SPC AC 151951
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0251 PM CDT MON JUN 15 2009
VALID 152000Z - 161200Z
...THERE IS A MDT RISK OF SVR TSTMS ACROSS PORTIONS OF CNTRL/ERN KS
AND EXTREME SRN NEB...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS A LARGE PART OF THE
PLAINS SEWD INTO THE TN VLY AND CAROLINAS...
PRIMARY CHANGES TO ONGOING FCST WERE IN THE CNTRL/SRN PLNS AND
MID-MS VLY TO THE TN VLY:
...CNTRL/SRN PLNS...
PRIMARY CHANGE ACROSS THE REGION WAS TO EXPAND MDT RISK NWD INTO SRN
NEB AND TRIM ALONG SRN EDGE IN SRN/WRN KS. NEXT MID-LVL SHORTWAVE
TROUGH WAS QUICKLY ADVANCING FROM THE FOUR CORNERS REGION AND WILL
ARRIVE ACROSS THE REGION THIS EVENING. MASS CONVERGENCE WAS
INCREASING OVER SCNTRL NEB INVOF SE-NW ORIENTED FRONT AT MID-AFTN
WITH A GROWING AGITATED CU FIELD EXTENDING SEWD INTO ECNTRL KS.
EXPECT CONVECTIVE INITIATION BY LATE AFTN/EARLY EVE ALONG N/NE EDGE
OF STRONGER CAPPING IN THIS REGION WITH UPSCALE DVLPMT INTO A
NOCTURNAL MCS. REST OF PREVIOUS FCST REASONING UNCHANGED.
...MID-MS VLY SEWD INTO TN VLY...
EXPANDED HIGHER PROBABILITIES OF TOR/WIND/HAIL EWD INTO TN VLY.
TSTMS HAVE FINALLY BECOME SFC-BASED INVOF OUTFLOW BOUNDARY/FRONT
SITUATED OVER SERN MO/NERN AR AND WRN TN. ELY LLVL WINDS VEERING
QUICKLY TO WLY IN THE MID-LVLS IS CREATING ADEQUATE SHEAR FOR
SUPERCELLS WITH A TORNADO OR TWO POSSIBLE. ACTIVITY SHOULD CONGEAL
INTO A MCS AND PROPAGATE/MOVE ESE INTO PARTS OF THE TN VLY THIS
EVENING WITH HIGH WINDS/HAIL.
..RACY.. 06/15/2009
.PREV DISCUSSION... /ISSUED 1114 AM CDT MON JUN 15 2009/
...SYNOPSIS...
OVERALL TODAYS CONVECTIVE OUTLOOK APPEARS TO BE IN GOOD SHAPE AS
IMPULSES CONTINUE TO TRACK OUT OF SWRN TROUGH ACROSS PLAINS AND MS
VALLEY. LARGE POOL OF VERY MOIST AND POTENTIALLY VERY UNSTABLE AIR
MASS RESIDES FROM CENTRAL PLAINS EWD TO THE ATLANTIC COAST.
...CENTRAL PLAINS...
SURFACE LOW CURRENTLY SWRN KS WILL DEEPEN SOME THIS AFTERNOON AND
MOVE EWD ALONG OK/KS BORDER THIS EVENING. EASTERLY LOW LEVEL WINDS
WILL BE MAINTAINED NORTH OF LOW ACROSS MUCH OF WESTERN KS.
