535  
FXUS62 KCHS 180834  
AFDCHS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHARLESTON SC  
334 AM EST SAT NOV 18 2017  
   
SYNOPSIS
 
 
HIGH PRESSURE WILL PREVAIL TODAY, THEN A COLD FRONT WILL PASS  
THROUGH LATE TONIGHT INTO SUNDAY MORNING. HIGH PRESSURE WILL  
THEN RETURN THROUGH MUCH OF NEXT WEEK, THOUGH A GULF LOW  
PRESSURE SYSTEM COULD IMPACT THE AREA MID TO LATE WEEK.  
 

 
   
NEAR TERM /THROUGH TONIGHT/
 
 
TODAY: ALOFT, THE FORECAST FEATURES WESTERLY FLOW AHEAD OF A  
SHARPENING TROUGH WITHIN A PROGRESSIVE OVERALL PATTERN IN THE  
MID AND UPPER LEVELS. AT THE SURFACE, WE WILL START OUT IN A  
WEAK PRESSURE PATTERN AROUND HIGH PRESSURE OFF THE NORTH  
CAROLINA OUTER BANKS. BY THE AFTERNOON, THE HIGH IS PROGGED TO  
PUSH OFFSHORE AND ITS INFLUENCE WILL WANE AS A STRONG COLD FRONT  
PUSHES INTO THE TENNESSEE VALLEY. SOUTHERLY FLOW WILL STEADILY  
STRENGTHEN THROUGH THE DAY, RESULTING IN A WARM AND BREEZY  
CONDITIONS BY THE MID TO LATE AFTERNOON HOURS. SCATTERED  
STRATOCUMULUS CLOUDS IN THE MORNING WILL DECREASE IN COVERAGE BY  
THE AFTERNOON AND THE FORECAST IS DRY AS THE AREA OF  
CONVERGENCE ALONG THE APPROACHING FRONT WILL REMAIN WELL TO THE  
WEST. TEMPERATURES WILL BE NOTABLY WARMER THAN PREVIOUS DAYS,  
WITH FORECAST HIGHS IN THE LOW TO MID 70S ACROSS MOST OF THE  
AREA. THERE COULD EVEN BE SOME UPPER 70S IN PORTIONS OF  
SOUTHEAST GEORGIA.  
 
TONIGHT: THE COLD FRONT WILL MOVE CLOSER IN THE EVENING AND  
BEGIN TO PUSH INTO THE FAR INLAND ZONES IN DURING THE EARLY  
MORNING HOURS. THE FRONT CONTINUES TO LOOK RELATIVELY MOISTURE  
STARVED AS IT APPROACHES THE FORECAST AREA WITH A WEAKENING BAND  
OF SHOWERS EXPECTED. IN FACT, IT'S HARD TO JUSTIFY MORE THAN  
MID RANGE CHANCE POP'S WITH THIS BOUNDARY, AND IT IS LIKELY THAT  
SOME AREAS DO NOT RECEIVE ANY MEASURABLE RAINFALL. THE FRONT  
SHOULD BE POSITIONED JUST OFFSHORE BY SUNRISE SUNDAY WHICH MEANS  
THE BULK OF THE COLD ADVECTION WILL BE DELAYED BEYOND THE  
TONIGHT PERIOD. THIS WILL RESULT IN LOW TEMPERATURES ONLY  
FALLING INTO THE MID/UPPER 50S FOR MOST AREAS. THOUGH THERE  
COULD BE SOME LOW 50S WELL INLAND RIGHT AT SUNRISE. WINDS WILL  
REMAIN ELEVATED THROUGH THE NIGHT AND WILL ACTUALLY STRENGTHEN  
IMMEDIATELY AHEAD OF THE FRONT WITH THE TIGHTEST PRESSURE  
GRADIENT.  
 

 
   
SHORT TERM /SUNDAY THROUGH TUESDAY/
 
 
THE PRONOUNCED UPPER SHORTWAVE WILL PUSH THE COLD FRONT QUICKLY  
OFFSHORE SUNDAY MORNING. RESIDUAL SHOWERS AND CLOUD COVER  
EXPECTED TO BE OUT OF THE AREA BY NOON SUNDAY. WEAK DOWNSLOPE  
FLOW COMBINED WITH AMPLE SUNSHINE WILL HELP TO OFFSET THE COLD  
AIR ADVECTION, PUSHING HIGH TEMPS INTO THE MID 60S.  
 
EXPANSIVE DRY HIGH PRESSURE WILL EXPAND OVER THE AREA SUNDAY  
NIGHT, YIELDING CLEAR SKIES AND LIGHT WINDS. STRONG RADIATIONAL  
COOLING WILL RESULT, ALLOWING TEMPS TO DROP INTO THE MID 30S  
INLAND AND UPPER 30S TO LOWER 40S CLOSER TO THE COAST. WE MAY  
NEED TO CONSIDER A FROST ADVISORY FOR SUNDAY NIGHT FOR A FEW FAR  
INLAND ZONES WHERE THE WINDS WOULD BE MORE LIKELY TO GO CALM.  
 
