259
FXUS62 KCHS 192041
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
341 PM EST WED FEB 19 2025
SYNOPSIS
COLD HIGH PRESSURE WILL BUILD INTO THE REGION THROUGH THE START
OF THE WEEKEND. AN AREA OF LOW PRESSURE WILL DEVELOP OFF THE
COAST ON SUNDAY, FOLLOWED BY MORE HIGH PRESSURE INTO EARLY NEXT
WEEK.
NEAR TERM /UNTIL 6 AM THURSDAY MORNING/
COLD AIR DAMMING (CAD) WILL PERSIST THROUGH THE REMAINDER OF THE
AFTERNOON ACROSS THE LOCAL FORECAST AREA AS HIGH PRESSURE BUILDS
INTO THE REGION FROM THE NORTH. JUST OFFSHORE LOW PRESSURE HAS
DEVELOPED, ANALYZED OFF THE SC/GA COAST IN THE 18Z WPC SURFACE
ANALYSIS. KCLX CONTINUES TO DETECT LIGHT RETURNS ACROSS THE REGION.
RAIN WILL CONTINUE INTO THE EVENING, TAPERING OFF FROM SW TO NE
AROUND MIDNIGHT. TEMPERATURES HAVE BEGUN TO DECREASE ACROSS SE SC,
WITH THE TEMPERATURE AT KCHS AT 43F AT 3 PM. COLD AIR ADVECTION
(CAA) WILL CONTINUE TO INCREASE AS THE OFFSHORE LOW TREKS
FURTHER TO THE NE AND WINDS BEGIN TO INCREASE AND SHIFT TO THE
N. NEAR THE END OF THE PRECIPITATION, THERE IS A LOW END CHANCE
FOR SOME FREEZING RAIN IN NORTHERN BERKELEY COUNTY, NORTH OF
LAKE MOULTRIE. NO IMPACTS ARE ANTICIPATED, HOWEVER A LIGHT GLAZE
OF ICE MAY BE POSSIBLE IN SOME TREES OR OTHER SHADED, COLD
LOCATIONS. SOIL TEMPERATURES APPEAR TOO WARM FOR ANY
ACCUMULATION. CLOUDY CONDITIONS WILL PERSIST THROUGH THE
OVERNIGHT, EVEN ONCE THE RAINFALL CONCLUDES, HOWEVER WITH
INCREASING CAA TEMPERATURES WILL DIP INTO THE 30S ACROSS THE
REGION, WITH BELOW FREEZING TEMPERATURES IN NORTHERN PORTIONS OF
THE FORECAST AREA AND UPPER 30S IN SE GA AND ALONG THE BEACHES.
SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY NIGHT/
THURSDAY AND THURSDAY NIGHT: ALOFT, THE FORECAST AREA WILL SIT JUST
TO THE SOUTH WITHIN ZONAL FLOW AROUND A CLOSED LOW TRACKING EAST
FROM THE OHIO VALLEY INTO THE MID ATLANTIC AND NEW ENGLAND. AT THE
SURFACE, A DEEPENING LOW OFF THE EAST COAST WILL TRACK OFF TO THE
NORTHEAST AS COLD HIGH PRESSURE BUILDS INTO THE REGION. DURING THE
DAY, A WELL DEFINED SURFACE TROUGH WILL PUSH SOUTHEASTWARD OUT OF
THE WESTERN CAROLINAS AND SHOULD GET INTO THE FORECAST AREA DURING
THE AFTERNOON HOURS. MODEL GUIDANCE IS IN GOOD AGREEMENT THAT AN
AREA OF SHOWERS WILL TRY TO DEVELOP ALONG THE SURFACE TROUGH
UPSTREAM OF THE AREA AND THEN GRADUALLY DIMINISH AS IT APPROACHES
DURING THE AFTERNOON. THERE ARE SOME INDICATIONS FROM HI-RES MODEL
OUTPUT THAT A FEW SHOWERS COULD MAKE IT INTO PORTIONS OF THE
CHARLESTON TRI-COUNTY REGION, BUT CURRENT THINKING IS THAT DOWNSLOPE
FLOW SHOULD HELP TO NEGATE SHOWER DEVELOPMENT AS IT ARRIVES. SO
WHILE THERE COULD BE A FEW LIGHT RETURNS ON RADAR, NO MEASURABLE
PRECIPITATION IS EXPECTED AND WE ARE NOW CARRYING A DRY FORECAST.
