998
FXUS62 KCHS 200145
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
845 PM EST TUE NOV 19 2024
SYNOPSIS
HIGH PRESSURE WILL PREVAIL UNTIL A STRONG COLD FRONT MOVES
THROUGH LATER WEDNESDAY. CANADIAN HIGH PRESSURE WILL BUILD
ACROSS THE AREA THURSDAY INTO SUNDAY.
NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/
RADAR SHOW A BROKEN LINE OF LIGHT SHOWERS MOVING SLOWLY EAST
ACROSS SOUTHEAST SOUTH CAROLINA AND SOUTHEAST GEORGIA. THIS
ACTIVITY IS BEING DRIVEN BY FORCING FROM A PASSING AREA OF
CHANNEL VORTICITY ALOFT AND WEAK ISENTROPIC ASCENT MOSTLY ROOTED
ALONG THE 295-305K SURFACES. BOTH FORCING MECHANISMS LOOK TO
REMAIN FAIRLY WEAK THROUGH THE NIGHT, BUT WITH A RIBBON OF
ELEVATED PWATS (1.50-2.00") IN PLACE, THE COVERAGE LOOKS TO
REMAIN FAIRLY LARGE DESPITE A RELATIVELY LIGHT QPF AND HIGH
CLOUD BASES. CATEGORICAL POPS AROUND 80% WERE EXPANDED TO
INCLUDE ALL OF SOUTHEAST GEORGIA AND SOUTHERN SOUTH CAROLINA
WITH 60-70% POPS FOR THE REMAINDER OF SOUTHEAST SOUTH CAROLINA
FOR THE LATE EVENING UPDATE. LOWS WILL BOTTOM OUT ON THE LOWER-
MID 60S.
SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/
WEDNESDAY: A MID-UPPER LVL TROUGH WILL ADVANCE EAST ACROSS THE
MIDWEST, WHILE A STRONG COLD FRONT SWEEPS ACROSS THE REGION BY LATE
DAY. CONDITIONS WILL WARM INTO THE MID-UPPER 70S AHEAD OF THE FRONT,
BUT INSTABILITY WILL BE SOMEWHAT LIMITED BY EXPANSIVE CLOUD COVER.
SUBSTANTIAL FORCING ALONG THE BACK EDGE OF DEEPER MOISTURE (PWATS
AROUND 1.5 INCHES) SHOULD FAVOR FEW TO SCATTERED SHOWERS DURING THE
DAY BEFORE COLD FROPA TAKES PLACE AND DRY HIGH PRESSURE OVERSPREADS
THE SOUTHEAST UNITED STATES BY EARLY NIGHT. WEST-SOUTHWEST WINDS
COULD ALSO BECOME GUSTY LATE AFTERNOON, THEN PERSIST INTO THE NIGHT
AS THE ONSET OF COLD AIR ADVECTION TAKES PLACE. TEMPS WILL BE
TRENDING ON THE COOLER SIDE DURING THE NIGHT, WITH LOW TEMPS
GENERALLY RANGING IN THE LOW-MID 40S INLAND TO UPPER 40S NEAR THE
COAST.
THURSDAY/FRIDAY: ALOFT, A LARGE MID-UPPER LVL LOW CENTERED ACROSS
THE EASTERN GREAT LAKES WILL DIVE SOUTHEAST ACROSS THE MID-ATLANTIC
AND SOUTHEAST WHILE SFC HIGH PRESSURE SPREADS ACROSS THE LOCAL AREA.
DRY AND CONSIDERABLY COLDER CONDITIONS ARE EXPECTED UNDER THIS
PATTERN, ESPECIALLY TO START OFF THE WEEKEND AS THE MID-UPPER LVL
TROUGH AXIS CROSSES OVER THE LOCAL AREA. IN GENERAL, HIGHS WILL PEAK
IN THE UPPER 50S/LOWER 60S THURSDAY AFTERNOON, THEN MID-UPPER 50S
FRIDAY AFTERNOON. LOW TEMPS SHOULD RANGE INTO THE MID-UPPER 30S
INLAND TO LOW-MID 40S NEAR THE COAST. STRONG COLD AIR ADVECTION
ACROSS THE REGION WILL FAVOR LOW-LVL MIXING INTO 1000 MB GEOSTROPHIC
WINDS NEAR 30-40 KT, WHICH SHOULD SUPPORT A GUSTY WESTERLY WIND
BETWEEN 20-30 MPH ON THURSDAY AND POSSIBLY AGAIN FRIDAY AFTERNOON,
STRONGEST NEAR COASTAL LOCATIONS.
LAKE WINDS: GUSTY WEST WINDS ARE EXPECTED TO DEVELOP OVER LAKE
MOULTRIE WEDNESDAY NIGHT INTO THURSDAY BEHIND A COLD FRONT. A LAKE
WIND ADVISORY WILL EVENTUALLY BE REQUIRED WEDNESDAY NIGHT INTO
FRIDAY MORNING WITH WIND GUSTS UP TO 25-30 KT BEING COMMON.
LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/
HIGH PRESSURE WILL CONTINUE TO BUILD OVER THE AREA OVER THE
WEEKEND AND REMAIN THE DOMINANT FEATURE THROUGH MONDAY. NO
THREAT FOR RAIN WITH A DRY FORECAST THROUGH THE ENTIRE PERIOD.
