000 FXUS62 KCHS 140750 AFDCHS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHARLESTON SC 344 AM EDT SAT JUL 14 2007 .SYNOPSIS... A COOL FRONT WILL STALL OVER THE REGION THIS MORNING...THEN WILL LIFT BACK TOWARD THE NORTH THIS AFTERNOON AND TONIGHT. THE INTERACTION OF THE FRONT AND AN UPPER LEVEL TROUGH OF LOW PRESSURE WILL INCREASE THE CHANCE FOR SHOWERS AND THUNDERSTORMS TODAY THROUGH SUNDAY. ATLANTIC HIGH PRESSURE WILL THEN BUILD OVER THE AREA FOR NEXT WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... THE SURFACE FRONT...SEPARATING DEWPOINTS IN THE LOWER TO MIDDLE 60S FROM DEWPOINTS IN THE MIDDLE TO UPPER 70S...HAD ADVANCED THROUGH ALL BUT SOUTHERN COUNTIES OF THE FORECAST AREA EARLY SATURDAY MORNING...MOST RECENTLY PUSHING THROUGH CHS AND NBC. MEANWHILE...AN UPPER TROUGH WAS PRESSING S/SE TOWARD THE N/NW GULF OF MEXICO. AHEAD OF THIS FEATURE...DEEP LAYER MOISTURE WAS INCREASING ACROSS THE REGION...AND A SERIES OF UPSTREAM SHORTWAVE WERE EXPECTED TO EMERGE FROM THE PARENT TROUGH TO PUSH THE REGION TODAY...ESPECIALLY THIS AFTERNOON/EVENING. THIS COMBINATION OF FACTORS WAS SETTING THE STAGE FOR A WET DAY ACROSS THE FORECAST AREA. GIVEN THE PRESENCE OF THE SURFACE BOUNDARY...WHICH SHOULD STALL THEN GRADUALLY PUSH BACK TOWARD THE NORTH AS THE SEA BREEZE DEVELOPS TODAY...ESPECIALLY THIS AFTERNOON...THE COMBINATION OF ONGOING DEEP LAYER MOISTURE ADVECTION AND LOW/MID LEVEL MOISTURE/MASS CONVERGENCE...SHOWERS AND A FEW THUNDERSTORMS COULD DEVELOP/MOVE INTO THE REGION AT ANY TIME THROUGH THIS MORNING. HOWEVER...RICH MOISTURE SUPPORTING PWATS IN THE 2-2.5 INCH RANGE...SOME DEGREE OF LOW LEVEL DESTABILIZATION DESPITE CLOUD COVER...ENHANCED LOW LEVEL MASS/MOISTURE CONVERGENCE AS THE SEA BREEZE PUSHES THE SYNOPTIC BOUNDARY TOWARD THE N/NW...HEIGHT FALLS AND 500-300 MB QG FORCING/400-200 MB DIVERGENCE ASSOCIATED WITH THE SHORTWAVES SHOULD SUPPORT NUMEROUS TO WIDESPREAD SHOWERS/THUNDERSTORMS THIS AFTERNOON. FOR THIS PACKAGE...UPGRADED POPS TO CATEGORICAL ALL AREAS FOR THIS AFTERNOON. SEVERE POTENTIAL WILL REMAIN LIMITED TODAY...AS CLOUD COVER WILL LIMIT DEGREE OF CLOUD COVER/DESTABILIZATION...AND AS DEEP LAYER MOISTURE WILL ELIMINATE MID LEVEL DRY AIR/ANY SOURCE OF EVAPORATIONAL COOLING TO CONTRIBUTE TO MICROBURST POTENTIAL. HOWEVER...WHERE PRECIPITATION HOLDS OFF UNTIL EARLY AFTERNOON... INITIAL THUNDERSTORM INTENSITY MAY BE ENHANCED BY SBCAPES AS HIGH AS 1500-2500 J/KG...WHILE A SMALL CHANCE FOR ROTATING UPDRAFTS WILL EXIST IN THE VICINITY OF THE SURFACE BOUNDARY...AND PRECIPITATION LOADING COULD PRODUCE ISOLATED DAMAGING WIND GUSTS. HOWEVER...GIVEN PWATS AT OR ABOVE 2 INCHES...THE MAIN ISSUE WILL BE THE POTENTIAL FOR LOCALLY HEAVY RAINFALL TODAY...ESPECIALLY WHERE SW-NE ECHO TRAINING CAN OCCUR. ALSO...HIGH TIDE WILL OCCUR IN THE 