COOL HIGH PRESSURE WILL LINGER ON MONDAY, KEEPING HIGHS IN THE  
UPPER 50S TO MID 60S. A DEVELOPING LONGWAVE TROUGH OVER THE  
EASTERN UNITED STATES MONDAY NIGHT INTO TUESDAY WILL YIELD WARM  
AIR ADVECTION AND INCREASING MOISTURE ACROSS THE AREA. A WEAK  
COASTAL TROUGH MAY DEVELOP, SUPPORTING ISOLATED SHOWERS ALONG  
WITH INCREASING LOW CLOUDS.  
 

 
   
LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/
 
 
THE PERIOD LOOKS POTENTIALLY UNSETTLED THOUGH THERE ARE  
SUBSTANTIAL DIFFERENCES IN THE GLOBAL MODELS. A LONGWAVE TROUGH  
WILL ANCHOR OVER THE EASTERN HALF OF THE COUNTRY WITH A SERIES  
OF SURFACE LOWS POSSIBLY SHIFTING UP THE COAST FROM THE GULF.  
GIVEN THE LARGE MODEL SPREAD, WE STARTED BY BUMPING POPS INTO  
THE 20-30% RANGE LATE WEEK.  
 

 
   
AVIATION /09Z SATURDAY THROUGH WEDNESDAY/
 
 
VFR CONDITIONS ARE EXPECTED TO PREVAIL THROUGH 06Z SUNDAY.  
SATELLITE IMAGERY SHOWS EXPANDING VFR STRATOCUMULUS DECK ACROSS  
SOUTHEAST GEORGIA. EXPECT CONDITIONS TO BE SCATTERED BUT THERE  
COULD BE PERIODS OF VFR CEILINGS AT KSAV. OTHERWISE, WINDS WILL  
TURN SOUTHERLY WITH SOME LOW END GUSTS POSSIBLE THIS AFTERNOON.  
 
EXTENDED AVIATION OUTLOOK: VFR.  
 

 
   
MARINE
 
 
TODAY: THE DAY WILL BEGIN WITH HIGH PRESSURE OFF THE NORTH  
CAROLINA OUTER BANKS AND WEAK 5-10 KNOT ONSHORE FLOW THIS  
MORNING. AS WE MOVE INTO THE AFTERNOON, THE HIGH WILL MOVE  
FURTHER OFFSHORE AND THE PRESSURE GRADIENT WILL TIGHTEN AS A  
STRONG COLD FRONT BEGINS TO APPROACH FROM THE WEST. THE  
INCREASED GRADIENT WILL RESULT IN STRENGTHENING SOUTHERLY FLOW,  
TOPPING OUT IN THE 15-20 KNOT RANGE BY THE LATE AFTERNOON HOURS  
ACROSS THE LOCAL WATERS. SEAS ARE EXPECTED TO BE IN THE 2-4 FT  
RANGE THROUGH THE DAY.  
 
TONIGHT: WINDS WILL CONTINUE TO INCREASE AND TURN A BIT MORE  
OUT OF THE SOUTHWEST, SUCH THAT SMALL CRAFT ADVISORIES ARE GOING  
TO BE NEEDED FOR ALL WATERS INCLUDING CHARLESTON HARBOR. THE  
STRONGEST WINDS WILL FIRST IMPACT THE CHARLESTON COUNTY WATERS  
IN THE EVENING, BUT WILL STEADILY INCREASE ACROSS ALL ZONES  
THROUGH THE EARLY MORNING HOURS. GUSTS TO AROUND 30 KNOTS ARE  
EXPECTED IN THE CHARLESTON COUNTY WATERS, WITH A MORE SOLID  
20-25 KNOTS OF FLOW ELSEWHERE. SEAS WILL INCREASE IN RESPONSE,  
BECOMING 4-6 FEET BEYOND ABOUT 10 NM OFFSHORE LATE TONIGHT.  
 
LOW-LEVEL WINDS WILL QUICKLY DIMINISH ON SUNDAY BEHIND THE COLD  
FRONT. WE EXPECT THE SMALL CRAFT ADVISORY WINDS TO SUBSIDE BY  
LATE SUNDAY MORNING. HIGH PRESSURE BUILDING FROM THE NORTHWEST  
WILL PRODUCE AN EXTENDED PERIOD OF NORTHEAST WINDS NEXT WEEK.  
THE GRADIENT IS EXPECTED TO INCREASE MID TO LATE WEEK, WITH  
MARGINAL SMALL CRAFT ADVISORY WINDS AND/OR SEAS POSSIBLE OVER  
PORTIONS OF THE WATERS WEDNESDAY NIGHT THROUGH FRIDAY.  
 

 
   
CHS WATCHES/WARNINGS/ADVISORIES
 
 
GA...NONE.  
SC...NONE.  
MARINE...SMALL CRAFT ADVISORY FROM 2 AM TO 7 AM EST SUNDAY FOR AMZ330.  
SMALL CRAFT ADVISORY FROM 11 PM THIS EVENING TO NOON EST  
SUNDAY FOR AMZ352-354-374.  
SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO NOON EST SUNDAY  
FOR AMZ350.  
 

 
 

 
 
NEAR TERM...BSH  
SHORT TERM...JRL  
LONG TERM...JRL  
AVIATION...BSH/JRL  
MARINE...BSH/JRL  
 
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