624  
FXUS62 KCHS 211128  
AFDCHS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHARLESTON SC  
728 AM EDT SAT OCT 21 2017  
   
SYNOPSIS
 
 
STRONG HIGH PRESSURE WILL SHIFT OFFSHORE THIS WEEKEND. A COLD  
FRONT WILL THEN MOVE THROUGH MONDAY NIGHT INTO TUESDAY WITH A  
STRONGER BUT DRY COLD FRONT TO MOVE THROUGH TUESDAY NIGHT. HIGH  
PRESSURE WILL THEN PREVAIL INTO LATE NEXT WEEK.  
 

 
   
NEAR TERM /THROUGH TONIGHT/
 
 
AS OF 725 AM: LATEST SATELLITE IMAGES INDICATE THAT THICKER  
CIRRUS CLOUDS WERE LIFTING NORTH ACROSS SOUTHERN AND  
SOUTHEASTERN GA. I WILL ADJUST THE TIMING AND COVERAGE OF THE  
SKY FORECAST THROUGH THE REST OF THIS MORNING. OTHERWISE, THE  
CURRENT FORECAST APPEARS IN GOOD SHAPE.  
 
AS OF 630 AM: SURFACE OBSERVATIONS INDICATED ONLY SPOTTY  
FOG/GROUND FOG EARLY THIS MORNING. I WILL UPDATE THE FORECAST TO  
LIMIT THE MENTION OF FOG TO AROUND RIVERS AND LAKES.  
 
AS OF 330 AM: GROUND FOG IS EXPECTED TO DISSIPATE WITHIN A HALF HOUR  
TO HOUR AFTER SUNRISE THIS MORNING. LATEST IR SATELLITE IMAGES  
INDICATED THAT THIN CIRRUS WAS APPROACHING THE FORECAST AREA FROM  
THE WEST. FORECAST SOUNDINGS INDICATE THAT THE CLOUD COVER WILL  
REMAIN VERY THIN THROUGH THE DAY, BUT MAY THICKEN TONIGHT AS THE H5  
TROUGH SWINGS OVER THE ARKLATX. THE CENTER OF A LARGE SFC HIGH WILL  
SHIFT OFF THE COAST OF THE MID ATLANTIC STATES BY THIS AFTERNOON,  
THEN PUSHING NE THROUGH TONIGHT. THE PRESSURE PATTERN ACROSS THE  
FORECAST AREA WILL REMAIN UNDER RIDGING, HOWEVER, THE PRESSURE  
GRADIENT SHOULD INCREASE SLIGHTLY STARTING THIS EVENING. THE SURFACE  
PATTERN IS EXPECTED TO SUPPORT ONSHORE FLOW TODAY, THEN BACKING FROM  
THE ENE OVERNIGHT. HIGH TEMPERATURES ARE FORECAST TO RANGE IN THE  
LOW 80S AS LOW TEMPERATURES RANGE FROM AROUND 60 INLAND TO NEAR 70  
ACROSS THE BEACHES.  
 

 
   
SHORT TERM /SUNDAY THROUGH TUESDAY/
 
 
A COASTAL TROUGH WILL PUSH INLAND ACROSS THE AREA SUNDAY AND THE  
ASSOCIATED ISENTROPIC ASCENT, LOW-LEVEL CONVERGENCE AND MOISTURE  
WILL LEAD TO SOME SHOWERS. THE TROUGH SHOULD MOVE WELL INLAND AND  
DISSIPATE BY SUNDAY NIGHT BUT STRENGTHENING LOW-LEVEL ONSHORE FLOW  
AND DEEPER MOISTURE MOVING IN FROM THE SOUTHWEST AHEAD OF AN  
APPROACHING COLD FRONT/UPPER TROUGH WILL CAUSE AN INCREASE IN RAIN  
CHANCES/AMOUNTS SUNDAY NIGHT AND ESPECIALLY MONDAY/MONDAY NIGHT.  
ALTHOUGH LOW-LEVEL SHEAR/HELICITY WILL BE ON THE INCREASE MONDAY,  
INSTABILITY WILL LIKELY BE MARGINAL AND THUS THE RISK FOR SEVERE  
THUNDERSTORMS IS LOW. TEMPERATURES WILL REMAIN ABOVE NORMAL THROUGH  
THE PERIOD, EVEN THROUGH TUESDAY GIVEN THE DOWNSLOPE WINDS AND  
SLACKING COLD ADVECTION.  
 