EXPECT A VERY CHILLY DAY THANKS TO LOW-LEVEL COLD ADVECTION AND
LINGERING LOW-LEVEL CLOUD COVER FOR MUCH OF THE AREA THROUGH THE
AFTERNOON. FORECAST HIGHS RANGE FROM THE LOW TO MID 40S FOR THE TRI-
COUNTY REGION TO THE UPPER 40S AND LOW 50S ACROSS SOUTHEAST GA. SUCH
VALUES WILL BE ON THE ORDER OF 15-20 DEGREES BELOW NORMAL. TO MAKE
IT FEEL EVEN MORE CHILLY, NORTHWEST WINDS WILL FREQUENTLY GUST INTO
THE 20-25 MPH RANGE WHICH WILL YIELD WIND CHILL VALUES IN THE UPPER
30S TO LOW 40S FOR SOUTHEAST GA AND THE MID TO UPPER 30S FOR
SOUTHEAST SC. OVERNIGHT, SKIES WILL CLEAR OUT AND THE MAIN STORY
WILL BE A VERY COLD NIGHT. LOWS ARE FORECAST TO DIP INTO THE LOW TO
MID 20S. WITH NORTH WINDS STAYING UP IN THE 5-10 MPH RANGE THROUGH
THE OVERNIGHT, WIND CHILLS ARE FORECAST TO FALL INTO THE UPPER TEENS
FOR NEARLY THE ENTIRE AREA LATE THURSDAY NIGHT AND EARLY FRIDAY
MORNING. A COLD WEATHER ADVISORY WILL VERY LIKELY BE NEEDED FOR THE
ENTIRE FORECAST AREA.
FRIDAY THROUGH SATURDAY: HIGH PRESSURE WILL PREVAIL ACROSS THE
REGION FOR FRIDAY AND SATURDAY. FRIDAY WILL BRING THE COLDEST
TEMPERATURES OF THE PERIOD WITH THE MORNING STARTING IN THE LOW TO
MID 20S AND HIGHS ONLY REACHING THE UPPER 40S IN MOST PLACES, WHICH
WOULD BE ON THE ORDER OF 15-18 DEGREES BELOW NORMAL. KCHS WILL
LIKELY COME CLOSE TO BOTH A RECORD LOW TEMPERATURE AND A RECORD LOW
MAXIMUM TEMPERATURE FOR 2/21 (SEE CLIMATE SECTION BELOW). FRIDAY
NIGHT WILL BE ANOTHER VERY COLD NIGHT, WITH LOWS IN THE MID TO UPPER
20S AWAY FROM THE IMMEDIATE COAST. SATURDAY IS EXPECTED TO BRING A
SOLID REBOUND IN TEMPERATURES WITH HIGHS IN THE MID TO UPPER 50S
ACROSS THE AREA.
LONG TERM /SUNDAY THROUGH WEDNESDAY/
AN AREA OF LOW PRESSURE IS EXPECTED TO DEVELOP OFF THE COAST ON
SUNDAY AND MOVE AWAY FROM THE AREA INTO MONDAY. WE ARE CARRYING A
DRY FORECAST, THOUGH THERE IS SOME SUPPORT IN DETERMINISTIC MODEL
OUTPUT FOR RAINFALL LATER SUNDAY INTO MONDAY MORNING. THEREAFTER,
HIGH PRESSURE SHOULD RETURN TO THE REGION AND THE FORECAST APPEARS
QUIET. TEMPERATURES SHOULD TREND WARMER THROUGH THE PERIOD, PERHAPS
GETTING BACK INTO THE 70S BY TUESDAY.
AVIATION /21Z WEDNESDAY THROUGH MONDAY/
18Z TAFS: SURFACE HIGH PRESSURE WILL RIDGE ACROSS THE TERMINALS
THROUGH THE TAF PERIOD. AN AREA OF LOW PRESSURE WILL DEVELOP
OFF THE GA/SC COAST THIS AFTERNOON, TRACKING TO THE NORTHEAST.
