555
FXUS62 KCHS 041933
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
333 PM EDT SUN MAY 4 2025
SYNOPSIS
A COLD FRONT WILL LINGER NEARBY BEFORE SHIFTING OFFSHORE ON
MONDAY. THEREAFTER, HIGH PRESSURE WILL BUILD IN AGAIN FROM THE
WEST. A COLD FRONT AND AN UPPER LEVEL LOW WILL APPROACH THE
REGION FROM THE WEST THURSDAY. THE UNSETTLED WEATHER PATTERN
WILL THEN PERSIST INTO NEXT WEEKEND.
NEAR TERM /UNTIL 6 AM MONDAY MORNING/
ISOLATED TO SCATTERED SHOWERS, AND PERHAPS A FEW
THUNDERSTORMS, REMAIN ON TAP FOR THIS AFTERNOON MAINLY ACROSS
PORTIONS OF THE LOWCOUNTRY AHEAD OF THE APPROACHING COLD FRONT
AND ALONG/INLAND OF THE SEA BREEZE. FURTHER SOUTH ACROSS GA AND
INLAND PORTIONS OF THE LOWCOUNTRY COVERAGE REMAINS LIMITED TO
NONE AS LOW LEVEL MOISTURE IS LIKELY NOT SUFFICIENT FOR
CONVECTIVE INITIATION UNTIL LATE TONIGHT, WHEN THERE IS A VERY
LOW CHANCE (<10%) THAT THE SEA BREEZE AND COLD FRONT COULD
INITIATE A QUICK SHOWER OR TWO AS THEY INTERSECT LATE ALONG AND
EAST OF THE I-95 CORRIDOR.
SKIES BEGIN TO CLEAR OVERNIGHT AND INTO THE EARLY MORNING HOURS,
WITH A LOW CHANCE (<10%) OF SOME LIGHT FOG FORMING ACROSS AREAS
OF THE LOWCOUNTRY THAT RECEIVE RAINFALL THIS AFTERNOON EVENING.
TEMPERATURES ARE EXPECTED TO BE NOTICEABLY COOLER THAN THE LAST
FEW NIGHTS WITH LOW TO MID 50S INLAND AND MID TO UPPER 50S
ALONG THE COAST.
SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY NIGHT/
MONDAY: WITH CLOSED UPPER-LVL LOW SITUATED OVER THE BLUEGRASS
REGION AND A SECONDARY UPPER-LVL LOW LOCATED NEAR THE CALIFORNIA
COASTLINE, THIS OMEGA BLOCKING PATTERN WILL CONTINUE DOMINATE
THE CONUS. AT THE SURFACE, THE COLD FRONT WILL BE OFFSHORE BY
DAYBREAK, THOUGH POST-FRONTAL CAA WILL BE VERY LIMITED BEYOND
SOME MILDER DEW POINTS. AMPLE SUNSHINE THROUGH THE DAY WITH HIGH
NEAR TO A FEW DEGREES ABOVE NORMAL. CONTINUED DRY CONDITIONS
UNDER STRENGTHENING MID LEVEL RIDGE CONTINUES OVERNIGHT, WITH
COOLER TEMPERATURES INTO THE MID 50S INLAND AND LOW TO MID 60S
ALONG THE COAST.
TUESDAY: THIS OMEGA BLOCKING PATTERN WILL BEGIN TO FINALLY
BREAK DOWN AS THE CLOSED UPPER-LVL LOW BEGINS TO MOVE SLIGHTLY
FURTHER AWAY. MID LEVEL RIDGE AXIS MOVES OVERHEAD DURING THE
DAY, WITH DRY CONDITIONS PERSISTING INTO THE NIGHT DESPITE THE
ONSET OF VERY MODEST HEIGHT FALLS ALOFT. VERY WEAK GRADIENT WILL
ENSURE THAT THE SEA BREEZE IS THE DOMINATE SURFACE FEATURE, WITH
TEMPS REACHING THE MID TO UPPER 80S AHEAD OF THE SEA BREEZE
FRONT. MODEST WAA ENSUES LATER IN THE DAY WITH LOW TUESDAY NIGHT
RETURNING TO NEAR-NORMAL.
LONG TERM /WEDNESDAY THROUGH SUNDAY/
A DECAYING OMEGA BLOCK WILL BE OVER THE OHIO RIVER VALLEY ON
WEDNESDAY WITH TWO CLOSED UPPER LEVEL LOWS LOCATED ACROSS THE UNITED
STATES. THE FIRST CLOSED LOW WILL BE LOCATED OVER NEW ENGLAND, WITH
THE SECOND CLOSED LOW LOCATED JUST EAST OF THE FOUR CORNERS REGION.
GLOBAL ENSEMBLE GUIDANCE IS ACTUALLY IN FAIRLY GOOD AGREEMENT WITH
THE PROGRESSION OF THESE TWO CLOSED LOWS WEDNESDAY THROUGH FRIDAY.
