SPC AC 300542
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1242 AM CDT SAT MAY 30 2009
VALID 311200Z - 011200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM PARTS OF THE MID MO VALLEY
INTO THE UPPER MIDWEST...
...SYNOPSIS...
POLAR BRANCH OF WESTERLIES WILL BECOME INCREASINGLY ZONAL FROM THE
N-CNTRL INTO NERN STATES AS HEIGHTS REBOUND OVER THE GREAT LAKES IN
WAKE OF STRONG VORTICITY MAXIMUM MOVING THROUGH NEW ENGLAND.
MEANWHILE...NEXT UPSTREAM SYSTEM INITIALLY OVER CNTRL PARTS OF
SASKATCHEWAN/MANITOBA WILL PROGRESS SEWD INTO WRN ONTARIO AND THE
UPPER GREAT LAKES DURING THE LATTER HALF OF THE FORECAST PERIOD.
IN THE LOW LEVELS...A COLD FRONT WILL PUSH EWD THROUGH NEW ENGLAND
SUNDAY WITH SRN EXTENSION OF THIS BOUNDARY SAGGING SWD THROUGH THE
CAROLINAS AND THE SRN APPALACHIANS. THIS BOUNDARY WILL THEN ARC
NWWD THROUGH THE OZARK PLATEAU BEFORE ASSUMING WARM FRONTAL
PROPERTIES FROM THE LOWER/MID MO VALLEYS INTO THE UPPER GREAT LAKES.
BY LATE SUNDAY AFTERNOON...THIS WARM FRONT WILL INTERSECT A
SEWD-MOVING COLD FRONT AND ASSOCIATED SURFACE LOW OVER CNTRL MN WITH
THE COLD FRONT TRAILING SWWD THROUGH CNTRL SD...WRN NEB INTO WY.
...MID MO VALLEY INTO UPPER MIDWEST...
WHILE RICHER BOUNDARY LAYER MOISTURE WILL REMAIN DISPLACED TO THE SE
OF THE REGION...THE COMBINATION OF STRONG DIABATIC HEATING...STEEP
MIDLEVEL LAPSE RATES AND DEWPOINTS IN THE 50S WILL RESULT A
MODERATELY UNSTABLE AIR MASS OVER THE MID MO VALLEY INTO ERN SD WITH
MLCAPE OF 1000-2000 J/KG. DAYTIME HEATING ALONG WITH ENHANCED
FRONTAL CONVERGENCE ALONG 30-35 KT SWLY LLJ SHOULD OVERCOME CAP BY
MID/LATE AFTERNOON...ALLOWING FOR SCATTERED TSTM DEVELOPMENT.
STRONGER LOW AND DEEP-LAYER SHEAR IS FORECAST TO REMAIN E OF SYSTEM
WARM SECTOR...NEARER TO STRONGER SEGMENT OF LLJ. NONETHELESS...THE
PRESENCE OF 35-40 KT EFFECTIVE BULK SHEAR AND LOCALLY STRONGER
LOW-LEVEL SHEAR INVOF WARM FRONT WILL BE SUPPORTIVE OF SUPERCELLS
WITHIN THE FIRST FEW HOURS OF STORM INITIATION. LARGE HAIL AND
DAMAGING WINDS APPEAR TO BE THE PRIMARY THREATS...THOUGH A TORNADO
OR TWO IS POSSIBLE.
THEREAFTER...OVERALL SETUP APPEARS TO FAVOR UPSCALE GROWTH INTO A
SEWD-MOVING MCS SUNDAY NIGHT WITH A CONTINUED THREAT OF DAMAGING
WINDS AND SOME HAIL.
...MT/WY...
THE COMBINATION OF TERRAIN INFLUENCES AND PRESENCE OF COLD FRONT
WILL SERVE TO FOCUS DIURNAL STORMS SUNDAY AFTERNOON/EVENING WITHIN A
STEEP LAPSE RATE/MARGINALLY UNSTABLE ENVIRONMENT. WHILE VERTICAL
SHEAR WILL REMAIN ON THE MARGINS OF THAT SUPPORTIVE OF ORGANIZED
STORMS...SOME HAIL WILL BE POSSIBLE IN ANY STRONGER CELLS GIVEN THE
PRESENCE OF COOL THERMODYNAMIC PROFILES.
