898
FXUS62 KCHS 212213
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
513 PM EST SUN DEC 21 2025
SYNOPSIS
A COLD FRONT WILL PASS THROUGH THE REGION THIS EVENING. HIGH
PRESSURE WILL THEN PREVAIL THROUGH THE REMAINDER OF THE HOLIDAY
WEEK.
NEAR TERM /UNTIL 6 AM MONDAY MORNING/
21/2130Z SURFACE OBSERVATIONS SHOW A BACKDOOR COLD FRONT HAS
ABOUT CLEARED THE CHARLESTON TRI-COUNTY AREA WILL MARCH QUICKLY
SOUTH AND OFFSHORE OVER THE NEXT FEW HOURS, CLEARING THE
ALTAMAHA RIVER PRIOR TO MIDNIGHT. A WIND SHIFT TO THE NORTH
ALONG WITH A LOWERING OF DEWPOINTS WILL OCCUR WITH FROPA. HIGH
PRESSURE WILL STEADILY BUILD SOUTH WITH A COOLER AND CONSIDERABLY
DRIER AIRMASS SETTLING IN. POST-FRONTAL COLD AIR ADVECTION
(CAA) IS MODERATE WITH 850 HPA TEMPERATURES FORECAST TO FROM
+10-12C TO +5-8C BY DAYBREAK. ONGOING CAA AND A TIGHTENING
PRESSURE GRADIENT ASSOCIATED WITH THE HIGH ITSELF WILL KEEP
WINDS ELEVATED THROUGH THE NIGHT. NEAR TERM GUIDANCE HAS WARMED
A BIT FROM EARLIER TODAY WHICH MATCHES SOME OF THE DIRECT MODEL
OUTPUT TRENDS. LOWS WERE NUDGED UP SLIGHTLY FROM THE EARLY
AFTERNOON FORECAST CYCLE GIVEN THIS TREND, RANGING FROM THE
UPPER 30S/LOWER 40S INLAND TO THE UPPER 40S/LOWER 50S AT THE
BEACHES. THE UPDATED LOW TEMPERATURE FORECAST IS STILL A BIT
COOLER THAN SOME GUIDANCE WOULD SUGGEST SO ADDITIONAL UPWARD
ADJUSTMENTS MAY BE NEEDED LATER THIS EVENING. DEWPOINTS WERE
ADJUST LOWERED A BIT BASED ON UPSTREAM OBSERVATIONS.
LAKE WINDS: WINDS ON LAKE MOULTRIE WILL BEGIN TO SURGE A BIT
THIS EVENING, PEAKING AROUND 15 KT WITH GUSTS TO 20 KT
OVERNIGHT. WINDS MAY REACH AS HIGH AS 15-20 KT AT TIMES WITH A
FEW GUSTS NEARING 25 KT, MAINLY OVER THE CENTRAL AND SOUTHWEST
PORTIONS OF THE LAKE WHERE OPEN WATER TRAJECTORIES ARE AT THEIR
LONGEST IN NORTHEAST FLOW REGIMES; HOWEVER, DURATIONS DO NOT
LOOK FREQUENT ENOUGH TO JUSTIFY A LAKE WIND ADVISORY AT THIS
TIME. THE AREA OF HIGHEST WINDS SHOULD LARGELY MISS THE PNOS1
LAKE WIND OBSERVATION SITE GIVEN THE FLOW SETUP, BUT WINDS WILL
BE MONITORED CLOSELY GIVEN CONDITIONS WILL BE CLOSE TO ADVISORY
THRESHOLDS. THE CHANCE FOR HITTING LAKE WIND ADVISORY CRITERIA
ARE RUNNING RIGHT AROUND 50%.
SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/
MONDAY: SURFACE HIGH PRESSURE WILL BE CENTERED OVER THE PIEDMONT OF
NORTH CAROLINA WITH HIGH CLOUDS STREAMING OVERHEAD. LOW LEVEL WINDS
WILL BE GUSTY AT TIMES IN THE MORNING HOURS WITH THE NOCTURNAL LOW
LEVEL JET EXPECTED TO PEAK AROUND 30 MPH WITH SOME SURFACE WIND
GUSTS OF 20 TO 25 MPH POSSIBLE. AS THE DAY PROGRESSES, WINDS WILL
BECOME LESS GUSTY AS THE LOW LEVEL JET SIGNIFICANTLY WEAKENS.
