Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 280017 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 815 PM EDT MON JUL 27 2015 .SYNOPSIS...A SERIES OF PERTURBATIONS ALOFT INTERACTING WITH A MOIST AND UNSTABLE AIR MASS WILL TRIGGER SCATTERED THUNDERSTORMS...MAINLY DURING THE AFTERNOON AND EVENING HOURS...THROUGH THE REMAINDER OF THE WORK WEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 325 PM MONDAY... A WEAK SURFACE TROUGH IMMEDIATELY TO THE NW OF CENTRAL NC WILL BE A FOCUS FOR THE DEVELOPMENT OF SCATTERED CONVECTION THROUGH EARLY EVENING. ATMOSPHERE ACROSS CENTRAL NC IS SLIGHTLY UNSTABLE AND EFFECTIVE BULK SHEAR REMAINS MARGINAL. MEAN STEERING FLOW WOULD USHER CONVECTION IN THE HIGHER TERRAIN OF WESTERN NC-SW VA INTO THE NW PIEDMONT LATE THIS AFTERNOON-EARLY EVENING. MAIN QUESTION IS HOW FAR EAST-SOUTH DOES THE SCATTERED CONVECTION GO BEFORE DIMINISHING. THE HRRR AND RAP BOTH SUGGEST THAT CONVECTION MAKES A RUN FOR THE TRIANGLE AREA BUT DIMINISHES IN COVERAGE AND INTENSITY BEFORE CROSSING THE REGION. CONSIDERING THAT A MINOR MOISTURE/INSTABILITY AXIS EXTENDS NW-SE ACROSS THE TRIANGLE...APPEARS THAT ANY CONVECTION THAT EXITS THE NW PIEDMONT SHOULD CONTINUE PROGRESS E-SE INTO THE TRIANGLE AREA. THUS...PLAN TO MAINTAIN A CHANCE POP OVER THIS REGION THROUGH MOST OF THE EVENING. AFTER MIDNIGHT...A MOIST LOW LEVEL AIR MASS SHOULD GENERATE AREAS OF FOG AND/OR LOW CLOUDS BY EARLY TUESDAY. NOT EXPECTING ANY DENSE FOG AS VISIBILITIES SHOULD BE NO WORSE THAN A MILE OR TWO. LOW CEILINGS MAY COVER MORE OF THE REGION THAN WHAT OCCURRED EARLY MONDAY MORNING. IN ADDITION...A SERIES OF WEAK PERTURBATIONS ALOFT MAY TRIGGER A SHOWER OR TWO ANYWHERE ACROSS THE CWA. MIN TEMPS 69-73. && .SHORT TERM /TUESDAY AND TUESDAY NIGHT/... AS OF 325 PM MONDAY... A WEAK SFC TROUGH WILL REMAIN STALLED IN VICINITY OF THE WESTERN PIEDMONT. ALOFT...AN UPPER RIDGE CENTERED OVER THE SOUTHERN PLAINS BRIEFLY AMPLIFIES INTO THE WESTERN LAKES...VEERING FLOW ALOFT OVER CENTRAL NC TO A NWLY DIRECTION. WEAK PERTURBATIONS EMBEDDED IN THIS FLOW ALOFT INTERACTING WITH THE STALLED SFC TROUGH AND AVAILABLE MOISTURE/INSTABILITY SHOULD TRIGGER SCATTERED CONVECTION...MAINLY IN THE AFTERNOON AND EVENING HOURS. PROBABILITY OF SCATTERED CONVECTION APPEARS BEST IN VICINITY OF THE STALLED SFC TROUGH IN THE WESTERN PIEDMONT...AND IN VICINITY WHERE THE PERTURBATIONS ALOFT TRACK THROUGH THE REGION. THUS...POPS WILL VARY FROM SOLID CHANCE(SCATTERED) ACROSS THE NORTHERN PIEDMONT-NORTHERN COASTAL PLAIN TO SLIGHT CHANCE(ISOLATED)OVER THE FAR SOUTHERN COUNTIES. BULK OF CONVECTION WILL DIMINISH WITH LOSS OF HEATING TUESDAY EVENING THOUGH A FEW SHOWERS MAY OCCUR WELL INTO THE NIGHT DUE TO PERTURBATIONS IN THE NW FLOW ALOFT INTERACTING WITH THE MOISTURE RICH AIR MASS OVER OUR REGION. WHILE A STRONG OR SEVERE STORM CANNOT BE RULED OUT TUESDAY AFTERNOON...BULK OF CONVECTIVE PARAMETERS POINT TOWARD MOST OF THE STORMS REMAINING BELOW SEVERE CRITERIA. MAX TEMPS TUESDAY HIGHLY DEPENDENT ON EXTENT OF EARLY MORNING CLOUDS AND TIMING OF AFTERNOON CONVECTION. FAVORING PARTIAL SUN TO OCCUR FOR MOST OF THE LATE MORNING-EARLY AFTERNOON...BOOSTING TEMPS WELL INTO THE 80S-AROUND 90. IF LOW CLOUDS LINGER PAST NOON OR CONVECTION DEVELOP BY NOON-2 PM...THAN MAX TEMPS MAY END UP BEING 3-5 DEGREES COOLER THAN FORECAST. MIN TEMPS TUESDAY NIGHT 70-74. