Area Forecast Discussion
Issued by NWS Charleston, SC

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000 FXUS62 KCHS 062026 AFDCHS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHARLESTON SC 326 PM EST FRI MAR 6 2015 .SYNOPSIS... ARCTIC HIGH PRESSURE WILL PREVAIL ACROSS THE AREA THROUGH EARLY SUNDAY...BEFORE IT SHIFTS INTO THE ATLANTIC FOR EARLY NEXT WEEK. AN UNSETTLED PATTERN WILL THEN DEVELOP BETWEEN A STATIONARY FRONT SOUTH AND EAST OF THE REGION AND HIGH PRESSURE CENTERED TO THE NORTH FROM LATE MONDAY OR MONDAY NIGHT THROUGH MUCH OF NEXT WEEK. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... TONIGHT...BASED ON VISIBLE SATELLITE IMAGERY SKIES APPEAR AS THOUGH THEY WILL BEGIN TO CLEAR FROM THE NORTH AND WEST THIS EVENING AS THE CLEARING LINE IS DRAPED JUST UPSTREAM AND THERE ARE SIGNS OF THE STRATUS STARTING TO SCATTER OUT. COLD HIGH PRESSURE CENTERED OVER THE LOWER MISSISSIPPI VALLEY WILL EXTEND ACROSS THE REGION...AND UNDER CLEARING SKIES AND A WEAKENING PRESSURE GRADIENT EXCELLENT RADIATIONAL COOLING CONDITIONS ARE ANTICIPATED. WINDS WILL DECOUPLE AND THE ONGOING FREEZE WARNING/FROST ADVISORY CONTINUES TO LOOK ON TRACK. FORECAST LOWS ARE GENERALLY IN THE UPPER 20S TO THE NORTH AND IN THE LOW 30S TO THE SOUTH...AWAY FROM THE COAST. ONCE THE STRATUS DISSIPATES AND SLIPS OFFSHORE...WE MAY SEE SOME THIN CIRRUS MOVE THROUGH...BUT THIS WILL HAVE NO IMPACT ON OVERNIGHT TEMPERATURES. SCATTERED FROST IS ALSO STILL MENTIONED IN THE FORECAST. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/... SATURDAY...QUASI-ZONAL FLOW ALOFT ATOP WILL CAUSE THE COLD ARCTIC HIGH PRESSURE ANCHORED ACROSS THE LOCAL AREA IN THE MORNING TO SLIDE TOWARD THE COAST BY NIGHTFALL...SUPPORTING A QUIET WEATHER PATTERN. AN EXTREMELY DRY VERTICAL COLUMN WITH PWATS NO MORE THAN 1/4 OR 1/3 INCH WILL SUPPORT PLENTY OF SUNSHINE /ASIDE FROM A FEW LINGERING JET STREAM CIRRUS EARLY IN THE MORNING/. FULL INSOLATION AND LOW LEVEL THICKNESS EXPANDS TO 1336-1345 METERS...PLUS SOME MODIFICATION OF THE AIR MASS WILL GENERATE A WARMER DAY. ALTHOUGH WE/LL STILL BE SOME 5-8F BELOW CLIMATOLOGICAL NORMS...HIGHS WILL RANGE FROM UPPER 50S OR NEAR 60 NORTH TO 62-64 SOUTH. AFTERNOON SEA BREEZE CIRCULATIONS WILL LIMIT THE COASTAL SECTIONS TO THE LOWER 50S NORTH AND MID-UPPER 50S CENTRAL AND SOUTH. SATURDAY NIGHT...SURFACE HIGH PRESSURE WILL PERSIST OVERHEAD ALLOWING FOR RAPID DECOUPLING WITH SUNSET. UNDER MAINLY CLEAR SKIES AND DEW POINTS DOWN IN THE LOWER AND MIDDLE 30S WILL LEAD TO ALMOST