DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 251953
SWODY1
SPC AC 251951

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0251 PM CDT TUE SEP 25 2012

VALID 252000Z - 261200Z

...THERE IS A SLGT RISK OF SVR TSTMS ERN TX PANHANDLE TO LOWER OH
VALLEY...

--- UPDATES ---
NERN PORTION OF CATEGORICAL RISK LINE AND RELATED PROBABILITIES ARE
SHIFTED SLIGHTLY S ACROSS MO AND EWD OVER PORTIONS SRN IL/INDIANA.
THIS IS IN DEFERENCE TO OBSERVATIONAL/CONVECTIVE TRENDS AND
SHORT-TERM GUIDANCE EACH SUGGESTING EWD SHIFT OF FAVORABLE SFC-BASED
EFFECTIVE INFLOW PARCELS LATER THIS AFTERNOON...BEHIND OUTFLOW
POOL...IN SUPPORT OF SVR POTENTIAL. CONVECTIVE INITIATION ALSO HAS
BEEN NOTED OVER ERN TX PANHANDLE...FOR WHICH MORE NEAR-TERM DETAILS
WILL BE FOUND IN FORTHCOMING MESOSCALE DISCUSSION.
OTHERWISE...MAINLY MINOR/PERIPHERAL CHANGES ARE MADE TO GEN THUNDER
LINES TO REFLECT ONGOING/DIURNAL DESTABILIZATION AND SATELLITE
TRENDS IN CONVECTION.

..EDWARDS.. 09/25/2012

.PREV DISCUSSION... /ISSUED 1115 AM CDT TUE SEP 25 2012/

...SYNOPSIS...

A SPLIT FLOW REGIME WILL PERSIST THROUGH THE PERIOD FROM THE
INTERMOUNTAIN WEST INTO GREAT PLAINS WITH GENERALLY A
CONFLUENT...WEAKLY CYCLONIC PATTERN ACROSS THE ERN THIRD OF THE
NATION. WITHIN THIS BROAD-SCALE PATTERN...A SHORTWAVE TROUGH OVER
THE MID/LOWER MO VALLEY WILL DEAMPLIFY OVER THE OH VALLEY WHILE
FARTHER TO THE WEST...A WEAK VORTICITY MAXIMUM OVER SERN CO/NERN NM
PROGRESSES SLOWLY EWD TOWARD THE OZARK PLATEAU.

IN THE LOW LEVELS...MID-MORNING SURFACE ANALYSIS SHOWS A BAROCLINIC
ZONE EXTENDING FROM A WEAK CYCLONE OVER CNTRL WI SWWD THROUGH
E-CNTRL KS/W-CNTRL MO INTO THE OK/NRN TX PNHDLS AND NERN NM. A
NUMBER OF WEAK LOW PRESSURE CENTERS WERE ANALYZED ON THIS
BOUNDARY...NEAR MKC...AVK...AND GUY. A WARM FRONT INTERSECTED THE
FORMER BOUNDARY AT THE MKC SURFACE LOW WITH THIS FEATURE STRETCHING
SEWD THROUGH CNTRL INTO SERN MO AND THEN MORE SWD ALONG THE MS
RIVER. MEANWHILE...AN OUTFLOW BOUNDARY ASSOCIATED WITH NOCTURNAL
MCS ONGOING ACROSS KY EXTENDED FROM NEAR OR JUST N OF STL ESEWD INTO
CNTRL KY. THESE THREE LOW-LEVEL BAROCLINIC ZONES ARE EXPECTED TO
SERVE AS LOCI FOR STRONG TO SEVERE TSTM DEVELOPMENT THIS AFTERNOON
INTO TONIGHT.

...MID MS/LOWER OH VALLEYS THIS AFTERNOON INTO TONIGHT...