ALL THREE OF THE GEFS/ GEPS/ AND EPS SHOW THE CLOSED LOW THAT WAS
EAST OF THE FOUR CORNERS REGION MOVING EAST TOWARDS THE SOUTHERN
MISSISSIPPI RIVER VALLEY WITH A STRONG UPPER LEVEL SHORTWAVE OVER
NEW ENGLAND. TAKING A LOOK AT THE WPC CLUSTER ANALYSIS THOUGH, DOES
REVEAL SOME IMPORTANT DIFFERENCES AND HIGHLIGHTS THE INHERENT
UNCERTAINTY WHEN DEALING WITH CLOSED LOWS THAT ARE BROKEN OFF FROM
THE MAIN LONGWAVE PATTERN. IN PARTICULAR, MOST OF THE ENSEMBLE
DIFFERENCES APPEAR TO BE WITH THE FIRST CLOSED LOW AND HOW IT EJECTS
NORTHEAST TOWARDS NEW ENGLAND. HOW THE LOW EJECTS (OR GETS ABSORBED
BACK INTO THE MAIN LONGWAVE PATTERN), APPEARS TO BE WHERE THE
UNCERTAINTY ORIGINATES FROM (FURTHER SUPPORTED BY THE WPC ENSEMBLE
SENSITIVITY ANALYSIS -- WESA WEBPAGE). ABOUT 60% OF THE GUIDANCE IS
SHOWING A SLOWER EXIT OF THE FIRST WAVE, WITH ABOUT THE OTHER 40% OF
GUIDANCE SHOWING A QUICKER EXIT OF THE FIRST WAVE. WHAT DOES THIS
MEAN LOCALLY?
SCENARIO 1 (SLOWER EXIT OF THE CLOSED UPPER LEVEL LOWS): AT THIS
POINT, THE SLOWER EXIT OF THE FIRST AND THEN SECOND CLOSED LOW IS
SLIGHTLY FAVORED. THIS DOES MAKE SYNOPTIC SENSE, SINCE THE SECOND
CLOSED LOW ACTUALLY TENDS TO DEVELOP A WEAK REX BLOCK AT IT MOVES
ACROSS THE CENTRAL UNITED STATES. THE SLOWER SOLUTION WOULD MAKE FOR
A SLIGHTLY DELAYED ONSET OF SHOWERS AND THUNDERSTORMS, BUT FOR A
THREAT OF HEAVIER RAINFALL FOR THURSDAY THROUGH SATURDAY (MULTIPLE
ROUNDS OF SHOWERS AND THUNDERSTORMS). A COLD FRONT WOULD THEN STALL
ACROSS THE REGION LATE SATURDAY WITH A CLOSED LOW LOCATED SOUTHWEST
OF THE REGION. THIS WOULD PROVIDE MORE THAN SUFFICIENT UPPER LEVEL
LIFT TO THE REGION.
SCENARIO 2 (FASTER EXIT OF THE FIRST AND SECOND CLOSED LOW): THIS
SOLUTION IS NOT AS FAVORED, BUT WOULD STILL BRING SEVERAL ROUNDS OF
SHOWERS AND THUNDERSTORMS TO THE REGION. THE SECOND CLOSED LOW WOULD
EJECT BACK INTO THE LONGWAVE PATTERN BY SATURDAY AND SUNDAY THOUGH.
THIS MEANS SHOWERS AND THUNDERSTORMS WOULD START WEDNESDAY, BUT COME
TO AN END QUICKER/ OVER THE WEEKEND. THIS SOLUTION IS ALSO SLIGHTLY
MORE OF AN AMPLIFIED WAVE PATTERN WHICH WOULD PUSH THE FRONT THROUGH
THE REGION. BOX AND WHISKER PLOTS OF THIS CLUSTER, CLEARLY SHOWS
THIS WITH LOW TEMPERATURES A GOOD 5 TO 10 DEGREES COOLER SUNDAY
COMPARED TO SCENARIO 1.
AVIATION /19Z SUNDAY THROUGH FRIDAY/
KCHS AND KJZI: ISOLATED TO SCATTERED SHOWERS AND MAYBE A
THUNDERSTORM OR TWO REMAINS POSSIBLE THROUGH LATE AFTERNOON AND
INTO EARLY EVENING, BUT DRY AIR ALOFT WILL KEEP COVERAGE TOO
LIMITED FOR ANYTHING OTHER THAN VCSH IN THE TAF FOR THE TIME
BEING. MODERATE S TO SW WINDS CONTINUE INTO THE EVENING, WITH
THE GRADIENT WEAKENING TONIGHT AS A DIFFUSE COLD FRONT CROSSES
THE AREA. THE OVERALL FOG THREAT TONIGHT IS TOO LOW TO INCLUDE
ANY MENTION OF VIS REDUCTIONS IN THE TAF, BUT THERE IS A LOW
(<10%) CHANCE AREAS THAT RECEIVE SOME RAINFALL THIS AFTERNOON
COULD SEE SOME LIGHT FOG TONIGHT. THE THREAT FOR THE TERMINALS
WILL COME INTO BETTER FOCUS AS THIS AFTERNOONS PRECIP UNFOLDS.
