Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 211732 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 132 PM EDT THU MAY 21 2015 .SYNOPSIS...LOW PRESSURE WILL TRACK ACROSS CENTRAL NORTH CAROLINA TO THE COAST THIS AFTERNOON...THEN MOVE OFFSHORE TONIGHT AS HIGH PRESSURE BUILDS INTO THE REGION FROM THE WEST. && .NEAR TERM /THROUGH TONIGHT/... AS OF 130 PM THURSDAY... OVERVIEW: A SMALL AMPLITUDE WAVE TRACKING EAST INTO THE WESTERN PIEDMONT THIS MORNING WILL PROGRESS TO THE COASTAL PLAIN BY 18Z AND THE CAROLINA COAST BY 21-00Z. AN ATTENDANT LOW PRESSURE SYSTEM... CENTERED NEAR ROCK HILL SC (JUST SOUTH OF CHARLOTTE) AT 14Z... IS PROGGED TO TRACK EAST TO FLORENCE SC/LUMBERTON NC BY 18Z AND THE CAROLINA COAST BY 00Z THIS EVENING. FURTHER UPSTREAM...POTENT SHORTWAVE ENERGY CENTERED IN VICINITY OF NORTHERN IL AT 14Z WILL TRACK EASTWARD INTO THE OH VALLEY THIS AFTERNOON...PROGRESS THROUGH THE MID-ATLANTIC THIS EVENING...AND MOVE OFFSHORE THE MID-ATLANTIC COAST LATE TONIGHT. PRECIP: EXPECT THE BEST CHANCE FOR PRECIP BETWEEN 15-21Z ALONG AND NORTH OF THE HWY 64 CORRIDOR WHERE 925-850 MB WARM ADVECTION...WEAK DPVA...AND MARGINAL ELEVATED INSTABILITY (250-500 J/KG MUCAPE) SHOULD SUPPORT SCATTERED ELEVATED SHOWERS. IN THIS AREA (NORTHERN PIEDMONT/NE COASTAL PLAIN)...WEAK UPPER LEVEL FORCING AND SHALLOW/ MARGINAL INSTABILITY (CAPE SITUATED ALMOST ENTIRELY BELOW THE -10C ISOTHERM) SHOULD PRECLUDE THUNDER. THE EXCEPTION MAY BE IN THE NE COASTAL PLAIN WHERE DIURNAL TIMING OF APPROACHING DPVA AND DESTABILIZATION WILL BE BETTER. CONVECTIVE DEVELOPMENT REMAINS MORE UNCERTAIN SOUTH OF HWY 64. FORCING FOR ASCENT WILL BE GREATEST BETWEEN ROUGHLY 15-20Z AS THE SMALL AMPLITUDE WAVE AND ATTENDANT SFC LOW TRACK EAST IN VICINITY OF THE SC/NC BORDER INTO THE COASTAL PLAIN...HOWEVER...SUFFICIENT DESTABILIZATION /EROSION OF CINH/ MAY NOT OCCUR UNTIL EARLY AFTERNOON...AT WHICH POINT THE NARROW WARM SECTOR WILL MOST LIKELY BE CONFINED TO EASTERN PORTIONS OF THE SANDHILLS AND SE COASTAL PLAIN. WITH THIS IN MIND...WILL INDICATE THE BEST POTENTIAL FOR SFC-BASED CONVECTION BETWEEN 16-20Z FROM SCOTLAND/HOKE COUNTIES NORTHEAST TO WILSON/EDGECOMBE COUNTIES. TEMPS: MID/UPPER 60S FAR NORTHERN PIEDMONT (VA BORDER) TO LOW/MID 80S FAR SOUTH (NEAR SC BORDER). LOWS TONIGHT RANGING FROM THE LOWER 50S FAR NORTH TO UPPER 50S /NEAR 60F/ FAR SOUTH/SE. SEVERE: DEEP LAYER SHEAR RANGES FROM ~30 KT NEAR THE SC BORDER TO ~40 KT NEAR THE VA BORDER. AT 14Z...THE BEST LOW-LEVEL SHEAR (ON THE EASTERN PERIPHERY OF THE 925 MB LOW) WAS SHIFTING INTO EASTERN NC IN ADVANCE OF THE EASTWARD PROGRESSING 925 MB LOW...AND IS EXPECTED TO SHIFT FURTHER EAST TO THE CAROLINA COAST THIS AFTERNOON. EXPECT THE RELATIVE BEST POTENTIAL FOR AN ISOLD SEVERE STORM IN THE COASTAL PLAIN BETWEEN 16-20Z...PRIMARILY IN WAYNE/WILSON/EDGECOMBE COUNTIES WHERE ANY SFC-BASED CONVECTION DEVELOPING WITHIN THE NARROW WARM SECTOR WILL ENCOUNTER 1) GREATER DIURNAL DESTABILIZATION AND 2) INCREASINGLY FAVORABLE DEEP-LAYER SHEAR (WITH NORTHWARD EXTENT). PRIMARY HAZARD APPEARS TO BE DAMAGING WINDS...THOUGH MARGINALLY SVR HAIL COULD NOT BE RULED OUT WITH ANY ROTATING UPDRAFTS. ISOLD TOR POTENTIAL SHOULD BE CONFINED TO FAR EASTERN/COASTAL NC WHERE ENHANCED LOW-LEVEL SHEAR WILL BE PRESENT THIS AFTERNOON ON THE EASTERN PERIPHERY OF THE ADVANCING 925 MB LOW. -VINCENT && .SHORT TERM /FRIDAY AND FRIDAY NIGHT/... AS OF 355 AM THURSDAY... A TROUGH ALOFT