SPC AC 171725
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1225 PM CDT FRI APR 17 2009
VALID 181200Z - 191200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM PORTIONS OF KS INTO ERN
HALF OF TX...
...SYNOPSIS...
SLOW MOVING...VERTICALLY STACKED LOW WILL REMAIN MAIN FOCUS FOR
SEVERE THUNDERSTORM FORECAST SATURDAY AS THE SYSTEM DRIFTS EWD
ACROSS THE CENTRAL PLAINS. SURFACE MOIST AXIS IS EXPECTED TO REMAIN
EXTEND FROM SRN/ERN TX ACROSS THE LOWER MO RIVER VALLEY AND REACH
BACK INTO PORTIONS OF NW OK/WRN KS NORTH OF MAIN SURFACE LOW
SATURDAY AFTERNOON. ALTHOUGH GREATEST GULF MOISTURE WILL LIKELY
REMAIN TRAPPED NEARER THE TX COAST FROM PRECEEDING CONVECTIVE
COMPLEXES. OVERALL SETUP APPEARS SUPPORTIVE OF TWO RELATIVE MAXIMA
IN SEVERE THUNDERSTORM POTENTIAL: 1) UNDER VERY COLD POCKET ALOFT
OVERRIDING MODEST SURFACE MOISTURE INTO KS/NRN OK AND 2) NEARER
COASTAL FRONT FROM SERN TX INTO SWRN LA. IN BETWEEN...MODEL
SIMULATED WV IMAGERY INDICATES STRONG SUBSIDENCE WITHIN DRY SLOT
OVERSPREADING CENTRAL/NERN TX INTO ERN OK. HOWEVER...STRONG SWLY
FLOW ALOFT WILL REMAIN SUPPORTIVE OF SEVERE THUNDERSTORMS/SUPERCELLS
ANYWHERE ALONG THE DRY LINE SATURDAY WHERE HEATING CAN OVERCOME
CAPPING AND HAVE THEREFORE CONNECTED THE TWO PRIMARY SEVERE AREAS.
...SRN KS/NRN OK...
MODELS ARE CONSISTENT IN BRINGING -22C TO -24C H5 COLD POCKET EWD
ATOP NWRN EDGE OF 45-55F SURFACE DEW POINT AXIS EXTENDING INTO THIS
REGION DURING THE AFTERNOON. FORECAST SOUNDINGS THEREFORE SUGGEST
LOW LEVEL AND MID LEVEL LAPSE RATES WILL BECOME QUITE STEEP WITH
EVEN MODEST SURFACE HEATING. EXPECT FAIRLY LOW-TOPPED SEVERE
THUNDERSTORMS TO DEVELOP BY THE MID AFTERNOON OVER NW/N-CENTRAL OK
AND WRN KS AND BECOME WIDESPREAD AS ACTIVITY SHIFTS EWD AND DEVELOPS
SEWD INTO NERN AND POSSIBLY CENTRAL OK ALONG DRY LINE INTO THE
EVENING. PRIMARY THREAT WILL BE LARGE HAIL...ALTHOUGH STEEP LOW
LEVEL LAPSE RATES WITHIN STRONG/DEEP VORTICITY FIELDS MAY FAVOR A
FEW TORNADOES AS WELL.
...ERN TX INTO THE LOWER MS RIVER VALLEY...
SEVERE THUNDERSTORM FORECAST WILL BE SOMEWHAT MESSY OVER THIS REGION
GIVEN UNCERTAINTY REGARDING IMPACTS/LOCATION OF PRECEEDING
CONVECTIVE CLUSTER/S. EXPECT LARGE MCC OVER ERN TX SATURDAY MORNING
WITH ISOLATED THREAT OF SEVERE AS IT PERSISTS/SHIFTS ENEWD THROUGH
THE DAY. SEVERE THREAT SHOULD RAMP-UP DURING THE MID TO LATE
MORNING EITHER WITH SRN PORTION OF THIS ACTIVITY OR IN THE FORM OF A
SEPARATE AREA OF STORMS INVOF RICHER GULF MOISTURE NEAR THE UPPER TX
COAST. ALTHOUGH LAPSE RATES/INSTABILITY MAY BE HINDERED FROM
EARLIER STORMS...SHEAR WILL BECOME QUITE STRONG AS 35-45 KT SWLY MID
LEVEL WINDS OVERSPREAD THE REGION. SUPERCELLS AND BOWING LINE
SEGMENTS ARE EXPECTED TO DEVELOP DURING THE MID TO LATE
AFTERNOON...WITH ATTENDANT TORNADO THREAT.
...CENTRAL/NERN TX INTO CENTRAL/ERN OK...
CONDITIONAL SEVERE RISK WILL PERSIST INVOF DRY LINE SATURDAY
AFTERNOON WITHIN DRY SLOT REGION. RESULTANT SUBSIDENT REGIME SHOULD
LIMIT OVERALL COVERAGE/POTENTIAL FOR DIURNAL TSTM DEVELOPMENT.
HOWEVER...VERY STEEP LAPSE RATES ATOP WRN EXTENT OF SURFACE MOIST
AXIS WILL SUPPORT A VERY UNSTABLE AIR MASS BY LATE IN THE DAY. DEEP
LAYER SHEAR WILL BE MORE THAN ADEQUATE FOR SUPERCELLS...ALTHOUGH LOW
LEVEL SHEAR WILL NOT BE VERY IMPRESSIVE WITH WEAK H85 FLOW. LARGE
HAIL AND DAMAGING WINDS WOULD LIKELY ACCOMPANY ANY STORM WHICH CAN
DEVELOP.
..EVANS.. 04/17/2009
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