789  
FXUS62 KCHS 201718  
AFDCHS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHARLESTON SC  
118 PM EDT SAT APR 20 2019  
   
SYNOPSIS
 
 
A WEAK SURFACE TROUGH WILL PREVAIL TO THE WEST THROUGH TONIGHT.  
HIGH PRESSURE IS FORECASTED TO DOMINATE THE WEATHER SUNDAY  
THROUGH WEDNESDAY OR THURSDAY. THE NEXT COLD FRONT MAY APPROACH  
LATE NEXT WEEK.  
 

 
   
NEAR TERM /UNTIL 6 PM THIS EVENING/
 
 
FOR THE EARLY AFTERNOON UPDATE WE INDEED HAVE HAD TO TRIM BACK  
TEMPS A BIT OVER PARTS OF OUR INTERIOR COUNTIES WHERE CLOUD  
COVER IS THE GREATEST. LITTLE TO NO CHANGES IN TEMPS ELSEWHERE.  
THE MID AND UPPER LOW HAS ALLOWED FOR THE LIGHT SHOWERS TO  
PROGRESS A LITTLE FURTHER EAST THAN PREVIOUS, AND WE HAVE POP IN  
THE 20-40% RANGE ALONG OUR NORTHWEST TIER. THAT IS WHERE THE  
COLDEST H5 TEMPS WILL BE LOCATED, AROUND -19 TO -20C. LITTLE TO  
NO MEASURABLE RAINFALL THOUGH WILL OCCUR WITH THESE SHOWERS.  
 
PREVIOUS DISCUSSION...  
AN UNUSUALLY STRONG DEEP LAYERED CYCLONE CENTERED OVER THE  
CUMBERLAND PLATEAU WILL SLOWLY PROPAGATE AWAY FROM THE SOUTHEAST  
U.S. LATER TODAY AS SURFACE HIGH PRESSURE OVER THE WESTERN GULF  
OF MEXICO EXPANDS TO THE EAST AND NORTHEAST. THE ASSOCIATED MID  
AND UPPER TROUGH EXTENDS SOUTH INTO THE NORTHEAST GULF OF  
MEXICO AS IT MOVES EASTWARD. STEEP MID LEVEL LAPSE RATES AND  
COLD MID LEVELS WHERE H5 TEMPS ARE AS LOW AS -16 TO -20C WILL  
LIFT THROUGH THIS AFTERNOON. THIS IS ALREADY GENERATING A FEW  
LIGHT SHOWERS OVER JENKINS COUNTY AS OF LATE MORNING, WHILE MORE  
ORGANIZED SHOWERS ARE SITUATED JUST WEST OF THE GEORGIA  
INTERIOR COUNTIES. WE ANTICIPATE THAT SOME OF THESE WILL MOVE  
INTO LOCATIONS NEAR AND WEST OF US-301, SO WE HAVE ADDED MENTION  
OF SLIGHT CHANCE POP THERE. CLOUD COVER WILL PLAY A CRITICAL  
ROLE IN MAX TEMPS THIS AFTERNOON, SO WE HAVE TRIMMED THE FAR  
INLAND AREAS 1-2F WHERE WE WILL EXPERIENCE MORE CLOUD COVER  
(70-90%), BUT LEFT THE COASTAL SECTIONS THE SAME WHERE CLOUD  
COVER WILL BE LESS (40-60F). WE STILL MIGHT NEED TO LOWER A FEW  
PLACES FROM ALLENDALE TO CANDLER FOR MAX TEMPS, AS THE HRRR AND  
RAP SHOW THOSE PLACES NOT HITTING 60F.  
 
DEEP MIXING WILL TAP INTO MODEST LOW LEVEL  
WINDS TO RESULT IN GUSTY SOUTHWEST AND WEST BREEZES AS HIGH AS  
25-30 MPH.  
 
