440  
FXUS62 KCHS 272020  
AFDCHS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHARLESTON SC  
420 PM EDT WED OCT 27 2021  
   
SYNOPSIS
 
 
A LOW PRESSURE SYSTEM WILL IMPACT THE REGION THURSDAY THROUGH  
THE END OF THE WEEK. HIGH PRESSURE WILL RETURN EARLY NEXT WEEK.  
 

 
   
NEAR TERM /UNTIL 6 AM THURSDAY MORNING/
 
 
THE MID-LEVELS WILL CONSIST OF A NARROW RIDGE, WITH ITS AXIS  
STRETCHING FROM APPROXIMATELY THE GREAT LAKES REGION DOWN INTO  
THE SOUTHEAST THIS EVENING. THE RIDGE WILL GRADUALLY SHIFT TO  
THE ENE WITH TIME. AT THE SURFACE, WEAK HIGH PRESSURE WILL MOVE  
OFFSHORE THIS EVENING AND OVERNIGHT. MEANWHILE, A WARM FRONT  
WILL APPROACH FROM THE SOUTHWEST OVERNIGHT. THOUGH, THE FRONT IS  
NOT EXPECTED TO REACH OUR AREA BY DAYBREAK THURSDAY. THE HIGH  
WILL CONTINUE TO BRING OUR AREA DRY CONDITIONS FOR MOST OF THE  
NIGHT. HOWEVER, MOISTURE WILL BE INCREASING ACROSS OUR AREA, IN  
ADVANCE OF THE FRONT. SOME OF THE MODELS INDICATE A FEW SHOWERS  
COULD REACH THE ALTAMAHA RIVER AND VICINITY JUST BEFORE DAYBREAK  
THURSDAY. THEREFORE, WE HAVE SLIGHT CHANCE POPS THERE.  
EVERYWHERE ELSE IS EXPECTED TO REMAIN DRY. OTHERWISE, HIGH  
CLOUDS WILL GRADUALLY INCREASE ACROSS OUR AREA OVERNIGHT, MOST  
NOTABLY ACROSS OUR GA COUNTIES. TEMPERATURES WILL GENERALLY BE  
IN THE UPPER 40S FAR INLAND. BUT THEY'LL BE WARMER (GENERALLY  
THE 50S) ALONG THE IMMEDIATE COAST DUE TO THE WINDS EVENTUALLY  
COMING OFF THE WARMER OCEAN, AND CLOSER TO THE ALTAMAHA RIVER  
AND VICINITY WHERE THERE WILL BE MORE CLOUDS.  
 

 
   
SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/
 
 
THURSDAY: AN ANOMALOUSLY DEEP MID LVL TROUGH/LOW AND ASSOCIATED SFC  
REFLECTION WILL TRACK ACROSS THE MISSISSIPPI RIVER VALLEY TO THE  
TENNESSEE AND OHIO RIVER VALLEYS DURING THE AFTERNOON/EVENING. AS  
THIS OCCURS, A WARM FRONT WILL SHIFT NORTH ACROSS THE LOCAL AREA BY  
LATE DAY, FOLLOWED BY A COLD FRONT SWEEPING THROUGH THE REGION  
OVERNIGHT. WITHIN THE WARM SECTOR AHEAD OF THE COLD FRONT, A 40-50  
KT LOW-LVL JET WILL HELP ADVECT DEEP MOISTURE INTO THE LOCAL AREA  
WITH PWATS AROUND 2 INCHES DURING THE AFTERNOON INTO EARLY EVENING.  
INSTABILITY SHOULD REMAIN MARGINAL GIVEN A FAIR AMOUNT OF CLOUD  
COVER ASSOCIATED WITH ISENTROPIC LIFT AND ESPECIALLY IF ONGOING  
CONVECTION FROM THE PREVIOUS NIGHT PROLONGS SOME STABILIZATION  
ACROSS THE LOCAL AREA DURING THE DAY. HOWEVER, LATEST GUIDANCE DOES  
SUGGEST SBCAPE INCREASING TO AROUND 1000-1500 J/KG WITHIN THE WARM-  
SECTOR LATE AFTERNOON INTO EARLY EVENING WHEN IMPRESSIVE  
FORCING/SHEAR ALSO COINCIDE ACROSS THE LOCAL AREA. BULK SHEAR (0-  
6KM) AROUND 50-55 KT AND HELICITY (0-1 KM) BETWEEN 300-500 M2/S2 IN  
COMBINATION WITH FORCING ASSOCIATED WITH AN ADVANCING H5 SHORTWAVE,  
UPPER LVL DIVERGENCE WITH AN H25 JET, AND THE APPROACHING COLD FRONT  
SUGGEST THE POTENTIAL FOR SOME THUNDERSTORMS TO BE STRONG AND/OR  
SEVERE WITH DAMAGING STRAIGHT LINE WINDS AND PERHAPS AN ISOLATED  
TORNADO OR TWO ACROSS PARTS OF SOUTHEAST GEORGIA AND SOUTHEAST SOUTH  
CAROLINA, ALTHOUGH THE BEST POTENTIAL FOR A TORNADO APPEARS TO BE  
ACROSS THE QUAD COUNTY AREA WHERE SFC WINDS ARE SLIGHTLY MORE BACKED  
CLOSER TO A FRONT DURING EARLY EVENING HOURS. GIVEN COLD TEMPS (-20  
C) ASSOCIATED WITH THE LARGE H5 LOW CENTERED FAR NORTHWEST OF THE  
REGION, POOR MID-LVL LAPSE RATES ACROSS THE LOCAL AREA, AND EXPECTED  
CONVECTIVE MODE (LINEAR OR CLUSTERS OF THUNDERSTORMS), LARGE HAIL  
WILL BE A CONSIDERABLY LESS THREAT. THE PROGRESSIVE NATURE OF THE  
EVENT SHOULD ALSO LIMIT OVERALL FLOODING POTENTIAL, BUT ISOLATED  
POCKETS OF HEAVY RAINFALL COULD PRODUCE MINOR FLOODING ALONG LOW-  
LYING AREAS AND ROADWAYS.  
 
