542
FXUS62 KCHS 190020
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
720 PM EST SAT JAN 18 2025
SYNOPSIS
AN AREA OF LOW PRESSURE AND ASSOCIATED COLD FRONT WILL IMPACT
THE REGION THROUGH SUNDAY MORNING. ARCTIC HIGH PRESSURE WILL
OVERSPREAD THE AREA MONDAY THROUGH MUCH OF NEXT WEEK.
MEANWHILE, GULF LOW PRESSURE WILL MOVE UP THE SOUTHEAST COAST
TUESDAY NIGHT AND WEDNESDAY. A SECONDARY LOW PRESSURE SYSTEM
COULD MOVE UP THE COAST THURSDAY INTO FRIDAY.
NEAR TERM /UNTIL 6 AM SUNDAY MORNING/
IT HAS BEEN ANOTHER RAW AND WET DAY ACROSS SOUTHEAST SOUTH
CAROLINA AND SOUTHEAST GEORGIA. A WEAK WARM FRONT WILL LIFT
NORTH THROUGH THE AREA THIS EVENING AS A COLD FRONT APPROACHES
FROM THE WEST AND NORTHWEST. AFTER A BRIEF RESPITE FROM THE
RAIN LATE THIS AFTERNOON, BANDS OF MODEST ISENTROPIC ASCENT
WILL KEEP A RISK FOR RAIN GOING THROUGH THE NIGHT WITH THE
GREATEST COVERAGE OCCURRING MAINLY THIS EVENING WITH THE PASSAGE
OF THE WARM FRONT. CATEGORICAL POPS OF 80-90% FOR WIDESPREAD
STRATIFORM RAINS WERE HIGHLIGHTED FOR THE AREA TONIGHT.
TEMPERATURES SHOULD RISE OVERNIGHT AS THE AREA BECOMES EMBEDDED
WITHIN THE WARM SECTOR OF THE APPROACHING FRONT. TEMPERATURES
SHOULD RISE INTO THE UPPER 50S/NEAR 60 BY DAYBREAK SUNDAY.
NIGHTTIME LOWS WILL OCCUR THIS EVENING AS A RESULT, RANGING FROM
THE UPPER 40S/LOWER 50S NORTH OF I-16 WITH MID 50S SOUTH OF
I-16.
SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/
THE POWERFUL LONGWAVE TROUGH WILL REMAIN OVER MOST OF THE CONUS
ON SUNDAY. THE ELONGATED SOUTHERN STREAM SHORTWAVE WILL SHIFT
OFF THE NC/SC COAST MIDDAY, PUSHING THE SURFACE LOW AND COLD
FRONT NORTH AND EAST OF THE LOCAL AREA. IT WON'T BE UNTIL SUNDAY
AFTERNOON THAT THE MUCH DRIER AIR MAKES ITS WAY INTO THE AREA.
LINGERING MOISTURE, COMBINED WITH RESIDUAL ISENTROPIC ASCENT,
COULD MAINTAIN A FEW SHOWERS OVER THE AREA THROUGH LATE MORNING
OR EARLY AFTERNOON, ALONG WITH EXTENSIVE CLOUD COVER. A WARM
ADVECTION REGIME WILL PERSIST FOR MOST OF THE DAYTIME HOURS SO
WE EXPECT FAIRLY WARM HIGH TEMPS IN THE MID 60S, THOUGH TEMPS
SHOULD RAPIDLY DECREASE LATE IN THE AFTERNOON ONCE COLD AIR
ADVECTION BEGINS IN EARNEST. BY SUNDAY AFTERNOON, 35-45 KT
GEOSTROPHIC WINDS WILL DEVELOP AS BL FLOW TURNS TO THE NW.
BREEZY CONDITIONS SHOULD DEVELOP, ESPECIALLY ON LAKE MOULTRIE
WHERE FREQUENT 25 KT GUSTS ARE EXPECTED. WE THEREFORE ISSUED A
LAKE WIND ADVISORY STARTING MIDDAY SUNDAY.
SUNDAY NIGHT WILL BE QUITE COLD AS THE ARCTIC HIGH EXPANDS OVER
THE AREA AND STRONG COLD AIR ADVECTION CONTINUES. LOW TEMPS
FORECAST TO DIP INTO THE LOW TO MID 20S EXCEPT UPPER 20S NEAR
THE COAST. WITH STEADY 8-12 MPH WINDS OVERNIGHT, WIND CHILL
VALUES ARE EXPECTED TO DIP TO 15-20 DEGREES AFTER MIDNIGHT IN
MOST AREAS. GIVEN THAT OUR COLD WEATHER ADVISORY IS 20 DEGREES
TEMP OR WIND CHILL, WE'LL LIKELY NEED TO ISSUE ONE EVENTUALLY.
