217
FXUS62 KCHS 201815
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
115 PM EST THU FEB 20 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 /THROUGH TONIGHT/
DOWNSLOPE FLOW IS DOMINATING THE FORECAST AREA THIS AFTERNOON
WITH HIGH PRESSURE CENTERED OVER THE SOUTHEASTERN STATES. AS THE
ATMOSPHERE DRIES OUT AS A RESULT OF THE DOWNSLOPE FLOW CLOUDS
WILL CLEAR FROM WEST TO EAST. AS OF 1 PM INTERIOR SE GA IS
CLEAR, WITH THE CLEARING LINE VERY PRONOUNCED ON VISIBLE GOES
SATELLITE. TEMPERATURES WILL CONTINUE TO BE A TRICKY FORECAST
INTO THE AFTERNOON, EVEN WITH CLEARING SKIES STRONG COLD AIR
ADVECTION WILL YIELD TEMPERATURES ONLY IN THE UPPER 40S TO MAYBE
50. ACROSS SE SC WHERE CLOUD COVER HASN'T ERODED YET HIGHS WILL
ONLY REACH INTO THE LOW TO MID 40S.
KCLX HAS DETECTED SOME VERY LIGHT RETURNS (~15DBZ) MOVING INTO
THE CHARLESTON TRI-COUNTY FROM THE NW. SOME DRIZZLE IS POSSIBLE
WITH THESE RETURNS, HOWEVER POPS WILL REMAIN LESS THAN 15% AND
NO WEATHER IS MENTIONED IN THE FORECAST.
TONIGHT, AN ARCTIC AIR MASS WILL SPREAD ACROSS THE FORECAST
AREA TONIGHT. THE CENTER OF THE 1040 MB HIGH WILL REMAIN
CENTERED OVER THE GREAT PLAINS OVERNIGHT. GIVEN COLD LLVL
THICKNESSES AND CLEAR SKY, TEMPERATURES SHOULD STEADILY COOL
THROUGH THE NIGHT. USING A BLEND OF THE COOLER MOS MEMBERS, LOW
TEMPERATURES ARE FORECAST TO RANGE IN THE LOW TO MID 20S. IN
FACT, THE LOW TEMPERATURE AT KCHS MAY REACH THE RECORD LOW
TEMPERATURE OF 22 DEGREES SET IN 1958. NORTH WINDS ARE FORECAST
TO REMAIN BETWEEN 5 TO 10 MPH OVERNIGHT, RESULTING IN WIND CHILL
VALUES TO FALL TO 14 TO 17 DEGREES. A COLD WEATHER ADVISORY HAS
BEEN POSTED FOR THE ENTIRE FORECAST AREA TONIGHT, ENDING BY
MID-MORNING FRIDAY.
SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/
A FEW MORE HOURS OF BELOW 20 DEGREE WIND CHILLS FRIDAY MORNING AS
THE SUN RISES, GETTING ABOVE THE 20 DEGREE THRESHOLD BY THE MID-
MORNING HOURS. BE SURE TO BUNDLE UP BEFORE HEADING OUT THE DOOR,
ESPECIALLY THE KIDS WAITING FOR THE SCHOOL BUS. THROUGHOUT THE DAY A
SURFACE HIGH PRESSURE WILL BE MOVING EASTWARDS OUT OF THE CENTRAL
CONUS, KEEPING THE AREA DRY AND CHILLY WITH HIGHS IN THE MID 40S TO
LOWER 50S. ENSEMBLE SITUATIONAL AWARENESS TABLES (ESATS) SHOW
TEMPERATURES AT THE SURFACE REMAIN IN THE BOTTOM 2.5TH PERCENTILE OF
CLIMATOLOGY, SETTING UP CHS TO POSSIBLY BREAK A RECORD LOW MAX
TEMPERATURE (THE COLDEST HIGH TEMPERATURE FOR THE DATE) OF 47
DEGREES WITH A HIGH OF 46, THOUGH SAV AND CXM HAVE MUCH COLDER
RECORDS OUT OF REACH IN THE MID 30S.
AS THE HIGH PRESSURE CONTINUES TO SLIDE EASTWARDS, WE'LL HAVE ONE
MORE OVERNIGHT PERIOD INTO SATURDAY WITH LOWS IN THE MID 20S TO
LOWER 30S. WINDS LOOK TO REMAIN WEAK ENOUGH TO KEEP MINIMUM WIND
CHILLS IN THE MID 20S TO LOWER 30S, ABOVE CRITICAL THRESHOLDS.
QUIET CONDITIONS CONTINUE ON SATURDAY AS THE SURFACE HIGH
PRESSURE BEGINS TO WEAKEN, WITH SOUTHERLY WINDS EXPECTED BY THE
AFTERNOON HOURS AS AN 850MB HIGH DEVELOPS OFF TO OUR SOUTH. THIS
WILL SEND WARM AIR ADVECTION (WAA) BACK ACROSS THE REGION,
BRINGING THE REGION UP INTO THE LOWER TO MID 50S ACROSS SC AND
MID 50S TO LOWER 60S ACROSS GA.
