960
FXUS62 KCHS 182127
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
427 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 /UNTIL 6 AM WEDNESDAY MORNING/
SURFACE HIGH PRESSURE WILL SLOWLY SHIFT OFFSHORE THROUGH THE
REMAINDER OF THE AFTERNOON. TEMPERATURES WERE ABLE TO REACH INTO
THE UPPER 50S TO LOW 60S, WITH CONDITIONS EXPECTED TO COOL OFF
HEADING INTO THE EVENING HOURS. CLOUD COVER WILL CONTINUE TO
INCREASE AHEAD OF AN APPROACHING UPPER LEVEL TROUGH. ASSOCIATED
WITH THE UPPER LEVEL TROUGH A LOW PRESSURE SYSTEM WILL DEVELOP
IN THE NORTHERN GULF, APPROACHING THE FORECAST AREA LATE TONIGHT
AND INTO THE EARLY MORNING HOURS. JUST OFFSHORE A WEAK INVERTED TROUGH
IS FORECAST TO DEVELOP. ISOLATED SHOWERS ARE POSSIBLE,
ASSOCIATED WITH THE COASTAL TROUGH, HOWEVER THE CURRENT FORECAST
KEEP SHOWER ACTIVITY OFFSHORE. AS THE LOW PRESSURE APPROACHES
THE REGION FROM THE SW SHOWERS WILL BEGIN TO ENTER THE
SOUTHERNMOST PORTIONS OF THE FORECAST AREA RIGHT AROUND
DAYBREAK. OVERNIGHT LOWS ARE FORECAST TO DIP INTO THE UPPER 30S
INLAND WITH MID TO UPPER 40S ALONG THE COASTLINE.
SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY NIGHT/
WEDNESDAY: ALOFT, THE FLOW REMAINS ZONAL INITIALLY UNTIL H5 VORT
ENERGY BEGINS TO RIPPLE ACROSS THE LOCAL AREA MID-LATE MORNING. THE
ENERGY WILL HELP PROMOTE A COASTAL LOW TO DEVELOP ALONG AN INVERTED
TROUGH JUST OFF THE COAST, ESPECIALLY AS A H25 JET CORE BECOMES
FAVORABLY POSITIONED ACROSS THE SOUTHEAST. LIGHT RAINS/SHOWERS ARE
EXPECTED TO DEVELOP BY MID-LATE MORNING HOURS ACROSS SOUTHERN AREAS,
EVENTUALLY SPREADING ACROSS SOUTHEAST GEORGIA INTO SOUTHEAST SOUTH
CAROLINA BY THE AFTERNOON. MOISTURE AMOUNTS ARE MODEST WITH LOW
PRESSURE PASSING SOUTH OF THE REGION ACROSS THE GULF AND A NORTHERLY
WIND OCCURRING ALONG THE WESTERN EDGE OF THE COASTAL LOW TAKING
SHAPE ACROSS THE WESTERN ATLANTIC. TEMPS WILL REMAIN BELOW NORMAL
FOR THE DAY, PEAKING IN THE MID 50S ALONG THE COASTAL CORRIDOR AND
ONLY INTO THE UPPER 40S INLAND.
THERE ARE SOME CONCERNS IN THE FORECAST HEADING INTO WEDNESDAY NIGHT
WITH A NORTHERLY WIND ANTICIPATED TO HOLD ON THROUGH MUCH OF THE
NIGHT AND DRIVE COLDER SFC TEMPS INTO NORTHERN AREAS LATE EVENING
AND AFTER MIDNIGHT. THE KEY WILL BE HOW LONG MOISTURE/LIGHT PRECIP
HOLDS ACROSS THE LOCAL AREA HEADING INTO OVERNIGHT HOURS AS LATEST
MODEL SOUNDINGS AND INCREASING HREF PROBABILITIES INDICATE A NON-
ZERO POTENTIAL FOR LIGHT FREEZING RAIN (TRACE TO 0.01 INCH), MAINLY
ALONG AND NORTH OF A LINE DRAWN FROM JAMESTOWN, SC TO MONCKS CORNER,
SC TO REEVESVILLE, SC WHERE SFC TEMPS DIP TO AROUND 30 DEGREES FOR A
FEW HOURS BEFORE PRECIP SHIFTS OFFSHORE LATE NIGHT. AT THIS POINT,
CONFIDENCE IS LOW IN ICE ACCUMULATIONS GIVEN SOME UNCERTAINTY IN
OVERALL PRECIP CHANCES AFTER MIDNIGHT AND ESPECIALLY GIVEN SOIL
TEMPS ARE GENERALLY AROUND 50 DEGREES AND LIKELY TO LIMIT ICE
ACCUMULATION ON THE GROUND. HOWEVER, THERE IS AT LEAST SOME RISK OF
LIGHT FREEZING RAIN ON ELEVATED SURFACES, SUCH AS BRIDGES AND
OVERPASSES AND PERHAPS ON TREES ACROSS NORTHERN BERKELEY COUNTY.
