DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 111632
SWODY1
SPC AC 111629

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1129 AM CDT THU OCT 11 2012

VALID 111630Z - 121200Z

...THERE IS A SLGT RISK OF SVR TSTMS TONIGHT OVER SRN KS/NRN OK
ACROSS NRN AR/SRN MO...

...SRN KS/NRN OK ACROSS NR AR/SRN MO...
SURFACE OBSERVATIONS AND 12Z RAOBS INDICATE LOW LEVEL MOISTURE IS
RETURNING NWD ACROSS THE SRN PLAINS AND THE OZARKS IN ASSOCIATION
WITH A BROADENING ZONE OF SLY WINDS IN THE WAKE OF THE RETREATING
ERN US ANTICYCLONE. A STRONG COLD FRONT EXTENDING FROM WI SWWD INTO
THE CENTRAL HIGH PLAINS WILL CONTINUE SWD AND GRADUALLY MERGE
WITH/OVERTAKE A NWD MOVING WARM FRONT /CURRENTLY NEAR THE TX/OK
BORDER/ LATER TONIGHT NEAR THE KS/OK BORDER EWD INTO SRN MO. THIS
WILL PROVIDE A FOCUS FOR CONVECTIVE DEVELOPMENT...MAINLY
TONIGHT...ALONG/NORTH OF THE COMPOSITE SURFACE BOUNDARY WHERE LOW
LEVEL CONVERGENCE AND WARM ADVECTION WILL ENHANCED. MODERATELY
STEEP MID LEVEL LAPSE RATES /7.0-7.5 C PER KM/ OVER THE HIGH PLAINS
ARE EXPECTED TO SPREAD EWD AND MAINTAIN OR ENHANCE EXISTING ELEVATED
INSTABILITY CHARACTERIZED BY MUCAPE OF 1000-1500 J/KG. THIS WILL
PROMOTE FORMATION ELEVATED STORMS CAPABLE OF PRODUCING SEVERE HAIL
AS THEY DEVELOP EWD THROUGH THE OVERNIGHT HOURS.

...SRN NV/SWRN UT/AZ...
WATER VAPOR IMAGERY SHOWS A COLD UPPER LOW OFF THE SRN CA COAST WITH
A SHORT WAVE TROUGH ROTATING AHEAD OF THE LOW ACROSS THE LOWER CO
RIVER VALLEY. THIS HAS ENHANCED A BAND OF CONVECTION FROM SRN NV
SWD INTO FAR SWRN AZ WHICH IS LOCATED WITHIN AN AXIS OF GREATER
MOISTURE AND INSTABILITY BASED ON 12Z YUM AND VEF RAOBS. STRONG
SSWLY WINDS ALOFT ARE PROVIDING SUFFICIENT EFFECTIVE SHEAR OF 35-45
KT TO SUPPORT ORGANIZED MULTICELL AND ISOLATED SUPERCELL STRUCTURES.
ACTIVITY IS EXPECTED TO SPREAD EWD THIS AFTERNOON AND EVENING AS
THE TROUGH ROTATES INTO THE SRN PLATEAU...WITH STRONGER CELLS
CAPABLE OF PRODUCING MARGINALLY SEVERE HAIL AND STRONG WIND GUSTS.

...SRN CA COASTAL AREAS AND ADJACENT COASTAL WATERS...
COLD UPPER LOW IS FORECAST TO MOVE SLOWLY TOWARD THE SRN CA COAST
AND MAINTAIN SUFFICIENT INSTABILITY WITH CAPE OF NEAR 500 J/KG OVER
THE COASTAL WATERS/IMMEDIATE COASTAL ZONES FROM SMO SWD TO SAN.
RADAR AND NLDN CONTINUE TO SHOW LOW-TOPPED CONVECTION WITH
OCCASIONAL LIGHTNING...AND THERE HAVE BEEN ISOLATED REPORTS OF
WATERSPOUTS THIS MORNING. A THREAT FOR MARGINAL HAIL AND ISOLATED
WATERSPOUTS/BRIEF TORNADO OR TWO WILL PERSIST WITH STRONGER CELLS
INTO THE AFTERNOON AS STORMS GRADUALLY MOVE TOWARD THE COAST AND
INLAND BEFORE WEAKENING.

...SRN HIGH PLAINS...
DIABATIC HEATING...STEEP LOW-LEVEL LAPSE RATES...AND
INCREASING BOUNDARY-LAYER MOISTURE SHOULD LEAD TO WEAKENING CINH AND
INCREASING TSTM POTENTIAL THROUGH AFTERNOON. ACTIVITY ALSO MAY
DEVELOP OVER ADJACENT MOUNTAINS OF SRN NM AND MOVE NEWD INTO REGIME
OF INCREASING LOW-LEVEL MOISTURE WITH EWD EXTENT AND WITH TIME.
LOW-LEVEL FLOW WILL BE RELATIVELY WEAK BENEATH RIDGING ALOFT WHICH
SHOULD LIMIT THE OVERALL CONVECTIVE COVERAGE. BUOYANCY MAY ALSO BE
TEMPERED SOMEWHAT BY EFFECTS OF CLOUD COVER AND WEAKER DIABATIC
HEATING. HOWEVER...30-40 KT EFFECTIVE SHEAR WILL HELP ENHANCE THE
ORGANIZATION AND INTENSITY OF ANY STORMS THAT DO FORM AND
PERSIST...WITH MULTICELLULAR MODES BEING DOMINANT AND TRANSIENT
SUPERCELL EVOLUTION POSSIBLE. THUS...WILL MAINTAIN LOW SEVERE
PROBABILITIES OVER THIS REGION.

..WEISS/SMITH.. 10/11/2012

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