LAKE WINDS: ALTHOUGH THE SENSOR AT PINOPOLIS WILL NOT BE  
SAMPLING CONDITIONS ON THE LAKE THAT WELL TODAY, GIVEN THE  
LATEST SOUNDING DATA, BOTH SURFACE AND ALOFT, AND THE FACT THAT  
WE'RE ALREADY SEEING WIND GUSTS IN THE UPPER TEENS, WE HAVE  
RAISED A LAKE WIND ADVISORY FOR LAKE MOULTRIE THROUGH 8 PM. THE  
STRONGEST GUSTS WILL GENERALLY BE OVER AND NEAR THE SHORES OF  
THE LAKE THIS AFTERNOON AND EARLY EVENING.  
 

 
   
SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY/
 
 
TONIGHT: WINDS WILL GRADUALLY DIMINISH TONIGHT UNDER CLEAR  
SKIES. WHILE A FULL DECOUPLING OF THE BOUNDARY LAYER DOES NOT  
APPEAR LIKELY, DECENT RADIATIONAL CONDITIONS ARE STILL EXPECTED  
TO DOMINATE. USED THE COLDER SIDE OF GUIDANCE TO CONSTRUCT  
OVERNIGHT LOWS WITH LOCALIZED ADJUSTMENTS TO TAKE INTO ACCOUNT  
THE NORMALLY COLDER LOCATIONS SUCH AS THE FRANCIS MARION  
NATIONAL FOREST. LOWS WILL RANGE FROM THE MID 40S INLAND TO THE  
LOWER-MID 50S AT THE BEACHES.  
 
SUNDAY: THE MID-LEVELS WILL CONSIST OF A STRONG TROUGH ALONG THE  
EAST COAST IN THE MORNING. THE TROUGH WILL WEAKEN AND LIFT TO THE  
NORTHEAST WITH TIME, ALLOWING HEIGHTS TO RISE OVER OUR AREA. AT THE  
SURFACE, BROAD HIGH PRESSURE INITIALLY CENTERED OVER FL WILL SPREAD  
ACROSS THE SOUTHEAST WITH TIME. A DRY FORECAST WITH MOSTLY SUNNY  
SKIES IS ON TAP. RISING 850 MB TEMPERATURES AND HEIGHTS WILL LEAD TO  
TEMPERATURES WITHIN A FEW DEGREES OF NORMAL FOR THIS TIME OF YEAR.  
 
MONDAY: THE MID-LEVELS WILL CONSIST OF A TROUGH OVER THE  
NORTHEASTERN U.S. IN THE MORNING. AS THIS TROUGH CONTINUES TO LIFT  
TO THE NORTHEAST WITH TIME, RIDGING WILL BUILD OVER THE SOUTHEAST.  
AT THE SURFACE, HIGH PRESSURE WILL PREVAIL OVER THE SOUTHEAST. THE  
DRY WEATHER AND SUNNY SKIES CONTINUE. TEMPERATURES ARE FORECASTED TO  
RISE A FEW DEGREES ABOVE NORMAL, BUT REMAIN COOLER AT THE BEACHES  
DUE TO THE SEA BREEZE.  
 
TUESDAY: THE MID-LEVELS WILL CONSIST OF RIDING OVER THE SOUTHEAST  
THAT WILL CONTINUE TO BUILD WITH TIME. AT THE SURFACE, THE CENTER OF  
BROAD HIGH PRESSURE INITIALLY OVER THE SOUTHEAST IN THE MORNING WILL  
START TO TREND OFFSHORE INTO THE EVENING. SAME STORY, DIFFERENT DAY.  
DRY WEATHER AND SUNNY SKIES. THEE ONLY DIFFERENCE IS TEMPERATURES  
ARE A FEW DEGREES WARMER.  
 