THE WAA COMBINED WITH A SHORTWAVE MOVING THROUGH QUASI-ZONAL FLOW
WILL LEAD TO THE DEVELOPMENT OF A COASTAL LOW, WHICH IS EXPECTED TO
MOVE NORTHEAST UP THE COAST DURING THE EARLY MORNING HOURS ON
SUNDAY. DETERMINISTIC AND ENSEMBLE GUIDANCE CONTINUES TO DISAGREE ON
WHETHER OR NOT PRECIPITATION WILL REACH THE COASTAL AREAS, WITH THE
LATEST NBM KEEPING RAIN CHANCES OFF THE COAST. GIVEN THE 10-20%
CHANCES SEEN IN THE GEFS AND GEPS FOR SOME LIGHT RAIN FOR THE
CHARLESTON AREA, DID INTRODUCE 15-20% POPS FOR LIGHT RAIN DURING THE
LATE EVENING SATURDAY INTO SUNDAY MORNING, WHICH ALSO CARRIES
SUPPORT VIA ENSEMBLE CLUSTERING. SOME HINTS VIA THE LATEST 00.Z
GUIDANCE THAT CHANCES FOR RAIN MAY NEED TO BE INCREASED OVERNIGHT
INTO MONDAY, BUT FOR NOW THE NBM DOES HAVE SOME LOW (<20%) FOR LIGHT
SHOWERS ALONG THE COAST.
LONG TERM /MONDAY THROUGH WEDNESDAY/
HIGH PRESSURE BUILDS ALONG THE GULF COAST KEEPING THE AREA DRY AND
WARM THROUGH TUESDAY. WHILE THE TIMING IS NOT WELL AGREED UPON,
ENSEMBLE GUIDANCE DOES SHOW THAT A BROAD AREA OF LOW PRESSURE WILL
BE MOVING OVER THE GREAT LAKES REGION, WITH UPPER LEVEL TROUGHING
EXTENDING DOWN INTO THE FORECAST AREA OVERNIGHT INTO WEDNESDAY.
CHANCES FOR RAIN OUT OF THAT SYSTEM ARE NOT WELL AGREED UPON, WITH
THE NBM KEEPING THE REGION DRY WITH THAT PASSAGE.
DETERMINISTIC AND ENSEMBLES GUIDANCE SHOWS ANOTHER TROUGH DEVELOP
ACROSS THE ROCKIES ON WEDNESDAY, WITH A SURFACE LOW DEVELOPING ON
THE LEESIDE OF THE ROCKIES AS IT MOVES ONTO THE CENTRAL PLAINS. WILL
LIKELY SEE SOME RAIN OUT OF THE SYSTEM BY LATE THURSDAY INTO FRIDAY,
WITH TEMPERATURES LOOKING TO STAY SEASONABLE/WARM IN THE 60S AND
70S.
AVIATION /18Z THURSDAY THROUGH TUESDAY/
KCHS/KJZI: BOTH TERMINALS WILL INITIALIZE WITH MVFR CIGS AS
CLOUD COVER REMAINS PERSISTENT ACROSS THE AREA DESPITE THE
DOWNSLOPE FLOW. CONDITIONS SHOULD RETURN TO VFR LATER THIS
AFTERNOON, WITH SKC EXPECTED BY MIDNIGHT. SOME GUSTY NW WINDS
ARE POSSIBLE THIS AFTERNOON AS WELL, WANING AROUND NIGHTFALL.
KSAV: THE 18Z TAF WILL FEATURE VFR CONDITIONS THROUGHOUT, WITH
SOME GUSTY NW WINDS THIS AFTERNOON WANING BY NIGHTFALL. SKC IS
EXPECTED BY MIDNIGHT.
EXTENDED AVIATION OUTLOOK: VFR CONDITIONS ARE EXPECTED TO
PREVAIL.
MARINE
TODAY THROUGH TONIGHT, THE COMBINATION OF A STEEPENING PRESSURE
GRADIENT AND COLD AIR ADVECTION SHOULD SUPPORT GUSTY NW WINDS. GUSTS
ARE FORECAST TO RANGE BETWEEN 25 TO 30 KTS ACROSS THE CHARLESTON
COUNTY NEARSHORE AND OUTER GA WATERS. SEAS WILL RANGE BETWEEN 3 TO 6
FT. SMALL CRAFT ADVISORIES WILL REMAIN IN EFFECT TO HIGHLIGHT THE
WIND AND WAVE HEIGHTS.
FRIDAY THROUGH TUESDAY: HIGH PRESSURE WILL RETURN TO THE REGION
FRIDAY THROUGH SATURDAY. WINDS AND SEAS SHOULD REMAIN BELOW SCA
CRITERIA. ANOTHER COASTAL LOW MAY DEVELOP OVER THE WATERS ON SUNDAY,
MOVING AWAY FROM THE REGION ON MONDAY. THERE MAY BE AN INCREASE IN
WINDS AND SEAS, BUT CONDITIONS SHOULD REMAIN BELOW ADVISORY
CRITERIA. HIGH PRESSURE WILL EXPAND ACROSS THE MARINE ZONES ON
TUESDAY. SOUTHWEST WINDS ARE FORECAST TO RANGE BETWEEN 10-15 KTS WITH
SEAS BETWEEN 2-3 FT.
CLIMATE
RECORD LOW MAXIMUM TEMPERATURES:
FEBRUARY 21:
KCHS: 47/2020
RECORD LOW TEMPERATURES:
FEBRUARY 21:
KCHS: 22/1958
CHS WATCHES/WARNINGS/ADVISORIES
GA...COLD WEATHER ADVISORY FROM 10 PM THIS EVENING TO 10 AM EST
FRIDAY FOR GAZ087-088-099>101-114>119-137>141.
SC...COLD WEATHER ADVISORY FROM 10 PM THIS EVENING TO 10 AM EST
FRIDAY FOR SCZ040-042>045-047>052.
MARINE...SMALL CRAFT ADVISORY UNTIL 10 AM EST FRIDAY FOR AMZ350.
SMALL CRAFT ADVISORY UNTIL 5 PM EST FRIDAY FOR AMZ374.
NEAR TERM...CPM/NED
SHORT TERM...
LONG TERM...
AVIATION...CPM
MARINE...NED
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