Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 271722 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 125 PM EDT MON JUL 27 2015 .SYNOPSIS...
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SURFACE HIGH PRESSURE WILL RETREAT OFFSHORE TODAY. A COUPLE OF WEAK DISTURBANCES IN NORTHWEST FLOW ALOFT WILL CROSS THE REGION THROUGH THE MIDDLE OF THE WEEK.
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&& .NEAR TERM /THROUGH TONIGHT/... AS OF 1025 AM MONDAY... 12Z UPPER AIR ANALYSIS DEPICTS A WEAK TROUGH DRIFTING SEWD ACROSS EASTERN-SOUTHERN VA THIS MORNING. WEAK CONVERGENCE NOTED ALONG THIS FEATURE AND NOSE OF 250MB JET ADDING ANOTHER SOURCE OF LIFT ALOFT. THIS HAS RESULTED IN A FEW SHOWERS SKIRTING ALONG THE VA BORDER COUNTIES SINCE 12Z. TROUGH RUNNING INTO A AIRMASS THAT IS NOT QUITE AS MOIST AS ACROSS VA...AND LOW LEVEL MOISTURE TRANSPORT NON- EXISTENT. THUS EXPECT CONVECTION TO BE NO WORSE THAN ISOLATED THROUGH EARLY AFTERNOON. AFTER 18Z...LOW LEVEL AIR MASS BECOMES SLIGHTLY UNSTABLE THOUGH SHEAR RELATIVELY WEAK AND LIFT APPEARS TO WANE AS BULK OF ENERGY WITH THE TROUGH MOVES TO OUR EAST-NE. STILL...PRESENCE OF BOUNDARY IN OUR VICINITY COUPLED WITH AFTERNOON HEATING SHOULD PROVIDE A FOCUS FOR CONVECTIVE DEVELOPMENT THIS AFTERNOON-EARLY EVENING ACROSS THE NORTHERN PIEDMONT AND THE NORTHERN COASTAL PLAIN. BASED ON LATEST WRF MODEL RUNS...MAJORITY OF THE CONVECTION OCCURS OVER THE TRIAD REGION AND THIS IS TIED TO CONVECTION THAT DEVELOPS IN THE HIGHER TERRAIN THEN DRIFTS SEWD DUE TO THE MEAN STEERING FLOW. FOR NOW WILL GO WITH A 30-40 PERCENT POP ACROSS THE I-85 CORRIDOR...DWINDLING TO SLIGHT CHANCE ALONG AND SOUTH OF HIGHWAY 64. PATCHY CLOUDINESS THIS MORNING IS GIVING WAY TO PARTLY SUNNY SKIES LATE MORNING-AFTERNOON. STILL SOME QUESTION AS TO HOW HOT IT WILL GET THIS AFTERNOON. IF ENOUGH SUN OCCURS...LOWER 90S SHOULD BE ACHIEVABLE MOST LOCATIONS. IF CLOUDS REMAIN PREVALENT AND SCATTERED CONVECTION OCCURS PRIOR TO 3 PM...THEN MAX TEMPS IN THE 86-90 DEGREE RANGE MAY BE MORE COMMON. TONIGHT...LINGERING SCATTERED CONVECTION SHOULD DISSIPATE WITHIN AN HOUR OR TWO OF SUNSET THOUGH A ROGUE SHOWER COULD OCCUR AFTER MIDNIGHT ANYWHERE ACROSS CENTRAL NC. OTHERWISE EXPECT AREAS OF LOW CLOUDS AND PATCHY FOG TO DEVELOP. NEAR SFC SLY FLOW WILL INCREASE MOISTURE ENOUGH THAT DEWPOINTS RISE TO NEAR 70-LOWER 70S. THUS IT WILL FEEL NOTICEABLY MORE HUMID THAN THE PAST FEW NIGHTS. MIN TEMPS 69-73. && .SHORT TERM /TUESDAY AND TUESDAY NIGHT/... AS OF 400 AM MONDAY... NORTHWEST FLOW ALOFT CONTINUES ON TUESDAY...THOUGH HEIGHTS ALOFT ALSO START TO RISE SLIGHTLY IN RESPONSE TO AN EASTWARD SHIFT OF THE CENTRAL US RIDGE AXIS. CONTINUED MOISTENING IN THE LOW-LEVELS WILL SUPPORT BETTER INSTABILITY THAN TODAY DESPITE WEAK LAPSE RATES. THE MAIN TRIGGERS FOR CONVECTION WILL AGAIN BE TERRAIN INDUCED CIRCULATION AND THE FLOW OF WEAK DISTURBANCES ALOFT. WITH BETTER INSTABILITY FORECAST..HOWEVER...WIDELY SCATTERED CONVECTION SEEMS POSSIBLE ACROSS MOST OF CENTRAL NC WITH HIGHER CONFIDENCE IN THE WESTERN PIEDMONT. HIGHS MAY BE A DEGREE OR TWO COOLER ON TUESDAY GIVEN INCREASED CLOUD COVER...BUT STILL INT HE UPPER 80S AND LOWER 90S. THE COVERAGE OF STORMS WILL LESSEN TUESDAY EVENING WITH LOSS OF HEATING...BUT GUIDANCE SUGGESTS A FEW STORMS COULD CONTINUE TO PERCOLATE WELL INTO THE NIGHT...ESPECIALLY OVER THE SOUTHERN AND WESTERN PIEDMONT AREAS. LOWS MORE SOLIDLY IN THE LOWER 70S. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... AS OF 400 AM MONDAY... A SUB-TROPICAL RIDGE CENTERED OVER THE SOUTHERN PLAINS AND MID-MS VALLEY WILL RETROGRESS INTO THE FOUR CORNERS REGION AND CONSEQUENTLY ALLOW A PROGRESSION OF SHORTWAVE TROUGHS TO CARVE A MEAN TROUGH OVER THE EASTERN US. AFTER THE DOMINANCE OF AN APPALACHIAN LEE TROUGH... BUT RELATIVELY MINIMAL CONVECTIVE DEVELOPMENT OWING TO WEAK LAPSE RATES ALOFT DURING THE MIDDLE OF THE WEEK...THE MODELS ARE IN GOOD AGREEMENT THAT A COLD FRONT RELATED TO THE PROGRESSION OF A LEAD SHORTWAVE TROUGH ACROSS THE GREAT LAKES WILL SETTLE EAST OF THE APPALACHIANS LATE THU-FRI...AT WHICH TIME SCATTERED SHOWERS AND STORMS ARE EXPECTED THROUGHOUT CENTRAL NC. THEREAFTER...THERE ARE MIXED SIGNALS REGARDING THE PROBABILITY OF PRECIPITATION THROUGH THE WEEKEND. THE OVERALL CONFIGURATION OF A TROUGH ALOFT IN THE EASTERN US SHOULD SUPPORT ABOVE AVERAGE CHANCES OF PRECIPITATION...BUT THE MODELS INDICATE THE LOW LEVEL FRONTAL ZONE MAY SETTLE JUST SOUTHEAST OF CENTRAL NC...WHICH WOULD TEND TO SUPPRESS THE BRUNT OF THE SHOWERS AND STORMS OVER THE SOUTHEASTERN PART OF THE STATE. GIVEN THE SOMEWHAT CONFLICTING SIGNALS...THIS FORECAST WILL BE WEIGHTED TOWARD CONTINUITY FROM THE PREVIOUS FORECASTS - SLIGHT TO CHANCE POP...HIGHEST SOUTHEAST AND MAXIMIZED DURING THE AFTERNOON AND EVENING. TEMPERATURES WILL PEAK MAINLY IN THE LOWER 90S DURING MID- WEEK...THEN TREND TO AOB AVERAGE FOR THE WEEKEND. LOWS AROUND 70. && .AVIATION /18Z MONDAY THROUGH SATURDAY/...
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AS OF 125 PM MONDAY... A WEAK SURFACE FRONT DRIFTING SOUTHWARD INTO NC FROM VA INTERACTING WITH AN INCREASINGLY MOIST AND SLIGHTLY UNSTABLE AIR MASS WILL GENERATE VARYING DEGREES OF CLOUDINESS AND ISOLATED-SCATTERED CONVECTION THIS AFTERNOON INTO THE EVENING HOURS. WHILE VFR CONDITIONS SHOULD DOMINATE AT THE TAF SITES THIS AFTERNOON-THIS EVENING...THERE WILL BE A CHANCE FOR MVFR CEILING/VISIBILITY DUE TO CONVECTION IN THE TRIAD VICINITY...ESPECIALLY BETWEEN 19Z-23Z. STILL HIGH UNCERTAINTY WHETHER SCATTERED CONVECTION WILL THREATEN THE KRDU VICINITY AFTER 21Z SO HAVE OPTED TO OMIT AT THIS TIME AND MONITOR CONDITIONS UPSTREAM. AFTER 03Z...BULK OF ISOLATED-SCATTERED CONVECTION WILL DIMINISH BY LATE EVENING THOUGH AN ISOLATED SHOWER WILL REMAIN POSSIBLE INTO THE OVERNIGHT PERIOD. AN INCREASINGLY MOIST LOW LEVEL AIR MASS SHOULD LEND TO THE DEVELOPMENT OF PATCHY STRATUS AND/OR FOG....ESPECIALLY AFTER 09Z. TUESDAY...EARLY MORNING LOW CLOUDS/FOG SHOULD LIFT INTO A BROKEN FLAT CU LAYER BY MID-LATE MORNING. AS ATMOSPHERE BECOME SLIGHTLY UNSTABLE..EXPECT SCATTERED CONVECTION ACROSS MOST OF CENTRAL NC IN THE MID-AFTERNOON-EVENING HOURS. THE PROBABILITY FOR EARLY MORNING FOG AND STRATUS WILL REMAIN RELATIVELY HIGH THROUGH THE REMAINDER OF THE WEEK. AFTERNOON CONVECTION MAY BE LESS LIKELY WEDNEDAY AFTERNOON AS A MID-UPPER LEVEL RIDGE BUILDS ACROSS THE REGION. THIS WEATHER FEATURE WILL WEAKEN IN RESPONSE TO A S/W TROUGH APPROACHING FROM THE NW. THIS TROUGH MAY INCREASE THE PROBABILITY OF SCATTERED CONVECTION LATE IN THE WEEK.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...22 NEAR TERM...WSS SHORT TERM...22 LONG TERM...26 AVIATION...WSS

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