DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 180520
SWODY1
SPC AC 180517

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1217 AM CDT WED MAR 18 2009

VALID 181200Z - 191200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...

THE PRIMARY FEATURE OF INTEREST DURING THE DAY ONE PERIOD IS
MIDLEVEL TROUGH /ANCHORED BY AN UPPER VORTEX OVER NRN QUEBEC/ WHICH
WILL AMPLIFY OVER ERN CANADA...THE GREAT LAKES REGION AND EVENTUALLY
INTO NEW ENGLAND. IN THE LOW LEVELS...COLD FRONT ATTENDANT TO THIS
SYSTEM IS FORECAST TO EXTEND FROM NRN NEW ENGLAND SWWD THROUGH THE
OH VALLEY...OZARK PLATEAU INTO THE SRN PLAINS BY LATE AFTERNOON.
THIS BOUNDARY WILL BE THE PRIMARY FOCUS FOR TSTM DEVELOPMENT THIS
AFTERNOON INTO TONIGHT.

...OH VALLEY INTO OZARK PLATEAU...

THE ESTABLISHMENT OF A QUASI-ZONAL MIDLEVEL FLOW PATTERN HAS ALLOWED
FOR THE EWD ADVECTION OF AN EML ACROSS THE PLAINS INTO OHIO VALLEY
WITH OBSERVED MIDLEVEL LAPSE RATES OF 7-8 C/KM. THIS CONDITIONAL
INSTABILITY WILL LARGELY CONTRIBUTE TO AFTERNOON MLCAPE APPROACHING
500-700 J/KG GIVEN THE RELATIVELY DRY BOUNDARY LAYER CONDITIONS
/DEWPOINTS IN THE 40S TO LOWER 50S/ FORECAST WITHIN PRE-FRONTAL WARM
SECTOR.

THE GLANCING INFLUENCE OF AMPLIFYING MIDLEVEL TROUGH OVER THE GREAT
LAKES COUPLED WITH LOW-LEVEL FRONTAL CONVERGENCE ARE EXPECTED TO
FOSTER SURFACE-BASED TSTM DEVELOPMENT BY AFTERNOON OVER THE OH
VALLEY WITH ACTIVITY GRADUALLY BACK-BUILDING SWWD INTO THE OZARK
PLATEAU AND PERHAPS AS FAR SW AS OK BY LATE AFTERNOON INTO TONIGHT.
THIS ZONE OF STORM INITIATION WILL LIE ON SRN FRINGE OF STRONGER MID
AND HIGH-LEVEL WIND FIELDS WITH GENERALLY 30-40 KT OF DEEP-LAYER
FORECAST. AS SUCH...ENVIRONMENT MAY SUPPORT A FEW ORGANIZED
MULTICELL STORMS WITH MARGINALLY SEVERE HAIL BEING THE PRIMARY
HAZARD. LOCALLY STRONG WIND GUSTS WILL ALSO BE POSSIBLE GIVEN 20-25
DEGREE T/TD SPREADS IN THE BOUNDARY LAYER AND DCAPE NEARING 700
J/KG.

ANY SEVERE WEATHER THREAT SHOULD DIMINISH BY LATE EVENING AS AIR
MASS SLOWLY COOLS AND STABILIZES.

..MEAD/SMITH.. 03/18/2009

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