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Apr 28, 2014 1300 UTC Day 1 Convective Outlook

April 28, 2014

Apr 28, 2014 1300 UTC Day 1 Convective Outlook

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DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0737 AM CDT MON APR 28 2014

VALID 281300Z – 291200Z

…THERE IS A MDT RISK OF SVR TSTMS OVER PARTS OF WRN AND MIDDLE TN…NRN AND CNTRL MS…NWRN AL…AND FAR NERN LA…

…THERE IS A SLGT RISK OF SVR TSTMS FROM PARTS OF THE MID MS AND OH VALLEYS SWD TO THE LOWER MS VALLEY AND CNTRL GULF STATES…AND EWD TO THE CNTRL AND SRN APPALACHIANS…

…SUMMARY…
A SEVERE WEATHER OUTBREAK IS FORECAST TODAY INTO TONIGHT FROM PARTS OF THE LOWER MISSISSIPPI VALLEY INTO THE TENNESSEE VALLEY AND CENTRAL GULF COAST STATES. NUMEROUS TORNADOES ARE EXPECTED…SOME OF WHICH COULD BE INTENSE. VERY LARGE HAIL AND DAMAGING STRAIGHT LINE WINDS ARE ALSO LIKELY.

…SYNOPSIS…

AN INTENSE MID TO UPPER-LEVEL TROUGH WILL EDGE ONLY SLIGHTLY EWD FROM THE CNTRL PLAINS INTO THE MID MS VALLEY WITH THIS SYSTEM BOUNDED ON IT/S SRN PERIPHERY BY A 500-MB JET IN EXCESS OF 70-80 KT CURVING CYCLONICALLY FROM THE FOUR-CORNERS REGION THROUGH LOWER MS AND TN VALLEYS INTO CNTRL APPALACHIANS. EMBEDDED WITHIN THIS HIGH-MOMENTUM AIR STREAM…A MIDLEVEL JET STREAK WILL PROGRESS FROM THE ARKLATEX AND OZARK PLATEAU EWD INTO THE MID SOUTH. THIS UPPER-AIR PATTERN EVOLUTION WILL MAINTAIN A 40-50+ KT SWLY LLJ OVER THE CNTRL GULF STATES AND TN VALLEY…ENHANCING BOTH VERTICAL SHEAR AND THE POLEWARD FLUX OF HEAT AND MOISTURE WITHIN THE WARM SECTOR OF THE SYNOPTIC SYSTEM.

AT THE SURFACE…AN OCCLUDED AREA OF LOW PRESSURE OVER ERN NEB WILL WEAKEN WHILE SLOWLY SHIFTING ACROSS SRN IA. MEANWHILE…AN ASSOCIATED COLD FRONT WILL GRADUALLY OVERTAKE A STALLED DRYLINE/PACIFIC FRONT OVER THE OZARKS INTO NERN TX BEFORE ADVANCING EWD THROUGH THE MID/LOWER MS VALLEY. THE TRAILING EXTENSION OF THIS FRONT WILL MOVE MORE SLOWLY SEWD THROUGH PARTS OF LA AND SERN/SRN TX. THERE IS SOME INDICATION IN LATEST MODEL GUIDANCE THAT A SECONDARY SURFACE LOW MAY FORM ALONG OR JUST AHEAD OF THE COLD FRONT OVER THE MID SOUTH TODAY WITH THIS FEATURE TRACKING NEWD INTO THE UPPER OH VALLEY. FINALLY…A WARM FRONT STRETCHING FROM THE MID MO VALLEY LOW ESEWD THROUGH THE OH VALLEY TO CAROLINAS WILL SLOWLY LIFT NWD.

…OH/LOWER MS VALLEYS EWD TO THE SRN APPALACHIANS TODAY THROUGH TONIGHT…

AS OF 12Z…REGIONAL RADAR INDICATED A COUPLE OF SEPARATE MCSS…ONE WITH A WELL-DEFINED MCV AND EWD/SEWD-ADVANCING COLD POOL FROM SRN IND/CNTRL KY SWWD THROUGH WRN TN WHERE IT INTERSECTED A MORE RECENTLY DEVELOPED SYSTEM WHICH TRAILED SSWWD THROUGH NWRN MS TO NRN LA AND ERN TX. THIS ACTIVITY WILL LIKELY CONTINUE EWD ACROSS PARTS OF TN…MS…LA…PERHAPS AL THIS MORNING INTO EARLY AFTERNOON…POSING A RISK FOR A COUPLE TORNADOES…DAMAGING WINDS AND LARGE HAIL BEFORE WEAKENING LATER TODAY.

