AREA THROUGH TONIGHT...

...20Z UPDATE...
VIGOROUS CONVECTIVE DEVELOPMENT IS UNDERWAY ACROSS PARTS OF
SOUTHWEST MISSOURI. THIS APPEARS TO BE WHERE AGEOSTROPHIC FORCING
IN THE EXIT REGION OF A 70-90+ KT 500 MB JET...DIGGING SOUTHEAST OF
THE CENTRAL ROCKIES THROUGH THE SOUTH CENTRAL PLAINS...IS ENHANCING
LOW-LEVEL FRONTOGENETIC FORCING FOR UPWARD VERTICAL MOTION IN THE
PRESENCE OF WEAK DESTABILIZATION. THIS FORCING IS EXPECTED TO
SPREAD EASTWARD INTO THE LOWER OHIO VALLEY...AND SOUTHWARD THROUGH
THE OZARK PLATEAU...TENNESSEE AND LOWER MISSISSIPPI VALLEYS BY LATE
EVENING...BEFORE WEAKENING OVERNIGHT.

HIGHER TORNADO PROBABILITIES ACROSS EASTERN ARKANSAS AND THE
MISSISSIPPI DELTA REGION ARE LARGELY CONTINGENT ON MORE SUBSTANTIVE
BOUNDARY LAYER DESTABILIZATION OCCURRING IN THE PRESENCE OF STRONGER
PRE-FRONTAL LOWER/MID TROPOSPHERIC WARM ADVECTION DEVELOPING
EASTWARD THROUGH THE LOWER MISSISSIPPI VALLEY LATE THIS AFTERNOON
AND EVENING. IT IS INCREASINGLY UNCERTAIN WHETHER LIFT AND
DESTABILIZATION WILL BECOME SUFFICIENT FOR SUBSTANTIVE DISCRETE
PRE-FRONTAL STORM DEVELOPMENT NECESSARY TO SUPPORT THESE
PROBABILITIES. HOWEVER...THE POTENTIAL FOR A STRONG TORNADO OR TWO
IS NOT NEGLIGIBLE...AND IT SEEMS MOST PRUDENT TO MAINTAIN THE
CURRENT OUTLOOK AS IS...AT LEAST UNTIL THE EVENING /01Z/ OUTLOOK
UPDATE.

..KERR.. 10/17/2012

.PREV DISCUSSION... /ISSUED 1126 AM CDT WED OCT 17 2012/

...MIDDLE AND LOWER MS VALLEY AREA THROUGH TONIGHT...
A WELL-DEFINED MIDLEVEL TROUGH OVER THE CENTRAL/NRN PLAINS THIS
MORNING WILL CONTINUE TO MOVE ESEWD WHILE GRADUALLY EVOLVING INTO A
LARGE CLOSED LOW OVER THE UPPER MS VALLEY...AS THE ASSOCIATED
SURFACE CYCLONE OCCLUDES OVER NRN MN. S OF THE CYCLONE...A COLD
FRONT WILL SURGE EWD/SEWD FROM CENTRAL IA AND ERN KS THIS MORNING TO
ROUGHLY A TXK-STL AXIS THIS EVENING AND THE LOWER MS/OH AND TN
VALLEY REGIONS BY THURSDAY MORNING. LOW-LEVEL MOISTENING IS
UNDERWAY IN ADVANCE OF THE COLD FRONT AS LOW-MID 60S BOUNDARY LAYER
DEWPOINTS SPREAD NEWD FROM ERN OK/NE TX TO SRN MO BY MID
AFTERNOON...AND UPPER 60S DEWPOINTS COULD REACH AS FAR AS SE AR BY
21-00Z. THE DEGREE OF SURFACE HEATING IS IN QUESTION WITHIN THE
MOIST AXIS FROM WRN AR INTO MO GIVEN THE PREVALENCE OF STRATUS THIS
MORNING...AND THE EXPECTED EARLIER ONSET OF FRONTAL PRECIPITATION IN
MO THIS AFTERNOON.

SATELLITE IMAGERY CONFIRMS A BELT OF ASCENT FROM NRN OK TO ERN KS
AND CENTRAL IA NEAR THE SURFACE COLD FRONT...AND IMMEDIATELY IN
ADVANCE OF THE AMPLIFYING MIDLEVEL TROUGH. THIS BELT OF ASCENT WILL
SPREAD ESEWD THROUGH THE AFTERNOON AND PHASE WITH THE INCREASINGLY
MOIST WARM SECTOR...WHICH WILL SUPPORT SURFACE-BASED THUNDERSTORM
DEVELOPMENT BY ABOUT 21Z ALONG THE COLD FRONT IN CENTRAL MO AS
ASCENT ERODES THE CAP ASSOCIATED WITH THE EML SAMPLED THIS MORNING
ACROSS KS/OK. THE CONVECTIVE MODE WILL BE LINEAR ACROSS MO IN
CONJUNCTION WITH LINEAR FORCING FOR ASCENT AND DEEP-LAYER FLOW/SHEAR
VECTORS LARGELY PARALLEL TO THE COLD FRONT. DAMAGING WINDS WILL BE
THE MAIN SEVERE THREAT WITH THE FRONTAL SQUALL LINE ACROSS
MO/IL...BEFORE THE SQUALL LINE PROGRESSES E OF THE LOW-LEVEL
INSTABILITY AXIS BY EARLY TONIGHT.

FARTHER S...ADDITIONAL CONVECTION IS EXPECTED TO FORM IN A NNE-SSW
ORIENTED BAND ALONG THE MOIST AXIS /POSSIBLY JUST AHEAD OF THE COLD
FRONT/...FROM NRN LA INTO ERN AR BY 00Z. SOMEWHAT STRONGER
INSTABILITY /MLCAPE OF 750-1500 J PER KG/ AND MORE CROSS-FRONTAL
FLOW/SHEAR VECTORS MAY SUPPORT SOME EMBEDDED SUPERCELLS WITHIN THE
LARGER CONVECTIVE BAND. THERE WILL BE A RISK FOR A FEW
TORNADOES...IN ADDITION TO DAMAGING WINDS AND ISOLATED LARGE
HAIL...GIVEN THE INCREASING LOW-LEVEL MOISTURE...STRENGTHENING
DEEP-LAYER SHEAR...AND FAVORABLE HODOGRAPH STRUCTURES SUPPORTING
EFFECTIVE SRH AOA 300 M2/S2. THE SEVERE RISK WILL SLOWLY DIMINISH
AROUND 03-06Z AS CONVECTION BEGINS TO PINCH OFF THE
MOISTURE/INSTABILITY AXIS...AND THE PRIMARY EMBEDDED SHORTWAVE
TROUGH/JET STREAK PIVOTS ENEWD OVER TN/KY EARLY THURSDAY.

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