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... AS OF 245 PM MONDAY... MEDIUM RANGE MODELS ARE IN GENERAL AGREEMENT IN SHOWING A MID LEVEL RIDGE CENTERED ACROSS THE CENTRAL/SOUTHERN PLAINS AND LOWER MS RIVER VALLEY TO START THE PERIOD (WEDNESDAY)... THEN RETROGRADING IT WESTWARD ACROSS THE WESTERN U.S. BY LATE WEEK. THE MID LEVEL RIDGE IS FORECAST TO BUILD NORTH/NORTHWESTWARD AS IT RETROGRADES... HELPING TO AMPLIFY THE MID/UPPER LEVEL FLOW PATTERN ACROSS THE CONUS. THIS SHOULD YIELD BROAD MID LEVEL TROUGHING FOR CENTRAL NC LATE WEEK INTO EARLY NEXT WEEK... WITH A SURFACE COLD FRONT PUSHING INTO THE AREA FROM THE NORTH AND WEST LATE THURSDAY INTO FRIDAY. HOWEVER... THE STRONGER FLOW ALOFT WILL REMAIN TO THE NORTH OF CENTRAL NC... YIELDING GENERALLY WEAK DEEP LAYER SHEAR. QUESTIONS STILL REMAIN IF THE FRONT WILL PUSH THROUGH THE AREA OR SETTLE ACROSS SOUTHEASTERN PORTIONS OF CENTRAL NC... AND RESULTANT HOW LONG PRECIP CHANCES WILL CONTINUE ACROSS CENTRAL NC. FOR NOW WILL TO TREND THE FORECAST TOWARDS AN UNSETTLED PATTERN FOR LATE THURSDAY THROUGH SUNDAY... WITH THE POTENTIAL FOR HIGH MOISTURE CONTENT AIR TO ADVECT INTO THE FROM THE NORTHEASTERN GULF OF MEXICO ALONG WITH POTENTIALLY A FEW WEAK DISTURBANCES LIFTING NORTH-NORTHEASTWARD AND ACROSS SOUTH/EASTERN PORTIONS OF THE FA. HOWEVER... DEPENDING ON HOW FAR SOUTH AND EAST THE BOUNDARY MAKES IT WILL DETERMINE HOW MUCH OF THE AREA SEE A GOOD CHANCE FOR SHOWERS AND STORMS OVER THE WEEKEND... ALONG WITH THE POTENTIAL FOR HEAVY RAIN. THUS... WILL LIMIT POPS TO CHANCE FOR NOW BUT RAISE THEM A BIT... WITH THE HIGHEST POPS SOUTH/SOUTHEAST THIS WEEKEND. HIGH TEMPS AHEAD OF THE FRONT ON WEDNESDAY AND THURSDAY ARE EXPECTED TO BE NEAR NORMAL... GENERALLY AROUND 90 TO THE LOWER TO MID 90S. HIGH BEHIND THE FRONT WILL GENERALLY BE IN THE MID TO UPPER 80S... WITH A FEW LOCATIONS TOUCHING THE LOWER 90S... DEPENDING ON THE PRECIP. LOWS AHEAD OF THE FRONT AREA EXPECTED TO BE IN THE LOWER TO MID 70S. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... AS OF 815 PM MONDAY... LATEST RADAR TRENDS INDICATE BULK OF SHOWER ACTIVITY REMAINS ACROSS WESTERN NC...INVOF KGSO AND KINT...WITH HI-RES NWP MODELS INDICATING THE STORMS DIMINISHING BY 03Z. PER FCST SOUNDINGS AND STATISTICAL GUIDANCE...SOUTHEASTERN AREAS WILL SEE THE BEST CHANCE OF MORNING LOW CLOUDS/STRATUS...WITH CEILINGS AT KFAY EXPECTED TO LOWER TO IFR/LIFR. ADDITIONALLY...ANY AREAS THAT SEE HEAVY RAINFALL THIS EVENING COULD SEE LOCALLY DENSE FOG. ANY STRATUS/FOG SHOULD LIFT INTO A BROKEN FLAT CU LAYER BY MID-LATE MORNING. EXPECT MAINLY DIURNAL SCATTERED SHOWERS AND STORMS AGAIN TUESDAY AFTERNOON...WITH THE PIEDMONT AIRPORTS(KGSO/KINT/KRDU)ONCE AGAIN THE FAVORED AREAS. OUTLOOK: THE PROBABILITY FOR EARLY MORNING FOG AND STRATUS WILL REMAIN RELATIVELY HIGH THROUGH THE REMAINDER OF THE WEEK. ISOLATED TO SCATTERED SHOWERS AND STORMS WILL BE POSSIBLE EACH AFTERNOON/EARLY EVENING...WITH HIGHEST CHANCE POPS IN THE WEST THROUGH THURSDAY. THE BETTER RAIN CHANCES WILL SHIFT TO EASTERN AREAS ON FRIDAY AND INTO SATURDAY AS A WEAK SURFACE FRONT COULD POTENTIALLY STALL NEAR THE COAST. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...WSS NEAR TERM...WSS SHORT TERM...WSS LONG TERM...BSD AVIATION...CBL

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