400
FXUS62 KCHS 050606
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
206 AM EDT MON MAY 5 2025
SYNOPSIS
A COLD FRONT WILL STALL JUST OFFSHORE AS HIGH PRESSURE BEGINS
TO BUILD INTO THE REGION. A COLD FRONT AND AN UPPER-LEVEL LOW
WILL APPROACH FROM THE WEST THURSDAY AND CAUSE AN UNSETTLED
WEATHER PATTERN TO PERSIST INTO THE WEEKEND.
NEAR TERM /UNTIL 6 AM THIS MORNING/
EARLY THIS MORNING: SURFACE ANALYSIS AND CURRENT RADAR IMAGERY
SHOW THAT THE FRONT IS BEING QUITE STUBBORN AND LINGERING ACROSS
THE TRI-COUNTY REGION DOWN THROUGH THE COLLETON/BEAUFORT COUNTY
COAST. JUST AHEAD OF THE FRONT, THERE IS STILL PLENTY OF
INSTABILITY (ESPECIALLY FOR THIS TIME OF NIGHT) AND WE ARE
SEEING A FEW RATHER ROBUST STORMS DEVELOP ALONG THE COAST AND
ACROSS THE COASTAL WATERS. IN FACT, A FEW STORMS HAVE LIKELY
HAD SUFFICIENT REFLECTIVITY SIGNATURES TO SUPPORT THERE BEING AT
LEAST SOME SMALL HAIL IN THESE STORMS. WE WILL LIKELY SEE THIS
ONGOING ACTIVITY CONTINUE, IF NOT BLOSSOM FURTHER, THROUGH ABOUT
5 AM MAINLY FAVORING THE COAST FROM AROUND EDISTO THROUGH THE
ENTIRE CHARLESTON COUNTY COAST. FOR THE REST OF THE AREA, DRY
CONDITIONS WILL CONTINUE AND LOWS ARE FORECAST TO DIP INTO THE
LOW TO MID 50S. THERE WILL BE A NOTABLE LOW TEMPERATURE GRADIENT
WITH LOW TO MID 50S INLAND RANGING TO MID TO UPPER 60S ALONG THE
CHARLESTON COUNTY COAST.
SHORT TERM /6 AM THIS 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 /06Z MONDAY THROUGH FRIDAY/
KCHS AND KJZI: SCATTERED SHOWERS AND THUNDERSTORMS WILL LIKELY
IMPACT THE TERMINALS THROUGH ABOUT 08Z. BRIEF MVFR OR EVEN IFR
CONDITIONS WILL BE POSSIBLE AS THESE SHOWERS AND STORMS PASS
THROUGH. THEREAFTER, VFR CONDITIONS WILL PREVAIL THROUGH 06Z
TUESDAY. WEST OR WEST-SOUTHWEST WINDS WILL PREVAIL FROM ABOUT
MID MORNING ONWARD UNTIL THE SEA BREEZE MOVES THROUGH LATE IN
THE AFTERNOON.
KSAV: VFR CONDITIONS WILL PREVAIL THROUGH 06Z TUESDAY. WESTERLY
WINDS WILL PREVAIL FROM ABOUT MID MORNING ONWARD UNTIL THE SEA
BREEZE MOVES THROUGH LATE IN THE AFTERNOON OR EARLY IN THE
EVENING.
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
SHORT TERM...CEB
LONG TERM...BSH
AVIATION...BSH
MARINE...BSH/CEB
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page