12Z SOUNDINGS FROM SGF/LZK/BNA SHOWED THE PRESENCE OF AN EML WHICH
HAS BEEN ADVECTED EWD FROM THE SRN ROCKIES WITHIN SUBTROPICAL
MIDLEVEL AIR STREAM. THE STEEP LAPSE RATES WILL OVERLAY A MOIST
BOUNDARY LAYER WHICH WILL DEVELOP NEWD THROUGH THE OH VALLEY ALONG A
SWLY LLJ. THESE DIFFERENTIAL ADVECTIONS WILL YIELD A MODERATELY
UNSTABLE AIR MASS BY AFTERNOON TO THE SOUTH AND WEST OF ONGOING MCS
WHERE MLCAPE VALUES WILL APPROACH 1500-3000 J/KG.

LOW-LEVEL WAA/ISENTROPIC ASCENT ALONG LLJ AXIS WILL COINCIDE WITH
CONVERGENCE ALONG THE WARM FRONT AND OUTFLOW BOUNDARY...AND WEAK
DCVA ASSOCIATED WITH SHORTWAVE TROUGH MENTIONED IN THE SYNOPSIS TO
FOSTER A GRADUAL INCREASE IN TSTM DEVELOPMENT ACROSS THE REGION THIS
AFTERNOON. A TIGHTENED...MID TO UPPER-LEVEL HEIGHT GRADIENT OWING
TO THE CONFLUENT LARGE-SCALE PATTERN WILL YIELD MODEST DEEP-LAYER
FLOW FIELDS WITH HODOGRAPHS EXHIBITING VERTICALLY VEERING WINDS WITH
HEIGHT. GIVEN THE MODERATE INSTABILITY FORECAST...THE SETUP WILL
FAVOR ORGANIZED STORM MODES INCLUDING SUPERCELLS AND BOWING
STRUCTURES CAPABLE OF DAMAGING WINDS...LARGE HAIL...AND PERHAPS A
BRIEF TORNADO.

THIS SEVERE WEATHER THREAT SHOULD CONTINUE THROUGH THE EVENING
BEFORE DECREASING LATER TONIGHT AS THE BOUNDARY LAYER COOLS AND
STABILIZES.

...WRN OK INTO THE OZARKS THIS AFTERNOON INTO TONIGHT...

THE WRN EXTENSION OF AN EML MENTIONED IN THE PREVIOUS SECTION IS
CLEARLY OBSERVED BY 12Z REGIONAL SOUNDINGS WHERE 700-500-MB LAPSE
RATES RANGED FROM 7.5-9.0 C/KM. AND WHILE BOUNDARY LAYER MOISTURE
CONTENT WILL BE LESS THAN THAT OVER THE LOWER/MID MS
VALLEY...STRONGER DIABATIC HEATING WILL YIELD WARMER SURFACE
TEMPERATURES...A DEEPLY MIXED BOUNDARY LAYER...AND MLCAPE OF
1500-2500 J/KG.

FORCING ASSOCIATED WITH THE VORTICITY MAXIMUM MOVING EWD FROM SERN
CO/NERN NM ALONG WITH A WEAKER CYCLONIC CIRCULATION OBSERVED OVER
CNTRL KS AS OF LATE MORNING WILL AUGMENT LOW-LEVEL UPLIFT ALONG THE
SYNOPTIC FRONT AND DEVELOPING DRYLINE TO SUPPORT AN INCREASE IN
TSTMS THIS AFTERNOON AND EVENING FROM CNTRL MO INTO WRN OK. WHILE
VERTICAL SHEAR WILL BE RELATIVELY WEAK /I.E. LESS THAN 25-30 KT
THROUGH THE LOWEST 6 KM/...THE PRESENCE OF THE STEEP LAPSE RATES AND
MODERATE INSTABILITY WILL SUPPORT MULTICELL CLUSTERS CAPABLE OF
DAMAGING WINDS AND HAIL. THIS THREAT MAY PERSIST INTO TONIGHT AS
STORMS GROW UPSCALE INTO AN MCS AT THE TERMINUS OF A DEVELOPING
NOCTURNAL LOW-LEVEL WIND MAXIMUM.

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