Area Forecast Discussion
Issued by NWS Charleston, SC

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000 FXUS62 KCHS 302317 AFDCHS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHARLESTON SC 717 PM EDT THU OCT 30 2014 .SYNOPSIS... HIGH PRESSURE WILL WEAKEN OVER THE AREA THROUGH FRIDAY. A STRONG COLD FRONT WILL SWEEP THROUGH THE REGION FRIDAY NIGHT...FOLLOWED BY ANOTHER HIGH PRESSURE BUILDING FROM THE WEST OVER THE WEEKEND. THE HIGH WILL SETTLE ALONG THE SOUTHEAST COAST EARLY NEXT WEEK...BEFORE SHIFTING OFFSHORE DURING THE MIDDLE OF NEXT WEEK AS ANOTHER COLD FRONT APPROACHES. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
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QUITE A CHANGE IN AIR MASS FROM THIS TIME YESTERDAY...WITH MORE TYPICAL LATE OCTOBER WEATHER NOW IN PLACE. A NEARLY STATIONARY FRONT OFF THE SE COAST WILL OSCILLATE AND EVENTUALLY SHIFT EAST OVERNIGHT AS A FAIRLY PROMINENT SHORT WAVE ALOFT ARRIVES FROM THE WEST AND CAUSES A SURFACE WAVE TO DEVELOP ALONG THE FRONT NEAR OR EAST OF THE GULF STREAM WATERS. THE BEST FORCING AND BETTER HEIGHT FALLS LOOK TO OCCUR IN THE ATLANTIC...SO FOR NOW WE HAVE MAINTAINED A RAIN-FREE FORECAST OVER LAND. HOWEVER...GIVEN ISENTROPIC ASCENT ON THE 295K SURFACE AND SOME BACKING OF THE TRAJECTORIES TO THE SW IN THE MID LEVELS WE CERTAINLY NEED TO MAINTAIN A SHARP EYE ON RADAR TRENDS AS THERE WILL BE TIGHT GRADIENT FROM WHERE IT RAINS TO WHERE IT DOESN/T. AND WE MAY NEED TO CONSIDER AT LEAST SMALL POPS OVER THE COASTAL ZONES IN FUTURE UPDATES. OTHER GRADIENTS THAT WILL BE MOST NOTABLE INCLUDE THE SKY COVER AND TEMP GRIDS. SKIES WILL RANGE FROM CLEAR OR MOSTLY CLEAR FAR INLAND...PARTLY CLOUDY CENTRAL ZONES...AND PARTLY-MOSTLY CLOUDY EXTREME EAST. TEMPS WILL BE SIMILARLY DELINEATED...RANGING FROM MID AND UPPER 40S WELL INLAND TO THE MID AND UPPER 50S ALONG THE COAST.
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&& .SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/...
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FRIDAY...A SHARPENING UPPER LEVEL TROUGH TAKES SHAPE OVER THE EASTERN 1/3 OF THE COUNTRY...WHICH WILL SET THE STAGE FOR THE COLDEST AIR OF THE SEASON FOR THE WEEKEND AND EARLY NEXT WEEK. THE REGION WILL BE BETWEEN A WEAK WAVE OF LOW PRESSURE MOVING AWAY TO THE NORTHEAST OVER THE ATLANTIC AND AN UPPER SHORTWAVE IN THE BASE OF THE LARGER TROUGH MOVING TOWARD THE AREA FROM THE NORTHWEST. EXPECT MOST OF FRIDAY TO BE DRY BETWEEN THESE SYSTEMS...BUT CLOUDS WILL BE ON THE INCREASE BY AFTERNOON AS THE UPPER TROUGH MOVES INTO THE AREA. IT WILL BE THE WARMEST DAY OF THE PERIOD BEFORE THE BIG COOL DOWN...WITH HIGHS NEAR NORMAL IN THE LOWER 70S. BY FRIDAY NIGHT...A STRONG UPPER TROUGH DIGS SOUTHWARD...REACHING JUST NORTH OF THE AREA BY SUNRISE. MOST OF THE MOISTURE SKIRTS ACROSS THE NORTHERN 1/3 OF THE AREA. HAVE KEPT SLIGHT CHANCE POPS FOR SHOWERS. THE LEADING EDGE OF THE STRONG POLAR FRONT WILL BE JUST REACHING THE COAST BY SUNRISE. THUS...LOWS WILL BE COOLER...BUT NOT AS COLD AS THE NEXT FEW NIGHTS...IN THE LOWER TO MID 40S. SATURDAY...A VERY COOL AND BLUSTERY DAY IS EXPECTED. THE STRONG UPPER TROUGH MOVES ACROSS THE