944  
FXUS62 KCHS 260212  
AFDCHS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHARLESTON SC  
1012 PM EDT SUN OCT 25 2020  
   
SYNOPSIS
 
 
A WEAK COLD FRONT WILL SLIDE ACROSS THE REGION TONIGHT. HIGH  
PRESSURE IS FORECAST TO LINGER THROUGH THE MIDDLE OF THE WEEK.  
A STORM SYSTEM IS EXPECTED TO BRING IMPACTS TO THE REGION LATE  
IN THE WORK WEEK. HIGH PRESSURE SHOULD RETURN TO THE REGION BY  
NEXT WEEKEND, RESULTING IN FAIR WEATHER.  
 

 
   
NEAR TERM /UNTIL 6 AM MONDAY MORNING/
 
 
THERE WILL BE A SMALL RISE IN HEIGHTS OVERNIGHT IN WAKE OF A  
SUBTLE SHORT WAVE THAT CONTINUES TO MOVE FURTHER OFFSHORE, AS  
THE FLOW BECOMES ZONAL. MEANWHILE, A COLD FRONT CONTINUES TO  
PROGRESS SOUTH AND WILL CLEAR THE ENTIRE FORECAST REGION BY  
AROUND 06Z, AS A HIGH PRESSURE WEDGE BUILDS IN ITS WAKE. THIS  
WILL FINALLY ALLOW FOR THE LAST OF THE ISOLATED SOUTH CAROLINA  
SHOWERS TO HAVE COME TO AN END.  
 
THE LEADING EDGE OF THAT WEDGE WAS FOUND ACROSS MUCH OF THE  
CHARLESTON QUAD-COUNTY DISTRICT AND ALLENDALE AND HAMPTON  
COUNTY PRIOR TO MIDNIGHT, BUT WILL PROGRESS FURTHER SOUTH  
OVERNIGHT. THIS WILL ALLOW FOR STRATUS TO DEVELOP, BUILD DOWN  
WITH TIME, AND GIVEN A SATURATED BOUNDARY LAYER ENVIRONMENT WILL  
LEAD TO THE FORMATION OF PATCHY DRIZZLE, PLUS PATCHY OR AREAS  
OF FOG.  
 
COOL ADVECTION IS WEAK, BUT THERE WILL BE ENOUGH OF A CHANGE IN  
AIR MASS TO ALLOW FOR MIN TEMPS TO GET DOWN TO 60-65F MOST  
PLACES INLAND FROM US-17, WITH MID AND UPPER 60S CLOSER TO THE  
COAST.  
 

 
   
SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/
 
 
MONDAY: THE CENTER OF A H5 RIDGE WILL SLIDE FROM FL MONDAY MORNING  
EAST OVER THE WESTERN ATLANTIC BY THE AFTERNOON. H5 HEIGHTS OVER THE  
FORECAST AREA WILL INCREASE TO AROUND 590 DM. AT THE SFC, THE CENTER  
OF HIGH PRESSURE WILL BUILD SOUTH OVER THE WESTERN CAROLINAS DURING  
THE AFTERNOON. CONDITIONS ACROSS THE FORECAST AREA ARE FORECAST TO  
REMAIN DRY. HIGH TEMPERATURES ARE EXPECTED TO RANGE FROM THE UPPER  
70S ACROSS THE SC LOWCOUNTRY TO THE LOW 80S ACROSS SE GA.  
 
TUESDAY AND WEDNESDAY: THE MID-LEVEL PATTERN WILL BE DOMINATED BY A  
STRONG RIDGE OVER THE WESTERN ATLANTIC AND A DEEP LOW SWINGING EAST  
ACROSS THE SOUTHERN PLAINS. BETWEEN THESE TWO FEATURES, TC ZETA IS  
EXPECTED TO LIFT NORTH ACROSS THE GULF OF MEXICO. BASED ON NHC  
FORECAST, ZETA WILL MAKE LANDFALL NEAR THE MISSISSIPPI DELTA  
WEDNESDAY PM. MOISTURE IS EXPECTED TO GRADUALLY INCREASE ACROSS THE  
FORECAST AREA TUESDAY AND WEDNESDAY, APPROACHING FROM THE SOUTH.  
ISOLATED TO SCATTERED SHOWERS ARE POSSIBLE EACH DAY, ESPECIALLY  
DURING THE AFTERNOON AND EVENING. TEMPERATURES ARE FORECAST TO  
REMAIN ABOVE NORMAL. BASED ON A BLEND OF MOS, LOW TEMPERATURES ARE  
FORECAST TO RANGE IN THE LOW TO MID 60S. HIGH TEMPERATURES WILL  
GENERALLY RANGE IN THE LOW TO MID 80S.  
 