PERFECT RADIATIONAL COOLING INLAND FROM THE BARRIER ISLANDS. THIS IN TURN WILL PRODUCE AT LEAST SCATTERED FROST NEAR AND WEST OF US- 17...AND A FROST ADVISORY WILL LIKELY BE REQUIRED. LOWS WILL RANGE FROM 34-37 INLAND TO THE LOWER-MIDDLE 40S ON THE COASTAL COMMUNITIES. SUNDAY...THE SYNOPTIC SITUATION IS CHARACTERIZED BY ZONAL FLOW UPSTAIRS AND THE SURFACE HIGH TO PULL EAST INTO THE ATLANTIC. WARM ADVECTION STARTS TO CRANK UP AS A SOUTH-SW FLOW IN THE LOWER LAYERS DEVELOPS WITH THIS TRANSITIONS...WITH 1000-850 MB THICKNESS TO STRETCH TO 1355-160 METERS. WHILE WE DO SEE AN INCREASE IN MID/HIGH LEVEL CLOUDS...THERE IS STILL SUFFICIENT INSOLATION TO YIELD MAX TEMPS OF 70-72 ACROSS THE MAJORITY OF THE CWFA. THE EXCEPTION WILL BE THE ATLANTIC SEABOARD WHERE HIGHS ARE RESTRICTED TO THE LOWER 60S WITH SEA BREEZE AND ONSHORE SYNOPTIC FLOW. SUNDAY NIGHT AND MONDAY...A SOUTHERN STREAM PERTURBATION WILL PROGRESS THROUGH THE SOUTHERN PLAINS...AS A SUB-TROPICAL RIDGE FROM THE ATLANTIC EXPANDS WEST/NW. THIS WILL INDUCE SLIGHTLY RISING HEIGHTS ALOFT AND ITS ACCOMPANYING WARM ADVECTION. HIGH PRESSURE AT THE SURFACE WILL PULL FURTHER OFFSHORE AS THE OLD BAROCLINIC ZONE AND STATIONARY FRONT TO THE SOUTH BEGINS TO CREEP CLOSER. ISENTROPIC ASCENT WILL DEVELOP AS THIS OCCURS...INITIALLY CAUSING AN INCREASE IN CLOUDINESS. IT/LL TAKE AWHILE FOR THE LOWEST LEVELS TO MOISTEN UP...SO WE HAVE DELAYED THE ONSET OF THE NEXT RAIN EVENT. AT LEAST THE FIRST HALF OF SUNDAY NIGHT WILL BE DRY...BUT WE HAVE SHOWN 20 POPS SOUTH OF I-16 OVERNIGHT. THEN ON MONDAY THE RAIN CHANCES CLIMB FROM SW TO NE...PEAKING IN THE 20 PERCENTILE NORTH AND 30 PERCENTILE SOUTH. NOTICEABLY WARMER SUNDAY NIGHT WITH INSULATING EFFECTS OF THE CLOUDS AND WARM ADVECTION. TEMPS ON MONDAY MIGHT NEED SOME ADJUSTMENTS PENDING HOW QUICKLY THE CLOUDS THICKEN/LOWER AND ARRIVAL OF THE RAIN. FOR NOW WE ARE SHOWING MID AND UPPER 60S INLAND AND CLOSER 60 ON THE BEACHES. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... CONFIDENCE IN THE DETAILS OF THE EXTENDED FORECAST REMAIN RATHER LOW CONSIDERING PERSISTENT MODEL DISCREPANCIES WITHIN A RELATIVELY CHANGEABLE PATTERN. RAIN CHANCES WILL BE DRIVEN BY THE LOCATION OF A LINGERING STATIONARY FRONT AND ANY WAVES OF LOW PRESSURE....AS WELL AS A RIBBON OF DEEP MOISTURE ENHANCED BY CONTINUAL SHORTWAVE ENERGY MOVING UP FROM THE GULF OF MEXICO. WITH THE SOUTHEAST COAST ALONG THE PERIPHERY OF THE SUBTROPICAL RIDGE...THE AXIS OF DEEP MOISTURE WILL LIKELY BE HELD JUST TO THE WEST AND