NORTHERN FORECAST AREA...WHICH IS WHERE THE BEST DEEP LAYER MOISTURE WILL ALSO RESIDE. EXPECT SCATTERED SHOWERS ACROSS THE NORTHERN 1/3 OF THE AREA UNDER THE UPPER LOW. MODEL SOUNDINGS STILL SUPPORT THE CHANCE FOR SOME FROZEN PRECIP/GRAUPEL...BUT NO ACCUMULATIONS EXPECTED...AND OVERALL LIQUID QPF AMOUNTS EXPECTED TO BE MAINLY 0.2 INCHES OR LESS. HIGHS WILL STRUGGLE TO GET OUT OF THE LOWER 50S...AND WOULD NOT BE SURPRISED IF THEY HELD AROUND 50 IF THE CLOUDS ARE THICK ENOUGH WITH STRONG COLD ADVECTION. WINDS WILL BE VERY BREEZY...WITH 15-25 MPH SUSTAINED AND GUSTS 30 TO 35 MPH. SATURDAY NIGHT...A STRONG SURFACE RIDGE BUILDS FROM THE NORTHWEST...AND WITH CLEARING SKIES AND WEAKENING PRESSURE GRADIENT...WILL ALLOW WINDS TO GRADUALLY DROP OFF. STILL EXPECT SOME LIGHT WINDS OF 5 TO 10 MPH MOST OF NIGHT...BUT WILL DROP TO VERY LIGHT WELL INLAND. LOWS WILL BE QUITE COLD...IN THE MID TO UPPER 30S...EXCEPT LOWER TO MID 40S COAST. COULD BE SOME PATCHY FROST WELL INLAND ACROSS WIND PROTECTED AREAS. SUNDAY...THE SURFACE RIDGE BUILDS RIGHT OVER THE REGION AS THE UPPER RIDGE AXIS BUILDS OVER THE MID ATLANTIC AND SOUTHEAST. STILL EXPECT COOL MAX TEMPERATURES...ONLY IN THE UPPER 50S TO AROUND 60 UNDER MOSTLY SUNNY SKIES. BY SUNDAY NIGHT...PROBABLY THE COLDEST TEMPERATURES OF THE SEASON AS THE SURFACE RIDGE IS NEARLY PERFECTLY POSITIONED OVER THE REGION FOR IDEAL RADIATIONAL COOLING UNDER CLEAR SKIES. EXPECT LOWS IN THE LOWER TO MID 30S MOST INLAND AREAS. RIGHT NOW...CHANCES FOR WIDESPREAD FROST SEEM TO BE INCREASING GIVEN SURFACE DEW POINT TEMPERATURES SHOWN BY GUIDANCE TO BE 30 TO 32 DEGS. LAKE WINDS...A STRONG COLD FRONT WILL MOVE ACROSS THE AREA BY EARLY SATURDAY...WHICH IS EXPECTED TO PRODUCE STRONG WINDS OF 20 TO 25 KT AND GUSTS AROUND 30. STRONG WINDS AND ROUGH WAVES WILL LIKELY PERSIST INTO THE FIRST PART OF SATURDAY NIGHT BEFORE SUBSIDING. A LAKE WIND ADVISORY IS EXPECTED TO BE ISSUED WITH LATER FORECASTS.
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&& .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... MEDIUM RANGE GUIDANCE IS IN GOOD AGREEMENT WITH THE GENERAL SYNOPTIC PATTERN THROUGH THE LONG TERM PERIOD. IN THE MID AND UPPER LEVELS OF THE ATMOSPHERE...A STRONG RIDGE WILL SHIFT EASTWARD AND EXPAND OVER THE REGION EARLY NEXT WEEK...BEFORE SHIFTING INTO THE ATLANTIC AS A TROUGH APPROACHES FROM THE WEST DURING THE MIDDLE OF THE WEEK. MEANWHILE AT THE SURFACE...STRONG HIGH PRESSURE WILL SETTLE ALONG THE SOUTHEAST COAST EARLY NEXT WEEK THEN SHIFT INTO THE ATLANTIC BY MID-WEEK...WITH A COASTAL TROUGH POSSIBLY DEVELOPING WEDNESDAY BEFORE A COLD FRONT MOVES THROUGH THURSDAY. OVERALL...THIS PATTERN WILL FAVOR RAIN-FREE CONDITIONS EARLY IN THE WEEK...WITH A SLIGHT CHANCE FOR SHOWERS WEDNESDAY WITH THE COASTAL TROUGH/ONSHORE FLOW AND THURSDAY WITH THE COLD FRONT. PATCHY FROST COULD OCCUR INLAND FROM THE COAST SUNDAY NIGHT...WITH SOME FREEZING TEMPERATURES POSSIBLE IN WELL SHELTERED LOCATIONS AS WELL. THEN...TEMPERATURES WILL MODERATE THROUGH THE REMAINDER OF THE LONG TERM PERIOD RETURNING TO NEAR OR SLIGHTLY ABOVE NORMAL BY THE MIDDLE OF NEXT WEEK. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/...