 
   
LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/
 
 
A STRONG COLD FRONT WILL MOVE THROUGH TUESDAY NIGHT AS A BROAD UPPER  
TROUGH ENVELOPES THE EASTERN U.S. DRY, BUT COOLER CONDITIONS WILL  
THEN PREVAIL THROUGH THURSDAY BEFORE SOME MODERATION OCCURS LATE IN  
THE WEEK AS HIGH PRESSURE QUICKLY SHIFTS OFFSHORE ALLOWING A MILDER  
RETURN FLOW TO SET UP. SOME UNCERTAINTY IN THE LONGER RANGE MODEL  
GUIDANCE IMPLIES LOWER FORECAST CONFIDENCE LATE NEXT WEEK BUT COULD  
SEE SOME RAIN RETURN TO THE AREA SATURDAY. TEMPERATURES WILL BE  
MOSTLY BELOW NORMAL THROUGH THURSDAY NIGHT BEFORE POSSIBLY RISING  
CLOSER TO OR EVEN ABOVE NORMAL THROUGH THE END OF THE WEEK. SOME  
INLAND LOCALES SHOULD GET INTO THE 40S EACH MORNING FROM WEDNESDAY  
THROUGH FRIDAY.  
 

 
   
AVIATION /12Z SATURDAY THROUGH WEDNESDAY/
 
 
VFR CONDITIONS WILL PREVAIL AT BOTH KCHS AND KSAV THROUGH 12Z  
SUNDAY. MID AND HIGH CLOUDS WILL INCREASE FROM FEW THIS MORNING  
TO SCT TO BKN BY 12Z SUNDAY.  
 
EXTENDED AVIATION OUTLOOK: BRIEF FLIGHT RESTRICTIONS ARE POSSIBLE  
SUNDAY DUE TO LOW CLOUDS/LIGHT SHOWERS. HIGHER CHANCES OF FLIGHT  
RESTRICTIONS ARE EXPECTED SUNDAY NIGHT INTO TUESDAY AS A COLD FRONT  
AFFECTS THE AREA WITH HEAVIER SHOWERS AND POTENTIALLY SOME  
THUNDERSTORMS. BREEZY/GUSTY WINDS ALSO POSSIBLE  
TUESDAY/WEDNESDAY.  
 

 
   
MARINE
 
 
TODAY AND TONIGHT: THE CENTER OF A LARGE SFC HIGH WILL SHIFT OFF THE  
COAST OF THE MID ATLANTIC STATES BY THIS AFTERNOON, THEN PUSHING NE  
THROUGH TONIGHT. THE PRESSURE PATTERN ACROSS THE COASTAL WATERS WILL  
REMAIN UNDER RIDGING, HOWEVER, THE PRESSURE GRADIENT SHOULD INCREASE  
SLIGHTLY STARTING THIS EVENING. THE SURFACE PATTERN IS EXPECTED TO  
SUPPORT ENE WINDS THROUGH TONIGHT. WAVE HEIGHTS TODAY ARE FORECAST  
TO RANGE BETWEEN 2-3 FEET WITHIN 20 NM, AROUND 4 FEET ACROSS AMZ374.  
TONIGHT, WAVE HEIGHTS ARE EXPECTED TO GRADUALLY INCREASE, WITH 6 FT  
WAVES REACHING THE OUTER PORTION OF AMZ374 LATE TONIGHT.  
 
SUNDAY THROUGH THURSDAY: CONDITIONS WILL DETERIORATE A BIT THIS  
WEEKEND AS A COLD FRONT APPROACHES FROM THE WEST AND LIKELY MOVES  
THROUGH EARLY TUESDAY. ANOTHER STRONGER COLD FRONT WILL THEN MOVE  
THROUGH TUESDAY NIGHT. A SMALL CRAFT ADVISORY WILL LIKELY BE NEEDED  
FOR THE NEARSHORE/OFFSHORE WATERS MONDAY INTO TUESDAY AND INTO  
WEDNESDAY MORNING BEYOND 20 NM AS SEAS REACH 6+ FEET.  
 
RIP CURRENTS...ONSHORE WINDS, SMALL SWELLS, AND LINGERING  
ASTRONOMICAL INFLUENCES WILL SUPPORT A MODERATE RISK OF RIP CURRENTS  
AT THE GA BEACHES TODAY. CONDITIONS WILL BE CLOSE TO A MODERATE RISK  
ON THE SC BEACHES, BUT THE WIND SPEED IS A LITTLE LESS THAN FURTHER  
SOUTH, SO A LOW RISK IS MAINTAINED FOR NOW.  
 

 
   
CHS WATCHES/WARNINGS/ADVISORIES
 
 
GA...NONE.  
SC...NONE.  
MARINE...NONE.  
 

 
 

 
NEAR TERM...BSH/NED  
SHORT TERM...RJB  
LONG TERM...RJB  
AVIATION...NED/RJB  
MARINE...NED/RJB  
 
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