...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF THE UPPER OH VALLEY AND NORTHEAST/MID-ATLANTIC STATES... ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE PACIFIC NORTHWEST/NORTHERN INTERMOUNTAIN REGION... ...SUMMARY... SCATTERED STRONG TO SEVERE STORMS ARE EXPECTED ACROSS PARTS OF THE UPPER OHIO VALLEY AND NORTHEAST AND MIDDLE-ATLANTIC REGION. CLUSTERS OF SEVERE STORMS ALSO APPEAR POSSIBLE ACROSS PARTS OF THE WESTERN UNITED STATES. ...SYNOPSIS... A HIGHLY AMPLIFIED LONGWAVE REGIME WILL REMAIN OVER THE CONUS TODAY THROUGH EARLY WEDNESDAY. AN UPPER RIDGE CENTERED OVER THE EASTERN SLOPES OF THE ROCKIES AND HIGH PLAINS WILL BE FLANKED BY DUAL TROUGHS...ONE OVER THE WESTERN STATES AND THE OTHER OVER THE GREAT LAKES/MIDWEST AND APPALACHIANS. ...UPPER OH VALLEY AND NORTHEAST/MID-ATLANTIC STATES... WHILE A SURFACE LOW CONTINUES TO DEEPEN ACROSS ONTARIO...SHOWERS/EMBEDDED THUNDERSTORMS WILL ACCOMPANY AN EASTWARD-SPREADING COLD FRONT/NARROW WARM SECTOR ACROSS THE REGION TODAY. THE GENERAL PREVALENCE OF CLOUD COVER AND THE MOIST NATURE OF THE THERMODYNAMIC PROFILES WILL GENERALLY KEEP BUOYANCY RELATIVELY MODEST...ALTHOUGH CLOUD BREAKS AND WESTERN-PERIPHERAL HEATING IN VICINITY OF UPPER DRY SLOT SHOULD ALLOW FOR MUCH AS 500-1250 J/KG OF MLCAPE THIS AFTERNOON ACROSS THE UPPER OH VALLEY/DELMARVA VICINITY. DIURNALLY INTENSIFYING THUNDERSTORMS IN THE PRESENCE OF A STRENGTHENING CYCLONIC WIND FIELD...WITH 30-45 KT OF EFFECTIVE SHEAR...WILL SUPPORT SUSTAINED MULTICELLS AND A LEAST A CONDITIONAL SUPERCELL POTENTIAL WITH DAMAGING WINDS/SEVERE HAIL POSSIBLE. PROVIDED SUFFICIENT CLOUD BREAKS/HEATING...A BRIEF TORNADO OR TWO MAY BE POSSIBLE IN VICINITY OF THE SURFACE OCCLUSION/WARM FRONT WHERE WIND PROFILES WOULD SUPPORT LOW-LEVEL MESOCYCLONES...PARTICULARLY THIS AFTERNOON/EARLY EVENING IN A CORRIDOR INCLUDING PA/WESTERN NY AND THE DELMARVA VICINITY. ...CAROLINAS/GA... A SECONDARY IMPULSE EMBEDDED WITHIN THE BASE OF THE UPPER TROUGH WILL APPROACH THE REGION LATER TODAY/TONIGHT...WHILE WEAK HEIGHT FALLS AND AN ATTENDANT ZONE OF 20-30 KT MID-LEVEL SOUTHWESTERLY WINDS OVERSPREAD THE REGION. ALTHOUGH MID-LEVEL LAPSE RATES WILL BE WEAK...DIURNALLY STEEPENING LOW-LEVEL LAPSE RATES WITH AS MUCH AS 1000-1500 J/KG OF MLCAPE WILL SUPPORT THE DEVELOPMENT/INTENSIFICATION OF MULTICELLS/LINE SEGMENTS CAPABLE OF LOCALLY DAMAGING WINDS THIS AFTERNOON/EARLY EVENING. ...PACIFIC NORTHWEST/NORTHERN INTERMOUNTAIN REGION/GREAT BASIN... A STRENGTHENING SOUTHERLY DEEP-LAYER WIND FIELD WILL ACCOMPANY APPRECIABLE DPVA OVER THE PACIFIC NORTHWEST/NORTHERN INTERMOUNTAIN REGION TODAY VIA THE NORTHEASTWARD ACCELERATION OF AN UPPER LOW CURRENTLY NEAR THE NORTHERN CA COAST. THIS SCENARIO...IN THE PRESENCE OF ABOVE-NORMAL PRECIPITABLE WATER VALUES /0.75-1.20 INCHES/...WILL LIKELY LEAD TO THE DEVELOPMENT OF STRONGER THUNDERSTORMS ACROSS THE REGION THIS AFTERNOON. THE STRONGEST STORMS WILL BE CAPABLE OF SEVERE HAIL...WITH STRONG DOWNDRAFTS/LOCALLY DAMAGING WINDS LIKELY TO BE THE MORE PREVALENT CONCERN. BY MID/LATE AFTERNOON...SUFFICIENT FORCING FOR ASCENT/COLD POOL GENERATION MAY ALLOW NORTHWARD-MOVING CLUSTERS TO EVOLVE WITH A SOMEWHAT MORE CONCENTRATED WIND POTENTIAL INTO THE EVENING. ...AZ/LOWER CO RIVER VALLEY... A STEADY NORTHWARD INCREASE OF MOISTURE SHOULD ACCOMPANY A DISTURBANCE MOVING OUT OF NORTHWEST MEXICO THROUGH TONIGHT. THE MAGNITUDE OF DESTABILIZATION LATER TODAY WILL LIKELY BE HINDERED BY THE INFLUENCE OF PRIOR OUTFLOWS/CONVECTION ASIDE FROM MOISTENING MID-LEVEL PROFILES. THAT SAID...POCKETS OF STRONGER HEATING AND MODERATELY STRONG MID-LEVEL WINDS MAY ALLOW THE DEVELOPMENT OF WEST/NORTHWESTWARD MOVING CONVECTIVE SEGMENTS WITH STRONG THUNDERSTORM OUTFLOWS/SMALL HAIL THIS AFTERNOON/EARLY EVENING. ...SOUTH TX... AT LEAST ISOLATED THUNDERSTORMS SHOULD DEVELOP/INTENSIFY THIS AFTERNOON NEAR/SOUTH OF A FRONTAL BOUNDARY ACROSS THE REGION...A SCENARIO WELL-SUPPORTED BY GUIDANCE SUCH AS THE 00Z WRF-NSSL. VERTICAL SHEAR WILL BE WEAK IN THE PRESENCE OF NORTH-NORTHERLY WINDS THROUGH THE LOWER/MIDDLE TROPOSPHERE...BUT STEEP LOW-LEVEL LAPSE RATES/MODERATE BUOYANCY MAY ACCOUNT FOR LOCALIZED DOWNBURSTS THIS AFTERNOON/EARLY EVENING.
Posted on: Tue, 12 Aug 2014 07:11:48 +0000
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