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MVFR CEILINGS WILL ATTEMPT TO ADVECT INTO OR FORM OVER THE TERMINALS LATER TONIGHT INTO FRIDAY MORNING IN RESPONSE TO A DEVELOPING AREA OF LOW PRESSURE IN THE ATLANTIC. FOR NOW THOUGH WE ARE CONTINUING WITH A VFR FORECAST THROUGH 00Z SATURDAY WITH NO CLEAR INDICATORS OF HOW FAR WEST THESE LOWER CEILINGS WILL BE FROM OFF THE OCEAN. EXTENDED AVIATION OUTLOOK... A STRONG UPPER TROUGH AND ASSOCIATED SURFACE COLD FRONT WILL MOVE ACROSS THE AREA LATE FRIDAY NIGHT AND SATURDAY. PERIODS OF MVFR CONDITIONS POSSIBLE MAINLY FOR KCHS WITH SCATTERED SHOWERS. WINDS WILL BE QUITE STRONG...WITH WEST- NORTHWEST SUSTAINED 20 TO 25 KT AND GUSTS AROUND 30 KT POSSIBLE. CONDITIONS EXPECTED TO IMPROVE LATER SATURDAY NIGHT AND SUNDAY WITH A RETURN TO VFR CONDITIONS SUNDAY INTO EARLY NEXT WEEK.
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&& .MARINE...
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TONIGHT...A STALLED OUT FRONT ALIGNED NORTH/NE TO SOUTH/SW AND OUT EAST OF THE GULF STREAM WILL CONTINUE THROUGH THE NIGHT...AWAITING FOR A MID LEVEL IMPULSE/S ENERGY TO SPARK A SURFACE LOW ABOUT 100 MILES OFF THE SC COAST LATE. THIS ALONG WITH AN INCREASE IN COOL ADVECTION...PLUS A PACKING OF THE GRADIENT WILL ALLOW FOR SOME HIGHER WINDS TO DEVELOP WITH TIME. WE/LL START THE NIGHT WITH NORTH/NE WINDS OF 10-17 KT OVER THE ATLANTIC AND 5-10 KT IN CHARLESTON HARBOR...THEN SLIGHT BACKING WILL TRANSPIRE OVERNIGHT AS SPEEDS CLIMB UPWARDS TO 13-20 KT IN THE OCEAN LATE AND UP NEAR 10-12 KT IN THE HARBOR. SEAS WILL BEGIN THE NIGHT AT 2-3 FT...BUILDING ABOUT A FOOT OR SO AFTER MIDNIGHT. ISOLATED TO SCATTERED SHOWERS WILL FORM DURING THE LATE EVENING AND OVERNIGHT HOURS...WITH MAYBE SOME T-STORMS OUT NEAR THE GULF STREAM WHERE THE BEST INSTABILITY WILL BE FOUND. FRIDAY THROUGH TUESDAY... NO HIGHLIGHTS FRIDAY BUT CONDITIONS WILL GO DOWNHILL FOR LATE FRIDAY NIGHT AND SATURDAY AS A STRONG COLD FRONT MOVES THROUGH. EXPECT WINDS TO INCREASE TO GALE CONDITIONS BY VERY LATE FRIDAY NIGHT AND EARLY SATURDAY MORNING. EXACT TIMING OF THE POTENTIAL GALE CONDITIONS A LITTLE UNCERTAIN RIGHT NOW...BUT THINK BY AFTER SUNRISE SATURDAY MOST MARINE AREAS WILL BE EXPERIENCING GALE/NEAR GALE CONDITIONS...ESPECIALLY WITH WIND GUSTS. THUS...HAVE RAISED A GALE WATCH FOR THE ATLANTIC WATERS LATE FRIDAY NIGHT THROUGH THE FIRST PART OF SATURDAY NIGHT. HAVE GONE WITH A SMALL CRAFT ADVISORY FOR THE HARBOR FOR NOW...BUT MONITORING THE POTENTIAL FOR GALE CONDITIONS THERE TOO. WINDS AND SEAS WILL GRADUALLY DECREASE LATER SATURDAY NIGHT AND EARLY SUNDAY...AND SHOULD SEE CONDITIONS FALL BELOW ANY HIGHLIGHTS BY LATER SUNDAY. HIGH PRESSURE BUILDS OVER THE WATERS MONDAY AND TUESDAY WITH WINDS 15 KT OR LESS AND SEAS 4 FT OR LESS.
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&& .CLIMATE... RECORD LOW MAX TEMPERATURES FOR SAT NOV 1... KCHS 56 /1993/... KSAV 52 /1925/... KCXM 52 /1925/... && .CHS WATCHES/WARNINGS/ADVISORIES...
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GA...NONE. SC...NONE. MARINE...SMALL CRAFT ADVISORY FROM 5 AM EDT SATURDAY TO 7 AM EST SUNDAY FOR AMZ330. GALE WATCH FROM LATE FRIDAY NIGHT THROUGH LATE SATURDAY NIGHT FOR AMZ350-352-354-374.
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&& $$ NEAR TERM... SHORT TERM...RFM LONG TERM...JAQ AVIATION... MARINE... CLIMATE...

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