567
FXUS62 KCHS 201433
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
933 AM EST WED NOV 20 2024
SYNOPSIS
A STRONG COLD FRONT WILL MOVE THROUGH THE AREA THIS EVENING.
CANADIAN HIGH PRESSURE WILL BUILD ACROSS THE AREA THURSDAY AND
WILL REMAIN THE PRIMARY FEATURE THROUGH EARLY NEXT WEEK.
NEAR TERM /THROUGH TONIGHT/
NO MAJOR CHANGES MADE WITH THE MID-MORNING UPDATE, JUST SOME
SLIGHT ADJUSTMENTS TO MATCH CURRENT OBSERVATIONS. FORECAST IS
ON TRACK.
TODAY: ALOFT, SHORTWAVE ENERGY WILL SHIFT OFF THE COAST LATER THIS
MORNING FOLLOWED BY STRENGTHENING ZONAL FLOW ON THE SOUTHEAST
PERIPHERY OF AN IMPRESSIVE LOW ACROSS THE NORTH-CENTRAL CONUS.
AT THE SURFACE, THE FORECAST AREA WILL SOLIDLY BE WITHIN THE
WARM SECTOR AHEAD OF THE MAIN COLD FRONT WHICH WILL PUSH EAST OF
THE MISSISSIPPI THIS MORNING AND MOVE INTO GEORGIA AND THE
WESTERN CAROLINAS LATER THIS AFTERNOON. ONGOING EARLY MORNING
SCATTERED SHOWER ACTIVITY IS BEING FORCED IN AN AREA WITH
PRECIPITABLE WATER VALUES IN THE 1.5-1.75" RANGE, COINCIDENT
WITH ISENTROPIC ASCENT IN ADVANCE OF A PRE-FRONTAL TROUGH.
SHOWER COVERAGE IS EXPECTED TO REMAIN SCATTERED AND VERY LIGHT AS
IT TRACKS EASTWARD THROUGH MID TO LATE MORNING. RAINFALL
AMOUNTS SHOULD BE ON THE LIGHT SIDE, MOSTLY A FEW HUNDREDTHS OF
AN INCH. RAIN CHANCES ARE EXPECTED TO DIMINISH GREATLY FROM
WEST TO EAST AROUND MIDDAY AND INTO THE EARLY AFTERNOON, SUCH
THAT MOST OF THE AREA SHOULD BE RAIN-FREE. THE LAST GASP OF
SHOWERS WILL LIKELY COME IN THE MID TO LATE AFTERNOON AHEAD OF
THE PRIMARY FRONT, BUT VERY LITTLE (IF ANY) COVERAGE IS
EXPECTED. LOW STRATUS IS EXPECTED TO SPREAD ACROSS THE AREA AND
PERSIST THROUGH THE DAY, RESULTING IN OVERCAST OR MOSTLY CLOUDY
CONDITIONS. IT WILL BE A WARM DAY, WITH HIGHS IN THE LOW TO MID
70S.
TONIGHT: THE COLD FRONT IS PROGGED TO ENTER THE FORECAST AREA
THIS EVENING AND THEN MOVE OFFSHORE BY ROUGHLY MIDNIGHT. MUCH
DRIER AND COLDER AIR WILL FILTER IN AND THE FORECAST FOR THE
OVERNIGHT IS DRY. THE MAIN STORY WILL BE STRENGTHENING WINDS IN
THE COLD ADVECTION. NORTHWEST WINDS WILL FREQUENTLY GUST INTO
THE 15-20 MPH RANGE IN THE EARLY MORNING HOURS, WITH GUSTS UP TO
AROUND 25 MPH ALONG THE IMMEDIATE COAST. LOWS ARE FORECAST TO
BE IN THE LOW TO MID 40S INLAND TONIGHT, WITH MID TO UPPER 40S
ALONG THE COAST.
LAKE WINDS: A STRONG COLD FRONT WILL SWEEP ACROSS LAKE MOULTRIE
THIS EVENING, RESULTING IN DEEPENING MIXING PROFILES OVER THE
LAKE AS COLDER AIR MOVES OVER THE RELATIVELY WARMER LAKE WATERS.