THE GREATEST POTENTIAL FOR SEVERE WEATHER SHOULD OCCUR ALONG AND  
EAST OF THE I-95 CORRIDOR (CURRENTLY OUTLOOKED WITH A SLIGHT RISK BY  
SPC) LATE AFTERNOON/EVENING (4-10 PM), STARTING ACROSS SOUTHEAST  
GEORGIA FIRST, THEN ADVANCING INTO SOUTHEAST SOUTH CAROLINA. FURTHER  
INLAND, A MARGINAL RISK FOR SEVERE WEATHER REMAINS ACROSS THE AREA  
AS WELL, BUT THE POTENTIAL SHOULD REMAIN SOMEWHAT MORE LIMITED GIVEN  
LESS INSTABILITY AND THE POTENTIAL OF ONGOING CONVECTION FROM THE  
PREVIOUS NIGHT STABILIZING THE ATMOSPHERE DURING THE DAY.  
 
OUTSIDE THE POTENTIAL OF STRONG/SEVERE THUNDERSTORMS, ATMOSPHERIC  
CONDITIONS WILL STILL FAVOR BREEZY WINDS ACROSS THE REGION MID-LATE  
AFTERNOON THROUGH THE EVENING. HIGHS SHOULD PEAK IN THE LOW/MID 70S,  
WARMEST ALONG THE COAST. CHANCES OF PRECIP WILL DECREASE WITH COLD  
FROPA OVERNIGHT, BUT SOME LINGERING SHOWERS ARE POSSIBLE LATE NIGHT  
GIVEN LINGERING MOISTURE AND THE LARGE MID-UPPER LVL LOW POSITIONED  
TO THE WEST-NORTHWEST. LOWS SHOULD DIP INTO THE MID 50S INLAND TO  
UPPER 50S/LOWER 60S AT THE BEACHES.  
 
FRIDAY AND SATURDAY: AN EXPANSIVE MID-UPPER LVL LOW COVERING MUCH OF  
THE EAST CONUS WILL SLOWLY SHIFT TOWARD THE EASTERN SEABOARD THIS  
WEEKEND. A FEW SHOWERS WILL BE POSSIBLE WITH LINGERING MOISTURE AND  
COOLER MID-LVL TEMPS ON FRIDAY, BUT MOISTURE IN THE MID-UPPER LVLS  
WILL LIKELY EXIT THE AREA SATURDAY, FAVORING DRIER CONDITIONS. TEMPS  
WILL BE COOLER THAN NORMAL, WITH HIGHS GENERALLY RANGING IN THE MID  
60S INLAND TO UPPER 60S/AROUND 70 NEAR THE COAST EACH DAY. LOW TEMPS  
SHOULD RANGE IN THE UPPER 40S INLAND TO MID-UPPER 50S CLOSER TO THE  
COAST FRIDAY NIGHT.  
 

 
   
LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/
 
 
MODELS ARE IN GOOD AGREEMENT THAT A LARGE MID-UPPER LVL LOW AS WELL  
AS SFC LOW PRESSURE WILL SLOWLY ADVANCE OFF THE MID-ATLANTIC AND  
NORTHEAST COASTS LATE WEEKEND AND INTO EARLY NEXT WEEK, WHILE HIGH  
PRESSURE BUILDS INTO THE LOCAL AREA FROM THE WEST, EVENTUALLY  
BECOMING CENTERED ACROSS THE SOUTHEAST UNITED STATES EARLY NEXT  
WEEK. DRIER AIR AND A LACK OF SIGNIFICANT FORCING MECHANISMS WILL  
SUPPORT A RAIN-FREE FORECAST THROUGH THE MIDDLE OF NEXT WEEK. TEMPS  
THROUGH THE PERIOD WILL MOSTLY BE BELOW NORMAL, ALTHOUGH WILL BE  
MODERATING WITH TIME EARLY NEXT WEEK. IN GENERAL HIGHS SHOULD PEAK  
IN THE LOWER 70S WHILE A FEW MIDDLE 70S ARE POSSIBLE ACROSS  
SOUTHEAST GEORGIA. LOWS SHOULD GENERALLY RANGE IN THE MID-UPPER 40S  
WELL INLAND TO UPPER 50S/AROUND 60 NEAR THE COAST.  
 

