SPC AC 061258
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0758 AM CDT TUE APR 06 2010
VALID 061300Z - 071200Z
...THERE IS A SLGT RISK OF SVR TSTMS THROUGH TONIGHT FOR LOWER MI
WWD TO NRN IL/ERN IA AND MO...ERN KS...ERN OK...
...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON ACROSS A NARROW
STRIP OF NY/PA INTO WRN MA/CT...
...OH VALLEY/GREAT LAKES TO ERN KS/OK THROUGH TONIGHT...
THE SURFACE CYCLONE IN SE NEB AS OF 12Z WILL PROGRESS GENERALLY
ENEWD TO S CENTRAL IA THIS AFTERNOON AND NW IL OVERNIGHT...ALONG A
SLOW-MOVING WARM FRONT ACROSS SRN IA/NRN IL/LOWER MI AND IN ADVANCE
OF A MIDLEVEL SHORTWAVE TROUGH MOVING EWD FROM CO. DESPITE SOME
APPARENT SUBSIDENCE AND DRYING ACROSS THE LOWER OH/MS VALLEY REGION
PER GOES PW IMAGERY AND REGIONAL SOUNDINGS...A NARROW CORRIDOR OF
BOUNDARY LAYER DEWPOINTS IN THE UPPER 50S TO LOW 60S PERSISTS ALONG
THE STALLED FRONT FROM OH WWD TO SRN IA. SOMEWHAT RICHER MOISTURE
IS PRESENT TO THE E OF THE DRYLINE IN KS/OK...WHERE LOW-MID 60S
DEWPOINTS ARE COMMON. THIS MOISTURE...ALONG WITH DAYTIME
HEATING...WILL AGAIN SUPPORT A NARROW SWATH OF MODERATE INSTABILITY
/MLCAPE VALUES OF 1500-2500 J PER KG/ IN ADVANCE OF THE SURFACE LOW
ACROSS SRN IA/NRN MO/NRN IL...AND IN ADVANCE OF THE DRYLINE ACROSS
ERN KS AND CENTRAL OK THIS AFTERNOON.
THE SHRINKING MOIST SECTOR AND PRESENCE OF A SUBSTANTIAL EML BOTH
SUGGEST THAT DEEP CONVECTION WILL BE FOCUSED IMMEDIATELY ALONG THE
SURFACE BOUNDARIES TODAY. THE ONGOING ELEVATED STORMS OVER NE IL
WILL SPREAD EWD TOWARD SRN LOWER MI...THOUGH SOME WEAKENING IS
EXPECTED LATER THIS MORNING. ADDITIONAL DEVELOPMENT WILL LIKELY BE
DELAYED UNTIL MID-LATE AFTERNOON INVOF THE SURFACE CYCLONE WHERE THE
CAP WILL FIRST WEAKEN. SUBSEQUENT SWD DEVELOPMENT OF STORMS IS
EXPECTED ALONG THE COLD FRONT/DRYLINE ACROSS NW MO AND ERN KS LATE
THIS AFTERNOON...AND LATE THIS EVENING OR EARLY TONIGHT FARTHER S
INTO CENTRAL/ERN OK ALONG THE DRYLINE.
THE MAGNITUDE OF INSTABILITY...IN COMBINATION WITH STRONG DEEP-LAYER
VERTICAL SHEAR /0-6 KM BULK SHEAR OF 50-70 KT/...SHOULD FAVOR
SUPERCELLS WITH THE INITIAL STORM DEVELOPMENT NEAR/E OF THE SURFACE
LOW...AND ALONG THE FRONT/DRYLINE TO THE S. WITH
TIME...HOWEVER...INCREASINGLY LINE-PARALLEL SHEAR VECTORS AND FLOW
ALOFT SHOULD PROMOTE UPSCALE GROWTH INTO LINE SEGMENTS. THE
SEMI-DISCRETE INITIAL CONVECTIVE MODES AND MODEST LOW-LEVEL
SHEAR/MOISTURE WILL CONTRIBUTE TO A THREAT FOR A FEW
TORNADOES...ALONG WITH LARGE HAIL. BY LATE EVENING AND EARLY
OVERNIGHT...THE DAMAGING WIND THREAT WILL BECOME A LITTLE MORE
PROMINENT...BEFORE THE SEVERE THREAT DIMINISHES LATE TONIGHT IN
CONJUNCTION WITH WEAKENING INSTABILITY.
...CENTRAL/SRN NY AND NRN PA TODAY...
A BELT OF ELEVATED CONVECTION ASSOCIATED WITH LOW-LEVEL WAA WILL
CONTINUE TO SPREAD EWD ACROSS ERN PA/CENTRAL NY AND WEAKEN LATER
THIS MORNING. IN THE WAKE OF THIS CONVECTION...SOME LOW-LEVEL
DESTABILIZATION AND NWD RETREAT OF THE BAROCLINIC ZONE WILL
CONTRIBUTE TO A MORE FAVORABLE ENVIRONMENT FOR SURFACE-BASED STORMS
ACROSS NRN PA AND SRN NY TOWARD MIDDAY/AFTERNOON. AN INITIAL SPEED
MAX/REMNANT MCV WILL MOVE OVER NY THIS MORNING...LIKELY BEFORE THE
LOW LEVELS WARM/MOIST SUFFICIENTLY. THIS LEAVES THE ARRIVAL OF
ANOTHER UPSTREAM MCV /NOW OVER NRN IL/ AS A POTENTIAL AID TO
THUNDERSTORM DEVELOPMENT ALONG THE RETREATING BOUNDARY BY LATE
AFTERNOON. IF SURFACE-BASED STORMS DO DEVELOP...INSTABILITY AND
VERTICAL SHEAR WILL BE SUFFICIENT FOR SUPERCELLS AND AT LEAST A
MARGINAL SEVERE HAIL/WIND THREAT.
..THOMPSON/ROGERS.. 04/06/2010
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z
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