SPC 1200Z Day 1 Outlook
DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0100 AM CDT THU MAY 30 2013 VALID 301200Z - 311200Z ...THERE IS A SLGT RISK OF SVR TSTMS IA TO PORTIONS NW TX... ...SYNOPSIS... AS SEVERAL VORTICITY LOBES PHASE/CONSOLIDATE OVER NRN PLAINS...MID-UPPER LEVEL CYCLONE IS FCST TO EVOLVE OVER BLACK HILLS REGION BY START OF PERIOD...DEEPENING SLIGHTLY AND PROCEEDING EWD ACROSS WRN/CENTRAL SD BEFORE 31/12Z. NEGATIVELY TILTED SHORTWAVE TROUGH -- NOW APPARENT IN MOISTURE CHANNEL IMAGERY AND PROFILER/VWP DATA FROM NERN CO SSEWD OVER ERN HIGH PLAINS -- IS FCST TO SHIFT NEWD TO EXTEND FROM WRN IA ACROSS WRN OZARKS REGION BY 31/00Z...THEN NEWD OVER UPPER MS VALLEY REGION OVERNIGHT. BEHIND THIS FEATURE...PRONOUNCED JET MAX ALOFT -- ALREADY APCHG 130 KT BASED ON 30/00Z 250-MB ANALYSIS -- IS STRONGER THAN HAS BEEN PROGGED BY PREVIOUS RUNS OF OPERATIONAL NAM AND SIMILAR TO 30/12Z SPECTRAL FCST. JET AXIS SHOULD SHIFT/EXPAND ESEWD OVER CENTRAL ROCKIES AND SRN KS THROUGH EVENING...WHILE DIRECTION OF MID-UPPER LEVEL FLOW BECOMES NEARLY ZONAL WITH GRADUAL CYCLONIC CURVATURE. AT SFC...NRN-PLAINS LOW IS FCST TO BECOME ESSENTIALLY VERTICALLY STACKED WITH CYCLONE ALOFT EARLY IN PERIOD...MIGRATING SLIGHTLY NEWD OVER ND AND N OF MID-UPPER LOW THROUGH 31/12Z. SFC TROUGH/WIND-SHIFT LINE AND WEAK FRONT SHOULD ARC SWD/SWWD FROM THAT LOW DURING AFTERNOON...SUPPORTING SOME DIURNAL TSTM POTENTIAL ACROSS PORTIONS SD AND NRN/WRN NEB. DRYLINE SHOULD MIX EWD DURING DAY...REACHING LATE-AFTN POSITION FROM NRN COAHUILA NNEWD ACROSS W-CENTRAL TX...W-CENTRAL OK AND S-CENTRAL KS...BEFORE RETREATING NWWD ACROSS NRN OK AND SRN KS DURING EVENING. ...PLAINS STATES TO UPPER MS VALLEY AND UPPER MIDWEST... PRIMARY CONCERN ATTM IS FOR ISOLATED TO WIDELY SCATTERED TSTMS TO DEVELOP INVOF DRYLINE DURING LATE AFTN AFTER STG/SUSTAINED SFC HEATING AND MOVE EWD...OFFERING RISK OF VERY LARGE/DAMAGING HAIL AND TORNADOES. NARROW SECTOR OF VERY FAVORABLE SUPERCELL-SUPPORTING PARAMETER SPACE IS APPARENT FROM ABOUT E-CENTRAL KS SWWD TO RED RIVER REGION OF OK AND N TX...FOR ANY TSTMS THAT CAN FORM AND PERSIST TO MATURITY. ROBUST MOIST-SECTOR AIR IS FCST AHEAD OF DRYLINE...WITH SFC DEW POINTS RANGING FROM MID-60S TO LOW-70S F SUPPORTING MLCAPE IN 3000-5000 J/KG RANGE...LYING BENEATH 55-65 KT EFFECTIVE SHEAR MAGNITUDES. HODOGRAPHS ARE EXPECTED TO ENLARGE CONSIDERABLY IN 00Z-03Z TIME FRAME OVER AREA OF LARGEST HAIL/TORNADO PROBABILITIES...AS LLJ STRENGTHENS. UNLIKE PREVIOUS DAY...GEOMETRY OF FLOW RELATED TO NEGATIVELY TILTED SHORTWAVE WILL RENDER DEEP-SHEAR AND MEAN-WIND VECTORS NEARLY ORTHOGONAL TO DRYLINE...INDICATING GREATER POTENTIAL FOR DISCRETE STORM CHARACTER AND SUPERCELL MODE. HOWEVER...SOME CAVEATS ARE EVIDENT THAT MAKE THREAT TOO CONDITIONAL TO INTRODUCE MDT-RISK PROBABILITIES YET...AND WHICH ALSO CAST GREAT UNCERTAINTY ON SVR POTENTIAL FARTHER N OVER MO VALLEY..NRN PLAINS AND CORN BELT. THESE INCLUDE... 1. ABUNDANT PRIOR AND ONGOING CONVECTION FROM ERN OK/OZARKS AREA NWD ACROSS MO VALLEY AND NWWD OVER PORTIONS KS...EARLY IN PERIOD. THIS ACTIVITY HAS OVERTURNED AIR MASS ACROSS MUCH OF THAT REGION...LOWERING DEW POINTS. RESULTING MODIFIED BOUNDARY LAYER WILL ADVECT NWD ACROSS CENTRAL PLAINS...IA...DAKOTAS AND MO VALLEY REGION WITH FRAGMENTED AND MODULATED MOISTURE FIELD...CHARACTERIZED BY EMBEDDED RIBBONS AND POCKETS OF LOW-THETAE AIR. 2. LACK OF WELL-DEFINED FOCI FOR INITIATION IN THAT AIR MASS...ESPECIALLY FROM ABOUT I-70 NWD. 3. HEIGHT RISES ARE EXPECTED BEHIND SHORTWAVE TROUGH THROUGHOUT AFTERNOON OVER SRN PLAINS...WITH WEAK MID-UPPER LEVEL VERTICAL MOTIONS. 4. CAPPING WILL INHIBIT TSTM COVERAGE...ESPECIALLY FROM RED RIVER AREA SWD ACROSS W-CENTRAL/SW TX. ANY TSTM THAT DOES DEVELOP OFF DRYLINE OVER TX STILL WILL POSE SVR WIND/HAIL RISK BEFORE NOCTURNAL DISSIPATION. 5. NARROWNESS OF MOST FAVORABLE MOIST SECTOR MAY LIMIT TIME WINDOW FOR SUPERCELLS. STILL...GIVEN RECOVERY EXPECTED OVER OK AND PROBABLY SERN KS...VERY LARGE CAPE WILL SUPPORT ENHANCED TORNADO/HAIL PROBABILITIES FOR NOW WITHIN SLGT-RISK FRAMEWORK. AS SOME OF THESE UNCERTAINTIES GET BETTER RESOLVED TODAY...NARROW AREA OF SIGNIFICANT-TORNADO AND/OR LARGER-HAIL PROBABILITIES MAY BECOME NECESSARY...ESPECIALLY OVER PORTIONS OK AND KS. ..EDWARDS/BUNTING.. 05/30/2013
via SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day1otlk_1200.html
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