Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 180547 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 150 AM EDT THU SEP 18 2014 .SYNOPSIS...A WEAK SURFACE TROUGH WILL EXTEND NORTH-TO-SOUTH OVER THE FOOTHILLS AND WESTERN PIEDMONT TODAY THEN DISSIPATE ON FRIDAY. COOL CANADIAN HIGH PRESSURE CENTERED OVER THE GREAT LAKES TODAY WILL DRIFT EAST AND EXTEND INTO THE CAROLINAS FRIDAY AND SATURDAY. && .NEAR TERM /OVERNIGHT/... AS OF 1120 PM WEDNESDAY... SHALLOW LOW-LEVEL CONVERGENCE ASSOC/W A WEAK INVERTED TROUGH EXTENDING NORTHWARD FROM COASTAL SC INTO CENTRAL NC HAS SERVED AS AN EFFECTIVE FOCUS FOR CONVECTION THIS EVENING...IN ADDITION TO ENHANCING THERMODYNAMIC PROFILES VIA MOISTURE POOLING IN VICINITY OF THE SFC TROUGH AXIS...AS EVIDENCED BY HIGHER DEWPOINTS ON SFC OBS AND MLCAPE VALUES OF ~500 J/KG WITH NO CIN ON 03Z SPC MESOANALYSIS. THIS FEATURE IS EXPECTED TO SHIFT SLOWLY WESTWARD OVERNIGHT IN THE PRESENCE OF A LIGHT E/NE LOW-LEVEL FLOW...WHILE SMALL AMPLITUDE SHORTWAVE ENERGY TRACKS ACROSS CENTRAL NC IN BROAD CYCLONIC FLOW ALOFT. AS A RESULT...ISOLD CONVECTION SHOULD REMAIN POSSIBLE OVERNIGHT...GENERALLY ALONG/WEST OF THE HWY 1 CORRIDOR. IT SHOULD BE NOTED THAT DEEP LAYER SHEAR IS ON THE ORDER OF 30-40 KT AND THAT DEEP CONVECTION...SHOULD IT DEVELOP...COULD REASONABLY ACQUIRE SUPERCELLULAR CHARACTERISTICS. HOWEVER...MARGINAL INSTABILITY AND WEAK/SHALLOW FORCING FOR ASCENT SHOULD ONLY SUPPORT SHALLOW CONVECTION...SIMILAR TO THE PAST 3-6 HRS WHEN CONVECTION EXHIBITED LITTLE IF ANY MOTION DUE TO LIGHT STEERING FLOW IN THE LOW/MID- LEVELS. WITH THIS IN MIND (ALONG WITH POOR DIURNAL TIMING)...EXPECT LITTLE OR NO POTENTIAL FOR AN ISOLD SEVERE STORM...WITH LOCALLY HEAVY RAINFALL THE PRIMARY CONVECTIVE ISSUE. -VINCENT && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... AS OF 310 PM WEDNESDAY... THE MCV RESULTING FROM THE MCS NOW OVER THE MO/AR BORDER IS STILL EXPECTED TO PUSH SOUTHEAST AWAY FROM THE AREA THU MORNING. THE MODELS SHOW TRAILING WEAK VORTICITY INSTIGATING ISOLATED CONVECTION OVER THE MOUNTAINS AND FAR SWRN PIEDMONT THU MORNING... AND THIS IS REASONABLE CONSIDERING THE POTENTIALLY DEEPER MOISTURE HERE AND UPSLOPE-DIRECTED LOW LEVEL FLOW... SO WILL LEAVE IN A MENTION OF ISOLATED SHOWERS OVER THE WRN/SRN CWA THU MORNING. BY AFTERNOON... EXPECT THE RISK OF ISOLATED SHOWERS TO SHIFT TO THE SOUTHEASTERN AND FAR ERN CWA WHERE WE SHOULD ONCE AGAIN SEE MARGINAL INSTABILITY (MUCAPE AROUND 1000 J/KG) AND SOMEWHAT IMPROVED DEEP LAYER SHEAR CLOSER TO 30 KTS. THE MID LEVELS REMAIN DRY AND FAIRLY STABLE HOWEVER... SO WILL RESTRICT POPS TO JUST ISOLATED SHOWERS OVER THE E/SE SECTIONS THU AFTERNOON... WITH NO POPS AFTER NIGHTFALL... AS HIGH PRESSURE CONTINUES TO BUILD IN FROM THE NORTH. ANOTHER ROUND OF LOW CLOUDS/FOG IS POSSIBLE LATE THU NIGHT... FOLLOWING PERSISTENCE. HIGHS 78-81... ON THE LOW END OF GUIDANCE BASED ON AT LEAST SOME CLOUDINESS AND SLIGHTLY BELOW NORMAL THICKNESSES. NEAR-NORMAL LOWS OF 59-63 LOOK GOOD. -GIH && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... AS OF 253 PM WEDNESDAY... FRIDAY THROUGH SATURDAY: EASTERN US TROUGH WILL PULL EAST AND OUT TO SEA OUT ON FRIDAY... BUT NOT WITHOUT LEAVING BEHIND A REMNANT MID- LEVEL CIRCULATION TO MEANDER OFF THE SE COAST THROUGH EARLY SUNDAY. AT THE SURFACE...PROGRESSIVE CANADIAN HIGH OVER NEW ENGLAND WILL QUICKLY MOVE EAST OUT INTO THE NORTHERN ATLANTIC...BECOMING ELONGATED AS IT SHIFTS FARTHER OFFSHORE. IN