333
FXUS62 KCHS 180828
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
328 AM 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/
BROAD SFC HIGH PRESSURE WILL REMAIN ACROSS THE FORECAST AREA TODAY.
IR SATELLITE SHOWS A LARGE SHIELD OF CIRRUS LEVEL CLOUDS SPREADING
EAST ACROSS THE DEEP SOUTH AND SOUTHEAST U.S. AHEAD OF MID-LEVEL
TROUGH. CLOUD COVER SHOULD GRADUALLY INCREASE THROUGH THE DAY,
BECOMING MOSTLY CLOUDY BY THIS AFTERNOON. H850 WINDS SHOULD REMAIN
FROM THE WEST THIS MORNING, EXPECTED TO BACK FROM THE SOUTHWEST THIS
AFTERNOON. AS A RESULT, LLVL THICKNESSES SHOULD GRADUALLY INCREASE
ACROSS THE CWA THIS AFTERNOON. HIGH TEMPERATURES ARE FORECAST TO
RANGE FROM AROUND 60 DEGREES ACROSS THE CHS TRI-COUNTY TO THE MID
60S ACROSS EXTREME SE GA.
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 /08Z TUESDAY THROUGH SATURDAY/
KCHS/KJZI/KSAV: VFR WILL PREVAIL THROUGH 06Z WEDNESDAY.
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...NED
SHORT TERM...AT
LONG TERM...AT
AVIATION...NED
MARINE...NED
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