IN THE MID LEVELS OF THE ATMOSPHERE A POTENT SHORTWAVE WILL BE
QUICKLY EXITING NEW ENGLAND WITH SURFACE HIGH PRESSURE FOLLOWING
SUITE. THIS MEANS BY LATE MONDAY, THE SURFACE HIGH WILL ALREADY BE
OFF OF THE COAST OF NORTH CAROLINA WITH A COASTAL TROUGH MOVING
INLAND OVER GEORGIA AND SOUTH CAROLINA. NO PRECIPITATION IS FORECAST
WITH THE COASTAL TROUGH AS AN UPTICK IN DEWPOINTS (AND RELATIVE
HUMIDITY) ARE THE ONLY SENSIBLE WEATHER CHANGES FORECAST. HIGH
CLOUDS WILL BE STREAMING OVERHEAD THROUGH THE DAY, BUT MOSTLY SUNNY
SKIES ARE STILL EXPECTED WITH HIGHS IN THE LOWER 60S. MONDAY NIGHT
EXPECT LOWS IN THE LOWER 40S WITH SOME GUIDANCE HINTING AT THE
POTENTIAL FOR FOG OR STRATUS DEVELOPMENT AS HIGHER DEWPOINTS SURGE
WEST.
TUESDAY THROUGH THURSDAY: ANOTHER MID-LEVEL WAVE WILL DIVE SOUTHEAST
ACROSS ONTARIO AND QUEBEC LATE TUESDAY WHICH WILL SPELL THE END OF
THE SURFACE HIGH PRESSURE AND THE AGEOSTROPHIC CONVERGENCE COMES TO
AN END. EXPECT WARMING TEMPERATURES TUESDAY AS THE AIR MASS QUICKLY
STARTS TO MODIFY. TO PUT IT INTO PERSPECTIVE, 1000/850MB THICKNESSES
MONDAY ARE FORECAST TO BE AROUND 1340M, AND BY TUESDAY AFTERNOON ARE
EXPECTED TO BE 1365 - 1370M. THIS MEANS TEMPERATURES WILL RAPIDLY
RISE INTO THE 50S BY MID TUESDAY MORNING WITH HIGHS AROUND 70
DEGREES FORECAST. TEMPERATURES WILL FURTHER WARM INTO THE LOWER TO
MID 70S FOR WEDNESDAY AND THURSDAY. THE LATEST RUN OF THE NBM SHOWS
A HIGH DEGREE OF CONFIDENCE WITH THESE TEMPERATURES AS THE
INTERQUARTILE RANGE (IQR) FOR HIGHS WEDNESDAY - FRIDAY IS ONLY 2 - 4
DEGREES. NO PRECIPITATION IS FORECAST.
LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/
THE FORECAST FOR FRIDAY REMAINS HIGH CONFIDENCE WITH ABOVE NORMAL
TEMPERATURES CONTINUING. FORECAST CONFIDENCE STARTS TO DECREASE
SATURDAY THANKS TO A POTENT MID-LEVEL LOW JUST EAST OF THE HUDSON
BAY. THIS LOW COULD POTENTIALLY PUSH A STRONG COLD FRONT THROUGH THE
AREA SATURDAY WITH TEMPERATURES RETURNING TO MORE SEASONABLE VALUES.