FREQUENT GUSTS INTO THE 25-30 KNOT RANGE ARE EXPECTED, AND A
LAKE WIND ADVISORY HAS BEEN ISSUED BEGINNING AT 10PM.
SHORT TERM /THURSDAY THROUGH SATURDAY/
MID LEVEL LOW INITIALLY OVER THE GREAT LAKES WILL ROTATE TO THE
MID-ATLANTIC AND NORTHEAST THURSDAY INTO FRIDAY, WITH THE
LARGER SCALE TROUGH EXTENDING DOWN THE ENTIRE EAST COAST.
SURFACE LOW WILL CONTINUE TO MEANDER OVER THE NORTHEASTERN PART
OF THE COUNTRY WHILE HIGH PRESSURE BEGINS TO BUILD. A TIGHT
PRESSURE GRADIENT BETWEEN THESE TWO FEATURES WILL SUPPORT GUSTY
WEST WINDS BOTH DAYS. DESPITE FULL SUNSHINE, COLD AIR MASS WILL
LIMIT HIGHS TO THE UPPER 50S/LOW 60S ON THURSDAY, THEN MID/UPPER
50S (~10 DEGREES BELOW NORMAL) FOR FRIDAY. LOWS WILL ALSO BE
CHILLY, ESPECIALLY FRIDAY NIGHT WHEN TEMPERATURES DIP WELL INTO
THE 30S INLAND OF THE IMMEDIATE COAST. WHILE THESE TEMPS WOULD
BE SUPPORTIVE FOR SOME FROST DEVELOPMENT FRIDAY NIGHT/SATURDAY
MORNING, CURRENT FORECAST KEEPS WINDS A BIT TOO HIGH FOR A
WIDESPREAD THREAT. WILL BE SOMETHING TO WATCH.
MAIN TROUGH AXIS WILL HAVE EXITED OFF THE COAST BY SATURDAY
WITH THE PATTERN BEGINNING TO FLATTEN. SURFACE HIGH PRESSURE
INITIALLY OVER THE MISSISSIPPI RIVER VALLEY WILL TRANSITION TO
OVER THE SOUTHEAST. COOL AND DRY CONDITIONS WILL PERSIST. HIGHS
WILL AGAIN BE BELOW CLIMO AROUND 60/LOW 60S.
LAKE WINDS: GUSTY WEST WINDS ARE EXPECTED TO PERSIST OVER LAKE
MOULTRIE ON THURSDAY, MAINTAINING THE ONGOING LAKE WIND
ADVISORY. CONDITIONS BECOME MORE MARGINAL FOR THURSDAY NIGHT AND
FRIDAY, BUT IT'S POSSIBLE THE CURRENT END TIME OF THE ADVISORY
(00Z FRIDAY) MAY NEED TO BE EXTENDED.
LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/
SURFACE HIGH PRESSURE WILL MAINTAIN INFLUENCE OVER THE LOCAL
WEATHER SUNDAY THROUGH TUESDAY. NOT MUCH GOING ON UPSTAIRS WITH
RELATIVELY ZONAL FLOW. RAIN-FREE FORECAST IN PLACE WITH WARMING
TEMPERATURES THROUGH THE PERIOD. MAIN FORECAST CONCERN REMAINS
THE POTENTIAL FOR FROST LATE SATURDAY NIGHT/EARLY SUNDAY MORNING
AS IDEAL RADIATIONAL COOLING CONDITIONS ALLOW TEMPERATURES TO
FALL TO THE MID/UPPER 30S INLAND OF THE COAST. FROST IS
POSSIBLE, MAINLY OVER FAR INTERIOR LOCATIONS.
