261
FXUS62 KCHS 181755
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1255 PM EST TUE FEB 18 2025
SYNOPSIS
HIGH PRESSURE WILL BUILD INTO THE AREA TODAY. A COASTAL LOW
WILL TRACK NORTHEASTWARDS OFF THE GEORGIA/SOUTH CAROLINA COAST
ON WEDNESDAY, WITH HIGH PRESSURE RETURNING AT THE END OF THE
WEEK.
NEAR TERM /THROUGH TONIGHT/
THE REGION WILL REMAIN UNDER THE INFLUENCE OF HIGH PRESSURE AT
THE SURFACE THROUGH THE AFTERNOON AND INTO THIS EVENING. TO THE
WEST A TROUGH ALOFT WILL SWING EASTWARD, WITH A LARGE SHIELD OF
CIRRUS CLOUDS SPREADING ACROSS THE FORECAST AREA AHEAD OF IT.
CLOUD COVER WILL CONTINUE TO INCREASE THROUGH THE REMAINDER OF
THE DAY. TEMPERATURES HAVE GENERALLY REACHED INTO THE MID TO
UPPER 50S, WITH ANY POCKETS OF SUNSHINE ALLOWING FOR ADDITIONAL
WARMING OF A FEW DEGREES THIS AFTERNOON.
SATELLITE WATER VAPOR THIS MORNING CLEARLY SHOWED THE POSITION
OF THE JET STREAM, ACROSS THE SOUTHERN PLAINS EAST ACROSS THE
MID- ATLANTIC STATES. BY LATE TONIGHT, THE JET WILL PIVOT OVER
THE SOUTHERN MISSISSIPPI RIVER VALLEY AND STRENGTHEN AHEAD OF
THE H5 TROUGH. NEAR TERM GUIDANCE SHOWS THAT A SFC LOW WILL
ORGANIZE NEAR THE MISSISSIPPI DELTA LATE TONIGHT. IN ADDITION,
AN INVERTED TROUGH IS EXPECTED TO DEVELOP OVER THE GULF STREAM
OFF THE GA/SC COAST DURING THE PRE-DAWN HOURS. GFS1DEG VIEW OF
H5 Q-VECTOR CONVERGENCE INDICATES THAT A SPOKE OF 5 TO 10 UNITS
WILL PUSH ACROSS THE FORECAST AREA AHEAD THE AMPLIFYING WAVE
TONIGHT. THE FORECAST WILL FEATURE DRY CONDITIONS THROUGH LATE
TONIGHT. HOWEVER, ISOLATED TO SCATTERED LIGHT SHOWERS SHOULD
SPREAD SW TO NE ACROSS THE REGION BEFORE DAYBREAK WEDNESDAY,
SUPPORTED BY THE SYNOPTIC SCALE FORCING. LOW TEMPERATURES ARE
FORECAST TO RANGE FROM AROUND 40 DEGREES INLAND TO THE MID TO
UPPER 40S ALONG THE COAST.
SHORT TERM /WEDNESDAY THROUGH FRIDAY NIGHT/
BY DAYBREAK WEDNESDAY MORNING, THE COASTAL LOW OR PREFRONTAL TROUGH
WILL CONTINUE TO SLOWLY DRIFT NORTHWARDS, WHILE THE LOW MOVING
ACROSS THE GULF HAS CONTINUED TO SLOW WITH EACH MODEL RUN. IN
ADDITION, MODEL TRENDS HAVE BROUGHT THE TRACK OF THE GULF LOW
FURTHER SOUTH BEFORE DISSIPATING BY THURSDAY MORNING. DESPITE NO
LONGER HAVING THE LIFT ASSOCIATED WITH THE GULF LOW, MID-LEVEL
SHORTWAVES ARRIVE THROUGHOUT THE MORNING HOURS, WHICH IN COMBINATION
WITH THE PREFRONTAL TROUGH WILL RESULT IN WIDESPREAD RAIN SHOWERS
FOR THE VAST MAJORITY OF THE DAY. AS HAS BEEN THE CASE, INSTABILITY
IS LOOKING TO BE RATHER MEAGER, SO NOT EXPECTING ANY THUNDERSTORMS
THROUGHOUT THE DAY. PRECIPITABLE WATER (PWAT) VALUES HAVE ALSO
COME DOWN FOR THE DAY, LARGELY DUE TO THE ABSENCE OF THE GULF
LOW, BUT WITH VALUES REMAINING IN THE 1-1.25" RANGE, RAINFALL
AMOUNTS LOOK TO REMAIN LARGELY IN THE 0.25-0.75" RANGE, HIGHEST
ALONG THE COASTS.
