AFDCHS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHARLESTON SC 417 AM EDT SAT JUL 9 2011 .SYNOPSIS... A WEAK COLD FRONT WILL MOVE INTO THE AREA OVER THE WEEKEND...THEN MOVE THROUGH AND DISSIPATE BY MON. ANOTHER FRONT WILL APPROACH FROM THE N BY THE MIDDLE OF NEXT WEEK. && .NEAR TERM /THROUGH TONIGHT/... CONVECTION HAS PERSISTED OVER THE SE U.S. OVERNIGHT IN POCKETS WITH MOST OF OUR REGION DRY EXCEPT FOR A DEVELOPING BAND OF CONVERGENCE ENHANCED SHOWERS PULLING NE THROUGH COASTAL CHARLESTON COUNTY AND ADJACENT WATERS. 925 WINDS WERE VEERING MORE W IN THE MIDLANDS AND A FEW MORE SHOWERS WERE ALSO BRUSHING THE SANTEE COOPER LAKES SW INTO E CENTRAL GEORGIA BUT THIS ACTIVITY HAS BEEN SPOTTY AND LIGHT SO FAR. AN ACTIVE DAY FOR DEEP CONVECTION APPEARS ON TAP ACROSS MUCH OF OUR FORECAST AREA AS A WELL DEFINED SHORT WAVE/ELONGATED MID LEVEL VORT AXIS DROPS SSE INTO THE CAROLINAS. DEEP MOISTURE IS IN PLACE ACROSS OUR REGION WITH PWATS AVERAGING 2.25 INCHES TODAY. EARLY MORNING SATELLITE IMAGERY SHOWS PLENTY OPPORTUNITY FOR ENOUGH MORNING INSOLATION FOR TEMPERATURES TO REACH 90-92 DEGREES WHICH ARE READINGS LIKELY TO INITIATE DEEP CONVECTION. OVERALL MODELS ARE IN VERY GOOD AGREEMENT ON SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS THIS AFTERNOON WITH PLENTY OF BOUNDARIES AVAILABLE FOR PULSE AND MULTICELL STORMS TO MIGRATE ALONG. MID LEVEL TEMPERATURES ARE QUITE WARM AND OVERALL INSTABILITY PARAMETERS LOOK TYPICAL FOR AN ACTIVE MID JULY DAY. MAINLY SUB-SEVERE TSTMS EXPECTED BUT LOCALIZED WET MICROBURSTS CERTAINLY COULD PRODUCE ISOLATED WIND DAMAGE REPORTS BUT WE THINK MOST STORMS SHOULD JUST PRODUCE VERY HEAVY DOWNPOURS AND FREQUENT LIGHTNING STRIKES AS TYPICAL FOR THIS TYPE OF AIR MASS. POPS MOST AREAS BECOMING LIKELY THIS AFTERNOON WITH WIDESPREAD AFTERNOON CLOUDS AND LATE DAY TEMPERATURES LOWERED BY THE NUMEROUS STORMS. THE DIRECT EFFECT OF THE MID LEVEL SHORT WAVE REALLY LOOKS TO BE TONIGHT AND THIS FEATURE MAY KEEP CONVECTION GOING ON THROUGH THE NIGHT IN SOME AREAS. MANY MODELS SHOW THIS TO BE TRUE N OF I-16 AND WE CONTINUED A CHANCE POP GOING MANY AREAS FOR MUCH OF TONIGHT. WE MAINTAINED MENTIONS OF PATCHY SMOKE OVER PARTS OF SE GEORGIA THIS MORNING AND IT MAY NEED TO BE EXTENDED A WHILE LONGER DEPENDING ON OBSERVATIONS AND VISIBLE SATELLITE IMAGERY AFTER SUNRISE. && .SHORT TERM /SUNDAY THROUGH TUESDAY/... ON SUNDAY...THE WEAK FRONT SHOULD ESSENTIALLY WASH OUT OVER THE AREA...BUT THERE WILL STILL BE ENOUGH SURFACE CONVERGENCE AND MID LEVEL MOISTURE TO SUPPORT DECENT CHANCES OF AFTERNOON CONVECTION...ESPECIALLY ALONG AND SOUTH OF THE SAVANNAH RIVER VALLEY WHERE A SHEAR AXIS AT MID LEVELS WILL RESIDE...PROVIDING MODEST SYNOPTIC SCALE SUPPORT FOR CONVECTIVE LIFT. PWS WILL STILL BE AROUND 2 INCHES AS WELL. FOR MONDAY AND TUESDAY...SOME DRIER AIR AT MID AND UPPER LEVELS WILL BUILD IN AND THE RIDGE WILL STRETCH ACROSS THE CWA...SO PRECIP CHANCES WILL DIMINISH TO THE SLIGHT CHANCE OR LOW END CHANCE CATEGORY...AND EVEN THAT MAY TURN OUT TO BE A BIT GENEROUS. PWS DROP BELOW 2 INCHES MONDAY AFTERNOON...AND POSSIBLY BELOW 1 1/2 INCHES BY TUESDAY AFTERNOON. WITH THE BUILDING HEIGHTS COMES SOME SYNOPTIC SCALE SUBSIDENCE...MEANING MORE SUNSHINE. THIS WILL ALLOW MAX TEMPS TO CLIMB TO THE MID TO UPPER 90S AWAY FROM THE COAST...AND WITH DEW POINTS IN THE STEAMY MID 70S...HEAT INDICES WILL GO WELL ABOVE 100. I IMAGINE HEAT ADVISORIES WILL BE NEEDED FOR AT LEAST