818  
FXUS62 KCHS 231812  
AFDCHS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHARLESTON SC  
112 PM EST SUN FEB 23 2020  
   
SYNOPSIS
 
 
HIGH PRESSURE WILL PERSIST THROUGH TONIGHT. A WARM FRONT WILL  
LIFT NORTH OF THE REGION ON MONDAY, FOLLOWED BY A PAIR OF COLD  
FRONTS DURING THE MIDDLE OF THE WEEK. HIGH PRESSURE RETURNS  
THURSDAY AND FRIDAY, WITH ANOTHER COLD FRONT EXPECTED ON  
SATURDAY.  
 

 
   
NEAR TERM /THROUGH TONIGHT/
 
 
AS OF 1 PM: CIRRUS CLOUDS HAVE INCREASED ACROSS THE FORECAST  
AREA SINCE THE LAST UPDATE. I WILL UPDATE THE FORECAST TO  
INCREASE CLOUD COVER THROUGH THIS AFTERNOON. IN ADDITION, I WILL  
LOWER THE AFTERNOON RH VALUES BASED ON RECENT OBSERVATIONS.  
 
AS OF 10 AM: SATELLITE IMAGES AND VIEW OUT THE WINDOW INDICATED  
THIN CIRRUS PASSING OVER THE FORECAST AREA THIS MORNING. I WILL  
MAKE MINOR EDITS TO THE HOURLY TEMPERATURES, MAINLY TO BETTER  
ALIGN WITH TRENDS IN OBSERVED VALUES. OTHERWISE, THE CURRENT  
FORECAST APPEARS ON TRACK.  
 
PREVIOUS DISCUSSION:  
TODAY: TEMPERATURES WILL CONTINUE TO MODERATE AS THE SURFACE  
HIGH PRESSURE BREAKS DOWN AND TRANSITIONS OFF MID ATLANTIC COAST  
LATE. LOW LEVEL THICKNESS VALUES AND WEAK AFTERNOON RETURN FLOW  
IN THE BOUNDARY LAYER SUGGEST MOST AREAS SHOULD HAVE NO TROUBLE  
REACHING THE 60S; LOWER 60S NORTH TO THE MID 60S SOUTH. WE  
SHOULD SEE PLENTY OF SUNSHINE THIS MORNING BUT MODELS INDICATE  
HIGH CLOUDS WILL TEND TO BECOME THICKER AND MORE WIDESPREAD  
TOWARD LATE AFTERNOON. A WEAK PRESSURE PATTERN OVER THE REGION  
IN THE LOW LEVELS WILL RESULT IN LIGHT WINDS ALL AREAS TODAY.  
 
TONIGHT: WARM AIR ADVECTION PROCESSES ALOFT, INCREASING LAYERED  
CLOUDS, AND ELEVATED LOW LEVEL DEW POINTS WILL RESULT IN MUCH  
MILDER TEMPS OVERNIGHT ACROSS THE AREA. MOST OF THE MOISTURE  
INITIALLY WILL BE MID AND HIGH CLOUDS AND WE HAVE DRY WEATHER  
AND SOME LOW SILENT POPS UNTIL LATE NIGHT. THERE COULD BE A FEW  
SHOWERS BREAKING OUT ACROSS EAST CENTRAL GA ACROSS THE SAVANNAH  
RIVER TO THE SC MIDLANDS LATE NIGHT, WE MAINTAINED SOME 20/30  
POPS ADJACENT TO THESE AREAS AROUND DAYBREAK. THERE COULD BE  
SOME PATCHY FOG IN A FEW SPOTS LATE TONIGHT, NOT ENOUGH  
CERTAINTY TO INSERT INTO OUR FORECAST AT THIS TIME.  
 

 
   
SHORT TERM /MONDAY THROUGH WEDNESDAY/
 
 
MONDAY: HIGH PRESSURE THAT COVERS THE WESTERN ATLANTIC WILL PULL A  
LITTLE FURTHER OFFSHORE. THIS ALLOWS FOR A WARM FRONT TO LIFT NORTH  
OF THE LOCAL AREA IN RESPONSE TO A SURFACE LOW AND ASSOCIATED SHORT  
WAVE TROUGH MOVING FROM THE CENTRAL AND SOUTHERN GREAT PLAINS TOWARD  
THE LOWER AND MIDDLE MISSISSIPPI VALLEY. STRENGTHENING ISENTROPIC  
ASCENT ALONG WITH MID LEVEL PERTURBATIONS AND A DEEP FLOW ALOFT OUT  
OF THE GULF OF MEXICO WILL SUPPORT SCATTERED POP NORTH AND  
NORTHWEST, WITH ISOLATED TO LOW END CHANCE POP SOUTH AND SOUTHEAST.  
QPF IS NO MORE THAN 1/10 TO 2/10 INCHES. EXPECT A LARGE RANGE OF  
TEMPS DEPENDENT UPON THE TIMING OF THE WARM FRONT LIFTING THROUGH,  
FOR NOW WE HAVE 60-63F NORTH AND NORTHWEST, MID 60S TO LOWER 70S  
ELSEWHERE.  
 