AS COLD AIR BEGINS TO FILTER DOWN INTO THE REGION OVERNIGHT, SOME
MODEL SOUNDINGS IN BERKELEY COUNTY SHOW SUB-FREEZING BOUNDARY LAYER
TEMPERATURES BEGIN TO EMERGE, THOUGH THE SURFACE LAYER REMAINS WELL
ABOVE FREEZING...RESULTING IN A COLD RAIN. WITH PRECIPITATION MOVING
OUT OF THE REGION BEFORE THE SUBFREEZING TEMPERATURE PROFILES
ARRIVE, NOT EXPECTING ANY SNOW OR FREEZING RAIN TO OCCUR. THE
COASTAL LOW CONTINUES TO INTENSIFY WEDNESDAY EVENING AS IT
LIFTS NORTHWARDS, WITH STRONG COLD-AIR ADVECTION (CAA) ON THE
BACKSIDE BRINGING THURSDAY MORNING LOWS DOWN INTO THE UPPER 20S
TO LOWER 30S ACROSS SE SC, AND LOWER TO MID 30S ACROSS SE GA.
WINDS WILL BE WEAKENING AS WE GET TOWARDS DAYBREAK ON THURSDAY,
WHICH SHOULD HELP TO KEEP THE WIND CHILL VALUES WELL ABOVE COLD
WEATHER THRESHOLDS, THOUGH WIND CHILLS IN THE MID 20S TO LOWER
30S WILL CERTAINLY NECESSITATE WARMER CLOTHING! THE REST OF THE
DAY WILL SEE SKIES CLEARING ALLOWING FOR AFTERNOON TEMPERATURES
TO INCREASE, THOUGH WE'LL LIKELY ONLY SEE MID 40S TO LOWER 50S.
ANOTHER PUSH OF COLD AIR IS EXPECTED OVERNIGHT INTO FRIDAY AS THE
SURFACE HIGH PRESSURE OVER THE CENTRAL US SLIDES EASTWARDS, WITH
TEMPERATURES EXPECTED TO DIP DOWN INTO THE LOWER TO UPPER 20S ACROSS
THE REGION. WHILE WINDS WILL REMAIN ON THE LIGHTER SIDE (BELOW 10
MPH), WHILE THE WIND CHILLS IN THE UPPER TEENS TO LOWER 20S MAY
REQUIRE A COLD WEATHER ADVISORY FRIDAY MORNING. AMPLE SUNSHINE WILL
HELP BRING THE REGION BACK UP INTO THE UPPER 40S TO LOWER 50S, BUT
ALAS THAT REMAINS A SOLID 15 TO 20 DEGREES BELOW NORMAL.
LONG TERM /SATURDAY THROUGH MONDAY/
SATURDAY WILL SEE THE AFOREMENTIONED SURFACE HIGH PRESSURE SLIDE
ONTO THE ATLANTIC, WITH WARMER SOUTHERLY WINDS ALREADY BRINGING THE
REGION BACK UP INTO THE 50S AND LOWER 60S. DETERMINISTIC GUIDANCE
BEGINS TO DIVERGE ON THE TIMING OF THE EXITING SURFACE HIGH WHICH
PROPAGATES THROUGH THE MID-LEVELS, WITH ENSEMBLE CLUSTERING
SHOWING THE MAIN FACTOR BEING THE STRENGTH OF THE TROUGH ALONG
THE EAST COAST. FOR NOW, POPULATED WITH THE NBM WHICH ADDS LOW
CHANCES (~20%) FOR RAIN SHOWERS THROUGHOUT THE DAY ON SUNDAY.
