Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 200102 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 859 PM EDT TUE AUG 19 2014 .SYNOPSIS...A SERIES OF UPPER LEVEL DISTURBANCES IN NORTHWEST FLOW ALOFT WILL CROSS THE REGION THIS WEEK. A BACK DOOR COLD FRONT IS THEN FORECAST TO SLIP INTO THE AREA OVER THE WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... AS OF 230 PM TUESDAY... A WEAK AND PERTURBED WEST-NORTHWESTERLY FLOW CONTINUES ALOFT...WITH A BROAD AREA TROUGH OF LOW PRESSURE AT THE SURFACE OVER FROM UPSTATE SC TO THE TIDEWATER AREA. VISIBLE IMAGERY SHOWS THE WEAK CIRCULATION OVER SOUTHEAST VA THIS MORNING NOW DRIFTING OFFSHORE...WITH A BROKEN DECK OF CU ENCOMPASSING MOST OF NC. SCATTERED SHOWERS AND STORMS WILL BE MOSTLY LIKELY WITHIN AN AXIS OF INSTABILITY OVER THE SOUTHWESTERN HALF OF THE CWA...FOCUSED PRIMARILY ALONG 1) AN UPPER DISTURBANCE MOVING ALONG THE NC/SC BORDER AND 2)A ZONE OF CONFLUENCE AND WEAK DIFFERENTIAL HEATING FROM THE TIRAD TOWARD FAYETTEVILLE. WIND FIELDS ARE WEAK AND SHEAR IS MOSTLY LESS THAN 25KT...SO CLUSTERS OF PULSE STORMS WILL BE THE MAIN STORM MODE. LOSS OF HEATING AFTER SUNSET AND STABILIZATION WILL BRING CONVECTION TO AN END. RESIDUAL MOISTURE FROM THE THE PRONOUNCED STRATUS EARLIER THIS MORNING AND NORTHEASTERLY LOW-LEVEL FLOW SHOULD LEAD TO STRATUS AND FOG AGAIN TONIGHT. SREF PROBABILITIES SUPPORT THIS WITH THE HIGHEST PROBABILITIES NORTHEAST OF THE TRIANGLE. LOWS IN THE UPPER 60S AND LOWER 70S. && .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/... AS OF 310 PM TUESDAY... NORTHWESTERLY FLOW ALOFT CONTINUES ON WEDNESDAY...WITH MODELS SHOWING A DISTURBANCE CURRENTLY ASSOCIATED WITH CONVECTION OVER SOUTHERN ILLINOIS SINKING SOUTH AND CROSSING VA/NORTHERN NC DURING THE DAY. AFTER THE EROSION OF ANY MORNING STRATUS...CONDITIONS ARE ARE EXPECTED TO BE SIMILAR TODAY WITH GUIDANCE GIVING HIGHS IN THE UPPER 80S/LOWER 90S. DEWPOINTS MAY MIX OUT A LITTLE MORE INT HE WESTERN PIEDMONT WITH MORE NORTHWESTERLY FLOW...BUT 1000-1500 J/KG OF MLCAPE IS STILL EXPECTED IN THE EAST. SHEAR WILL AGAIN BE WEAK AND THE SEVERE THREAT IS RELATIVELY LOW. LOWS IN THE UPPER 60S AND LOWER 70S. && .LONG TERM /THURSDAY THROUGH MONDAY/... AS OF 240 PM TUESDAY... EXPECT A MERIDIONAL UPPER LEVEL PATTERN...WITH RIDGING OVER THE MIDWEST AND TROUGHING ALONG THE NE AND ATLANTIC COAST THROUGH THE PERIOD. THIS WILL RESULT IN NORTHWESTERLY FLOW ALOFT OVER CENTRAL NC. THE GFS AND ECMWF BOTH INDICATE THE CHANCE FOR SHOWERS AND STORMS THROUGHOUT THE PERIOD AS A SERIES OF SHORT WAVES MOVE OVER THE AREA AROUND THE BASE