SPC Day 2 Threat
SPC AC 251730 DAY 2 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1230 PM CDT WED JUL 25 2012 VALID 261200Z - 271200Z ...THERE IS A MDT RISK OF SVR TSTMS FROM OH TO PARTS OF THE NORTHEAST... ...THERE IS A SLGT RISK OF SVR TSTMS FROM THE UPPER GREAT LAKES/MID-MS VALLEY NEWD TO SRN NEW ENGLAND... ...POTENTIAL FOR A WIDESPREAD DAMAGING WIND EVENT/DERECHO ON THU AFTERNOON FROM PARTS OF THE MIDWEST TO THE NORTHEAST... ...SYNOPSIS... VIGOROUS SHORT WAVE TROUGH OVER THE SRN CANADIAN PRAIRIES WILL MOVE SEWD AND REACH THE UPPER GREAT LAKES BY EARLY FRI...WITH A MODERATELY FAST ZONAL FLOW REGIME EXISTING DOWNSTREAM ACROSS THE NERN CONUS. AT THE SURFACE...A WARM FRONT WILL ADVANCE NEWD IN THE NORTHEAST AND SHOULD REMAIN QUASI-STATIONARY ACROSS THE CNTRL GREAT LAKES. A SERIES OF WEAK CYCLONES SHOULD BE PREVALENT ALONG THIS BOUNDARY...WHICH WILL INTERSECT A SLOW-MOVING COLD FRONT MOVING SEWD FROM THE MID-MS VALLEY TO THE SRN PLAINS. IN THE WEST...MID-LEVEL RIDGING WILL BUILD FROM THE SOUTHWEST ACROSS THE INTERMOUNTAIN WEST. ...MID-MS/OH VALLEYS TO THE NORTHEAST/SRN NEW ENGLAND... CONFIDENCE CONTINUES TO GROW WITH POTENTIAL FOR SCATTERED TO NUMEROUS ORGANIZED SEVERE TSTMS...PARTICULARLY FROM THE MIDWEST TO THE NORTHEAST. AN MCS SHOULD BE ONGOING ACROSS PARTS OF THE LOWER GREAT LAKES...SUPPORTED BY AN INITIAL MID-LEVEL SPEED MAX AND ROBUST LOW-LEVEL WAA ADVECTION. THIS SHOULD RETARD THE NERN ADVANCEMENT OF THE WARM FRONT AND SUBSEQUENT EVOLUTION OF THIS ACTIVITY DOES BREED UNCERTAINTY OVER WHERE THE FRONT WILL ULTIMATELY ANCHOR. AN EXPANSIVE UNCAPPED WARM SECTOR CHARACTERIZED BY 90S/60S SURFACE TEMPERATURES/DEW POINTS WILL CONTRIBUTE TO MODERATE TO STRONG BUOYANCY THU AFTERNOON WITH MLCAPE OF 2000-4000 J/KG. A LARGE SWATH OF 30-50 KT 700-500 MB WLYS WILL OVERLAP THIS INSTABILITY...AND WITH WEAK MID-LEVEL HEIGHT FALLS COMBINING WITH FRONTAL CONVERGENCE...THIS SETUP WILL YIELD SCATTERED TO NUMEROUS TSTMS FORMING ALONG AND AHEAD OF THE COLD FRONT. THE UNIDIRECTIONAL WIND PROFILES AND STEEP LOW-LEVEL LAPSE RATES SHOULD SUPPORT UPSCALE GROWTH INTO SEVERAL CLUSTERS WITH BOWING SEGMENTS AND EMBEDDED SUPERCELL STRUCTURES. DAMAGING WINDS /POTENTIALLY WIDESPREAD AND SIGNIFICANT/ WILL BE THE PRIMARY THREAT. A RELATIVELY NARROW CORRIDOR OF ENHANCED TORNADO RISK SHOULD DEVELOP ALONG THE WARM FRONTAL ZONE WHERE EFFECTIVE SRH AND STRONGEST DEEP-LAYER SHEAR WILL BE MAXIMIZED. ALTHOUGH PINPOINTING THIS CORRIDOR IS DIFFICULT GIVEN LIKELIHOOD OF PRECEDING OVERNIGHT CONVECTION...IT APPEARS MOST PROBABLE FROM PARTS OF NY INTO SRN NEW ENGLAND. SOME CONVECTION-ALLOWING GUIDANCE SUGGESTS THAT DISCRETE CONVECTION MAY FORM WITHIN A PERSISTING WAA REGIME THU AFTERNOON. ...UPPER GREAT LAKES... DCVA DOWNSTREAM OF THE APPROACHING SHORT WAVE TROUGH OVER NRN MN SHOULD FOSTER ISOLATED TO SCATTERED TSTMS THU AFTERNOON. THIS ACTIVITY SHOULD FORM ALONG/AHEAD OF A SECONDARY COLD FRONT SURGE THAT WILL ACT MORE AS A DRYLINE CROSSING THE UPPER MS VALLEY. THE COMBINATION OF BUOYANCY/SHEAR SHOULD BE MODEST...BUT SUFFICIENT FOR ISOLATED SEVERE HAIL AND LOCALLY DAMAGING WINDS. ...NRN ROCKIES... A BELT OF CONFLUENT MID-LEVEL FLOW WILL STRENGTHEN N OF THE BUILDING RIDGE IN THE WEST. ALTHOUGH BUOYANCY WILL REMAIN LIMITED...ISOLATED TSTMS SHOULD FORM HIGHER TERRAIN. SUFFICIENT DEEP-LAYER SHEAR WILL EXIST FOR A MARGINAL RISK OF SEVERE WIND/HAIL. ..GRAMS.. 07/25/2012 CLICK TO GET WUUS02 PTSDY2 PRODUCT NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0600Z CURRENT UTC TIME: 2137Z (5:37PM), RELOAD THIS PAGE TO UPDATE THE TIME
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