DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 261609
SWODY1
SPC AC 261607

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1107 AM CDT WED SEP 26 2012

VALID 261630Z - 271200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM PORTIONS OF THE CNTRL AND
SRN HIGH PLAINS INTO OZARK PLATEAU...

...THERE IS A SLGT RISK OF SVR TSTMS FROM THE LOWER OH VALLEY INTO
PORTIONS OF THE MID ATLANTIC STATES...

...SYNOPSIS...

A SPLIT FLOW PATTERN WILL BE MAINTAINED W OF THE MS VALLEY WITH THE
PRIMARY FEATURE OF INTEREST BEING UPPER LOW CURRENTLY ALONG THE
UT/CO BORDER WHICH WILL TRANSITION TO AN OPEN WAVE WHILE SHIFTING
SLOWLY EWD. THIS FEATURE ALONG WITH A SMALLER-SCALE VORTICITY
MAXIMUM LOCATED OVER S-CNTRL CO/N-CNTRL NM AS OF MID-MORNING WILL
ENHANCE FORCING FOR ASCENT ACROSS THE CNTRL/SRN HIGH PLAINS LATER
TODAY INTO TONIGHT. IN THE EAST...LARGE-SCALE PATTERN IS
CHARACTERIZED AS CONFLUENT AND BROADLY CYCLONIC WITH THE PREDOMINANT
FEATURE BEING A POSITIVELY-TILTED SHORTWAVE TROUGH WHICH WILL
PROGRESS ESEWD THROUGH THE NORTHEASTERN STATES. A BIT FARTHER
SOUTH...MORNING WATER VAPOR AND RADAR MOSAIC DATA INDICATE
SMALLER-SCALE VORTICITY MAXIMA /SOME OF CONVECTIVE ORIGIN/ EMBEDDED
WITHIN ONGOING TSTMS OVER THE OH VALLEY.

IN THE LOW LEVELS...COLD FRONT ASSOCIATED WITH THE NERN U.S.
SHORTWAVE TROUGH MENTIONED ABOVE WILL LIKEWISE ADVANCE THROUGH THE
LOWER GREAT LAKES AND NEW ENGLAND BY 27/12Z WITH TRAILING PORTION OF
BOUNDARY OVER THE OH VALLEY SETTLING MORE SLOWLY SWD.
MEANWHILE...FAR WRN EXTENSION OF THIS BAROCLINIC ZONE WHICH HAS
ALREADY PROGRESSED SWD INTO E-CNTRL NM AND W-CNTRL TX MAY RETREAT
SLOWLY NWD AS A WARM FRONT IN RESPONSE TO THE APPROACH OF CO UPPER
LOW.

...CNTRL/SRN HIGH PLAINS INTO OZARK PLATEAU THIS AFTERNOON INTO
TONIGHT...

12Z HIGH PLAINS SOUNDINGS SHOW THE CONTINUED PRESENCE OF AN EML WITH
700-500-MB LAPSE RATES OF 7.5-8.0 C/KM. VEERING LOW-LEVEL WIND
FIELD WITHIN POST-FRONTAL AIR MASS WILL ALLOW FOR THE WWD/NWWD
RETURN OF AN INCREASINGLY MOIST BOUNDARY LAYER INTO THE HIGH PLAINS
/AND BENEATH EML/ CONTRIBUTING TO AFTERNOON MLCAPE OF AROUND 1000
J/KG OVER SERN CO/NERN NM. ACROSS LOWER ELEVATIONS...A
COMPARATIVELY MORE MOIST BOUNDARY LAYER WILL YIELD MLCAPE
APPROACHING 2000-2500 J/KG.