VFR THEN PREVAILS WITH MAINLY LIGHT WINDS MONDAY.
KSAV: A DIFFUSE COLD FRONT WILL CROSS THE TERMINAL OVERNIGHT,
WITH MODERATE S WINDS BECOMING LIGHT. DRY CONDITIONS EXPECTED
THIS AFTERNOON, WITH ANY SHOWER AND THUNDERSTORM ACTIVITY
FOCUSED NORTH OF THE SAVANNAH RIVER. BL MOISTURE CONTENT IS TOO
LOW TO JUSTIFY AND FOG CONCERNS OVERNIGHT, AND VFR CONDITIONS
ARE EXPECTED TO PREVAIL THROUGH MONDAY AS WELL.
EXTENDED AVIATION OUTLOOK:
WEDNESDAY THROUGH FRIDAY: MULTIPLE ROUNDS OF SHOWERS AND
THUNDERSTORMS ARE EXPECTED THROUGH THE PERIOD AS AN UPPER LEVEL
LOW APPROACHES FROM THE WEST. SIMULTANEOUSLY, A COLD FRONT WILL
POTENTIALLY STALL NEAR THE AREA LATE FRIDAY INTO SATURDAY.
PERIODS OF MVFR/ IFR CONDITIONS ARE POSSIBLE AT ALL TERMINALS.
MARINE
TONIGHT: SOUTHWEST FLOW IS EXPECTED TO MOSTLY BE IN THE 10-15
KNOT RANGE TODAY, WITH GUSTS UP TO AROUND 20 KNOTS POSSIBLE. THE
FRONT WILL SHIFT THROUGH THE WATERS AFTER MIDNIGHT WHICH WILL
TURN WINDS NORTHWESTERLY, THOUGH WITH SPEEDS GENERALLY NO MORE
THAN 10 KNOTS. SEAS ARE EXPECTED TO AVERAGE 3-4 FEET TODAY, THEN
2-3 FEET OVERNIGHT. THUNDERSTORMS WILL LIKELY MOVE THROUGH
PORTIONS OF THE WATERS THROUGH THE DAY AND OVERNIGHT. THESE
STORMS WILL BE CAPABLE OF PRODUCING STRONG WIND GUSTS AND
FREQUENT LIGHTNING.
MONDAY - TUESDAY: HIGH PRESSURE RIDGING IN FROM THE WEST BEHIND
THE DEPARTING COLD FRONT WILL KEEP A WEAK GRADIENT AND
RELATIVELY FAVORABLE MARINE CONDITIONS IN PLACE BOTH DAYS WITH
SLIGHTLY GUSTY CONDITIONS ONLY NEARSHORE AS THE AFTERNOON SEA
BREEZE DEVELOPS.
WEDNESDAY - THURSDAY: SEAS WILL GENERALLY BE 2 TO 4 FT WITH WINDS
OUT OF THE SOUTH AT 10 KT. A SLIGHT BACKING IN THE WINDS CAN BE
EXPECTED WEDNESDAY AS A SEA BREEZE POTENTIALLY DEVELOPS. MULTIPLE
ROUNDS OF SHOWERS AND THUNDERSTORMS ARE LIKELY (60 - 80%) THROUGH
THE PERIOD.
FRIDAY: AN UPPER LEVEL LOW WILL APPROACH FROM THE WEST AND NORTH
WITH THE PRESSURE GRADIENT TIGHTENING OVER THE MARINE ZONES. OUT
AHEAD OF A COLD FRONT, WINDS WILL BACK FROM THE NORTHEAST AND
INCREASE 10 TO 15 KT. GUSTS UP TO 20 KT WITH SEAS BUILDING 3 TO 4 FT
POSSIBLE. AS WINDS INCREASE OUT OF THE NORTHEAST, A 9 TO 10S PERIOD
WILL BE INTRODUCED. AS OF CURRENT, NO SMALL CRAFT ADVISORIES ARE
FORECAST. MULTIPLE ROUNDS (80%) OF SHOWERS AND THUNDERSTORMS ARE
EXPECTED THOUGH.
CHS WATCHES/WARNINGS/ADVISORIES
GA...NONE.
SC...NONE.
MARINE...NONE.
NEAR TERM...BSH/CEB
SHORT TERM...CEB
LONG TERM...BSH
AVIATION...BSH/CEB
MARINE...BSH/CEB
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