THIS PATTERN WILL RESULT IN A STRENGTHENING AREA OF COLD AIR
DAMMING ACROSS THE REGION THROUGH THE REMAINDER OF THE AFTERNOON
THROUGH TONIGHT. BOTH KCHS AND KJZI WILL INITIALIZE THE 18Z TAF
PERIOD WITH MVFR CIGS AND A TEMPO GROUP OF IFR CIGS. KSAV WILL
INITIALIZE WITH IFR CIGS. A STEADY LIGHT RAIN WILL ALSO PERSIST
THROUGH THE AFTERNOON, ALTHOUGH SIGNIFICANT REDUCTIONS IN
VISIBILITIES ARE NOT EXPECTED. LINGERING CAD AND COOLING
TEMPERATURES TONIGHT WILL LIKELY RESULT IN THE LOW LEVEL
INVERSION TO LOWER TONIGHT. CLOUD BASES ARE FORECAST TO DROP
BELOW 500 FT AT KSAV/KCHS/KJZI THIS EVENING, CEILINGS MAY SLOWLY
RISE DURING THE PRE-DAWN HOURS THURSDAY MORNING. LIFR CIGS ARE
MENTIONED IN ALL THREE TAF SITES FOR A PORTION OF THE OVERNIGHT
HOURS. FLIGHT RESTRICTIONS WILL LIKELY PERSIST INTO THURSDAY,
WITH MVFR CIGS FORECAST THROUGH THE END OF THE 18Z TAF PERIOD.
EXTENDED AVIATION OUTLOOK: VFR CONDITIONS ARE EXPECTED TO
PREVAIL.
MARINE
TONIGHT: A LOW PRESSURE CENTER HAS DEVELOPED OFF THE SC/GA
BORDER AND THE RESULTANT PINCHED PRESSURE GRADIENT HAS YIELDED
NE WIND GUSTS TO INCREASE ACROSS THE LOCAL WATERS. A SMALL CRAFT
ADVISORY IS IN EFFECT FOR THE CHARLESTON COUNTY NEARSHORE AND 20
TO 60 NM OFFSHORE GA WATERS FOR GUSTS TO 25 KNOTS AS WELL AS
SOME 6 FT SEAS. GUSTS COULD APPROACH 25 KNOTS IN THE OTHER LOCAL
WATERS, HOWEVER CONDITIONS SHOULD BE SHORT LIVED.
THURSDAY THROUGH MONDAY: HIGH PRESSURE WILL BUILD IN FROM THE
NORTHWEST AND THE COMBINATION OF COLD ADVECTION AND A TIGHTENING
PRESSURE GRADIENT WILL PRODUCE STRONG NORTHWESTERLY TO NORTHERLY
FLOW ACROSS THE LOCAL WATERS. WINDS WILL PEAK THURSDAY NIGHT INTO
FRIDAY MORNING, WITH SUSTAINED WINDS OF 20-25 KNOTS AND GUSTS UP TO
30 KNOTS. SMALL CRAFT ADVISORIES ARE ALREADY IN EFFECT FOR THE
CHARLESTON COUNTY WATERS AND THE OUTER GA WATERS AND HAVE BEEN
EXTENDED THROUGH FRIDAY MORNING. WE WILL LIKELY ALSO NEED ADVISORIES
FOR THE SOUTHERN SC WATERS AND THE NEARSHORE GA WATERS, BUT THERE IS
ENOUGH OF A LAG TO HOLD OFF ON ISSUING FOR NOW. CONDITIONS WILL THEN
STEADILY IMPROVE FRIDAY AND INTO THE WEEKEND. OVERALL CONDITIONS
SHOULD REMAIN BELOW SMALL CRAFT ADVISORY THRESHOLDS INTO EARLY NEXT
WEEK.
CLIMATE
RECORD LOW MAXIMUM TEMPERATURES:
FEBRUARY 21:
KCHS: 47/2020
RECORD LOW TEMPERATURES:
FEBRUARY 21:
KCHS: 22/1958
CHS WATCHES/WARNINGS/ADVISORIES
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 10 AM EST FRIDAY FOR AMZ350.
SMALL CRAFT ADVISORY UNTIL 1 PM EST FRIDAY FOR AMZ374.
NEAR TERM...CPM
SHORT TERM...BSH
LONG TERM...BSH
AVIATION...BSH/CPM
MARINE...BSH/CPM
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