HOWEVER, MODEL GUIDANCE VARIES WITH THE STRENGTH AND POSITION OF
THIS LOW. SOME ENSEMBLE MEMBERS SHOW A STRONGER MID-LEVEL LOW AND
SLOWER MOVEMENT OF THE WAVE NORTHEAST, WHILE OTHER MEMBERS SHOW A
MUCH WEAKER WAVE AND QUICKER MOVEMENT TO THE NORTHEAST. THE DEEPER
WAVE WOULD FAVOR NEAR NORMAL TO SLIGHTLY BELOW NORMAL TEMPERATURES
SATURDAY INTO SUNDAY, WHILE THE LESS AMPLIFIED WAVE AND FASTER
MOVEMENT WOULD FAVOR SEASONABLE TEMPERATURES AGAIN MODERATING TO
ABOVE NORMAL. TAKING A LOOK AT THE LATEST WPC CLUSTER ANALYSIS
REVEALS AROUND 65% OF MODEL SOLUTIONS FAVORING THE FASTER/ LESS
AMPLIFIED PATTERN WITH 20% SHOWING A HIGHLY AMPLIFIED SOLUTION AND
AROUND 15% ADVERTISING A BLEND BETWEEN THESE SOLUTIONS. EITHER WAY,
NO PRECIPITATION IS FORECAST.
AVIATION /21Z SUNDAY THROUGH FRIDAY/
22/00Z TAF DISCUSSION:
KCHS/KJZI/KSAV: VFR THROUGH 23/00Z.
EXTENDED AVIATION OUTLOOK:
MONDAY AND TUESDAY: MOSTLY VFR CONDITIONS. TWO PERIODS OF MVFR
CIGS OR LOWER ARE POSSIBLE WITH THE FIRST BEING MONDAY MORNING
BEHIND THE COLD FRONT. THE SECOND CHANCE WILL BE TUESDAY MORNING
AS MOISTURE RICH AIR RETURNS TO THE REGION. THESE RESTRICTIONS
WILL BE POSSIBLE DUE TO FOG OR STRATUS DEVELOPMENT.
WEDNESDAY AND THURSDAY: VFR CONDITIONS.
MARINE
THROUGH TONIGHT: SMALL CRAFT ADVISORIES REMAIN IN PLACE FOR ALL
AREAS WITH THE EXCEPTION OF THE CHARLESTON HARBOR. WINDS AND
SEAS WILL BUILD TONIGHT AS A COLD FRONT DROPS THROUGH THE
WATERS. NORTHEAST WINDS WILL REACH AS HIGH AS 20-25 KT WITH
GUSTS TO 30 KT WITH SEAS BUILDING TO 4-7 FT. WINDS WILL LIKELY
PEAK AROUND 15-20 KT IN THE CHARLESTON HARBOR, ALTHOUGH GUSTS
COULD GET CLOSE TO 25 KT CLOSER THE HARBOR ENTRANCE LATER THIS
EVENING. FOR NOW, THE SITUATION LOOK TOO BORDERLINE TO HOIST AN
ADVISORY FOR THE CHARLESTON HARBOR. THIS WILL BE RECONSIDERED
LATER THIS EVENING/OVERNIGHT AS TRENDS BECOME MORE APPARENT.
MONDAY AND TUESDAY: BREEZY NORTHEAST WINDS BEHIND A COLD FRONT ARE
EXPECTED MONDAY MORNING WITH GUSTS 25 TO 30 KT. SEAS 4 TO 7 FT. THE
NORTHEAST WINDS WILL THEN START TO RELAX LATE MONDAY MORNING WITH
SEAS SLOWLY STARTING TO COME DOWN MONDAY AFTERNOON. ALL NEARSHORE
WATER SMALL CRAFT ADVISORIES WILL BE DONE BY LATE MONDAY EVENING
WITH THE OFFSHORE GEORGIA WATERS REMAINING THROUGH TUESDAY AFTERNOON
DUE TO THE POTENTIAL FOR 6 FT SEAS.
WEDNESDAY AND THURSDAY: HIGH CONFIDENCE IN NO MARINE HEADLINES. WIND
GUSTS 15 KT OR LESS WITH SEAS 2 TO 3 FT.
CHS WATCHES/WARNINGS/ADVISORIES
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 9 PM THIS EVENING TO MIDNIGHT EST
MONDAY NIGHT FOR AMZ350.
SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO MIDNIGHT EST
MONDAY NIGHT FOR AMZ352-354.
SMALL CRAFT ADVISORY FROM 9 PM THIS EVENING TO 6 PM EST
TUESDAY FOR AMZ374.
NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...
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