 
   
AVIATION /20Z WEDNESDAY THROUGH MONDAY/
 
 
18Z TAFS:  
VFR THROUGH TONIGHT. A STORM SYSTEM WILL BRING IMPACTS TO THE  
AREA TOWARDS THE END OF THE TAF TIME PERIOD, FIRST TO SAV, THEN  
TO CHS/JZI. FOR CHS/JZI, WE INTRODUCED MVFR VIA A PROB30 AFTER  
15Z. FOR SAV, WE HAVE MVFR VIA A PROB30 AFTER 13Z. WE THEN, HAVE  
PREVAILING IMPACTS AFTER 16Z ALONG WITH GUSTY WINDS. THOUGH,  
MORE ADJUSTMENTS TO THE TIMING/IMPACTS ARE EXPECTED.  
 
EXTENDED AVIATION OUTLOOK: A STORM SYSTEM WILL BRING FLIGHT  
RESTRICTIONS WITHIN SHOWERS/THUNDERSTORMS AND GUSTY WINDS AT  
SAV/CHS/JZI TERMINALS ON THURSDAY, ESPECIALLY DURING THE AFTERNOON  
INTO EARLY EVENING HOURS. GUSTY WINDS SHOULD PERSIST FRIDAY, BUT  
CONDITIONS ARE EXPECTED TO BE VFR DURING THE WEEKEND AND INTO EARLY  
NEXT WEEK AT ALL TERMINALS.  
 

 
   
MARINE
 
 
TONIGHT: WEAK HIGH PRESSURE WILL MOVE OFFSHORE THIS EVENING AND  
OVERNIGHT. MEANWHILE, A WARM FRONT WILL APPROACH FROM THE  
SOUTHWEST OVERNIGHT. THOUGH, THE FRONT IS NOT EXPECTED TO REACH  
OUR AREA BY DAYBREAK THURSDAY. THESE SYNOPTIC FEATURES WILL  
CAUSE WINDS TO BE LIGHT AND VARIABLE THIS EVENING, THEN SHIFTING  
TO THE ESE AND INCREASING TO 5-10 KT BY DAYBREAK THURSDAY. SEAS  
WILL BE 1-2 FT WITHIN 20 NM AND 2-3 FT FOR THE GA WATERS BEYOND  
20 NM.  
 
THURSDAY THROUGH MONDAY: CONDITIONS WILL DETERIORATE ACROSS COASTAL  
WATERS THURSDAY AS A STRONG LOW PRESSURE SYSTEM TRACKS ACROSS THE  
REGION. OUTSIDE SHOWERS AND THUNDERSTORMS, SOME OF WHICH COULD BE  
SEVERE WITH DAMAGING WINDS AND WATERSPOUTS THURSDAY AFTERNOON INTO  
THURSDAY EVENING, AN ENHANCED PRESSURE GRADIENT WILL SUPPORT SMALL  
CRAFT ADVISORIES, STARTING ACROSS GEORGIA WATERS THURSDAY AFTERNOON,  
THEN FOR THE REMAINDER OF COASTAL WATERS OUTSIDE THE CHS HARBOR LATE  
THURSDAY AFTERNOON. THERE IS A POTENTIAL FOR SMALL CRAFT ADVISORY  
LEVEL CONDITIONS IN THE CHS HARBOR THURSDAY NIGHT, BEFORE CONDITIONS  
SLOWLY IMPROVE HEADING INTO DAYBREAK FRIDAY. ELEVATED WINDS/SEAS  
WILL THEN PERSIST ACROSS ALL OTHER WATERS FOR MUCH OF FRIDAY BEFORE  
ADDITIONAL IMPROVEMENT OCCURS FRIDAY NIGHT INTO SATURDAY, WHEN THE  
LAST OF SMALL CRAFT ADVISORIES COMES TO AN END. CONDITIONS ARE THEN  
EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY LEVELS SUNDAY AND  
MONDAY AS HIGH PRESSURE EXPANDS ACROSS THE AREA.  
 

 
   
CHS WATCHES/WARNINGS/ADVISORIES
 
 
GA...NONE.  
SC...NONE.  
MARINE...SMALL CRAFT ADVISORY FROM 5 PM THURSDAY TO 8 PM EDT FRIDAY FOR  
AMZ352.  
SMALL CRAFT ADVISORY FROM 2 PM THURSDAY TO 8 AM EDT SATURDAY  
FOR AMZ374.  
SMALL CRAFT ADVISORY FROM 5 PM THURSDAY TO 8 AM EDT SATURDAY  
FOR AMZ350.  
SMALL CRAFT ADVISORY FROM 2 PM THURSDAY TO 8 PM EDT FRIDAY FOR  
AMZ354.  
 

 
 

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