830-10 PM TIME FRAME TONIGHT...AND THE LOCAL FLOOD THREAT WILL BE ENHANCED IN COASTAL AREAS IF HEAVY RAIN IS STILL OCCURRING AT THIS TIME. && .SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY NIGHT/... AS A LOGICAL FOLLOW ON TO CATEGORICAL AFTERNOON POPS..RAISED POPS TO LIKELY UNTIL MIDNIGHT TONIGHT. THEN...THE SURFACE BOUNDARY WILL HAVE PUSHED NORTH OF THE REGION...AND CONVECTION SHOULD UNDERGO SOME DEGREE OF DIURNAL DECREASE IN COVERAGE OVERNIGHT...ALTHOUGH EXPECT AT LEAST SCATTERED SHOWERS/ISOLATED THUNDERSTORMS TO PERSIST THROUGH THE NIGHT...AS SHORTWAVES CONTINUE TO PUSH OUT OF THE PARENT TROUGH AND TOWARD THE NE. SUNDAY...EXPECT ANOTHER DIURNAL EXPANSION/ INTENSIFICATION OF SHOWERS/THUNDERSTORMS...ESPECIALLY DURING THE AFTERNOON/EVENING...WITH COVERAGE AGAIN ENHANCED BY SHORTWAVE ENERGY EMERGING FROM THE PARENT TROUGH TO THE W/SW. THE MAIN DIFFERENCES BETWEEN TODAY AND SUNDAY WILL BE SLIGHTLY HIGHER HEIGHTS AS THE ATLANTIC RIDGE BEGINS TO EXPAND W...AND THE LACK OF A SYNOPTIC BOUNDARY...ALTHOUGH THE SEA BREEZE BOUNDARY WILL PUSH INLAND AND WILL PROVIDE A FOCUS FOR DEEP MOIST CONVECTION. ALSO...MID LEVELS WILL BE SLIGHTLY DRIER PER 0Z MODEL SOUNDINGS...AND THIS COULD ENHANCE MICROBURST POTENTIAL. CONTINUED ONGOING 50% POPS...BUT LATER SHIFTS MAY OPT TO PUSH POPS HIGHER. SUNDAY NIGHT...EXPECT A DIURNAL DECREASE IN SHOWER/THUNDERSTORMS...TAPERING TO SLIGHT CHANCE POPS OVERNIGHT. TONIGHT AND AGAIN SUNDAY NIGHT...FOG COULD DEVELOP AND COULD BECOME LOCALLY DENSE...ESPECIALLY WHERE RAIN FALLS...BUT WILL DEFER FURTHER ASSESSMENT OF FOG POTENTIAL TO THE IMPROVED PERSPECTIVE OF LATER SHIFTS. && .LONG TERM /MONDAY THROUGH FRIDAY/... FIRST PART OF THE WORK WEEK WILL SEE DAILY CHANCE POP. THE AIRMASS WILL BE HOT AND HUMID...AND UPPER LOW OVER THE LOWER MS VALLEY MAY SUPPLY ENOUGH UPPER ENERGY TO KEEP SCATTERED CONVECTION IN THE FORECAST. THIS WILL LAST THROUGH AT LEAST WEDNESDAY AS THE RIDGING OVER THE ATLANTIC KEEPS A SOUTHERLY WIND OVER THE COUNTY WARNING AREA. WILL DECREASE POP TO AROUND 20 PERCENT ON THURSDAY AS UPPER RIDGING SHIFTS WEST AND INTO THE NORTHERN GULF COAST AND SOUTH ATLANTIC AREA. THE RIDGE IS NOT FORECAST TO BE OVERLY STRONG SO AS IT SHIFTS WEST...A RETURN OF CHANCE POP WILL COME ON FRIDAY. TEMPS IN THE LOW TO MIDDLE 90S ARE EXPECTED THROUGH THE FORECAST PERIOD...FAIRLY TYPICAL FOR MID JULY. && .AVIATION /07Z SATURDAY THROUGH WEDNESDAY/... THE SURFACE FRONT HAD PUSHED THROUGH KCHS THIS MORNING. POST FRONTAL STRATOCUMULUS WILL SUPPORT AT LEAST BRIEF PERIODS OF MVFR CEILING THROUGH THE EARLY MORNING. MEANWHILE...SOUTH OF THE FRONT AT KSAV...CANNOT RULE OUT A BRIEF PERIOD OF MVFR VISIBILITY THIS MORNING...BUT THICKENING MID/HIGH LEVEL CLOUD COVER WILL LIMIT FOG POTENTIAL. MEANWHILE...GIVEN INCREASING DEEP LAYER MOISTURE