442  
FXUS62 KCHS 250158  
AFDCHS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHARLESTON SC  
958 PM EDT MON APR 24 2017  
   
SYNOPSIS
 
 
A LOW PRESSURE SYSTEM WILL AFFECT THE AREA TONIGHT, BEFORE PULLING  
AWAY TUESDAY. ALTHOUGH A SHORT WAVE COULD IMPACT THE AREA LATE  
THURSDAY, HIGH PRESSURE WILL PREVAIL MOST OF THE TIME INTO THE  
WEEKEND. A COLD FRONT COULD AFFECT THE AREA EARLY NEXT WEEK.  
 

 
   
NEAR TERM /UNTIL 6 AM TUESDAY MORNING/
 
 
THE RISK FOR HEAVY RAINS HAS SHIFTING INTO NORTHERN PORTIONS OF  
BERKELEY COUNTY WITHIN A CORRIDOR OF ENHANCED UPPER DIFLUENCE  
ALONG THE NORTHERN EDGE OF THE UPPER LOW. EXPERIMENTAL GOES-16  
MID-LEVEL WATER VAPOR DATA SHOW WHAT APPEARS TO BE A TRANSIENT  
ENHANCED-V SIGNATURE OVER EASTERN PORTIONS OF CALHOUN AND  
ORANGEBURG COUNTIES, WHICH HAS LIKELY HELPED MAINTAIN DEEP  
CONVECTION WITHIN AN OTHERWISE MEAGER THERMODYNAMIC ENVIRONMENT.  
INSTABILITY IS SLOWLY WANING WITH THE LOSS OF INSOLATION AND AS  
THE UPPER LOW MEANDERS FARTHER TO THE EAST, EXPECT CONVECTION  
TO GRADUALLY WIND DOWN.  
 
PER COORDINATION WITH WFO COLUMBIA, THE FLASH FLOOD WATCH AS  
BEEN EXTENDED ONCE AGAIN UNTIL MIDNIGHT FOR INLAND BERKELEY  
COUNTY. THE WATCH HAS BEEN CANCELLED FOR CHARLESTON AND TIDAL  
BERKELEY COUNTIES NOW THAT HIGH TIDE AS PASSED. WHILE SOME  
POCKETS OF ADDITIONAL MINOR FLOODING OF LOW- LYING AND POOR  
DRAINAGE AREAS COULD STILL OCCUR IN THESE AREAS, THE RISK FOR  
FLASH FLOODING HAS DIMINISHED.  
 

 
   
SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/
 
 
TUESDAY: THE SEPARATION BETWEEN THE SURFACE LOW AND IT'S  
ACCOMPANYING CYCLONE ALOFT WITH SHRINK AS THE ASSOCIATED SURFACE  
WARM AND COLD FRONTS OCCLUDE AND THE RESULTING VERTICALLY STACKED  
LOW PULLS AWAY TO THE NE. THE LAST LOBE OF VORTICITY SPINNING  
COUNTER-CLOCKWISE WILL PULL THROUGH THE AREA IN THE MORNING, AND  
WITH CONSIDERABLE WRAP-AROUND MOISTURE TO CONTINUE ACROSS OUR  
NORTHERN ZONES, WE STILL HAVE A SLIGHT CHANCE TO CHANCE OF SHOWERS  
FOR THE CHARLESTON QUAD-COUNTY AREA THROUGH 1-3 PM. WIDESPREAD LOW  
STRATUS TO START THE DAY WILL LIFT INTO AN EXTENSIVE CUMULUS DECK,  
AND WILL BE SLOW IN DIMINISHING IN COVERAGE UNTIL LATE MORNING SOUTH  
AND NOT UNTIL MID TO LATE AFTERNOON NORTH. DEPENDING UPON THIS  
TRANSITION, IT WILL HAVE HUGE IMPLICATIONS ON MAX TEMPS. FOR NOW WE  
HAVE MID 70S NORTH OF I-26 WHERE CLOUD COVER WILL LAST LONGEST,  
UPPER 70S OVER THE REST OF SC, AND 80-83F ACROSS OUR GA COUNTIES  
WHERE INSOLATION WILL B MOST PREVALENT.  
 
TUESDAY: MID AND UPPER LEVEL WILL DEVELOP AND THE W-NW EXTENSION OF  
ATLANTIC HIGH PRESSURE POKES IN BEHIND THE DEPARTING STACKED LOW  
PULLING THROUGH THE GREAT DISMAL SWAMP AND VA TIDEWATER TO THE  
NEARBY ATLANTIC OFF THE DELMARVA. WINDS WILL DECOUPLE AND WITH  
MOSTLY CLEAR SKIES SOUTH AND PARTLY CLOUDY NORTH, THERE WILL BE  
ENOUGH RADIATIONAL COOLING TO GET LOWS DOWN TO THE UPPER 50S-LOWER  
60S INLAND FROM THE WARMER BEACHES.  
 
WEDNESDAY: DEEP-LAYERED HIGH PRESSURE WITH RISING SURFACE PRESSURES  
AND CLIMBING HEIGHTS ALOFT WILL PROVIDE THE REGION WITH PLENTIFUL  
SUNSHINE AND DRY CONDITIONS. TEMPS AT 850 MB ARE AS HIGH AS 14-16C,  
OR BETWEEN THE 75TH AND 90TH PERCENTILE FOR LATE APRIL, AND EQUATES  
TO TEMPS REACHING THE MID AND UPPER 80S. COASTAL SECTIONS WILL  
EXPERIENCE A RESULTANT SEA BREEZE, SO HIGHS WILL GENERALLY BE HELD  
BELOW 80F.  
 
