621  
FXUS62 KCHS 250556  
AFDCHS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHARLESTON SC  
156 AM EDT MON MAY 25 2020  
   
SYNOPSIS
 
 
A WEAK COLD FRONT WILL PUSH INTO THE AREA LATER TONIGHT AND  
MONDAY, AND HIGH PRESSURE WILL BUILD OVER THE REGION FROM THE  
NORTH. A COASTAL TROUGH SHOULD DEVELOP AROUND MID WEEK, AND LOW  
PRESSURE COULD TRACK OVER OR NEAR THE SOUTHEAST COAST MID TO  
LATE WEEK. A COLD FRONT COULD APPROACH THE REGION NEXT WEEKEND.  
 

 
   
NEAR TERM /UNTIL 6 AM THIS MORNING/
 
 
AS OF 150 AM: A BACKDOOR COLD FRONT WAS PUSHING ACROSS THE  
SANTEE RIVER BASIN. SURFACE BASED OBSERVATIONS ALONG AND NORTH  
OF THE FRONT WERE OBSERVING LOW CEILINGS WITH LIGHT FOG. BASED  
ON THE LATEST RUN OF THE HRRR, IT APPEARS THAT A PERIOD  
OF FOG WILL SLIDE ACROSS THE SC LOWCOUNTRY BETWEEN 07-11Z AND  
SE GA BETWEEN 10-13Z.  
 
PREVIOUS DISCUSSION:  
ONE LAST CONVECTIVE CLUSTER WILL WORK WEST ACROSS NORTHERN  
JENKINS COUNTY OVER THE NEXT HOURS, THEN DRY WEATHER WILL  
PREVAIL. ADJUSTED POPS BASED ON SHORT TERM RADAR TRENDS.  
 
EXPECT LOW STRATUS AND POSSIBLE SOME FOG TO FILL IN ALONG/AHEAD  
OF THE BACKDOOR FRONT EARLY MONDAY. THE FOG IS NOT EXPECTED TO  
HAVE MUCH IMPACT, BUT SOME AREAS OF REDUCED VISIBILITIES COULD  
OCCUR. DENSE FOG IS NOT EXPECTED AT THIS TIME.  
 
WARM AND HUMID CONDITIONS WILL PERSIST WITH LOWS RANGING FROM  
THE UPPER 60S/NEAR 70 INLAND, LOWER 70S AT THE COAST, WITH MID  
70S AT THE BEACHES AND DOWNTOWN CHARLESTON.  
 

 
   
SHORT TERM /6 AM THIS MORNING THROUGH WEDNESDAY/
 
 
MONDAY: HIGH PRESSURE WILL BUILD INTO THE REGION FROM THE NORTH AND  
WILL PUSH A WEAKENING COLD FRONT TOWARD THE SOUTH. AT LEAST  
SCATTERED SHOWERS AND THUNDERSTORMS COULD DEVELOP NEAR THIS  
BOUNDARY, WITH HIGHER POPS ACROSS NORTHERN COUNTIES DURING THE  
MORNING FOLLOWED BY HIGH POPS SHIFTING INTO SOUTHERN/WESTERN  
SECTIONS DURING THE AFTERNOON. FORECAST INSTABILITY SUGGESTS ONLY A  
LOW CHANCE FOR A BRIEF/ISOLATED PULSE SEVERE THUNDERSTORM OR TWO.  
 
MONDAY NIGHT: DUE TO DIURNAL STABILIZATION, ISOLATED/SCATTERED  
SHOWERS AND PERHAPS ISOLATED THUNDERSTORMS NEAR THE STALLING COLD  
FRONT ACROSS SOUTHERN/WESTERN COUNTIES SHOULD DIMINISH IN COVERAGE  
THROUGH AT LEAST THE FIRST HALF OF THE NIGHT. THEN, GUIDANCE DEPICTS  
A BAND OF DEEPER MOISTURE TO SPREADING FROM THE SOUTH IN AT LEAST  
SOUTHERN COUNTIES LATER ON.  
 
TUESDAY AND WEDNESDAY: GUIDANCE INDICATES A WET PERIOD AS A POOL OF  
PWAT VALUES AROUND 2 INCHES SETTLES OVER THE REGION. HOWEVER,  
TIMING/COVERAGE OF SHOWERS/THUNDERSTORMS WILL BE LINKED WITH  
STRENGTH OF THE SURFACE HIGH N/NE OF THE REGION AND TO THE UNCERTAIN  
EVOLUTION OF A SURFACE TROUGH/SURFACE LOW S/SE OF THE AREA. THE  
LATEST FORECAST RAMPS POPS UP TO LIKELY ALL BUT FAR NORTHERN/INLAND  
COUNTIES TUESDAY. THEN, POPS VARY FROM LIKELY ALONG THE SC COAST TO  
CHANCE ELSEWHERE TUESDAY NIGHT. WEDNESDAY, POPS RANGE FROM LIKELY  
NORTH TO CHANCE SOUTH. HOWEVER, FORECAST CONFIDENCE DECREASES  
TUESDAY NIGHT AND REMAINS RATHER LOW THROUGH WEDNESDAY.  
 