MONDAY NIGHT: A CONTINUED FEED OF RICH TROPICAL-LIKE MOISTURE OUT OF  
THE GULF WILL PREVAIL IN ADVANCE OF A COLD FRONT WITHIN A DEEP  
SOUTHWEST FLOW ALOFT. PWAT CLIMBS NEAR 1.5 INCHES, OR CLOSE TO THE  
CLIMATOLOGICAL MAX FOR FEBRUARY OVER THE AREA. THERE IS LARGE SCALE  
FORCING FOR ASCENT WITH A NEARBY 135-145 KT UPPER LEVEL JET, SUPPORTING  
WIDESPREAD RAINS SPREADING IN FROM THE WEST AND SOUTHWEST. WE HAVE  
CATEGORICAL POP AS A RESULT. AFTER COORDINATION WITH WPC WE HAVE  
OPTED TO EXPAND THE "MARGINAL RISK" OF EXCESSIVE RAINFALL INTO  
MOST OF OUR COUNTIES INLAND FROM I-95. QPF WILL REACH AT LEAST  
1/2 TO 1 INCH, WITH LOCALLY HIGHER AMOUNTS. GIVEN THE RECENT HEAVY  
RAIN EVENT IN SOME AREAS, THERE COULD BE A NEED FOR A FLASH  
FLOOD WATCH AT A LATER TIME. TEMPS WILL BE CONSIDERABLY WARMER  
THAN RECENT NIGHTS WITHIN A STRONG WARM ADVECTION PATTERN.  
EXPECT TEMPS TO HOLD FAIRLY STEADY OR EVEN RISE DURING THE  
OVERNIGHT PERIOD.  
 
TUESDAY: A COLD FRONT THAT TRAILS FROM LOW PRESSURE LIFTING INTO THE  
OHIO VALLEY, WILL STALL OVER THE LOCAL AREA AS IT BECOMES ALIGNED TO  
THE FLOW ALOFT. MODELS DIFFER SLIGHTLY ON WHERE THE MAIN MOISTURE  
AXIS BECOMES SITUATED IN RELATION TO SOUTH CAROLINA AND GEORGIA. BUT  
GIVEN MID LEVEL IMPULSES PASSING THROUGH AND LARGE SCALE FORCING  
FOR ASCENT DUE TO THE PRESENCE OF THE 140-150 KT UPPER JET, WE  
MAINTAINED 70-80% POP. WE ADDED MENTION OF ISOLATED T-STORMS GIVEN  
SOME INSTABILITY AND CAPE AND A MID LEVEL JET NEARBY. TEMPS WILL BE  
SEVERAL DEGREES ABOVE CLIMO GIVEN THE WARM ADVECTION REGIME IN  
PLACE.  
 
WEDNESDAY: A SECONDARY AND STRONGER COLD FRONT WILL SWEEP THROUGH IN  
RESPONSE TO A ROBUST SHORT WAVE TROUGH SHIFTING INTO THE EAST. THIS  
SHUNTS THE DEEP PLUME OF MOISTURE FURTHER OFFSHORE, AND CONVECTIVE  
RAIN CHANCES WILL DIMINISH THROUGHOUT THE DAY. GIVEN GOOD QG FORCING  
WE DID HOLD ONTO CHANCE POP, BUT SOUNDINGS AND TIME CROSS-SECTIONS  
DO SHOW CONSIDERABLE DRIER AIR WORKING IT'S WAY IN BEHIND THE SECOND  
COLD FRONT. THE COLD ADVECTION IS RATHER SLUGGISH IN ARRIVING, THUS  
WE STILL HAVE TEMPS WELL ABOVE CLIMO.  
 

 
   
LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/
 
 
A HIGHLY AMPLIFIED MID AND UPPER PATTERN WILL COVER THE LOWER 48  
STATES, SHOWING A BROAD TROUGH OVER THE EASTERN HALF OF THE COUNTRY  
AND RIDGING OUT WEST DURING MOST OF THE PERIOD. AT THE SURFACE, HIGH  
PRESSURE WILL DOMINATE INTO FRIDAY, FOLLOWED BY A COLD FRONT NEXT  
SATURDAY. AS OF THIS TIME THE FRONT LOOKS TO BE MOISTURE STARVED, SO  
WE DON'T HAVE ANY MENTION OF POP. CONFIDENCE IS EXCELLENT THAT GIVEN  
THE LOW HEIGHTS ALOFT AND 850 MB TEMPS THAT ARE AS AS MUCH AS  
SEVERAL DEGREES BELOW 0C, THAT THE END OF FEBRUARY WILL BE WELL  
BELOW CLIMO.  
 