THURSDAY: SUB-TROPICAL RIDGING AT THE SURFACE AND LOW LEVELS, AND A  
W-SW FLOW ALOFT WILL DOMINATE. THE RESULTING SUBSIDENT CAP AROUND 5-  
6K FT LOOKS TO KEEP THE MAJORITY OF THE AREA RAINFREE, BUT A  
DAMPENING MID LEVEL SHORT WAVE SITUATED IN THE PACIFIC NW AS OF LATE  
MONDAY, WILL SKIRT THE REGION LATE IN THE DAY, ACTUALLY TAKING ON A  
SLIGHT NEGATIVE TILT. THIS COULD SPARK A FEW SHOWERS AND T-STORMS  
FAR INLAND SECTIONS BEFORE DARK. DESPITE A LITTLE GREATER CLOUD  
COVER THAN WEDNESDAY, SIMILAR 850 MB TEMPS WILL PRODUCE HIGHS AGAIN  
THE IN THE MID OR UPPER 80S INLAND FROM THE BARRIER ISLANDS.  
 

 
   
LONG TERM /THURSDAY NIGHT THROUGH MONDAY/
 
 
A STRENGTHENING UPPER RIDGE AND STRONG ATLANTIC HIGH PRESSURE  
WILL MAINTAIN ABOVE-NORMAL TEMPERATURES AND MAINLY DRY WEATHER.  
FRIDAY AND SATURDAY WILL PROBABLY REACH THE LOWER 90S ACROSS  
INLAND SOUTHEAST GA WITH UPPER 80S ELSEWHERE. A COLD FRONT IS  
EXPECTED TO APPROACH NEXT MONDAY, POSSIBLY BRINGING SOME RAIN.  
 

 
   
AVIATION /02Z TUESDAY THROUGH SATURDAY/
 
 
EXPECT IFR CIGS TO FILL IN BEHIND THE UPPER LOW TONIGHT,  
ESPECIALLY AT KCHS. KSAV IS A BIT MORE QUESTIONABLE AS TO HOW  
LOW CIGS WILL GET. LATEST RAP SOUNDINGS SUGGEST LOW-END MVFR,  
BUT IFR IS POSSIBLE. EXPECT PREVAILING IFR OR LOWER AT KCHS, BUT  
OPTED TO LIMIT CIGS TO ALTERNATE MINIMUM THRESHOLDS FOR NOW.  
 
EXTENDED AVIATION OUTLOOK: NO SIGNIFICANT CONCERNS.  
 

 
   
MARINE
 
 
TONIGHT: WINDS EXPECTED TO TURN WESTERLY BEHIND DEPARTING LOW  
PRESSURE, MAINLY REACHING 15-20 KT WITH SEAS 3-5 FEET, EXCEPT  
UP TO 6 FEET IN THE CHARLESTON COUNTY WATERS AND THE OUTER  
GEORGIA WATERS WHERE AN ADVISORY REMAINS IN EFFECT.  
 
TUESDAY: THERE REMAINS A CYCLONIC FLOW AROUND LOW PRESSURE OFF TO  
THE NORTH THROUGH THE DAY TO HOLD ANY RESULTANT SEA BREEZE  
CIRCULATIONS AT BAY UNTIL MAYBE LATE IN THE DAY. WINDS AND SEAS WILL  
BE BELOW ANY ADVISORY LEVELS ON ALL WATERS, WITH ONE EXCEPTION, THE  
OUTER GA WATERS, WHERE THE SCA CONTINUES INTO THE AFTERNOON.  
 
WEDNESDAY THROUGH SATURDAY: ATLANTIC HIGH PRESSURE WILL DOMINATE  
WITH A S-SW SYNOPTIC FLOW TO PREVAIL. DESPITE SOME BOOST FROM THE  
SEA BREEZE, WINDS WON'T BE ANY HIGHER THAN ABOUT 15-18 KT AND SEAS  
WILL BE CAPPED AT 3 OR 4 FT.  
 

 
   
TIDES/COASTAL FLOODING
 
 
ASTRONOMICALLY HIGH TIDES WILL PREVAIL DURING THE MIDDLE OF THE  
WEEK DUE TO THE PERIGEAN SPRING TIDES, LIKELY RESULTING IN THE  
RISK FOR SHALLOW COASTAL FLOODING ALONG AT LEAST PARTS OF THE  
COAST WITH THE EVENING HIGH TIDES WEDNESDAY AND THURSDAY.  
 

 
   
CHS WATCHES/WARNINGS/ADVISORIES
 
 
GA...NONE.  
SC...FLASH FLOOD WATCH UNTIL MIDNIGHT EDT TONIGHT FOR SCZ045.  
MARINE...SMALL CRAFT ADVISORY UNTIL 2 PM EDT TUESDAY FOR AMZ374.  
SMALL CRAFT ADVISORY UNTIL 6 AM EDT TUESDAY FOR AMZ350.  
 

 
 

 
 
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