DCVA ASSOCIATED WITH INITIAL S-CNTRL CO/N-CNTRL NM VORTICITY MAXIMUM
WILL AUGMENT LOW-LEVEL UPSLOPE MECHANISM AND CONVERGENCE ALONG
SYNOPTIC FRONT AND DRYLINE TO FOSTER AN INCREASE IN TSTMS THROUGH
THE AFTERNOON FROM SERN CO INTO SWRN KS AND THE OK/TX PNHDLS...AND
PERHAPS AS FAR SOUTH AS W-CNTRL TX. ACROSS THE NRN PORTION OF THIS
AREA...THE COMBINATION OF MODERATE INSTABILITY AND VERTICALLY
VEERING WIND PROFILES WITH 35-45 KT OF EFFECTIVE BULK SHEAR WILL
SUPPORT SUPERCELLS AS THE INITIAL STORM MODE WITH AN ASSOCIATED RISK
FOR LARGE HAIL...DAMAGING WINDS...AND PERHAPS A BRIEF TORNADO.
ADDITIONAL STORMS WILL BE POSSIBLE THIS AFTERNOON FARTHER EAST ALONG
SYNOPTIC FRONT AND RESIDUAL OUTFLOW BOUNDARY ACROSS OK INTO AR/SRN
MO. VERTICAL SHEAR IS FORECAST TO BE WEAKER THAN POINTS TO THE
NW...BUT THE MODERATE INSTABILITY WILL STILL PROMOTE MULTICELL
CLUSTERS CAPABLE OF DAMAGING WINDS AND HAIL.

UPSCALE GROWTH OF DIURNAL STORMS INTO ONE OR MORE MCSS IS POSSIBLE
TONIGHT WITH A CONTINUED RISK FOR SPOTTY WIND/HAIL OCCURRENCES.

...LOWER OH VALLEY TO MID ATLANTIC COAST THIS AFTERNOON AND
EVENING...

12Z REGIONAL SOUNDINGS INDICATE THAT CONSIDERABLE CONVECTIVE
OVERTURNING HAS OCCURRED NORTH OF THE OH RIVER OWING TO NOCTURNAL
TSTM ACTIVITY. HOWEVER...DATA FROM BNA EWD THROUGH RNK AND GSO
INDICATE THE CONTINUED PRESENCE OF AN ELONGATED EML PLUME WHERE
700-500-MB LAPSE RATES OF 7.5-8.0 C/KM WERE OBSERVED. THE STRONGEST
AFTERNOON INSTABILITY /I.E. MLCAPE OF 2000-2500 J PER KG/ IS
FORECAST TO THE S OF CLOUD/PRECIPITATION SHIELD OVER THE LOWER OH
VALLEY WHERE THESE LAPSE RATES OVERLAY THE NERN EXTENSION OF RICHER
BOUNDARY LAYER MOISTURE. FATHER E...DAYTIME HEATING...DEWPOINTS IN
THE 50S... AND THE STEEP LAPSE RATES WILL YIELD POCKETS OF MODEST
INSTABILITY /I.E. MLCAPE OF 500-1000 J PER KG/.

CONVECTIVE EVOLUTION TODAY REMAINS UNCERTAIN OWING TO THE WEAKLY
FORCED CHARACTER OF THE LARGE-SCALE PATTERN. CURRENT THINKING IS
THAT STORMS SHOULD INCREASE IN COVERAGE AND INTENSITY THIS AFTERNOON
ALONG THE SRN FRINGE OF DENSER CLOUD COVER WHERE DIFFERENTIAL
HEATING AND THE PRESENCE OF A WSW-ENE ORIENTED OUTFLOW BOUNDARY WILL
FOCUS DESTABILIZATION AND ASCENT. GIVEN THAT REGION WILL RESIDE
WITHIN A TIGHTENED MIDLEVEL HEIGHT GRADIENT OWING TO CONVERGING
POLAR AND SUBTROPICAL AIR STREAMS...RELATIVELY STRONG DEEP-LAYER WLY
FLOW IS FORECAST. THIS WILL ENHANCE DAMAGING WIND POTENTIAL FOR ANY
CONVECTIVE BANDS/LINE SEGMENTS WHICH CAN BECOME ALIGNED ORTHOGONAL
TO THE DEEP-LAYER WIND FIELD.

..MEAD/MOSIER.. 09/26/2012

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