SHOULD WINDS BECOME LIGHT OVERNIGHT, THERE IS ALSO A NON-ZERO RISK
OF BLACK ICE DEVELOPING PRIOR TO DAYBREAK, BUT AGAIN WARMER SOIL
TEMPS SHOULD LIMIT THIS OVERALL CONCERN. ELSEWHERE, INCLUDING THE
CHARLESTON METRO AREA, PRECIP IS EXPECTED TO REMAIN IN THE FORM OF
RAIN/SHOWERS.
THURSDAY AND FRIDAY: COLDER AIR ARRIVES LATE WEEK AS THE REGION
BECOMES POSITIONED ALONG THE BASE OF A MID-UPPER LVL TROUGH WHILE
DRY SFC HIGH PRESSURE IS REINFORCED ACROSS THE SOUTHEAST. ALTHOUGH
PRECIP-FREE CONDITIONS ARE EXPECTED, THURSDAY NIGHT/EARLY FRIDAY
TEMPS WILL BECOME CHILLY (DIPPING INTO THE LOW-MID 20S). THE
COMBINATION OF THESE TEMPS AND A LIGHT NORTHWESTERLY WIND SHOULD
RESULT IN WIND CHILL VALUES IN THE UPPER TEENS ACROSS MANY AREAS,
AND LIKELY RESULT IN THE NEED FOR A COLD WEATHER ADVISORY PRIOR TO
DAYBREAK FRIDAY. DESPITE FULL DAYS OF SUNSHINE, AFTERNOON HIGHS WILL
STRUGGLE TO REACH THE MID-UPPER 40S NORTH TO AROUND 50 SOUTH, SOME
15-20 DEGREES BELOW NORMAL.
LONG TERM /SATURDAY THROUGH TUESDAY/
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. AT THIS TIME, CONDITIONS LOOK TO REMAIN DRY THIS WEEKEND WITH
HIGH PRESSURE CONTINUING ACROSS THE REGION WHILE WEAK SFC LOW
PRESSURE ATTEMPTS TO DEVELOP OFFSHORE. OTHERWISE, THE MAIN STORY IS
THE RETURN OF WARMER TEMPS IN THE 60S AND 70S TO START OFF NEXT
WEEK.
AVIATION /21Z 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: TEMPO FLIGHT RESTRICTIONS ARE POSSIBLE AT
CHS/JZI/SAV TERMINALS WEDNESDAY AFTERNOON AND NIGHT WITH PASSING
RAIN/SHOWERS AND LOW CLOUDS ASSOCIATED WITH A COASTAL LOW PASSING
JUST OFFSHORE. VFR CONDITIONS ARE THEN EXPECTED AT THE TERMINALS
THROUGH LATE WEEK.
MARINE
A COASTAL TROUGH WILL DEVELOP OVER THE MARINE WATERS TONIGHT. A
SLIGHT ENHANCEMENT OF WINDS IS EXPECTED WITH A PINCHED PRESSURE
GRADIENT IN THE VICINITY OF THE INVERTED TROUGH, WITH NE GUSTS
AROUND 15 KNOTS. SEAS WILL AVERAGE 2 TO 3 FT.
WEDNESDAY THROUGH SUNDAY: LATEST GUIDANCE SUGGESTS A COASTAL LOW
DEVELOPING JUST OFF THE SOUTHEAST COAST WEDNESDAY AS H5 SHORTWAVE
ENERGY PASSES OVER AN INVERTED TROUGH AXIS NEARBY. THE PRESSURE
GRADIENT WILL STRENGTHEN IN RESPONSE TO THE CHANGING CONDITIONS,
POTENTIALLY LEADING TO MARGINAL SMALL CRAFT ADVISORY LEVEL
CONDITIONS (~25 KT WIND GUSTS) ACROSS NORTHERN SC WATERS OFF THE
CHARLESTON COUNTY AND OUTER GEORGIA WATERS MID-LATE WEDNESDAY
AFTERNOON/EVENING. HIGH PRESSURE SHOULD THEN BECOME REINFORCED
ACROSS LOCAL WATERS THURSDAY, BUILDING SEAS UPWARDS TO 3-5 FT ACROSS
MOST NEARSHORE WATERS AND 4-6 FT ACROSS NORTHERN SC WATERS OFF THE
CHARLESTON COUNTY COAST AS WELL AS ACROSS OUTER GEORGIA WATERS.
ADDITIONAL SMALL CRAFT ADVISORIES COULD BE NEEDED THURSDAY AFTERNOON
AND NIGHT. HIGH PRESSURE WILL THEN PREVAIL THIS WEEKEND WITH
WINDS/SEAS EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY LEVELS.
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
SHORT TERM...DPB
LONG TERM...DPB
AVIATION...CPM/DPB
MARINE...CPM/DPB
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