093
FXUS62 KCHS 191125
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
625 AM EST WED FEB 19 2025
SYNOPSIS
A COASTAL LOW WILL TRACK NORTHEASTWARDS OFF THE GEORGIA/SOUTH
CAROLINA COAST TODAY, WITH HIGH PRESSURE BUILDING INTO THE
REGION BY END OF THE WEEK. A BROAD AREA OF LOW PRESSURE OFF THE
COAST WILL FORM ON SUNDAY.
NEAR TERM /THROUGH TONIGHT/
EARLY THIS MORNING, SATELLITE WATER VAPOR SHOWED A MID-LEVEL LOW
OVER THE MN/IA STATE LINE. NEAR TERM GUIDANCE INDICATES THAT THE
CLOSED LOW WILL TRACK SE ACROSS THE MID WEST TODAY INTO TONIGHT.
GFS1DEG TIMES A BAND OF H5 Q-VECTOR CONVERGENCE, AROUND 15 UNITS,
PASSING OVER THE FORECAST AREA DURING THE DAYLIGHT HOURS. AT THE
SFC, HIGH PRESSURE WILL BUILD ACROSS THE SOUTHEAST U.S. TODAY,
PUSHING AS FAR SOUTH AS FL. AN INVERTED TROUGH OVER THE GULF STREAM
WILL GRADUALLY DEEPEN THIS MORNING, WITH A COASTAL LOW DEVELOPING
THIS AFTERNOON. ONCE THE COAST LOW ORGANIZES, IT SHOULD TRACK TO THE
NORTHEAST ALONG THE CAROLINA COAST. HIGH RESOLUTION GUIDANCE
INDICATES THAT ISENTROPIC LIFT WILL DEVELOP OVER THE WEDGED HIGH.
THE COMBINATION OF DEEPENING FORCING AND PW BUILDING IN EXCESS OF AN
INCH SHOULD SUPPORT WIDESPREAD LIGHT RAIN FOR MUCH OF THE DAY. QPF
VALUES WERE REDUCED, RANGING FROM AROUND .3 ACROSS THE CHS TRI-
COUNTY TO .75 ACROSS EXTREME SE GA. CAMS INDICATE THAT A SQUALL LINE
MAY RACE ACROSS THE EASTERN GULF THROUGH EARLY THIS AFTERNOON, THIS
FEATURE MAY CUT OFF SOME MOISTURE FROM REACHING THE FORECAST AREA.
GIVEN THICK CLOUD COVER, WIDESPREAD LIGHT RAIN, AND STEADY NE WINDS
HIGH TEMPERATURES WILL BE LIMITED TO THE UPPER 40S INLAND TO THE LOW
TO MID 50S ALONG THE COAST.
TONIGHT, THE COASTAL LOW WILL CONTINUE TO DEEPEN AS IT TRACKS OFF
THE COAST OF NC. AS THE LOW DEPARTS, H85 TEMPERATURES OVER LAKE
MOULTRIE ARE FORECAST TO FALL FROM 5C AT 0Z TO -3C BY 12Z THURSDAY.
IN ADDITION, FORECAST SOUNDINGS INDICATE THAT DRY AIR WILL INCREASE
FROM THE TOP-DOWN TONIGHT. POPS WILL SHARPLY DECREASE ACROSS THE
FORECAST AREA THIS EVENING, WITH GENERALLY DRY CONDITIONS AFTER
MIDNIGHT. LATE THIS EVENING, TEMPERATURES, AT LEAST WET-BULB
TEMPERATURES, ARE FORECAST TO FALL TO AROUND FREEZING ACROSS
PORTIONS OF BERKELEY AND DORCHESTER COUNTIES. ISOLATED TO SCATTERED
SHOWERS OR DRIZZLE MAY TRACK ACROSS AREA OF TEMPERATURES AROUND
FREEZING. IT IS POSSIBLE THAT SOME LOCATIONS COULD SEE A LIGHT GLAZE
OF ICE. GIVEN SOIL TEMPS IN THE LOW 50 AND MARGINAL
TEMPERATURES, IT APPEARS THAT ICE ACCUMULATION ON THE SFC IS
UNLIKELY. HOWEVER, A GLAZE OF ICE IS POSSIBLE IN THE TREE TOPS
AND OTHER ELEVATED SURFACES. LOW TEMPERATURES ARE FORECAST TO
RANGE FROM THE UPPER 20S ACROSS PORTIONS OF BERKELEY AND
DORCHESTER COUNTIES. THERE IS A CHANCE THAT SOME BLACK ICE IS
POSSIBLE ON SHADED BRIDGES OR OTHER ELEVATED SURFACE. HOWEVER,
WINDS BETWEEN 5 TO 10 MPH AND WARM SOIL TEMPERATURES SHOULD
LIMIT ANY BLACK ICE. ELSEWHERE, LOW TEMPERATURES ARE FORECAST TO
RANGE FROM THE LOW 30S TO MID 30S.
SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/
WHILE THE BULK OF THE PRECIPITATION WILL HAVE FALLEN BY THURSDAY
MORNING, MAJORITY OF HIGH-RESOLUTION GUIDANCE IS NOW SHOWING ANOTHER
ROUND OF LIGHT RAIN SHOWERS IS EXPECTED BY LATE MORNING INTO THE
AFTERNOON HOURS, CONFINED TO OUR NORTHERN SOUTH CAROLINA COUNTIES.
THIS IS EXPECTED TO OCCUR AS SOME LAST REMAINING LOW/MID-LEVEL
SHORTWAVES MOVE DOWN TOWARDS THE COAST, WITH ENOUGH MOISTURE
REMAINING AVAILABLE TO SQUEEZE OUT SOME LIGHT RAIN SHOWERS. AND YES,
DESPITE STARTING OFF THE MORNING NEAR FREEZING, THE SURFACE AND
BOUNDARY LAYER QUICKLY RISE TO WELL ABOVE FREEZING RESULTING IN NO
CONCERN WINTRY PRECIP. AFTERNOON HIGHS PEAK IN THE LOWER TO UPPER
40S BEFORE COLD AIR ADVECTION (CAA) PUSHES THE RAIN SHOWERS OUT TO
SEA THROUGHOUT THE AFTERNOON HOURS, LEADING TO SOME BREEZY WESTERLY
WINDS SUSTAINED IN THE TEENS WITH GUSTS IN THE LOWER TO MID 20S.
THE PRESSURE GRADIENT DECREASES INTO THE EVENING HOURS ALLOWING FOR
WINDS TO ALSO DECREASE, THOUGH CAA WILL CONTINUE ALOFT. WE'LL HAVE
TO SEE HOW CALM WE GET, AS IT'S SHAPING UP TO BE A GOOD NIGHT FOR
RADIATIONAL COOLING GIVEN CLEAR SKIES. LATEST MODEL GUIDANCE HAS THE
REGION DIPPING DOWN INTO THE LOWER TO UPPER 20S, COOLEST FURTHEST
INLAND, WITH SOME WIGGLE ROOM REMAINING AS TEMPERATURES MAY FURTHER
COOL GIVEN THE AFOREMENTIONED RADIATIONAL COOLING SETUP. RECORD LOWS
ARE IN THE UPPER TEENS TO LOWER 20S, AND WE'RE STILL A FEW DEGREES
ABOVE. WHILE THE WINDS ARE EXPECTED TO BE LIGHT, IT WILL NOT TAKE
MUCH WIND TO CAUSE WIND CHILL VALUES TO DIP DOWN INTO THE TEENS
FRIDAY MORNING, SO WILL LIKELY NEED A COLD WEATHER ADVISORY AT SOME
POINT TO HIGHLIGHT THE COLD.
AFTER THE COLD START TO THE DAY, WE'LL BE WATCHING AS A SURFACE HIGH
PRESSURE OVER THE CENTRAL CONUS SLIDES EASTWARDS, KEEPING COOL
CONDITIONS CONTINUING WITH NO CHANCES FOR PRECIPITATION. ANOTHER
AFTERNOON WITH HIGHS IN THE LOWER TO UPPER 40S, THOUGH THANKFULLY
THIS WILL BE OUR LAST DAY WITH HIGHS 15 TO 20 DEGREES BELOW NORMAL
FOR THE FORESEEABLE FUTURE PER THE LATEST ENSEMBLES.
QUIET CONDITIONS CONTINUE ON SATURDAY AS THE SURFACE HIGH PRESSURE
BEGINS TO WEAKEN, WITH SOUTHERLY WINDS EXPECTED BY THE AFTERNOON
HOURS WHICH SHOULD HELP WARM THE REGION INTO THE LOWER TO UPPER 50S.
OVERNIGHT INTO SUNDAY, ENSEMBLES SHOW A BROAD AREA OF LOW PRESSURE
DEVELOPING OFF THE COAST, WITH SOME DETERMINISTIC MODELS SHOWING
SIMILAR SOLUTIONS.
LONG TERM /SUNDAY THROUGH TUESDAY/
SUNDAY WILL SEE THE AFOREMENTIONED BROAD AREA OF LOW PRESSURE RESULT
IN SOME LIGHT RAIN SHOWERS THROUGHOUT THE MORNING AND EARLY
AFTERNOON HOURS, WITH TEMPERATURES IN THE UPPER 50S TO MID 60S.