NORTH OF THE FORECAST AREA...WITH BEST RAIN CHANCES ACROSS INLAND AND NORTHERN ZONES AS A RESULT. HAVE INCLUDED RAIN CHANCES IN THE FORECAST FOR THE ENTIRE WEEK...HIGHEST MONDAY NIGHT INTO TUESDAY. OTHERWISE...PREFER TO REMAIN SOMEWHAT GENERIC AND FLEXIBLE REGARDING THE FORECAST...AS RAIN POTENTIAL AND COVERAGE EXPECTATIONS FOR THE MID TO LATE WEEK PERIOD WILL LIKELY CHANGE AS MODELS HOPEFULLY COME INTO BETTER AGREEMENT. HIGH TEMPERATURES WILL GENERALLY REACH THE 60S EACH AFTERNOON...EXCEPT FOR LOW 70S SOUTHEAST GEORGIA ZONES WEDNESDAY AND THURSDAY. LOW TEMPERATURES WILL BE WARMER THAN NORMAL...MAINLY A RESULT OF THE INSULATING EFFECTS OF CLOUD COVER THAT IS EXPECTED TO LINGER THROUGH THE MAJORITY OF THE WEEK. && .AVIATION /20Z FRIDAY THROUGH WEDNESDAY/... MVFR CONDITIONS WILL PERSIST AT BOTH KCHS AND KSAV THROUGH THE REST OF THE AFTERNOON AS MOIST SOUTHWESTERLY FLOW CONTINUES TO OVERRIDE COLD SURFACE AIR. THIS LAYER OF STRATUS WILL ADVECT OFF THE COAST THIS EVENING AND DRY NORTHWESTERLY FLOW FILLS IN AT THE LOW AND MID LEVELS. THERE IS SOME UNCERTAINTY IN THE TIMING OF WHEN THE STRATUS WILL CLEAR...BUT CURRENT THINKING IS THAT THE TRANSITION FROM MVFR TO VFR SHOULD BE SHORTLY BEFORE SUNSET FOR KCHS...WHERE DEEP DRY AIR FROM THE NORTH WILL FILL IN FIRST...AND AROUND SUNSET FOR KSAV. SOME HIGH CIRRUS CLOUDS COULD REMAIN INTO THE NIGHTTIME HOURS...ESPECIALLY AT KCHS...AS AN UPPER LEVEL PASSING OVER THE CAROLINAS MOVES OFF TO THE NORTHEAST. LIGHT WINDS ARE EXPECTED TONIGHT AS THE LOW LEVELS DECOUPLE FROM THE ALREADY MINOR SYNOPTIC FLOW. HIGH PRESSURE BUILDING IN FROM THE WEST WILL KEEP VFR CONDITIONS...IN CLEAR SKIES AND LIGHT WINDS...IN THE FORECAST FOR SATURDAY. EXTENDED AVIATION OUTLOOK...VFR WILL CONTINUE FROM SATURDAY AFTERNOON INTO MONDAY. OCCASIONAL WAVES OF LOW PRESSURE RIDING ALONG A NEARBY STATIONARY FRONT MONDAY NIGHT THROUGH WEDNESDAY COULD BRING PERIODS OF MVFR AND IFR CONDITIONS IN LOW CEILINGS AND RAIN. && .MARINE... THIS EVENING...THE SMALL CRAFT ADVISORIES FOR THE NEAR SHORE WATERS HAVE BEEN EXTENDED THROUGH 7 PM TO ACCOUNT FOR THE PERSISTENTLY TIGHT GRADIENT AND 20-25 KT WINDS OUT CLOSER TO 20 NM OFFSHORE. TONIGHT...AS THE HIGH CONTINUES TO BUILD IN THE PRESSURE GRADIENT WILL WEAKEN A BIT AND ALLOW WINDS TO COME DOWN. EXPECT 15-20 KT WITHIN 20 NM. THE SMALL CRAFT ADVISORY FOR THE OUTER GEORGIA WATERS CONTINUES THROUGH THE OVERNIGHT WHERE CONDITIONS WILL BE MORE LIKE 20-25 KT. SEAS WILL GRADUALLY RELENT AS WELL DUE TO THE DISSIPATING WINDS. SEAS