 
   
LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/
 
 
HIGH PRESSURE WILL PREVAIL ALONG THE SOUTHEAST TUESDAY NIGHT INTO  
WEDNESDAY, THEN SHIFT FURTHER OFFSHORE WEDNESDAY NIGHT INTO  
THURSDAY. THE RESULT WILL BE DRY CONDITIONS AND ABOVE NORMAL  
TEMPERATURES. BY THURSDAY NIGHT AND FRIDAY A TROUGH OR COLD FRONT IS  
EXPECTED TO MOVE OVER THE REGION, BRINGING SHOWERS AND COOLER  
TEMPERATURES. THOUGH, MODELS DIFFER ON THE STRENGTH, TIMING, AND  
POTENTIAL IMPACTS. HENCE, WE WENT WITH A BLEND FOR THE FORECAST.  
 

 
   
AVIATION /18Z SATURDAY THROUGH WEDNESDAY/
 
 
VFR CEILINGS WITH GUSTY SW-W WINDS THAT REACH 20-30 KT THIS  
AFTERNOON, BEFORE WINDS SUBSIDE AND SKIES CLEAR TONIGHT.  
 
EXTENDED AVIATION OUTLOOK: VFR.  
 

 
   
MARINE
 
 
THIS AFTERNOON: ALTHOUGH CONDITIONS ARE IMPROVED FROM YESTERDAY,  
BOTH WINDS AND SEAS WILL REMAIN HIGH ENOUGH TO KEEP SMALL CRAFT  
ADVISORIES IN PLACE FOR ALL MARINE ZONES. SW AND W WINDS WILL  
BE AS HIGH AS 20-25 KT WITH GUSTS TO 30 KT, WHILE SEAS WILL  
RANGE FROM 4-7 FT WITHIN 20 NM AND 5-7 FT FURTHER OUT. EARLIER  
THIS MORNING WE RECEIVED A REPORT FROM THE CHARLESTON PILOT BOAT  
FROM BUOY 6, WHERE THERE WAS A 2-3 FOOT WIND WAVE FROM THE  
WEST- SOUTHWEST, BUT A 4-6 FOOT SWELL FROM THE EAST- SOUTHEAST,  
CREATING HAZARDOUS WAVE CONDITIONS.  
 
TONIGHT: SEAS WILL FINALLY DROP BELOW ADVISORY THRESHOLDS FOR  
THE CHARLESTON AND GEORGIA OFFSHORE LEGS THIS EVENING.  
OTHERWISE, WEST WINDS WILL AVERAGE 15-20 KT THIS EVENING, THEN  
DIMINISH THROUGH THE NIGHT. SEAS WILL SUBSIDE 3-5 FT GEORGIA  
OFFSHORE AND CHARLESTON COUNTY LEGS WITH 1-4 F REMAINING LEGS BY  
DAYBREAK SUNDAY.  
 
SUNDAY THROUGH WEDNESDAY: BROAD HIGH PRESSURE INITIALLY  
CENTERED OVER FL SUNDAY MORNING WILL SPREAD ACROSS THE SOUTHEAST  
INTO SUNDAY EVENING. THE HIGH WILL PREVAIL THROUGH WEDNESDAY,  
THEN MOVE OFFSHORE. THE END RESULT IS TRANQUIL MARINE  
CONDITIONS.  
 
RIP CURRENTS: LINGERING SWELL ENERGY COUPLED WITH BREEZY  
CONDITIONS WILL SUPPORT A MODERATE RISK FOR RIP CURRENTS ALL  
BEACHES THIS AFTERNOON.  
 

 
   
CHS WATCHES/WARNINGS/ADVISORIES
 
 
GA...NONE.  
SC...LAKE WIND ADVISORY UNTIL 8 PM EDT THIS EVENING FOR SCZ045.  
MARINE...SMALL CRAFT ADVISORY UNTIL 5 PM EDT THIS AFTERNOON FOR AMZ330-  
352.  
SMALL CRAFT ADVISORY UNTIL 11 PM EDT THIS EVENING FOR AMZ350-  
374.  
 

 
 

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