116 FXUS62 KCHS 221445 AFDCHS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHARLESTON SC 1045 AM EDT WED MAY 22 2013 .SYNOPSIS... ATLANTIC HIGH PRESSURE WILL PREVAIL THROUGH THURSDAY. A COLD FRONT WILL MOVE ACROSS THE AREA THURSDAY NIGHT...WITH HIGH PRESSURE BUILDING OVER THE REGION THROUGH EARLY NEXT WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... THE WEAK UPPER LEVEL PATTERN WILL GRADUALLY TRANSITION TODAY...AS THE BAGGY TROUGH OVER THE SOUTHEAST STATES BECOMES MORE ABSORBED INTO THE PERIPHERY OF A STRONGER TROUGH CURRENTLY OVER THE MISSISSIPPI VALLEY. DEEP MOISTURE STILL LINGERS OVER THE AREA...SEEN IN VERTICAL SOUNDINGS WITH PRECIPITABLE WATER VALUES AROUND 1.5 INCHES. WITH THE FORECAST AREA STILL UNDER THE INFLUENCE OF ATLANTIC SURFACE HIGH PRESSURE...SOLID SOUTHERLY FLOW WILL PREVAIL AND HAS ALLOWED THE SEABREEZE TO DEVELOP EARLY. SEABREEZE FORCING BY LATE MORNING WITHIN ABUNDANT MOISTURE HAS ALREADY SUPPORTED THE INITIATION OF ISOLATED SHOWERS ACROSS COASTAL COUNTIES BY 10 AM EDT. LACKING ANY OTHER NOTABLE FORCING MECHANISMS...CONVECTIVE DEVELOPMENT AND EVOLUTION TODAY IS EXPECTED TO BE MAINLY DRIVEN BY THE SEABREEZE PROGRESSION AND TYPICAL DIURNAL HEATING AND INSTABILITY. THE PRECIPITATION FORECAST WILL THUS INDICATE THUNDERSTORMS DEVELOPING ALONG AND INLAND OF THE SEABREEZE BY LATE MORNING...THEN SPREADING INLAND INTO THE AFTERNOON HOURS. HAVE MAINTAINED RAIN CHANCES IN THE 20 TO 30 PERCENT RANGE. MODIFYING THE MORNING SOUNDING AT KCHS FOR HIGH TEMPERATURES IN THE MID TO UPPER 80S STILL INDICATES RATHER UNIMPRESSIVE INSTABILITY BY THIS AFTERNOON...AND WHEN CONSIDERING WEAK LAPSE RATES AND VERTICAL WIND PROFILES...SEVERE THUNDERSTORM POTENTIAL APPEARS LOW. HOWEVER...AS COMMON THIS TIME OF YEAR...AN ISOLATED STRONG TO SEVERE THUNDERSTORM CANNOT BE RULED OUT WHERE BOUNDARY INTERACTIONS OCCUR. OTHERWISE...THE MAIN HAZARD ASSOCIATED WITH THUNDERSTORMS WILL BE HEAVY DOWNPOURS. && .SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY/... DIURNAL CONVECTION WILL TAPER OFF EARLY THIS EVENING OVER LAND...WHILE ISOLATED SHOWERS OR STORMS WILL REMAIN POSSIBLE OVER THE COASTAL WATERS TONIGHT. SOME FOG IS POSSIBLE LATE TONIGHT/EARLY THURSDAY MORNING...ESPECIALLY IN AREAS WHERE RAIN OCCURS TODAY. THURSDAY...ATLANTIC HIGH PRESSURE WILL PREVAIL WHILE WEAK TROUGHING PERSISTS INLAND. A SHORTWAVE EMBEDDED WITHIN BROAD UPPER LEVEL TROUGHING WILL CROSS THE REGION AND PUSH THE DEEP LAYERED MOISTURE OFFSHORE AS THE DAY PROGRESSES. THERE IS THE POTENTIAL FOR ISOLATED CONVECTION ACROSS THE AREA IN THE MORNING AHEAD OF THE SHORT WAVE...WITH THE COVERAGE INCREASING TO SCATTERED IN THE AFTERNOON ACROSS MUCH OF SOUTHEAST SOUTH CAROLINA WHERE PRECIPITABLE WATER VALUES AND LOW LEVEL CONVERGENCE WILL BE MAXIMIZED. A WESTERLY/DOWNSLOPE FLOW ALOFT WILL PUSH TEMPERATURES TO HIGHS IN THE UPPER 80S TO AROUND 90 AWAY FROM THE IMMEDIATE COAST. THURSDAY NIGHT...AN UPPER LEVEL TROUGH WILL DIG TOWARD THE APPALACHIANS...PUSHING A COLD FRONT ACROSS THE AREA. OTHER THAN SOME ISOLATED CONVECTION EARLY IN THE EVENING MAINLY ACROSS THE CHARLESTON TRI-COUNTY AREA...THE FRONT SHOULD PASS THROUGH RELATIVE RAIN-FREE DUE TO A LACK OF DEEP LAYERED MOISTURE. LOWS WILL BE IN THE LOWER TO MID 60S. FRIDAY...THE UPPER LEVEL TROUGH WILL MOVE OVER THE MID-ATLANTIC AS SURFACE HIGH PRESSURE BEGINS TO BUILD IN FROM THE GREAT LAKES REGION IN WAKE OF THE DEPARTING COLD FRONT. MUCH DRIER AIR WILL FILTER INTO THE AREA WITH A STRONG NORTHWEST/DOWNSLOPE WIND COMPONENT. THERE WILL BE CONSIDERABLE SUNSHINE ALONG WITH BREEZY CONDITIONS IN THE AFTERNOON. THE DOWNSLOPE