988 FXUS62 KCHS 311917 AFDCHS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHARLESTON SC 317 PM EDT SAT AUG 31 2013 .SYNOPSIS... WEAK ATLANTIC HIGH PRESSURE WILL RESIDE OVER THE AREA THROUGH EARLY NEXT WEEK. A COLD FRONT WILL PUSH THROUGH TUESDAY NIGHT AND WEDNESDAY WITH WEAK CANADIAN HIGH PRESSURE BUILDING IN FROM THE NORTH. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... THIS AFTERNOON...MAINLY ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS WILL CONTINUE PRIMARILY ALONG AND WEST OF I-95. FOR THE NEXT COUPLE OF HOURS MOST OF THE ACTIVITY WILL IMPACT AREAS ACROSS SOUTHEAST GEORGIA FROM AROUND LUDOWICI TO HINESVILLE. OVERALL STEERING FLOW IS QUITE WEAK SO THESE SHOWERS/STORMS WILL EXHIBIT VERY LITTLE MOTION. AN OUTFLOW BOUNDARY PUT OUT BY EARLIER STORMS AROUND SAVANNAH MAY RESULT IN ADDITIONAL DEVELOPMENT UP THE SAVANNAH RIVER TOWARDS SYLVANIA AND ALLENDALE. THE SEVERE THREAT CONTINUES TO BE LOW...THOUGH SOME LOCALLY HEAVY RAINFALL WILL BE POSSIBLE. TONIGHT...ANY LINGERING SHOWER/THUNDERSTORM ACTIVITY SHOULD DIMINISH WITH THE LOSS OF DIURNAL HEATING. SOME OF THE HI-RES MODELS HAVE BEEN HINTING AT SOME UPSTREAM ACTIVITY FROM THE UPSTATE MAKING A RUN AT OUR INLAND ZONES LATE. I DO MAINTAIN SLIGHT CHANCE POPS UP AGAINST THE MIDLANDS TILL AROUND MIDNIGHT TO ACCOUNT FOR THIS...THOUGH I IMAGINE THAT ANYTHING THAT DOES APPROACH AROUND THAT TIME SHOULD BE RAPIDLY DECREASING IN COVERAGE AND INTENSITY. OTHERWISE...A LIGHT LOW LEVEL FLOW WILL BECOME INCREASINGLY SW OVERNIGHT WITH A SUBTLE SURFACE TROUGH INLAND AND A SURFACE HIGH WELL OUT OVER THE ATLANTIC. THIS FLOW REGIME SHOULD PRECLUDE THE DEVELOPMENT OF ANY DENSE FOG LIKE WE HAD LAST NIGHT...BUT GUIDANCE DOES HINT AT SOME LIGHT FOG. HAVE ADDED PATCHY FOG TO AREAS AWAY FROM THE IMMEDIATE COAST. LOOK FOR LOWS TO BE AROUND 73-75 IN MOST LOCATIONS. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/... SUNDAY MORNING COULD START WITH A LITTLE BIT OF FOG AGAIN...BUT IT SHOULD BE PATCHY AS OPPOSED TO THE WIDESPREAD COVERAGE SATURDAY MORNING. THE FOG SHOULD ALSO BREAK UP A LITTLE QUICKER AS THE SURFACE PRESSURE GRADIENT WILL BE A LITTLE TIGHTER...HELPING TO PROMOTE EARLIER MIXING OF THE BOUNDARY LAYER. I EXPECT THERE MAY BE A LITTLE CONVECTION OVER THE COASTAL WATERS AS WELL...BUT CURRENT THINKING IS THAT ACTIVITY WILL REMAIN OVER THE COASTAL WATERS FOR THE MOST PART...SO POPS WILL START THE DAY LOW. WITH TEMPERATURES EXPECTED TO CLIMB INTO THE LOWER 90S AWAY FROM THE IMMEDIATE COAST BY AFTERNOON...SOME SCATTERED CONVECTION SHOULD FIRE UP...WITH THE SLOW MOVING SEA BREEZE AND ANY REMAINING CONVECTIVE BOUNDARIES INLAND BEING THE INITIAL FOCUSING MECHANISM. TEMPS IN THE MID LEVELS WILL BE A BIT COOLER SUNDAY AFTERNOON...BUT A CAP IS STILL EXPECTED TO BE IN PLACE AROUND 15K FEET...SO THE CONVECTION SHOULD NOT BE ANY MORE WIDESPREAD THAN CLIMO WOULD INDICATE...SO I LOWERED THE POPS A BIT FROM THE PREVIOUS FORECAST...TOWARD THE LOWER END OF THE CHANCE CATEGORY. THE PRESSURE GRADIENT TIGHTENS A BIT MORE ON MONDAY AS FALLING HEIGHTS ALOFT WILL HELP ENHANCE THE TYPICAL