PORTIONS OF THE AREA MONDAY AND TUESDAY. && .LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/... WEDNESDAY WILL BE ANOTHER VERY WARM DAY WITH HEAT INDICES IN EXCESS OF 100...ALTHOUGH THERE LOOKS TO BE A SLIGHTLY BETTER CHANCE FOR DIURNAL CONVECTION...GIVING A FEW PLACES SOME TEMPORARY COOLING...AS MID LEVEL MOISTURE BEGINS TO RETURN AND THE UPPER LEVEL RIDGE SLOWLY WEAKENS. THE GFS IS MOST AGGRESSIVE WITH THE CHANCES OF PRECIP...BUT EVEN THE SLOWER ECMWF INDICATES SOME THUNDERSTORM ACTIVITY DURING THE TIME OF AFTERNOON MAXIMUM HEATING. TIMING DIFFERENCES BETWEEN THE MODELS MAKE THE END OF THE WEEK SOMEWHAT DIFFICULT FOR DETAILS...BUT THE GENERAL CONCEPT OF A STRONGER FRONT MOVING THROUGH IS SIMILAR. FOR NOW...I AM GOING WITH THE FRONT PASSING THROUGH THE CWA DURING THE DAY ON THURSDAY FROM NORTH TO SOUTH...BUT I COULD BE BRINGING IT THROUGH A BIT QUICK IF THE ECMWF/GEM SOLUTION TURN OUT TO BE BETTER. IN ANY CASE...THE CHANCE OF PRECIP INCREASES AGAIN WITH THE FRONT ON THURSDAY INTO THURSDAY EVENING. THE GFS INDICATES SOME DRYING AND SLIGHT COOLING FOR FRIDAY AND SATURDAY BEHIND THE FRONT...AND I HAVE FOLLOWED THIS SOLUTION FOR NOW. IF THE FRONT IS SLOWER...HOWEVER...I MAY BE COOLING OFF THE OVERNIGHT MINS TOO QUICKLY IN THE CURRENT FORECAST. && .AVIATION /08Z SATURDAY THROUGH WEDNESDAY/... OVERNIGHT...OCCASIONAL MVFR CIGS MAY BRUSH KCHS WITH MAINLY VFR CONDITIONS ANTICIPATED AT KSAV. WE WILL MONITOR FOR VICINITY OF SHOWERS OR TSTMS AT KCHS OVERNIGHT BUT MUCH OF THE ACTIVITY MAY SKIRT JUST OFF TO THE E WHERE CONVERGENCE BOUNDARIES ARE IN PLACE. POTENTIAL FOR TSTMS AT BOTH TERMINALS LOOKS FAIRLY SIGNIFICANT THIS AFTERNOON. TIMING ESTIMATES MAINLY BETWEEN 17Z-23Z. EXTENDED AVIATION...THE BEST CHANCE FOR MVFR/IFR CIGS/VSBYS IS WITH THE CHANCES OF AFTERNOON AND EVENING CONVECTION NEAR THE TERMINALS ON SUN...THEN AGAIN WED AND THU. I THINK THERE MAY BE SOME GROUND FOG/HAZE/SMOKE AROUND IN THE EARLY MORNING HOURS AS WELL...ALTHOUGH I WOULD BE SURPRISED IF CONDITIONS GOT ANY WORSE THAN MVFR. && .MARINE... WE HAVE EXTENDED OUR SMALL CRAFT ADVISORIES FOR THE CHARLESTON COUNTY WATERS AND OUTER GEORGIA WATERS UNTIL MID MORNING AS THE LATEST OBSERVATIONS ARE SOLIDLY IN SCA CRITERIA. BY LATE MORNING THERE SHOULD BE SOME SIGNIFICANT IMPROVEMENTS WITH WINDS BECOMING 15 KT OR LESS AND WIND WAVES COMING DOWN FAIRLY STEADILY. THERE IS STILL A BIT OF A GROUND SWELL OUT THERE AS WELL BUT THE SWELL COMPONENT IS GENERALLY AVERAGING AROUND 2 FT. THE SW FLOW WILL PERSIST THROUGH TONIGHT. WINDS WILL BE COMING DOWN GRADUALLY ON SUNDAY...THEN BE SEASONABLY LIGHT ON MONDAY AND TUESDAY WITH THE HIGH PRESSURE RIDGE NEARBY CAUSING THE SURFACE PRESSURE GRADIENT TO COLLAPSE. WINDS WILL PICK UP A BIT AGAIN ON WEDNESDAY AHEAD OF THE NEXT FRONT. WINDS MAY BE BACK INTO THE 15 TO 20 KNOT RANGE FROM THE NORTHEAST OR EAST BEHIND THE FRONT LATE IN THE WEEK...BUT THE TIMING IS SOMEWHAT UNCERTAIN AT THIS POINT. RESIDUAL MORNING WAVE ACTION ALONG THE SOUTH CAROLINA COAST ALONG WITH THE FACT WE HAVE HAD 2 CONSECUTIVE DAYS OF RIP CURRENT REPORTS FROM TYBEE ISLAND GEORGIA HAS TIPPED US TOWARD A MODERATE RISK OF RIP CURRENTS TODAY. AFTER SOME EARLY LIFEGUARD REPORTS FROM SOME OF OUR BEACHES... WE MAY BE ABLE TO LOWER THE RISK BY THIS AFTERNOON. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...NONE. SC...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 9 AM EDT THIS MORNING FOR AMZ350- 374. && $$