LAKE WINDS: COLDER AIR MOVING ATOP THE RELATIVELY WARMER WATERS OF  
LAKE MOULTRIE WILL LIKELY RESULT IN THE ISSUANCE OF A LAKE WIND  
ADVISORY WEDNESDAY NIGHT INTO THURSDAY NIGHT.  
 

 
   
AVIATION /18Z SUNDAY THROUGH FRIDAY/
 
 
VFR THROUGH 24/12Z AT BOTH KSAV/KCHS. SLIGHT CHANCE OF SOME LOW  
CIGS AT KSAV TOWARD DAYBREAK ON MON.  
 
EXTENDED AVIATION OUTLOOK: A WARM FRONT WILL LIFT NORTH OF THE AREA  
MONDAY, FOLLOWED BY A PAIR OF COLD FRONTS INTO WEDNESDAY. THIS WILL  
RESULT IN PERIODS OF SHOWERS AND MAYBE EVEN A FEW T-STORMS, ALONG  
WITH AT LEAST PERIODIC FLIGHT RESTRICTIONS. VFR ALONG WITH BREEZY TO  
WINDY CONDITIONS WILL THEN PREVAIL BEHIND THE SECOND COLD FRONT INTO  
THURSDAY.  
 

 
   
MARINE
 
 
THROUGH TONIGHT: A WEAK PRESSURE PATTERN ACROSS THE WATERS AS  
HIGH PRESSURE WEAKENS ALONG THE COAST TODAY THEN SETS UP OFF THE  
MID ATLANTIC COAST TONIGHT. WIND SPEEDS WILL MAINLY BE LESS THAN  
10 KT WITH VARIABLE DIRECTIONS, BECOMING ONSHORE. WEAK FLOW WILL  
THEN BECOME SE TO S LATE TONIGHT. SEAS CONTINUE TO SLOWLY SUBSIDE.  
WE HAVE 6 FT SEAS WELL OFFSHORE NEAR THE GULF STREAM OVER THE  
20-60 NM GA WATERS THIS MORNING AND THEN SUSPECT THAT THE SCA  
IN THAT MARINE LEG WILL COME DOWN FOR THIS AFTERNOON.  
 
MONDAY: A WARM FRONT WILL PASS NORTH OF THE LOCAL WATERS, WITH HIGH  
PRESSURE ANCHORED WEST OF BERMUDA. EVEN THOUGH WIND FIELDS ARE  
LIMITED, SEAS ARE SOMEWHAT ELEVATED DUE TO CONTINUED SWELLS  
IMPACTING THE AREA.  
 
MONDAY NIGHT THROUGH WEDNESDAY: ONE COLD FRONT WILL APPROACH ON  
TUESDAY AND STALLS OUT OVER OR NEAR THE LOCAL VICINITY, BEFORE A  
SECOND AND STRONGER COLD FRONT MOVES THROUGH WEDNESDAY. WINDS WILL  
TURN S AND SW AND INCREASE, ALLOWING FOR SEAS TO ALSO CLIMB. WE  
COULD NEED SMALL CRAFT ADVISORIES AT A LATER TIME ON AT LEAST SOME  
OF THE MARINE ZONES. CONVECTIVE RAINS WILL OCCUR DURING MUCH OF THE  
TIME, ALONG WITH SOME POTENTIAL FOR T-STORMS. THERE ARE HINTS OF SEA  
FOG PER MODEL GUIDANCE, BUT THE CONDITIONS OVERALL DON'T APPEAR  
HIGHLY FAVORABLE FOR IT TO OCCUR AS OF THIS TIME.  
 
WEDNESDAY NIGHT THROUGH FRIDAY: STRONG HIGH PRESSURE BUILDS IN FROM  
THE WEST, AND WITH VARYING DEGREES OF COLD ADVECTION AND STEADY  
ISALLOBARIC PRESSURE RISES, WE ANTICIPATE THE NEED FOR ADDITIONAL  
SMALL CRAFT ADVISORIES.  
 

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

 
 

 
NEAR TERM...NED  
SHORT TERM...33  
LONG TERM...33  
AVIATION...RAD  
MARINE...  
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab SC Page
The Nexlab GA Page Main Text Page