IN THE WAKE OF THESE INITIAL STORMS…CONVECTION-ALLOWING MODEL GUIDANCE IS QUITE CONSISTENT IN SUGGESTING THE REDEVELOPMENT OF TSTMS BY AFTERNOON ALONG REMNANT OUTFLOW BOUNDARIES AND THE EWD-MOVING COLD FRONT FROM WRN OR MIDDLE TN SWWD THROUGH NRN/CNTRL MS INTO NERN LA. 12Z OBSERVED SOUNDINGS FROM THE LOWER MS VALLEY INDICATE THAT A PRONOUNCED EML HAS BEEN ADVECTED EWD INTO THE REGION WITH 700-500-MB LAPSE RATES OF 7.5-8.0 C/KM. THESE STEEP LAPSE RATES OVERLIE A VERY MOIST BOUNDARY LAYER /I.E. LOWEST 100-MB MEAN-MIXING RATIOS OF 13.5-15.5 G PER KG/ WHICH WILL PROMOTE AFTERNOON MLCAPE VALUES OF 1500-2500 J/KG IN AREAS WHERE STRONGER DAYTIME HEATING CAN OCCUR. THIS INSTABILITY WILL ALIGN WITH 50-70 KT DEEP-LAYER SHEAR AND EFFECTIVE SRH VALUES OF 200-300 M2/S2…SETTING THE STAGE FOR A POTENTIALLY VOLATILE ENVIRONMENT…SUPPORTIVE OF SUPERCELLS CAPABLE OF INTENSE TORNADOES AND VERY LARGE HAIL. MESOSCALE TRENDS WILL CONTINUE TO BE MONITORED FOR A POSSIBLE UPGRADE TO HIGH RISK LATER TODAY.

THE NRN EXTENT OF THIS FAVORABLE WARM SECTOR ENVIRONMENT WILL BE DICTATED BY THE LINGERING EFFECTS OF THE CURRENT COLD POOL IN PLACE ACROSS THE LOWER OH INTO PARTS OF THE TN VALLEY. WHERE STRONGER BOUNDARY-LAYER HEATING CAN OCCUR…THE LARGE-SCALE ENVIRONMENT WILL SUPPORT SUPERCELLS CAPABLE OF TORNADOES AND LARGE HAIL NWD INTO SRN PARTS OF THE MID OH VALLEY.

AN EVENTUAL UPSCALE GROWTH OF DIURNALLY ENHANCED TSTMS INTO ONE OR MORE LINEAR CONVECTIVE SYSTEMS APPEARS LIKELY LATE THIS EVENING INTO THE OVERNIGHT HOURS OVER PARTS OF THE MID OH AND TN VALLEYS SWD TOWARD THE CNTRL GULF COAST. THIS ACTIVITY WILL PROGRESS EWD INTO THE CNTRL/SRN APPALACHIANS AND ERN GULF STATES WITH A CONTINUING THREAT FOR PRIMARILY DAMAGING WINDS.

…MID MS VALLEY THIS AFTERNOON INTO EVENING…

ANALOGOUS TO YESTERDAY/S EVENTS OVER CNTRL NEB…A SIMILAR SETUP WILL EVOLVE OVER THE REGION TODAY WHEREBY THE MIDLEVEL COLD POOL ASSOCIATED WITH THE UPPER LOW OVERLIES A WARMING BOUNDARY LAYER…YIELDING STEEP LAPSE RATES AND MLCAPE OF 1000-1500 J/KG. A PRONOUNCED GRADIENT IN DEEP-LAYER SHEAR WILL EXIST BY AFTERNOON…RANGING FROM GENERALLY LESS THAN 30 KT ALONG THE OCCLUDED FRONT OVER SRN IA INTO W-CNTRL IL…TO 50-60 KT OVER CNTRL/SRN PARTS OF IL/IND AND POINTS SOUTH. AS SUCH…MIXED STORM MODES WILL LIKELY EVOLVE THIS AFTERNOON…INCLUDING MULTICELL AND SUPERCELL STRUCTURES. LARGE HAIL WILL BE THE PRIMARY HAZARD…THOUGH TORNADOES ARE ALSO POSSIBLE OWING TO THE PRESENCE OF A VERTICAL-VORTICITY-RICH ENVIRONMENT.

…CNTRL/ERN NC CAROLINA THIS AFTERNOON…

DESPITE THE PRESENCE OF A BUILDING MIDLEVEL RIDGE…LOW-LEVEL MOISTENING COUPLED WITH DAYTIME HEATING AND CONVERGENCE ALONG THE SLOWLY RETREATING WEDGE FRONT MAY FOSTER AN ENVIRONMENT FAVORABLE FOR ISOLATED SEVERE STORMS THIS AFTERNOON. FORECAST SOUNDINGS INDICATE MLCAPE APPROACHING 500-1500 J/KG AND A VERTICALLY VEERING WIND PROFILE WITH 30-35 KT OF VERTICAL SHEAR WHICH WOULD SUPPORT ORGANIZED/ROTATING UPDRAFTS WITH A RISK FOR ISOLATED OCCURRENCES OF LARGE HAIL AND/OR LOCALLY DAMAGING WIND GUSTS.

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