SPC 1200Z Day 1 Outlook
DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1210 AM CDT SUN APR 29 2012 VALID 291200Z - 301200Z ...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS LOWER OH VALLEY TO SRN/CENTRAL HIGH PLAINS... ...SYNOPSIS... OVERALL UPPER-AIR PATTERN DEAMPLIFICATION IS FCST THIS PERIOD. PRONOUNCED MID-UPPER LEVEL CYCLONE -- NOW EVIDENT IN MOISTURE CHANNEL IMAGERY OVER SERN MT/SWRN ND/NWRN SD REGION -- IS FCST TO DRIFT NWD UNTIL EARLY DAY-1. AS LOWER-AMPLITUDE PERTURBATION AND RELATED SPEED MAX NOW OVER N PAC APCH PAC NW COAST...NRN PLAINS PERTURBATION WILL DEAMPLIFY AND ACCELERATE NEWD. BY 30/00Z...CYCLONE WILL BE DEVOLVING TO OPEN WAVE OVER SWRN MB...WITH SLIGHTLY POSITIVELY TILTED TROUGH SSWWD OVER CENTRAL ND TO NRN PANHANDLE OF NEB. THIS PERTURBATION WILL CONTINUE TO EJECT NEWD AND DEAMPLIFY OVERNIGHT. WEAK SHORTWAVES AND SMALL VORTICITY MAXIMA WILL MOVE NEWD IN TRAILING SWATH OF CYCLONIC FLOW ACROSS ROCKIES AND GREAT PLAINS STATES...BUT WITHIN BROADER REGIME OF PRONOUNCED HEIGHT RISES. MEANWHILE...WELL-DEFINED/SYNOPTIC-SCALE RIDGE --INITIALLY LOCATED FROM TN VALLEY REGION NNWWD ACROSS NRN MN AND CENTRAL/NRN MB -- WILL SHIFT EWD TO CENTRAL/SRN APPALACHIANS...LOWER GREAT LAKES...AND JAMES BAY BY END OF PERIOD. AT SFC...QUASISTATIONARY FRONTAL ZONE WAS EVIDENT AT 29/03Z FROM SRN SC NWWD ACROSS NERN GA...NNEWD OVER ERN PORTIONS TN/KY...WWD ACROSS SRN IL TO SERN MO...SWWD OVER CENTRAL/SWRN OK...TO W-CENTRAL TX BETWEEN LBB-MAF. SRN-PLAINS SEGMENT OF THIS FRONT IS EXPECTED TO BECOME SOMEWHAT MORE DIFFUSE AND MOVE NWD AS WARM FRONT ACROSS WRN OK...TX PANHANDLE AND SRN KS. MORE PRECISE FCST OF ITS LOCATION/MOVEMENT STILL IS QUITE UNCERTAIN...GIVEN OFFSETTING FACTORS OF SYNOPTIC-SCALE FRONTOLYTIC INFLUENCE UNDER RISING HEIGHTS...BUT MESOSCALE POTENTIAL FOR BAROCLINIC ENHANCEMENT/REPOSITIONING DUE TO EARLIER/ONGOING CONVECTION. FARTHER E ACROSS MO AND OH VALLEY REGION...HOWEVER...FRONT SHOULD MOVE NWD SLOWLY OVER CENTRAL MO WHILE REMAINING QUASISTATIONARY FARTHER E. AFTERNOON DRYLINE SHOULD SET UP FROM NRN COAHUILA NNWWD ACROSS EXTREME ERN NM. GIVEN MESOSCALE UNCERTAINTIES REGARDING FOCI FOR CONVECTIVE LIFT...OUTLOOK IS NECESSARILY RATHER BROAD-BRUSHED AND GENERALIZED TO 15% UNCONDITIONAL WIND/HAIL PROBABILITIES ATTM. WITHIN OUTLOOK AREA...ONE OR TWO RELATIVE CONCENTRATIONS OF POTENTIAL -- I.E. 30% PROBABILITY AND/OR MORE SIGNIFICANT-HAIL AREAS -- MAY BE NEEDED ONCE MORE FOCUSED MESOSCALE