OF THE UPPER LEVEL TROUGH. ALTHOUGH THE CONVECTION SHOULD BE DIURNAL IN NATURE...COVERAGE AND LOCATION ARE STILL FAIRLY UNCERTAIN AT THIS TIME. AT THE SURFACE...EXPECT A TROUGH TO LINGER ALONG THE COAST...WITH WEAK RIDGING TO THE NORTH- NORTHWEST. THE LATEST GFS STILL PUSHES A BACKDOOR COLD FRONT INTO THE NE PORTIONS OF THE AREA THIS WEEKEND...RESULTING IN HIGHS 80-85 DEGREES ACROSS THE NORTH AND 85-90 DEGREES ACROSS THE SOUTH FOR SATURDAY THROUGH MONDAY. THE ADVECTION OF WARM MOIST AIR FROM THE GULF AROUND THE HIGH AND THE RESULTING SUBSIDENCE IN THE LEE OF THE MOUNTAINS COULD MEAN INCREASING TEMPERATURES FOR THE MIDDLE OF NEXT WEEK. ALSO...THE GFS INCREASES PWAT VALUES FROM AROUND 1.5 TO AROUND 2 INCHES THROUGH THE WEEKEND...BEFORE DECREASING AGAIN TO NEAR 1.5 INCHES. THUS...EXPECT THE CONVECTION OVER THE WEEKEND TO BE CAPABLE OF PRODUCING SOME LOCALLY HEAVY RAINFALL. OVERNIGHT LOW TEMPS SHOULD GRADUALLY DECREASE...FROM THE LOW TO MID 70S THURSDAY NIGHT TO THE MID TO UPPER 60S SUNDAY AND MONDAY NIGHTS. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... AS OF 840 PM TUESDAY... ISOLATED TO LOCALLY SCATTERED SHOWERS AND STORMS HAVE GENERALLY DISSIPATED WITH THE LOSS OF DAYTIME HEATING THIS EVENING. HOWEVER... WE CANT COMPLETELY RULE OUT A STRAY SHOWER OR TWO ACROSS CENTRAL NC THIS EVENING INTO THE OVERNIGHT... BUT PROBABILITY ARE TOO LOW TO INCLUDE ANY MENTION IN THE TAFS AT THIS TIME PAST 02Z. A RENEWED LOW LEVEL NORTHEASTERLY FLOW WILL USHER IN ADDITIONAL LOW LEVEL MOISTURE AND THE THREAT OF LOW STRATUS AND/OR FOG... ESPECIALLY AT KRDU AND KRWI. FURTHER WEST AND SOUTH.... CONFIDENCE IS NOT AS HIGH IN WIDESPREAD STRATUS AND/OR FOG DURING WEDNESDAY MORNING. THUS... WILL LIMIT KGSO/KINT/KFAY TO ONLY A TEMPO FOR MVFR CONDITIONS AT THIS TIME GENERALLY IN THE 09-13Z TIME FRAME. AT KRDU AND KRWI (WITH A MEDIUM CONFIDENCE) EXPECT IFR TO EVEN LIFR CONDITIONS TO DEVELOP AFTER MIDNIGHT... WITH CONDITIONS SLOWLY IMPROVING BY MID TO LATE MORNING... THEN VFR BY EARLY AFTERNOON. ISOLATED TO SCATTERED SHOWERS AND STORMS WILL BE POSSIBLE AGAIN ON WEDNESDAY AFTERNOON/EVENING... WITH THE HIGHEST PROBABILITY ACROSS THE NORTHERN TAF SITES. HOWEVER... CONFIDENCE IS NOT HIGH ENOUGH TO INCLUDE ANY MENTION OF CONVECTION IN THE TAFS AT THIS TIME. OUTLOOK... EARLY MORNING STRATUS/FOG...ALONG WITH AFTERNOON SHOWERS AND STORMS WILL BE POSSIBLE EACH DAY THIS WEEK INTO THE WEEKEND. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...BLS NEAR TERM...BLS SHORT TERM...BLS LONG TERM...KC AVIATION...BSD/BLS

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