 
   
LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/
 
 
MID-LEVEL HIGH PRESSURE LOCATED OFFSHORE WILL MOVE AWAY ON THURSDAY.  
MEANWHILE, A STRONG TROUGH WILL APPROACH FROM THE WEST ON THURSDAY,  
THEN PASS OVERHEAD OR JUST TO OUR NORTH ON FRIDAY. ZONAL FLOW IS  
EXPECTED ON SATURDAY. AT THE SURFACE, A STORM SYSTEM WILL CROSS  
THROUGH OUR REGION THURSDAY INTO THURSDAY NIGHT, BRINGING RAINFALL.  
CONDITIONS DRY OUT FRIDAY AS HIGH PRESSURE BUILDS IN FROM THE WEST,  
AND REMAIN DRY INTO SATURDAY. TEMPERATURES WILL BE COLDER BEHIND THE  
FRONT.  
 

 
   
AVIATION /02Z MONDAY THROUGH FRIDAY/
 
 
KCHS WILL FLUCTUATE BETWEEN VFR AND MVFR EARLY TONIGHT, WHILE  
KSAV WILL TRANSITION FROM VFR EARLY TONIGHT TO MVFR OVERNIGHT.  
BOTH SITES WILL EVENTUALLY DROP TO IFR OR EVEN POTENTIALLY LIFR  
LATE TONIGHT INTO MONDAY MORNING. THIS OCCURS AS THE HIGH  
PRESSURE WEDGE DEVELOPS IN WAKE OF A COLD FRONT, WITH A MODEST  
WEDGE INVERSION TO FORM AND TRAP CONSIDERABLE MOISTURE  
UNDERNEATH. EXPECT STRATUS BUILD DOWN, ALONG WITH PATCHY DRIZZLE  
AND MAYBE A LITTLE FOG, WITH THE WORST CONDITIONS ROUGHLY  
07-15Z MONDAY, ALTHOUGH IT CERTAINLY COULD OCCUR EARLIER AS  
WELL.  
 
VFR WILL THEN RETURN FOR MONDAY AFTERNOON, MAYBE TAKING A  
LITTLE LONGER TO DO SO AT KSAV THAN AT KCHS, AS THE INVERSION  
WEAKENS AND RISES, AND MOISTURE BEGINS TO SLOWLY SCOUR OUT.  
 
EXTENDED AVIATION OUTLOOK: BRIEF RESTRICTIVE CEILINGS AND FOG MAY  
DEVELOP ACROSS THE TERMINALS AROUND DAWN TUESDAY. A STORM SYSTEM IS  
EXPECTED TO BRING FLIGHT RESTRICTIONS WEDNESDAY INTO THURSDAY.  
 

 
   
MARINE
 
 
OVERNIGHT: A HIGH PRESSURE RIDGE WILL BUILD FROM THE NORTH,  
BEHIND A COLD FRONT THAT PUSHES SOUTH OF THE LOCAL WATERS. THIS  
WILL ALLOW FOR E AND NE WINDS TO BACK AROUND TO THE N AND NE,  
WITH SPEEDS TO INCREASE TO AS HIGH AS AROUND 12-17 KT. SEAS WILL  
RISE TO AS MUCH AS 3 OR 4 FEET WITHIN 20 NM AND HOLD AROUND 4 OR  
5 FEET FURTHER OFFSHORE. THERE IS A CHANCE THAT AFTER THE LOWER  
STRATUS MOVES IN THAT THERE COULD BE SOME MINOR REDUCTION IN  
VISIBILITY IN CHARLESTON HARBOR.  
 
MONDAY THROUGH FRIDAY: SFC HIGH PRESSURE WILL REMAIN RIDGED ACROSS  
THE MARINE ZONES MONDAY AND TUESDAY. CONDITIONS WILL FEATURE A  
STEADY NE WIND AND SEAS BETWEEN 2-4 FT. BASED ON NHC FORECAST, TC  
ZETA WILL MAKE LANDFALL NEAR THE MISSISSIPPI RIVER DELTA WED PM,  
TRACKING NE TO THE SOUTHERN APPALACHIANS ON THURSDAY. WINDS WILL  
SHIFT FROM THE SE ON WEDNESDAY, SPEEDS BETWEEN 10-15 KTS. THE  
PRESSURE GRADIENT WILL BEGIN TO TIGHTEN ACROSS THE MARINE ZONES  
THURSDAY MORNING, WITH A COLD FRONT SWEEPING ACROSS THE REGION  
THURSDAY EVENING. VEERING WINDS AND GUSTY WINDS ARE EXPECTED,  
ESPECIALLY IN THE WAKE OF THE FRONT THURSDAY NIGHT AND FRIDAY  
MORNING ACROSS AMZ350 AND 374.  
 

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

 
 

 
 
NEAR TERM...  
SHORT TERM...NED  
LONG TERM...  
AVIATION...  
MARINE...  
 
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