961
FXUS62 KCHS 050207
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1007 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/
LATE THIS EVENING, A SLOW MOVING COLD FRONT AND A SEA BREEZE
CONTINUED TO DRIFT OVER THE FORECAST AREA. ISOLATED SHOWERS AND
THUNDERSTORM HAVE TRIGGERED ALONG THE BOUNDARIES THIS EVENING.
RECENT RUNS OF THE HRRR INDICATES THAT CONVECTION MAY DEVELOP
NEAR THE SC COAST THROUGH LATE TONIGHT. THE FORECAST WILL
CONTINUE TO INDICATE SCHC TO CHC POPS THROUGH LATE TONIGHT.
SKIES BEGIN TO CLEAR DURING 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 /02Z MONDAY THROUGH FRIDAY/
PRIOR TO THE 0Z TAFS, KCLX AND SFC OBSERVATIONS SHOWED A SLOWING
SEA BREEZE GENERALLY OVER THE I-95 CORRIDOR. ISOLATED TO
SCATTERED SHOWERS AND THUNDERSTORMS SHOULD DEVELOP ALONG THE
BOUNDARY THROUGH MUCH OF THIS EVENING. IT APPEARS THE KCHS WILL
SEE THE GREATEST CHANCE FOR CONVECTION, HIGHLIGHTED WITH A
MENTION OF VCSH UNTIL 2Z. BY LATE TONIGHT, A WEAK COLD FRONT
SHOULD DRIFT ACROSS THE TERMINALS, RESULTING IN LIGHT WINDS
TO SHIFT FROM THE SW. SOUTHWEST WINDS SHOULD STRENGTHEN BY EARLY
MONDAY AFTERNOON, WITH GUSTS AROUND 20 KTS AT KCHS AND KJZI.
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...NED
SHORT TERM...CEB
LONG TERM...BSH
AVIATION...NED
MARINE...BSH/CEB
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