MAIN FORECAST CONCERN WILL BE THE POTENTIAL FOR FROST EARLY
SATURDAY MORNING AND AGAIN SUNDAY MORNING. PERHAPS THE BETTER
CHANCE WOULD BE SUNDAY MORNING AS WINDS COULD STAY A BIT TOO
HIGH FOR FROST DEVELOPMENT FRIDAY NIGHT/SATURDAY MORNING.
AVIATION /02Z WEDNESDAY THROUGH SUNDAY/
20/00Z TAF DISCUSSION:
KCHS/KJZI/KSAV: VFR SHOULD PREVAIL THROUGH TONIGHT WITH THE RISK
FOR IFR AND MVFR CIGS INCREASING AFTER DAYBREAK AT ALL THREE
TERMINALS. A BAND OF LIGHT RAIN WILL MOVE SLOWLY WEST-EAST
ACROSS THE AREA TONIGHT. GIVEN THE RELATIVELY HIGH CLOUD BASES,
VSBYS SHOULD BE SOMEWHAT LIMITED, GOING NO LOWER THAN 5-6SM.
RAIN SHOULD END BY MID-MORNING WITH CIGS LOWER IN ITS WAKE.
CONFIDENCE IS HIGH THAT MVFR CIGS WILL DEVELOP BY MID-MORNING
WITH A CHANCE OF IFR CIGS DEVELOPING BY LATE MORNING/EARLY
AFTERNOON AS A COLD FRONT APPROACHES. CIGS WERE HELD AT MVFR
THRESHOLDS FOR NOW ALONG WITH A SCATTERED CLOUD DECK 700-800 FT.
EXTENDED AVIATION OUTLOOK: BRIEF FLIGHT RESTRICTIONS ARE POSSIBLE
AT KCHS/KJZI/KSAV TERMINALS WEDNESDAY AFTERNOON, BEFORE HIGH
PRESSURE SPREADS ACROSS THE REGION AND SUPPORTS VFR CONDITIONS
WEDNESDAY NIGHT THROUGH SATURDAY. GUSTY WEST WINDS ARE LIKELY AT
ALL TERMINALS POST COLD FROPA THURSDAY AND FRIDAY.
MARINE
THIS EVENING AND TONIGHT: THE NORTHWEST EXTENSION OF HIGH
PRESSURE CENTERED NORTHEAST OF THE BAHAMAS WILL FINALLY
RELINQUISH ITS GRIP ON THE AREA, AS WEAK LOW NEAR THE FLORIDA
PANHANDLE DRIFTS EASTWARD. THE GRADIENT WILL BE MOST RELAXED ON
THE SOUTH CAROLINA WATERS, WHERE S AND SW WINDS WILL BE NO MORE
THAN 10 OR 15 KT, AND SEAS BUILDING TO NO GREATER THAN 2 OR 3
FEET. THERE IS A BIT MORE OF A GRADIENT ON THE GEORGIA WATERS,
AND DESPITE WARM ADVECTION, WE STILL LOOK FOR S AND SW WINDS TO
REACH 15 OR 20 KT DURING THE LATE EVENING AND POST MIDNIGHT
PERIOD. THERE COULD BE SOME GUSTS AT TIMES NEAR OR GREATER THAN
25 KT, AS THE DESI DOES HAVE 30-50% PROBABILITIES OF ADVISORY
WIND GUSTS. BUT THE SREF AND HREF HAVE LITTLE TO NO CHANCE. OUR
LATEST THINKING IS THAT THE FREQUENCY AND COVERAGE IS TOO LIMITED
TO RAISE A SMALL CRAFT ADVISORY. SEAS ON THE GEORGIA WATERS WILL
CLIMB THROUGH THE NIGHT, REACHING 4 OR 5 FEET.
WEDNESDAY THROUGH SATURDAY: A STRONG COLD FRONT WILL MOVE ACROSS THE
REGION WEDNESDAY AFTERNOON INTO EARLY EVENING, LEADING TO STRONG
COLD AIR ADVECTION ACROSS LOCAL WATERS IN ITS WAKE AND DETERIORATING
WINDS/SEAS WEDNESDAY NIGHT INTO EARLY THURSDAY. LATEST GUIDANCE HAS
COME IN A BIT STRONGER WITH 1000 MB GEOSTROPHIC WINDS IN THE 40-45
KT RANGE SUGGESTING A GREATER POTENTIAL FOR FREQUENT GALE FORCE WIND
GUSTS ACROSS A BULK OF LOCAL WATERS AND SEAS BUILDING UP TO 5-7 FT
(LARGEST ACROSS OUTER GEORGIA WATERS). A GALE WATCH/WARNING SHOULD
EVENTUALLY BE REQUIRED WEDNESDAY NIGHT INTO LATE MORNING THURSDAY.
THEREAFTER, HIGH PRESSURE BUILDING ACROSS THE REGION ALONG WITH COLD
AIR ADVECTION PERSISTING SHOULD SUPPORT SMALL CRAFT ADVISORY LEVEL
CONDITIONS INTO LATE FRIDAY AND/OR EARLY SATURDAY. IMPROVEMENT IS
EXPECTED LATE SATURDAY AS THE PRESSURE GRADIENT EASES ACROSS LOCAL
WATERS.
CHS WATCHES/WARNINGS/ADVISORIES
GA...NONE.
SC...NONE.
MARINE...NONE.
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