OTHERWISE, THE MAIN STORY IS THE RETURN OF NICE AND WARM
TEMPERATURES IN THE 60S AND 70S TO START OFF NEXT WEEK.
AVIATION /18Z TUESDAY THROUGH SUNDAY/
KCHS/KJZI: VFR WILL PREVAIL THROUGH 18Z WEDNESDAY. MVFR CIGS ARE
POSSIBLE NEAR THE VERY END OF THE TAF PERIOD, BUT NO
RESTRICTIONS WERE EXPLICITLY MENTIONED.
KSAV: THE 18Z TAF PERIOD WILL BE VFR THROUGH AROUND 15Z 2/19
WHEN MVFR CIGS ARE LIKELY TO IMPACT THE TERMINAL. ADDITIONALLY
VICINITY SHOWERS ARE FEATURED NEAR THE END OF THE 18Z TAF PERIOD
AS SHOWERS OVERSPREAD THE FORECAST AREA FROM SW TO NE.
EXTENDED AVIATION OUTLOOK: EXPECT VFR CONDITIONS TO PREVAIL INTO
TUESDAY NIGHT. BRIEF PERIODS OF FLIGHT RESTRICTIONS WILL BE
POSSIBLE WEDNESDAY AS A COASTAL LOW PASSES JUST OFFSHORE
BRINGING NUMEROUS TO WIDESPREAD SHOWERS TO THE AREA THAT COULD
IMPACT CHS/JZI/SAV TERMINALS. VFR IS EXPECTED TO RETURN
THEREAFTER.
MARINE
WEAK HIGH PRESSURE WILL REMAIN ACROSS MARINE ZONES TODAY. THE
PRESSURE PATTERN SHOULD SUPPORT NORTHEAST WINDS GENERALLY BETWEEN 10
TO 15 KTS. SEAS ARE FORECAST TO REMAIN BETWEEN 2 TO 3 FT.
AN INVERTED TROUGH WILL DEVELOP OVER THE GULF STREAM LATE TONIGHT.
GUIDANCE INDICATES THAT PINCHED PRESSURE GRADIENT MAY DEVELOP ACROSS
THE NEARSHORE WATERS, JUST WEST OF THE INVERTED TROUGH. NORTHEAST
WINDS BETWEEN 10 TO 15 KTS WITH GUSTS TO 20 KTS ARE FORECAST FOR THE
NEARSHORE WATERS. WINDS MAY REMAIN A BIT WEAKER ACROSS THE OUTER GA
WATERS. WAVE HEIGHTS SHOULD PERSIST BETWEEN 2 TO 3 FT.
WEDNESDAY THROUGH SUNDAY: ON WEDNESDAY, A COASTAL LOW IS EXPECTED TO
DEEPEN ACROSS THE GULF STREAM, TRACKING TO THE NORTHEAST. WINDS
SHOULD STRENGTHEN ON WEDNESDAY INTO THURSDAY NIGHT, WITH GUSTS
AROUND 25 KTS POSSIBLE OUTSIDE THE CHS HARBOR. IN ADDITION, SEAS
SHOULD BUILD DURING THE MID-WEEK, GENERALLY BETWEEN 3 TO 5 FT WITH
PERIODS OF 6 FT SEAS ACROSS THE OUTER GA AND POSSIBLY THE CHARLESTON
COUNTY NEARSHORE WATERS. SMALL CRAFT ADVISORIES WILL BE POSSIBLE FOR
PORTIONS OF THE ATLANTIC WATERS WEDNESDAY INTO THURSDAY NIGHT. HIGH
PRESSURE WILL RETURN TO THE REGION FRIDAY THROUGH THIS WEEKEND.
WINDS AND SEAS SHOULD REMAIN BELOW SCA CRITERIA.
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...NONE.
NEAR TERM...CPM/NED
SHORT TERM...0
LONG TERM...0
AVIATION...CPM
MARINE...NED
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