SPC AC 180600 DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0100 AM CDT MON AUG 18 2014 VALID 181200Z - 191200Z ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF SERN MN/WRN WI/IA... ...SUMMARY... ISOLATED SEVERE STORMS -- AND ASSOCIATED THREAT FOR DAMAGING WINDS AND LARGE HAIL -- WILL BE POSSIBLE MONDAY AFTERNOON AND EVENING FROM PORTIONS OF MINNESOTA AND WISCONSIN SOUTH-SOUTHWESTWARD ACROSS IOWA AND INTO PORTIONS OF MISSOURI AND KANSAS. A FEW STRONG TO SEVERE STORMS CAPABLE OF PRODUCING GUSTY WINDS AND MARGINAL HAIL CAN ALSO BE EXPECTED FROM SOUTHERN ARKANSAS AND NORTHERN LOUISIANA EAST-NORTHEASTWARD TO THE CAROLINAS AND SOUTHERN VIRGINIA. ...SYNOPSIS... A MID-LEVEL SHORT-WAVE TROUGH IS PROGGED TO SHIFT ESEWD FROM THE NRN PLAINS TO THE UPPER MS VALLEY/WRN UPPER GREAT LAKES REGION THROUGH THE PERIOD. THIS FEATURE WILL BE ACCOMPANIED BY A BELT OF 30 TO 50 KT MID-LEVEL WNWLYS -- THE CORE OF WHICH SHOULD RESIDE ACROSS THE MID MO VALLEY VICINITY DURING THE AFTERNOON AND EVENING HOURS. ELSEWHERE...AN UPPER LOW IS PROGGED TO SHIFT SWD ALONG THE OREGON/CA COAST WITH TIME...WHILE A VORT MAX EMBEDDED IN A BELT OF SOMEWHAT ENHANCED MID-LEVEL WSWLYS CROSSES THE CENTRAL GULF COAST REGION THROUGH 19/12Z. ...SERN MN/WRN WI SWD ACROSS IA... CONVECTIVE/SEVERE RISK ACROSS THE UPPER MS/MID AND LOWER MO VALLEYS REMAINS DIFFICULT TO ASCERTAIN WITH ANY DEGREE OF CERTAINTY ATTM...IN PART DUE TO AREAS OF CONVECTION AND ASSOCIATED OUTFLOW BOUNDARIES/CLOUD DEBRIS EXPECTED TO BE ONGOING AT THE START OF THE PERIOD. IN GENERAL...THE CONTINUED ESEWD ADVANCE OF THE NRN PLAINS VORT MAX WILL PROVIDE LARGE-SCALE ASCENT FROM ROUGHLY THE MID MO VALLEY REGION NWD...WHILE A WEAK SURFACE FRONT CROSSES THE MN/IA/ERN NEB/NERN KS VICINITY DURING THE AFTERNOON. THOUGH GREATER INSTABILITY -- ASSOCIATED WITH A PLUME OF STEEP MID-LEVEL LAPSE RATES -- IS FORECAST ACROSS THE CENTRAL PLAINS...WEAKER SYNOPTIC-SCALE UVV SHOULD PROVE GENERALLY INSUFFICIENT TO ALLOW CONVECTIVE UPDRAFTS ALONG THE ADVANCING SURFACE FRONT TO BREACH THE CAPPING LAYER. THUS -- WILL MAINTAIN ONLY 5% CONDITIONAL SEVERE RISK SW OF THE MID MO VALLEY. WITH GREATER CONVECTIVE COVERAGE CONFINED TO AREAS FARTHER N -- WHERE WEAKER INSTABILITY IS PROGGED...DEGREE OF SEVERE RISK REMAINS SOMEWHAT UNCERTAIN. WITH THAT SAID...PRESENCE OF THE MID-LEVEL JET CROSSING SRN MN/IA DURING THE AFTERNOON SHOULD SUPPORT UPDRAFT ORGANIZATION/ROTATION...AND THUS AN UPGRADE TO SLIGHT RISK IS BEING INCLUDED THIS FORECAST FOR STORMS EXPECTED TO DEVELOP NEAR THE FRONT AS IT CROSSES MN/WRN IA DURING THE AFTERNOON. LARGE HAIL AND LOCALLY DAMAGING WINDS WILL BE THE PRIMARY SEVERE RISK ACROSS THIS AREA...WITH SOME RISK PERSISTING INTO THE EVENING HOURS AND PERHAPS EXPANDING SWD INTO NRN MO AFTER DARK...AS A SWLY LOW-LEVEL JET DEVELOPS SUPPORTING CONTINUED CONVECTION. ...SRN AR/NRN LA EWD ACROSS THE SOUTHEAST TO THE CAROLINAS/SRN VA... SCATTERED TO WIDESPREAD SHOWERS AND THUNDERSTORMS ARE FORECAST TO DEVELOP THROUGH THE DIURNAL PEAK HEATING CYCLE FROM THE LOWER MS VALLEY VICINITY ENEWD ACROSS THE CENTRAL GULF COAST STATES AND INTO THE CAROLINAS/SRN VA...AS THE MOIST AIRMASS IN PLACE DESTABILIZES MODESTLY THROUGH THE AFTERNOON. HOWEVER...WIDESPREAD CONVECTION WILL FACILITATE MAINTENANCE OF WEAK MID-LEVEL LAPSE RATES -- WHICH SHOULD HINDER MORE SUBSTANTIAL CAPE DEVELOPMENT. DESPITE LACK OF A CLEAR SYNOPTIC-SCALE LOW-LEVEL FOCUS FOR CONVECTIVE INITIATION...ASCENT ASSOCIATED WITH THE EWD PROGRESSION OF A WEAK MID-LEVEL VORT MAX SHOULD SUPPORT WIDESPREAD CONVECTION. THOUGH THE LACK OF MORE SUBSTANTIAL CAPE IN MOST AREAS SHOULD LIMIT OVERALL SEVERE RISK...20 TO 30 KT WSWLY FLOW IN THE H8 TO H5 LAYER SUGGESTS SOME POTENTIAL FOR STORMS TO ORGANIZE INTO SMALL BANDS -- AND ASSOCIATED RISK FOR ISOLATED/MARGINAL HAIL AND/OR WIND GUSTS SUPPORT EXPANSION OF 5% RISK AREA ACROSS THIS REGION. ..GOSS/ROGERS.. 08/18/2014
Posted on: Mon, 18 Aug 2014 07:16:27 +0000
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