WILL AMPLIFY ACROSS THE NORTHEAST AND MIDDLE ATLANTIC STATES FRI...THEN OFFSHORE FRI NIGHT. DESPITE THE AMPLIFICATION OF THE TROUGH...HEIGHT RISES ALOFT AND ASSOCIATED SUBSIDENCE WILL BE UNDERWAY OVER VA AND THE CAROLINAS...IN THE WAKE OF A LEAD SHORTWAVE TROUGH FORECAST TO CROSS THE MIDDLE ATLANTIC STATES TONIGHT. SURFACE HIGH PRESSURE WILL CONSEQUENTLY BUILD EAST FROM THE TN VALLEY ON FRI IN ASSOCIATION WITH THE LEAD MIDDLE ATLANTIC SHORTWAVE TROUGH... FOLLOWED BY THE FRI NIGHT PASSAGE OF A DRY COLD FRONT RESULTING FROM THE LARGER SCALE TROUGH AMPLIFICATION OVER THE NORTHEAST. TEMPERATURES WILL BE IN THE 70S ON FRI...WITH LOWER HUMIDITY VALUES OWING TO SURFACE DEWPOINTS IN THE 40S. TEMPERATURES FRI NIGHT WILL LIKELY VARY WILDLY...WITH PE-FRONTAL RADIATIONAL COOLING INITIALLY; THEN MIXING AND ASSOCIATED WARMING WITH FROPA; AND ENDING WITH CAA LATE...WITH LOWS BY THE END OF THE NIGHT IN THE 50S. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... AS OF 220 AM THURSDAY... SATURDAY THROUGH WEDNESDAY: VERY LITTLE SIGNIFICANT WEATHER IS EXPECTED DURING THE LONG TERM PERIOD WITH HIGH PRESSURE DOMINATING THE PATTERN FOR MUCH OF THE PERIOD. INITIALLY...SURFACE HIGH PRESSURE WILL BE TO THE NORTH OF THE AREA BRINING COOLER NORTHEASTERLY FLOW TO CENTRAL NC FOR SATURDAY BEFORE THE HIGH SLIDES OFFSHORE AND SETS UP EAST OF THE AREA. THIS WILL SHIFT WINDS TO SOUTHERLY (ALTHOUGH LIGHT) AND BEGIN A WARMING TREND THAT WILL CONTINUE THROUGH WEDNESDAY. INITIALLY...EXPECT TEMPERATURES IN THE UPPER 70S TO NEAR 80 DEGREES ON SATURDAY BUT STEADILY RISING A FEW DEGREES EACH DAY UP TO NEAR 90 DEGREES BY WEDNESDAY AFTERNOON. LOWS WILL FOLLOW A SIMILAR PATTERN...RISING A COUPLE DEGREES EACH DAY FROM THE UPPER 50S ON SATURDAY NIGHT UP TO THE UPPER 60S BY TUESDAY NIGHT/WEDNESDAY MORNING. MUCH OF THE PERIOD LOOKS DRY AS HIGH PRESSURE KEEPS MUCH OF THE PRECIPITATION THREAT WELL AWAY FROM THE AREA. LATE IN THE PERIOD...A FRONTAL SYSTEM WILL APPROACH FROM THE WEST AND THERE IS A LITTLE DISCREPANCY ON TIMING BUT MODELS THIS MORNING LOOK TO HOLD OFF PRECIPITATION WITH THIS FRONT A LITTLE LONGER THAN THE PREVIOUS DAYS RUNS AND THEREFORE HAVE CUT BACK POPS ON TUESDAY AND WEDNESDAY...INTRODUCING A SLIGHT CHANCE IN THE WEST ON TUESDAY AFTERNOON AND THEN CHANCE IN THE WEST...SLIGHT CHANCE IN THE EAST ON WEDNESDAY AFTERNOON. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... AS OF 130 PM THURSDAY... 24-HR TAF PERIOD: IFR CEILINGS AT INT/GSO WILL GRADUALLY IMPROVE TO MVFR LATE THIS AFTERNOON...FOLLOWED BY VFR THIS EVENING AS A DRIER AIRMASS ADVECTS INTO CENTRAL NC FROM THE NW IN THE WAKE OF A LOW PRESSURE SYSTEM TRACKING EAST TOWARD THE CAROLINA COAST. FURTHER EAST AT RDU/FAY/RWI...MVFR CEILINGS AND SHOWERS/STORMS ARE EXPECTED THROUGH ~21Z THIS AFTERNOON. ONCE CONVECTION CLEARS A GIVEN TERMINAL AND PASSES TO THE EAST...A SHORT PERIOD (1-3 HR) OF MVFR/IFR CEILINGS WILL BE POSSIBLE AS LOW CEILINGS NORTH OF THE WARM FRONT ADVECT SOUTHEASTWARD. VFR CONDITIONS WILL RETURN THIS EVENING (~00Z) FROM WEST/NW TO EAST/SE AS THE SFC LOW TRACKS OFFSHORE AND A DRIER AIRMASS ADVECTS INTO THE REST OF CENTRAL NC. LOOKING AHEAD: VFR CONDITIONS WILL PREVAIL THROUGH EARLY NEXT WEEK IN ASSOC/W HIGH PRESSURE. -VINCENT && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...VINCENT NEAR TERM...VINCENT SHORT TERM...26 LONG TERM...ELLIS AVIATION...VINCENT

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