THE POTENTIAL FOR LOCALLY HEAVY RAIN WILL INCREASE TUESDAY THROUGH  
WEDNESDAY, ESPECIALLY NEAR THE COAST WHERE TIDES WILL BE ELEVATED  
DUE TO PERSISTENT E/NE FLOW. IF STRONGER LOW PRESSURE TRACKS OVER OR  
INLAND FROM THE COAST TUESDAY NIGHT THROUGH WEDNESDAY, THE POTENTIAL  
FOR SEVERE WEATHER COULD INCREASE.  
 
ALSO OF NOTE, GREATER THAN EXPECTED COVERAGE/PERSISTENCE OF  
CLOUDS/PRECIPITATION COULD TRANSLATE TO COOLER DAYTIME TEMPERATURES  
THAN INDICATED WITHIN THE LATEST FORECASTS.  
 

 
   
LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/
 
 
THE START OF THIS PERIOD REMAINS UNCERTAIN AND WILL DEPEND ON  
WHETHER SURFACE LOW PRESSURE REMAINS IN THE VICINITY INTO THURSDAY.  
OTHERWISE, ON THE WESTERN PERIPHERY OF ATLANTIC SURFACE HIGH  
PRESSURE/BENEATH A WEAK RIDGE OF HIGH PRESSURE ALOFT, A SURFACE  
TROUGH SHOULD LINGER OVER THE REGION WITH ABOVE NORMAL PRECIPITATION  
AND TEMPS INTO THIS WEEKEND. A COLD FRONT COULD APPROACH OR MOVE  
INTO THE AREA BY LATE NEXT WEEKEND.  
 

 
   
AVIATION /06Z MONDAY THROUGH FRIDAY/
 
 
PRIOR TO THE 6Z TAFS, A BACKDOOR COLD FRONT WAS PUSHING ACROSS  
THE SANTEE RIVER BASIN. SURFACE BASED OBSERVATIONS ALONG AND  
NORTH OF THE FRONT WERE OBSERVING LIFR TO IFR CEILINGS WITH MVFR  
VISIBILITIES. BASED ON THE LATEST RUN OF THE HRRR, IT APPEARS  
THAT A PERIOD RESTRICTIVE CEILINGS WILL PASS OVER KCHS BETWEEN  
07-11Z AND KSAV BETWEEN 10-13Z, HIGHLIGHTED WITH TEMPO GROUPS.  
THE PRESSURE GRADIENT BETWEEN A DEVELOPING TROPICAL WAVE OVER FL  
AND HIGH PRESSURE ACROSS THE MID-ATLANTIC STATES WILL INCREASE  
THIS AFTERNOON. GUSTY SE WINDS SHOULD DEVELOP BY MID-DAY AND  
REMAIN UNTIL AROUND SUNSET. CONDITIONS TONIGHT SHOULD FEATURE  
STEADY EAST WINDS WITH VFR CEILINGS.  
 
EXTENDED AVIATION OUTLOOK: PERIODS OF FLIGHT RESTRICTIONS, ESPECIALLY  
RELATED TO SHOWERS/THUNDERSTORMS IN THE AREA, SHOULD PERSIST INTO  
LATE WEEK.  
 

 
   
MARINE
 
 
TONIGHT: SOUTH TO SOUTHEAST WINDS WILL GRADUALLY BACK AS A WEAK  
COLD FRONT APPROACHES. SPEEDS WILL REMAIN <10KT WITH SEAS 1-2 FT  
NEARSHORE WATERS AND 2-3 FT OFFSHORE WATERS.  
 
MONDAY THROUGH FRIDAY: ON MONDAY, AS A HIGH PRESSURE SYSTEM BUILDS  
OVER THE AREA THROUGHOUT THE DAY, WINDS WILL INCREASE AS THE  
PRESSURE GRADIENT TIGHTENS. THEN, AS A LOW PRESSURE SYSTEM LINGERS  
OFF THE EAST COAST OF FLORIDA, THE PRESSURE GRADIENT WILL TIGHTEN  
MORE, CAUSING WINDS AND SEAS TO GRADUALLY INCREASE. SMALL CRAFT  
ADVISORIES WILL LIKELY BE NEEDED STARTING TUESDAY AFTERNOON INTO AT  
LEAST WEDNESDAY MORNING. WHILE THERE IS STILL SOME UNCERTAINTY ABOUT  
THE TRACK OF THE LOW OVER OR CLOSE TO THE SOUTHEAST COAST MID TO  
LATE WEEK. SOME GUIDANCE SUGGESTS THAT THE PRESSURE GRADIENT STARTS  
TO RELAX MID TO LATE WEEK, BUT THE LOW PRESSURE COULD MAINTAIN  
ELEVATED WINDS AND SEAS THROUGH FRIDAY.  
 

 
   
TIDES/COASTAL FLOODING
 
 
PERSISTENT E/NE FLOW WILL SUPPORT ELEVATED TIDES THIS WEEK. MID TO  
LATE WEEK, THERE EXISTS A LOW PROBABILITY FOR MINOR SALT WATER  
FLOODING AROUND THE TIMES OF THE OVERNIGHT HIGH TIDES. ALSO, WE'LL  
CONTINUE TO ASSESS THE POTENTIAL FOR HEAVY RAINFALL TO COINCIDE WITH  
HIGH TIDES AT THE COAST, ESPECIALLY DURING THE TUESDAY-THURSDAY  
PERIOD.  
 

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

 
 

 
NEAR TERM...NED  
SHORT TERM...  
LONG TERM...  
AVIATION...NED  
MARINE...  
TIDES/COASTAL FLOODING...  
 
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