966
FXUS62 KCHS 190604
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
104 AM EST WED FEB 19 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 THIS MORNING/
THE FORECAST UPDATE WILL ALIGN HOURLY TEMPERATURES AND SKY TO
RECENT OBSERVATIONS. THE CURRENT FORECAST REMAINS GENERALLY ON
TRACK.
A ZONAL FLOW WILL PREVAIL ALOFT, WHILE UPSTREAM A FAST MOVING
SHORT WAVE NEAR THE LOWER MISSISSIPPI VALLEY EARLY ON APPROACHES
THE IMMEDIATE VICINITY LATE. AT THE SURFACE, A TROUGH WILL BE
SITUATED OUT NEAR THE GULF STREAM, WHILE HIGH PRESSURE RELAXES
ACROSS INLAND SECTIONS. MOISTURE WILL INCREASE AHEAD OF THE
SHORT WAVE, MAINLY IN THE MID AND UPPER LEVELS, AND THIS WILL
ALLOW FOR AN INCREASE IN CLOUD COVER. THAT ALONG WITH JUST
ENOUGH MIXING WILL ALLOW FOR A WARMER NIGHT THAN LAST NIGHT.
BASED ON RECENT TRENDS THROUGH WE DID MAKE SOME MINOR TWEAKS TO
BOTH THE HOURLY TEMPERATURES AND THE OVERALL LOWS. WE HAVE UPPER
30S AND LOWER 40S WELL INLAND, WITH MID AND UPPER 40S CLOSER TO
THE OCEAN. WHILE THERE SOME FORCING DUE TO THE APPROACHING SHORT
WAVE, AND THE PROXIMITY TO THE OFFSHORE TROUGH, IT LOOKS LIKE
THE MAJORITY OF ANY RAINS ILL HOLD OFF UNTIL AFTER 6 AM. THE
EXCEPTION WOULD BE SOUTH OF I-16 IN GEORGIA, AND MAYBE COASTAL
CHARLESTON CLOSE TO DAYBREAK.
SHORT TERM /6 AM THIS 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 /06Z WEDNESDAY THROUGH SUNDAY/
6Z 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 THIS EVENING. 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 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 THIS EVENING.
EXTENDED AVIATION OUTLOOK: TEMPO FLIGHT RESTRICTIONS ARE POSSIBLE AT
CHS/JZI/SAV TERMINALS WEDNESDAY 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
REST OF TONIGHT: AN INVERTED TROUGH WILL PREVAIL EAST OF THE
LOCAL WATERS, WHILE HIGH PRESSURE INLAND WEAKENS. FURTHER
UPSTREAM WILL BE THE DEVELOPMENT OF LOW PRESSURE ALONG THE
SOUTHERN LOUISIANA COAST. THERE REMAINS ENOUGH PINCHING EARLY
TONIGHT LOCALLY TO GENERATE NE WINDS AS HIGH AS 15 OR 20 KT,
WITH SOME HIGHER GUSTS. LATE TONIGHT THE GRADIENT DOES EASE OFF
A BIT, AND WINDS DROP ABOUT OFF AROUND 5 KT. SEAS WILL AVERAGE
2-4 FEET, HIGHEST ON THE CHARLESTON COUNTY WATERS AND THE OUTER
GEORGIA WATERS EARLY ON.
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...NED
SHORT TERM...DPB
LONG TERM...DPB
AVIATION...NED
MARINE...
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