DIURNAL SURFACE TROF THAT SETS UP OVER THE MIDLANDS DURING THE HEAT OF A SUMMER AFTERNOON. HOWEVER...THE UPPER LEVELS OF THE ATMOSPHERE LOOK TO REMAIN WARM...PUTTING A CAP ON THE POTENTIAL INSTABILITY DESPITE TEMPS BACK INTO THE 90S BY AFTERNOON. THE EXPECTATION OF SCATTERED AFTERNOON CONVECTION CONTINUES...WITH LOCATIONS CLOSER TO THE COAST MAYBE HAVING A BETTER CHANCE OF GETTING IN ON THE SHOWER ACTIVITY DUE TO THE SEA BREEZE BEING VERY SLOW TO MOVE INLAND. BY TUESDAY...THE UPPER TROF DIGS DEEP ENOUGH TO MOVE A COLD FRONT TOWARD THE AREA BY LATE IN THE DAY. THE ENHANCED CONVERGENCE...ALONG WITH SOME SLIGHT UPPER LEVEL COOLING...SHOULD LEAD TO A SOMEWHAT BETTER CHANCE FOR CONVECTION DURING THE AFTERNOON HOURS. I HAVE GONE JUST A TOUCH COOLER FOR TEMPS TUESDAY DUE MAINLY TO INCREASED CLOUD COVER. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... THE COLD FRONT WILL GRADUALLY SHIFT SOUTH OF THE AREA TUESDAY NIGHT WITH RAIN CHANCES DIMINISHING ON WEDNESDAY. DRIER...MORE STABLE CANADIAN HIGH PRESSURE WILL SHIFT IN WEDNESDAY THROUGH THURSDAY NIGHT BEFORE DRIFTING OFFSHORE. RAIN CHANCES WILL RETURN FRIDAY INTO SATURDAY AS ONSHORE FLOW INCREASES LOW-LEVEL MOISTURE. && .AVIATION /19Z SATURDAY THROUGH THURSDAY/... MAINLY VFR CONDITIONS ARE EXPECTED TO PREVAIL THROUGH THE 18Z TAF CYCLE AT KCHS AND KSAV. ISOLATED SHOWERS ACROSS COASTAL GEORGIA COULD BRIEFLY IMPACT KSAV EARLY THIS AFTERNOON PRIOR TO TRANSITIONING INLAND WITH THE SEA BREEZE. THEREFORE...WILL MAINTAIN VCSH THROUGH 20Z WITH A BRIEF TEMPO OF TSRA AT KSAV. HIGH RESOLUTION MODELS SHOW EVEN LESS COVERAGE ACROSS THE CHARLESTON AREA...THEREFORE WILL CONTINUE TO EXCLUDE ANY MENTION OF RAIN AT KCHS. OVERNIGHT...LIGHT WINDS AND PLENTY OF LOW LEVEL MOISTURE COULD RESULT IN SOME PATCHY MVFR FOG PRIOR TO DAYBREAK....BUT POTENTIAL IS TOO LOW TO INCLUDE IN TAFS AT THIS TIME. EXTENDED AVIATION OUTLOOK...GENERALLY VFR CONDITIONS EXPECTED OUTSIDE OF DIURNAL CONVECTION SUNDAY AFTERNOON THROUGH TUESDAY. THERE MAY BE SOME LOW CIG ISSUES WEDNESDAY DEPENDING ON THE SPEED OF THE FRONTAL PASSAGE CURRENTLY EXPECTED TUESDAY NIGHT. && .MARINE... TONIGHT...EXPECT ANOTHER QUIET NIGHT WITH THE LOW LEVEL FLOW VEERING FROM SOUTHERLY TO MORE SOUTHWESTERLY BY SUNDAY MORNING. THERE WILL BE A BIT OF A SURGE...BUT SPEEDS WILL TOP OUT IN THE 10-15 KT RANGE OVER THE OUTER WATERS. SEAS WILL BE 1-2 FT WITHIN 20 NM AND 2-3 FT BEYOND. WINDS WILL GENERALLY BE SOUTH TO SOUTHWEST SUNDAY THROUGH TUESDAY ON THE BACK SIDE OF AN AREA OF HIGH PRESSURE IN THE WESTERN ATLANTIC. SCATTERED CONVECTION WILL BE THE RULE THROUGH THAT TIME PERIOD AS WELL. THE WINDS WILL BE A BIT STRONGER MONDAY AND TUESDAY...BUT STILL SHOULD REMAIN BELOW ANY SCA CONCERNS WITH WINDS 15 KNOTS OR LESS AND SEAS 4 FEET OR LESS. WINDS WILL BECOME EVEN LIGHTER MID WEEK AS A FRONT MOVES SOUTH OF THE AREA AND WASHES OUT...CAUSING THE SURFACE PRESSURE GRADIENT TO COLLAPSE. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...NONE. SC...NONE. MARINE...NONE. && $$ SYNOPSIS... NEAR TERM...BSH SHORT TERM...FWA LONG TERM...JRL AVIATION...JHP MARINE...BSH/FWA