SPC 2000Z Day 1 Outlook
DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0253 PM CDT THU OCT 11 2012 VALID 112000Z - 121200Z ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF KS/OK INTO THE OZARKS... ...SRN KS/NRN OK ACROSS NRN AR/SRN MO... THE ONGOING FORECAST FOR OVERNIGHT EVOLUTION OF ELEVATED CONVECTION ACROSS THIS REGION REMAINS ON TRACK...WITHIN A LOW-LEVEL WARM-ADVECTION REGIME TO EVOLVE ACROSS THE AREA AHEAD OF THE MAIN UPPER SYSTEM. MARGINAL HAIL WILL BE POSSIBLE WITH SOME OF THE STRONGER STORMS ACROSS THIS REGION. ...ELSEWHERE... LIMITED/MARGINAL SEVERE WEATHER POTENTIAL CONTINUES ACROSS PORTIONS OF THE SWRN U.S. INVOF THE UPPER LOW NOW CENTERED NEAR THE SRN CA COAST. ALONG WITH POTENTIAL FOR GUSTY WINDS AND/OR HAIL WITH A STRONGER CELL OR TWO WITHIN THE WARM CONVEYOR ACROSS WRN AZ/NV...MARGINAL HAIL OR A BRIEF TORNADO WILL BE POSSIBLE OVER PARTS OF SRN CA UNDER THE IMMEDIATE LOW CENTER THROUGH THIS EVENING. FARTHER E INTO THE ERN NM VICINITY...LATEST GUIDANCE HINTS THAT GREATER CONVECTIVE POTENTIAL MAY HOLD OFF UNTIL THE SECOND HALF OF THE PERIOD...MORE IN CONJUNCTION WITH THE BROADER ZONE OF DEVELOPMENT FARTHER NE. THUS... ANY SEVERE POTENTIAL ACROSS THIS AREA APPEARS LESS LIKELY TO OCCUR DURING THE DAYLIGHT HOURS WITHIN THIS REGION. ..GOSS.. 10/11/2012 .PREV DISCUSSION... /ISSUED 1129 AM CDT THU OCT 11 2012/ ...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.
via SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day1otlk_2000.html
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