...ORE...
SCATTERED...DIURNAL STORMS WILL BE POSSIBLE ALONG THE CASCADES
WITHIN SWLY MIDLEVEL FLOW REGIME DOWNSTREAM FROM ERN PACIFIC TROUGH.
AIR MASS WILL NOT BE OVERLY MOIST...BUT THE PRESENCE OF STEEP LAPSE
RATES WILL CONTRIBUTE TO AT LEAST WEAK CONVECTIVE INSTABILITY BY
AFTERNOON. THE STRONGER STORMS WILL BE CAPABLE OF SOME MARGINALLY
SEVERE HAIL THROUGH THE EVENING HOURS.
...CAROLINAS WWD INTO THE OZARK PLATEAU...
DEWPOINTS IN THE 50S TO LOWER/MID 60S WILL BE MAINTAINED INVOF
SURFACE FRONT WHERE ENVIRONMENT WILL BECOME MODERATELY UNSTABLE BY
AFTERNOON WITH MLCAPE OF 1000-2000 J/KG OVER THE CAROLINAS INTO SRN
APPALACHIANS...TO 1500-3000 J/KG OVER MO. THIS STRONGER INSTABILITY
WILL RESIDE WITHIN SRN EXTENSION OF EML WHERE A STRONGER CAP MAY
INHIBIT STORM INITIATION THROUGH THE DIURNAL HEATING CYCLE.
THUS...SEVERE PROBABILITIES IN THIS AREA ARE CONDITIONAL ON STORM
DEVELOPMENT. FARTHER SE FROM NRN PARTS OF THE GULF STATES INTO
CAROLINAS...THE CAP WILL BE WEAKER WITH A HIGHER LIKLIHOOD OF AT
LEAST ISOLATED STORM DEVELOPMENT. VERTICAL SHEAR WILL REMAIN
RELATIVELY WEAK...THOUGH THE MORE INTENSE STORMS WILL BE CAPABLE OF
GUSTY WINDS AND SOME HAIL.
...ME...
PRESENCE OF 70-80 KT MIDLEVEL JETSTREAK ATTENDING VORTICITY MAXIMUM
WILL RESULT IN A STRONGLY SHEARED ENVIRONMENT INVOF COLD FRONT.
HOWEVER...PRE-FRONTAL BOUNDARY LAYER IS FORECAST TO REMAIN RATHER
COOL WHICH WILL LIMIT THE DEGREE OF INSTABILITY. TSTMS SHOULD
BECOME MORE NUMEROUS BY AFTERNOON ALONG COLD FRONT AS DEEP ASCENT
ASSOCIATED WITH UPPER SYSTEM ACTS ON DESTABILIZING AIR MASS. GIVEN
THE STRONG WIND FIELDS AND COOL THERMODYNAMIC PROFILES...SOME OF THE
STRONGER STORMS WILL BE CAPABLE OF LOCALLY DAMAGING WINDS AND HAIL.
...CNTRL/SRN HIGH PLAINS...
ISOLATED...DIURNAL STORMS WILL BE POSSIBLE ALONG LEE TROUGH/WEAK
DRYLINE WITHIN A HOT AND DEEPLY-MIXED BOUNDARY LAYER. BOTH VERTICAL
SHEAR AND CONVECTIVE INSTABILITY WILL REMAIN SOMEWHAT MARGINAL.
BUT...THE PRESENCE OF THE STEEP LAPSE RATES MAY BE SUPPORTIVE OF
SOME HAIL AND GUSTY WINDS IN ANY STRONGER STORMS INTO THE EVENING
HOURS.
..MEAD.. 05/30/2009
CLICK TO GET WUUS02 PTSDY2 PRODUCT
NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 1730Z
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