AGREEMENT AMONGST THE DETERMINISTIC MODELS CONTINUES TO DIVERGE INTO
THE EXTENDED, WITH ENSEMBLE CLUSTERING SHOWING TWO COMPETING
CLUSTERS EACH CARRYING 36%/31% OF MEMBERS RESPECTIVELY. THE DOMINANT
CLUSTER KEEPS CHANCES FOR LIGHT RAIN CONTINUING INTO MONDAY BEFORE
MOVING THE RAIN OFF TO SEA, WHILE THE SECOND KEEPS THE AREA DRY. NBM
BASICALLY SPLITS THOSE TWO SOLUTIONS, KEEPING CHANCES FOR RAIN
BEFORE DRYING OUT SUNDAY NIGHT INTO MONDAY. HEADING OUT INTO NEXT
WEEK, A SURFACE HIGH PRESSURE DEVELOPS ACROSS THE NORTHERN GULF
KEEPING THE AREA DRY AND WARM WITH TEMPERATURES IN THE 70S EXPECTED
TUESDAY AND WEDNESDAY.
AVIATION /11Z WEDNESDAY THROUGH SUNDAY/
12Z TAFS: SFC HIGH PRESSURE WILL RIDGE ACROSS THE TERMINALS
THROUGH THE TAF PERIOD. AN AREA OF LOW PRESSURE WILL DEVELOP OFF
THE GA/SC COAST TODAY, TRACKING TO THE NORTHEAST. THIS PATTERN
WILL RESULT IN A STRENGTHEN AREA OF COLD AIR DAMMING ACROSS THE
REGION TODAY THROUGH TONIGHT. NORTHEAST WINDS WITH LOWERING VFR
CEILINGS WILL OCCUR ACROSS THE TERMINALS THROUGH DAYBREAK THIS
MORNING. A LARGE AREA OF RAIN IS FORECAST TO LIFT NORTH THIS
MORNING, REACHING KSAV BY 14Z AND KCHS AND KJZI BY 15-16Z.
FORECAST SOUNDINGS AND MOS INDICATES THAT CEILINGS WOULD LIKELY
DROP TO IFR 2-3 HOURS AFTER THE ARRIVAL OF THE RAIN. LINGERING
CAD AND COOLING TEMPERATURES TONIGHT WILL LIKELY RESULT IN THE
LLVL 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.
EXTENDED AVIATION OUTLOOK: VFR CONDITIONS EXPECT THROUGH THE
LATE WORK WEEK.
MARINE
TODAY, HIGH PRESSURE WILL RIDGE OVER LAND AS A COASTAL LOW DEVELOPS
OVER THE GULF STREAM. THE PRESSURE GRADIENT IS EXPECTED TO PINCH
OVER THE NEARSHORE WATERS OF CHARLESTON COUNTY THIS AFTERNOON.
NORTHEAST WINDS ARE FORECAST TO INCREASE TO 20 KTS WITH GUSTS TO 25
KTS THIS AFTERNOON INTO EARLY THIS EVENING. A SMALL CRAFT ADVISORY
HAS BEEN ISSUED FOR THE CHARLESTON COUNTY NEARSHORE WATERS FROM NOON
UNTIL 8 PM. ELSEWHERE, NORTHEAST WINDS OUTSIDE THE HARBOR SHOULD
FREQUENTLY GUSTS TO AROUND 20 KTS. SEAS SHOULD GRADUALLY BUILD
THROUGH THE DAY, RANGING FROM 3 TO 5 FT BY LATE THIS AFTERNOON.
TONIGHT, THE COASTAL LOW WILL DEPART THE MARINE ZONES TO THE
NORTHEAST. WINDS ACROSS THE COASTAL WATERS ARE FORECAST TO SHIFT
FROM THE NORTHWEST, SPEEDS BETWEEN 15 TO 20 KTS. SEAS ARE FORECAST
TO RANGE BETWEEN 3 TO 5 FT.
THURSDAY THROUGH MONDAY: THURSDAY, THE COMBINATIONS 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 ALL
MARINE ZONES OUTSIDE THE CHS HARBOR THURSDAY AFTERNOON THROUGH
THURSDAY NIGHT. SEAS WILL BUILD DURING THE PERIOD, RANGING BETWEEN 3
TO 6 FT. SMALL CRAFT ADVISORIES WILL LIKELY BE NEEDED FOR THE NEAR
AND OUTER WATERS. 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.
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 FROM NOON TODAY TO 8 PM EST THIS EVENING
FOR AMZ350.
NEAR TERM...NED
SHORT TERM...AT
LONG TERM...AT
AVIATION...NED
MARINE...NED
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