FLOW WILL NEGATE MUCH OF THE COLD AIR ADVECTION...ALLOWING TEMPERATURES TO REACH HIGHS IN THE MID AND UPPER 80S ACROSS THE AREA AWAY FROM THE IMMEDIATE COAST. FRIDAY NIGHT...RADIATIONAL COOLING WILL BE LIMITED BY A COUPLED NORTHERLY FLOW THROUGH MUCH OF THE NIGHT...BUT THE DRY AIR MASS AND CLEAR SKIES SHOULD STILL ALLOW TEMPERATURES TO FALL INTO THE THE MID AND UPPER 50S...WITH SOME LOWER 50S POSSIBLE WELL INLAND. SATURDAY...AN EXTREMELY DRY AIR MASS WILL BE IN PLACE TO START THE WEEKEND...WITH PRECIPITABLE WATER VALUES AS LOW AS .25 TO .50 INCHES WHICH IS MORE THAN 2 STANDARD DEVIATIONS BELOW NORMAL FOR THIS TIME OF YEAR. GIVEN THIS DRY AIR MASS...THERE WILL BE CONSIDERABLE SUNSHINE BUT A NORTH-NORTHEAST FLOW WILL LIMIT HIGHS TO THE UPPER 70S TO LOWER 80S ACROSS SOUTHEAST SOUTH CAROLINA AND THE LOWER TO MID 80S ACROSS SOUTHEAST GEORGIA. && .LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/... MEDIUM RANGE GUIDANCE IS IN GOOD OVERALL AGREEMENT THROUGH THE LONG TERM PERIOD. THE MID AND UPPER LEVEL PATTERN WILL FEATURE A NEARLY ZONAL FLOW OVER THE REGION LATE IN THE WEEKEND INTO EARLY NEXT WEEK...WITH A RIDGE THEN BUILDING TOWARD THE MIDDLE OF NEXT WEEK. AT THE SURFACE...HIGH PRESSURE WILL PASS NORTH OF THE AREA LATE IN THE WEEKEND...THEN SETTLE OVER THE WESTERN ATLANTIC THROUGH THE MIDDLE OF NEXT WEEK. RAIN-FREE CONDITIONS ARE EXPECTED TO PERSIST INTO EARLY NEXT WEEK...THEN INCREASING MOISTURE COULD ALLOW FOR SOME MAINLY DIURNAL ISOLATED CONVECTION ALONG AND AHEAD OF THE SEA BREEZE TUESDAY AND WEDNESDAY. TEMPERATURES WILL BE SLIGHTLY BELOW NORMAL SUNDAY...THEN RETURN TO NEAR OR SLIGHTLY ABOVE NORMAL NEXT WEEK. && .AVIATION /14Z WEDNESDAY THROUGH SUNDAY/... ISOLATED CONVECTION IS EXPECTED TO DEVELOP IN THE VICINITY OF THE TERMINALS BY LATE MORNING/EARLY AFTERNOON ALONG THE SEA BREEZE...THEN SHIFT INLAND OF THE TERMINALS LATER THIS AFTERNOON. COVERAGE/TIMING UNCERTAINTIES PRECLUDE ANY MENTION IN THE TAFS OTHER THAN VICINITY SHOWERS THROUGH MID-AFTERNOON AT KCHS AND LATE AFTERNOON AT KSAV. ABUNDANT LOW LEVEL MOISTURE COULD RESULT IN SOME REDUCED CEILINGS/VISIBILITIES LATE TONIGHT. EXTENDED AVIATION...ATLANTIC HIGH PRESSURE WILL PREVAIL THROUGH THURSDAY. A COLD FRONT WILL MOVE ACROSS THE AREA THURSDAY NIGHT WITH HIGH PRESSURE THEN BUILDING OVER THE REGION THROUGH EARLY NEXT WEEK. && .MARINE... MARINE CONDITIONS WILL BE FAIRLY BENIGN THROUGH TONIGHT...AS THE AREA REMAINS ON THE WESTERN PERIPHERY OF ATLANTIC HIGH PRESSURE. THE SEABREEZE WILL DEVELOP BY LATE MORNING...HOWEVER WIND SPEEDS AT THE COAST ARE STILL EXPECTED TO GENERALLY REMAIN BELOW 15 KT. THURSDAY THROUGH MONDAY...ATLANTIC HIGH PRESSURE WILL DOMINATE WITH SOUTHERLY FLOW UNTIL A COLD FRONT PUSHES OFFSHORE EARLY FRIDAY. A NORTHERLY SURGE IS EXPECTED TO DEVELOP IN WAKE OF THE FRONT FRIDAY NIGHT INTO EARLY SATURDAY AND COULD RESULT IN SMALL CRAFT ADVISORY CONDITIONS. CONDITIONS WILL THEN IMPROVE LATER IN THE WEEKEND INTO EARLY NEXT WEEK WITH WINDS/SEAS EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY THRESHOLDS. && .TIDES/COASTAL FLOODING... HIGH ASTRONOMICAL TIDES AND FAVORABLE NORTH/NORTHEAST WINDS COULD LEAD TO MINOR SALTWATER INUNDATION NEAR THE COAST DURING THE HIGH TIDE FRIDAY AND SATURDAY EVENING. BY THE TIME OF THE HIGH TIDE SUNDAY EVENING AND MONDAY EVENING...WINDS WILL NOT BE AS CONDUCIVE...YET MINOR SALTWATER FLOODING WILL STILL BE POSSIBLE. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...NONE. SC...NONE. MARINE...NONE. && $$ NEAR TERM...WMS SHORT TERM...JAQ LONG TERM...JAQ AVIATION...JAQ MARINE...JAQ/JRL TIDES/COASTAL FLOODING...WMS