INFLUENCES ARE APPARENT. ...SRN-CENTRAL HIGH PLAINS... SCATTERED ELEVATED TSTMS WITH POTENTIAL FOR OCNL HAIL WILL BE POSSIBLE AT START OF PERIOD FROM TX PANHANDLE ENEWD ACROSS NWRN OK TO SRN KS. THIS ACTIVITY SHOULD MOVE NEWD AND WEAKEN THROUGH REMAINDER MORNING. SCATTERED TO WIDELY SCATTERED TSTMS...WITH SOME CLUSTERING AROUND MESOSCALE BOUNDARIES...ARE EXPECTED TO FORM DURING LATE AFTERNOON BETWEEN DRYLINE AND FRONTAL ZONE OVER SRN HIGH PLAINS...AND NEAR LEE TROUGH/CONVERGENCE ZONE FARTHER N ACROSS ERN CO. STG VEERING WITH HEIGHT AND 30-40 KT 500-MB FLOW ARE EXPECTED...YIELDING FAVORABLE DEEP-LAYER SHEAR. DESPITE MESOSCALE UNCERTAINTIES...CONFIDENCE IN POTENTIAL FOR MULTIPLE REGIONAL SIGNIFICANT HAIL EVENTS IS GREATER HERE THAN FARTHER NE ALONG FRONT. EXPECT STEEP DEEP-LAYER LAPSE RATES...MLCAPE 2000-2500 J/KG AND FAVORABLE DEEP-LAYER SHEAR/HODOGRAPHS FOR SUPERCELLS OF BOTH LEFT- AND RIGHT-MOVING NATURE. SOME OF THIS ACTIVITY MAY PERSIST AFTER DARK AND PERHAPS GROW UPSCALE INTO MCS...MOVING ENEWD FROM TX/OK PANHANDLES OVER NWRN OK/SRN KS. ANY SUCH COMPLEX SHOULD BE INCREASINGLY ELEVATED ABOVE BOUNDARY LAYER OVERNIGHT. HOWEVER...POTENTIAL WILL EXIST FOR SVR HAIL/WIND AT LEAST INTO LATE EVENING HOURS. ...CENTRAL OK TO LOWER OH VALLEY... DESPITE RIDGING AND/OR RISING HEIGHTS ALOFT OVER MOST OF THIS AREA...SCATTERED TO WIDELY SCATTERED AFTERNOON TSTMS ARE LIKELY TO DEVELOP INVOF FRONTAL ZONE...ONCE SEVERAL HOURS OF STG SFC DIABATIC HEATING MINIMIZES MLCINH. THIS PROCESS WILL BE AIDED BY AT LEAST WEAK LOCAL LIFT INVOF FRONT AND ANY RESIDUAL/REINFORCING OUTFLOW BOUNDARIES. LAPSE RATES ALOFT ARE FCST TO INCREASE WITH WWD EXTENT...YIELDING HIGHER VALUES OF CAPE FOR SIMILAR LOW-LEVEL MOISTURE CONTENT. ALTHOUGH NEAR-SFC WINDS WILL REMAIN WEAK OVER MUCH OF AREA...EFFECTIVE SHEAR MAGNITUDES 35-50 KT ARE POSSIBLE...ALONG WITH ENHANCED LOW-LEVEL VORTICITY AND STORM-RELATIVE INFLOW IN FRONTAL ZONE. AS SUCH...MULTICELLS AND AT LEAST ISOLATED/TRANSIENT SUPERCELLS ARE EXPECTED...WITH BOTH WIND/HAIL THREAT. FCST HODOGRAPHS APPEAR ON LOW MARGINS FOR TORNADO POTENTIAL...THOUGH STORM-SCALE/BOUNDARY PROCESSES COULD AID THREAT IN LOCALIZED FASHION SOMEWHERE WITHIN THIS SWATH. OVERALL SVR RISK SHOULD DIMINISH AFTER ABOUT 04Z-06Z AS BOUNDARY LAYER COOLS/STABILIZES SUBSTANTIALLY. ..EDWARDS/GARNER.. 04/29/2012
via SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day1otlk_1200.html
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