MEANWHILE...STRONG HEATING WILL OCCUR WEST OF THE DRYLINE NEAR THE
SWRN KS/CO BORDER YIELDING AFTERNOON MLCAPE VALUES OF 2000-3000
J/KG. THE CAPPING INVERSION IS EXPECTED TO BE ELIMINATED BY
MID/LATE AFTERNOON ALONG THE DRYLINE...WITH ISOLATED THUNDERSTORM
DEVELOPMENT LIKELY. STORMS WILL MOVE INTO A VERY MOIST LOW LEVEL
AIRMASS WITH SUFFICIENT DEEP LAYER EFFECTIVE SHEAR TO PROMOTE
SUPERCELL STORM STRUCTURES. BACKED LOW LEVEL WINDS AND SUFFICIENT
LOW LEVEL SHEAR WILL ALSO POSE A RISK OF A FEW TORNADOES DURING THE
EARLY EVENING. HOWEVER...THE MAIN THREATS APPEAR TO BE VERY LARGE
HAIL AND DAMAGING WINDS AS STORMS ORGANIZE AND TRACK EASTWARD ACROSS
MUCH OF KS OVERNIGHT. ONE OR MORE FORWARD PROPAGATING MCS/S ARE
LIKELY WITH ORGANIZED DAMAGING WIND POTENTIAL.
...MO/AR/IL/KY/TN...
WIDESPREAD SHOWERS AND THUNDERSTORMS ARE OCCURRING THIS MORNING
ACROSS MUCH OF NORTHERN AND EASTERN MO INTO LWR OH VALLEY. THESE
STORMS ARE IN A REGION OF STRONG LOW LEVEL WARM/MOIST ADVECTION. S
OF THE PCPN THE WARM SECTOR IS VERY MOIST WITH DEWPOINTS INTO MID
70S AND ONLY WEAKLY CAPPED. MLCAPES AOA 3000 J/KG IN WARM SECTOR
ALONG WITH 30-40KT EFFECTIVE SHEAR...WILL SUPPORT SEVERE
THUNDERSTORMS WITH LARGE HAIL AND DAMAGING WINDS THE PRIMARY THREAT.
A COLD POOL COULD ORGANIZE ACROSS MID MS VALLEY AND TRACK E/SEWD
WITH MORE OF AN ORGANIZED WIND THREAT LATER IN THE AFTERNOON.
SUPERCELLS ARE ALSO POSSIBLE NEAR THE INSTABILITY GRADIENT ENHANCING
SEVERE THREAT INCLUDING ISOLATED TORNADOES.
..WESTERN SD/NEB...
SIMILAR TO YESTERDAY...IT APPEARS LIKELY THAT SCATTERED
THUNDERSTORMS WILL DEVELOP AGAIN THIS AFTERNOON AND EVENING FROM THE
BLACK HILLS SOUTHWARD INTO WESTERN NEB AND NERN CO. STEEP LOW/MID
LEVEL LAPSE RATES AND 25-40 KNOTS OF EFFECTIVE SHEAR WILL PROMOTE
SUPERCELLS CAPABLE OF LARGE HAIL AND PERHAPS ISOLATED TORNADOES.
...CAROLINAS...
A BROAD AREA OF 30-35 KNOT WESTERLY MID LEVEL WINDS WILL BE PRESENT
TODAY OVER THE CAROLINAS. DESPITE WEAK LOW LEVEL WINDS...THIS WILL
PROVIDE SUFFICIENT DEEP LAYER SHEAR TO SUPPORT ORGANIZED MULTICELL
STORMS CAPABLE OF LOCALLY DAMAGING WINDS AND HAIL THIS AFTERNOON.
STORMS SHOULD WEAKEN RAPIDLY AROUND SUNSET WITH THE LOSS OF DAYTIME
HEATING.
...NY/PA/VT/MA/CT...
COOL MID LEVEL TEMPERATURES ASSOCIATED WITH AN UPPER TROUGH OVER THE
NORTHEAST UNITED STATES WILL PROVIDE RELATIVELY STEEP MID LEVEL
LAPSE RATES THIS AFTERNOON OVER PARTS OF NY/PA AND WESTERN NEW
ENGLAND. LOW TOPPED THUNDERSTORMS HAVE ALREADY DEVELOP LATE THIS
MORNING AND A FEW CELLS COULD BECOME STRONG/SEVERE WITH A RISK OF
HAIL AND GUSTY/DAMAGING WINDS. SEVERE ACTIVITY IS EXPECTED TO
REMAIN RATHER ISOLATED AND DISORGANIZED AT THIS TIME.
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