AVIATION /15Z WEDNESDAY THROUGH SUNDAY/
THE 12Z TAF PERIOD BEGINS WITH VFR CONDITIONS AT KCHS AND KJZI,
AND LIGHT RAIN AND MVFR CEILINGS AT KSAV. THE LIGHT RAIN SHOULD
FINALLY SHIFT OUT OF THE KSAV AREA BY MID MORNING, WITH THIS
LIGHT RAIN POTENTIALLY HANGING AROUND KCHS AND KJZI THROUGH
AROUND MIDDAY. THE MAIN FORECAST CHALLENGE WILL BE THE POTENTIAL
ARRIVAL OF IFR CEILINGS OVER THE NEXT FEW HOURS. MODEL GUIDANCE
CONTINUES TO BE VERY CONFIDENT THAT IFR CONDITIONS WILL OCCUR
AND HANG AROUND INTO THE AFTERNOON AT ALL 3 TAF SITES. WE HAVE
DELAYED THE ONSET OF IFR FROM THE PREVIOUS FORECAST, BRINGING IT
INTO KSAV BY 14Z, AND THEN KCHS AND KJZI AROUND 15-16Z. THESE
IFR CEILINGS WILL LIKELY PERSIST INTO THE AFTERNOON BEFORE
LIFTING TO MVFR. A COLD FRONT WILL PUSH THROUGH THIS EVENING,
CLEARING OUT THE LOW STRATUS AND ALLOWING VFR CONDITIONS TO
RETURN. WINDS WILL TURN NORTHWESTERLY AND BECOME GUSTY (UP TO 20
KNOTS AT TIMES) BEGINNING AROUND 02-03Z AND PERSISTING THROUGH
THE END OF THE TAF PERIOD.
EXTENDED AVIATION OUTLOOK: VFR. GUSTY WEST WINDS ARE EXPECTED
THURSDAY AND FRIDAY.
MARINE
TODAY AND TONIGHT: THE FLOW ACROSS THE LOCAL WATERS TODAY WILL
MOSTLY BE SOUTHWESTERLY AND UP TO AROUND 15 KNOTS. THE BIG
CHANGE WILL COME THIS EVENING AND OVERNIGHT AS A COLD FRONT
SWEEPS THROUGH AND BRINGS A STRONG SURGE OF NORTHWEST FLOW.
WINDS ARE EXPECTED TO RAMP UP BEGINNING LATE THIS EVENING AND
PEAK THROUGH THE EARLY MORNING HOURS. ACROSS THE NEARSHORE
WATERS AND CHARLESTON HARBOR, FREQUENT GUSTS UP TO AROUND 30
KNOTS ARE EXPECTED, WITH A FEW INTO THE LOW 30 KNOT RANGE
POSSIBLE. SMALL CRAFT ADVISORIES HAVE BEEN ISSUED FOR THESE
AREAS. FOR THE OUTER GEORGIA WATERS, THERE IS SUFFICIENT
POTENTIAL FOR A PERIOD OF GALE FORCE WIND GUSTS TO GO WITH A
GALE WATCH. SEAS WILL RAMP UP IN RESPONSE TO THE WINDS,
INCREASING TO 3-5 FEET FOR THE NEARSHORE WATERS AND 5-7 FEET FOR
THE OUTER WATERS.
THURSDAY THROUGH MONDAY: GUSTY WEST WINDS WILL PERSIST OVER THE
COASTAL WATERS THURSDAY THROUGH FRIDAY NIGHT, MAINTAINING THE
ONGOING SMALL CRAFT ADVISORIES. FOR THE CHARLESTON HARBOR, GUSTS
TO 25 KNOTS ARE EXPECTED THURSDAY INTO THURSDAY NIGHT, THEN IT
LOOKS A BIT MORE MARGINAL FOR FRIDAY. IMPROVEMENT IS EXPECTED
SATURDAY WITH WINDS AND SEAS REMAINING BELOW ADVISORY LEVELS
THROUGH MONDAY.
CHS WATCHES/WARNINGS/ADVISORIES
GA...NONE.
SC...LAKE WIND ADVISORY FROM 10 PM THIS EVENING TO 7 PM EST
THURSDAY FOR SCZ045.
MARINE...SMALL CRAFT ADVISORY FROM 10 PM THIS EVENING TO 7 AM EST
FRIDAY FOR AMZ330.
SMALL CRAFT ADVISORY FROM 10 PM THIS EVENING TO 7 AM EST
SATURDAY FOR AMZ350-352-354.
GALE WATCH FROM THIS EVENING THROUGH THURSDAY MORNING FOR
AMZ374.
NEAR TERM...BSH/CPM
SHORT TERM...ETM
LONG TERM...ETM
AVIATION...BSH/ETM
MARINE...BSH/ETM
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