THE WAKE OF THE EXITING TROUGH...HEIGHTS INCREASE OVER THE AREA...WHICH SHOULD KEEP THE MID- LEVEL CIRCULATION OFF THE SE COAST AT BAY AND SECURE DRY CONDITIONS ACROSS CENTRAL NC. AS FAR AS TEMPERATURES...PROGRESSIVE NATURE OF THE PARENT HIGH AND ORIENTATION OF THE ASSOCIATED RIDGE AXIS IS EXPECTED TO YIELD A LONG FETCH OF EAST-NORTHEASTERLY LOW-LEVEL MARITIME FLOW INTO THE AREA AND KEEP THE BRUNT OF THE COOLER AND DRIER AIR TO OUR NORTH...WHILE SUPPORTING PERIODIC PARTLY TO BROKEN CLOUDINESS IN THE WAY OF MORNING STRATUS AND A DIURNALLY ENHANCED CU FIELD. HIGHS IN THE MID 70S NORTH TO AROUND 80 SOUTH. LOWS FRIDAY NIGHT IN THE MID 50S NORTH TO NEAR 60 SOUTH. LOWS SATURDAY NIGHT A GOOD CATEGORY WARMER...IN THE UPPER 50S TO LOWER 60S. SUNDAY THROUGH MONDAY: 40 TO 60 METER HEIGHT FALLS TRAVERSING THE REGION IN ADVANCE OF THE AMPLIFYING UPPER LEVEL TROUGH SWINGING EASTWARD ACROSS THE EASTERN US WILL DRIVE A SURFACE COLD FRONT THROUGH THE AREA MONDAY AFTERNOON. IN ADVANCE OF THE UPPER TROUGH...AFOREMENTIONED MID-LEVEL CIRCULATION/LOW OFF THE SOUTHEAST COAST WILL FINALLY GET KICKED EAST-NORTHEASTWARD...LIFTING UP THE NC COAST AND THEN OUT INTO THE ATLANTIC ON SUNDAY. THE LATEST 12Z/17 GFS IS STRONGER WITH THIS FEATURE AND SUGGEST IT COULD POTENTIALLY ENHANCE THE ONSHORE MARITIME FLOW...POSSIBLY RESULTING IN SLIGHTLY CLOUDIER/COOLER CONDITIONS...MAINLY ACROSS EASTERN PORTIONS OF THE FORECAST AREA ON SUNDAY. OTHERWISE...WITH LOW-LEVEL THICKNESSES PROJECTED TO CLIMB 20 METERS ABOVE NORMAL...HIGHS IN THE LOWER TO MID 80S. THERE ARE SOME MINOR MODEL TIMING DIFFERENCES WITH FROPA ON MONDAY...WITH THE EC A GOOD 12 HOURS FASTER TO PUSH THE FRONT THROUGH THE AREA. GIVEN LIMITED/SHALLOW MOISTURE AVAILABILITY...CONVECTION ALONG THE FRONT WILL NEED TO UTILIZE FAVORABLE DIURNAL TIMING/INSTABILITY TO SUPPORT SLIGHT/SMALL CHANCE POPS MONDAY AFTERNOON/EARLY EVENING. TUESDAY AND WEDNESDAY: BELOW NORMAL TEMPERATURES ARE EXPECTED UNDERNEATH THE EASTERN US TROUGH AND SUPPORTED IN THE LOW-LEVELS BY NORTHERLY FLOW VIA BUILDING STRONG ~1030MB SURFACE HIGH. HIGHS 70 TO 75. LOWS IN THE 50S. && .AVIATION /06Z THURSDAY THROUGH MONDAY/... AS OF 150 AM THURSDAY... CURRENT VFR CONDITIONS ACROSS CENTRAL NC AT 05Z WILL PRETTY MUCH PERSIST OVERNIGHT INTO THE MORNING HOURS. THERE WILL BE A FEW PATCHES OF MVFR/IFR CEILING AND MVFR/IFR VISIBILITY DUE TO GROUND FOG. THE PROBABILITY OF THIS OCCURRING LOOKS HIGHEST IN THE VICINITY OF KFAY. A WEAK SURFACE TROUGH OVER THE WESTERN PIEDMONT AND FOOTHILLS WILL SERVE AS A FOCUS FOR MOISTURE POOLING. THIS FEATURE COUPLED WITH HEATING AND THE PASSAGE OF A WEAK MID LEVEL TROUGH MAY TRIGGER A FEW SHOWERS LATE THIS MORNING INTO THE AFTERNOON. DUE TO EXPECTED SPARSE COVERAGE...WILL OMIT FROM MENTIONING IN THE TRIAD TERMINALS AT THIS TIME. OTHERWISE...EXPECT VFR CONDITIONS WITH CLOUD BASES GENERALLY BET3500-5000FT. LATE TONIGHT INTO EARLY FRIDAY...MAY SEE AREAS OF LOW CLOUDS AND/OR FOG WITH ASSOCIATED MVFR/IFR CONDITIONS. THIS OCCURRENCE LOOKS MORE PROBABLE IN THE KFAY VICINITY. EXPECT VFR CONDITIONS FOR MOST OF FRIDAY THROUGH SUNDAY WITH JUST BRIEF INSTANCES OF EARLY MORNING FOG. AN APPROACHING SURFACE FRONT LATE SUNDAY INTO MONDAY MAY BRING A BRIEF PERIOD OF ADVERSE AVIATION CONDITIONS ON MONDAY. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...WSS NEAR TERM...VINCENT SHORT TERM...HARTFIELD LONG TERM...CBL AVIATION...WSS

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