WILL BECOME 3-5 FT OUT TO 20 NM AND 5-7 FT BEYOND BY THE LATTER PART OF THE OVERNIGHT. SATURDAY...THE REMAINING SMALL CRAFT ADVISORY ON THE OUTER GA WATERS IN THE MORNING WILL EXPIRE BY 16Z...AS THE CONTINENTAL HIGH OVER THE SE IN THE MORNING SLIDES TOWARD THE COAST AND COLD ADVECTION FADES IN THE AFTERNOON. NE WINDS WILL PEAK AS HIGH AS 8-12 KT IN CHARLESTON HARBOR AND 13-19 KT OVER THE OPEN ATLANTIC IN THE MORNING...VEERING SOME 20-50 DEGREES IN THE AFTERNOON AS SPEEDS DIMINISH TO LESS THAN 10 OR 15 KT. SEAS UP TO 6 FT BEYOND 40 NM OFF THE GA COAST IN THE MORNING...DROPPING TO 5 FT OR LESS. ELSEWHERE SEAS WILL BE AT OR BELOW 3 OR 4 FT THROUGH THE DAY. SATURDAY NIGHT THROUGH SUNDAY...CONDITIONS WILL BE BENIGN ACROSS THE MARINE COMMUNITY AS THE SURFACE HIGH REMAINS ACROSS THE WATERS. THE END RESULT IS FOR WINDS OF VARYING DIRECTIONS /DRIVEN MAINLY BY LAND BREEZE AND SEA BREEZE CIRCULATIONS/ AT LESS THAN 10 KT AND SEAS RESTRICTED TO MAINLY 3 FT OR LESS. SUNDAY NIGHT AND MONDAY...THE SURFACE HIGH SLIDES FURTHER EAST ACROSS THE ATLANTIC AS A STATIONARY FRONT TAKES SHAPE TO OUR SOUTH. THIS CAUSES S SLOW BUT STEADY TIGHTENING OF THE PRESSURE GRADIENT FROM LATE SUNDAY NIGHT INTO MONDAY...ENOUGH SO THAT NE WINDS CLIMB TO AT LEAST A SOLID 12-18 KT ON MONDAY...MAYBE HIGHER. SEAS WILL HOLD AT 4 FT OR LOWER. FORECAST CONFIDENCE REMAINS RATHER LOW EARLY INTO THE MIDDLE OF NEXT WEEK DUE TO THE UNCERTAINTY REGARDING A FLUCTUATING STATIONARY FRONT AND POSSIBLE WAVES OF LOW PRESSURE TRACKING ALONG THE FEATURE. WILL CONTINUE TO KEEP WINDS/SEAS BELOW ADVISORY LEVELS...HOWEVER ANY CHANGES TO THE LOCATION OF THE FRONT AND/OR THE STRENGTH OF LOW PRESSURE WAVES COULD SUPPORT STRONGER WINDS AND HIGHER SEAS. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...FREEZE WARNING FROM 11 PM THIS EVENING TO 9 AM EST SATURDAY FOR GAZ099>101. FREEZE WARNING FROM 2 AM TO 9 AM EST SATURDAY FOR GAZ114>116- 118-137-138-140. FROST ADVISORY FROM 2 AM TO 9 AM EST SATURDAY FOR GAZ117-119- 139-141. FREEZE WARNING FROM 8 PM THIS EVENING TO 9 AM EST SATURDAY FOR GAZ087-088. SC...FREEZE WARNING FROM 11 PM THIS EVENING TO 9 AM EST SATURDAY FOR SCZ047>052. FREEZE WARNING FROM 8 PM THIS EVENING TO 9 AM EST SATURDAY FOR SCZ040-042>045. MARINE...SMALL CRAFT ADVISORY UNTIL 7 PM EST THIS EVENING FOR AMZ350- 352-354. SMALL CRAFT ADVISORY UNTIL NOON EST SATURDAY FOR AMZ374. && $$ NEAR TERM...BSH SHORT TERM... LONG TERM...WMS AVIATION...CEB MARINE...BSH

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