AND THE PRESENCE OF THE SURFACE FRONT...CANNOT RULE OUT A SHOWER AT EITHER TERMINAL THROUGH THIS MORNING. HOWEVER...ADDED PREVAILING/ TEMPO GROUPS FOR PRECIPITATION DURING THE AFTERNOON/EVENING...DUE TO HIGHER POPS PROVIDED BY THE COMBINATION OF DESTABILIZATION...THE SURFACE FRONT IN THE REGION...DEEP LAYER MOISTURE AND ASCENT PROVIDED BY A SHORTWAVE PUSHING ACROSS THE REGION. SCENARIO SHOULD SUPPORT AT LEAST BRIEF PERIODS OF HEAVY RAIN/IFR VISIBILITY THIS AFTERNOON/EARLY EVENING. ALSO...THUNDERSTORMS COULD OCCUR AT EITHER SITE THIS AFTERNOON/EVENING...ALTHOUGH AS OF EARLY SATURDAY MORNING THUNDER APPEARED MORE LIKELY WITHIN THE MORE UNSTABLE AIRMASS SOUTH OF THE FRONT AT KSAV. THEN...EVEN AS CONVECTION DIMINISHES IN COVERAGE THIS EVENING...LEFTOVER LOW LEVEL MOISTURE SHOULD SUPPORT AT LEAST PERIODS OF MVFR/IFR CEILINGS/VISIBILITIES AT BOTH TERMINALS INTO TONIGHT. EXTENDED AVIATION OUTLOOK...SUNDAY WILL SEE A CONTINUATION OF SCATTERED STORMS...BRINGING THE POSSIBILITY OF SOME IFR CEILINGS AND VISIBILITIES MAINLY IN THE AFTERNOON AND EVENING HOURS. GENERALLY VFR CONDITIONS ARE EXPECTED MON THROUGH FRI OF NEXT WEEK WITH SOME MVFR EXPECTED WITH SCATTERED CONVECTION IN THE AFTERNOONS. && .MARINE... THE COOL FRONT HAD PUSHED THROUGH SC COASTAL WATERS THIS MORNING...COULD PUSH BRIEFLY INTO GA WATERS..BEFORE THE BOUNDARY STALLS THIS MORNING...THEN PUSHES N/NW WITH THE SEA BREEZE THIS AFTERNOON. THIS WILL RESULT IN CHANGEABLE WIND DIRECTION ACROSS NORTHERN WATERS TODAY. TONIGHT...EXPECT A DIURNAL INCREASE IN S/SW WINDS...ALTHOUGH ONGOING CONVECTION MAY SIGNIFICANTLY ALTER LOW LEVEL WIND FIELDS. SUNDAY...S/SW WINDS WILL BECOME ENHANCED BY THE SEA BREEZE NEAR THE COAST...THEN...S/SW WINDS MAY AGAIN INCREASE SUNDAY NIGHT. TONIGHT AND SUNDAY NIGHT...WILL NEED TO MONITOR POTENTIAL FOR SCSEC WINDS ACROSS THE OUTER GA WATERS. MEANWHILE...BUMPED POPS TO LIKELY TODAY AND TONIGHT...AS ADVECTION OF DEEP MOISTURE SHOULD SUPPORT AT LEAST NUMEROUS SHOWERS/ THUNDERSTORMS. NO MAJOR CHANGES WERE MADE IN THE EXTENDED PORTION OF THE MARINE FORECAST. A CONTINUE ONSHORE WIND WILL KEEP LOCAL SEABREEZE EFFECTS DURING THE AFTERNOONS. SURFACE HIGH CENTERED OVER THE ATLANTIC WILL KEEP A MODERATE GRADIENT OVER THE REGION. LOOK FOR MAINLY SOUTHERLY WINDS DURING THE FORECAST PERIOD WITH SPEEDS GENERALLY LESS THAN 15 KT. THIS WILL KEEP SEAS IN THE 2-3 FOOT RANGE...WHICH FITS WELL WITH THE LATEST WAVEWATCH GUIDANCE. && .TIDES/COASTAL FLOODING... EXPECT TIDES TO REMAIN BELOW CRITICAL LEVELS THIS EVENING AND SUNDAY EVENING. HOWEVER...SINCE EVENING HIGH TIDES WILL BE LESS THAN 1/2 FOOT BELOW SHALLOW COASTAL FLOODING THRESHHOLDS...THIS WILL BEAR CLOSE SCRUTINY THIS WEEKEND. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...NONE. SC...NONE. MARINE...NONE. && $$ SPR/PY