THE LARGE ARCTIC SURFACE HIGH WILL CONTINUE TO EXPAND INTO THE
SOUTHEAST ON MONDAY. THE DAY SHOULD BE SUNNY AND COLD WITH
HIGHS IN THE LOWER 40S. BREEZY CONDITIONS WILL CONTINUE, THOUGH
WIND CHILL VALUES SHOULD RISE ABOVE 20 DEGREES BY LATE MONDAY
MORNING.
MONDAY NIGHT INTO TUESDAY, THE HIGHLY AMPLIFIED UPPER TROUGH
TRENDS TOWARD A POSITIVE TILT WHILE SEVERAL SOUTHERN STREAM
SHORTWAVES DEVELOP. LATE MONDAY NIGHT, A WEAK COASTAL TROUGH IS
FORECAST TO DEVELOP JUST OFF THE GA COAST. ALTHOUGH THE BRUNT OF
THE MOISTURE AND FORCING ARE EXPECTED TO REMAIN OFFSHORE, WEAK
MOIST ISENTROPIC ASCENT COULD PRODUCE SOME LIGHT PRECIP ALONG
THE GA COAST LATE MONDAY NIGHT. OUR HOURLY TEMPERATURE VALUES
DURING THIS TIME WOULD BE RIGHT AROUND FREEZING, SO IF ANY
PRECIPITATION DOES DEVELOP, IT COULD FALL AS LIGHT FREEZING
RAIN.
DURING THE DAY TUESDAY, A STRONG DIGGING SHORTWAVE WILL TRAVERSE
THE SOUTH CENTRAL UNITED STATES. EXTENSIVE CLOUD COVER AND COLD
AIR ADVECTION WILL YIELD A CHILLY DAY WITH HIGHS ONLY IN THE
MID/UPPER 30S IN SOUTHERN SC AND LOW/MID 40S IN SOUTHEAST GA.
MOISTURE WILL SLOWLY OVERSPREAD THE AREA FROM THE SOUTHWEST LATE
TUESDAY, AND EVENTUALLY SOME FORCING FOR ASCENT WILL TRANSPIRE.
HOWEVER, MOST GUIDANCE HAS TRENDED A BIT DRIER ON TUESDAY WITH
LITTLE TO NO PRECIPITATION THROUGH SUNSET. WE HAVE NOT FULLY
JUMPED ON THIS POSSIBILITY GIVEN THAT MODELS ARE NOTORIOUS FOR
STARTING PRECIPITATION TOO LATE IN THESE SCENARIOS, SO WE
MAINTAINED CHANCE POP TUESDAY AFTERNOON. AS FAR AS
PRECIPITATION TYPE, MODEL SOUNDINGS SUPPORT SNOW ACROSS THE
INLAND HALF OF OUR AREA, THEN THINGS GET TRICKY AS ONE MOVES
CLOSER TO THE COAST. A DECENT WARM LAYER IN THE LOWEST COUPLE
THOUSAND FEET, COMBINED WITH FAIRLY DRY AIR WITHIN THE DENDRITIC
GROWTH ZONE, INDICATES THE POTENTIAL FOR RAIN OR SNOW IN THE
REST OF THE FORECAST AREA. ALONG THE GA COAST THE ATMOSPHERE
LOOKS TOO WARM TO SUPPORT ANYTHING OTHER THAN RAIN. THIS IS ALL
CONTINGENT ON ANY PRECIPITATION EVEN OCCURRING, WHICH STILL
LOOKS IFFY FOR TUESDAY AFTERNOON. AT THIS POINT, GIVEN THE LOW
CONFIDENCE IN ANY QPF, WE DO NOT SHOW ANY SNOW OR ICE
ACCUMULATIONS FOR TUESDAY AFTERNOON.
LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/
THE FORECAST IS QUITE INTERESTING IN THE LONG TERM PERIOD,
ALBEIT EXTREMELY CHALLENGING. THE PRIMARY UPPER SHORTWAVE WILL
PASS THROUGH THE SOUTHEAST TUESDAY NIGHT AND WEDNESDAY.
MEANWHILE THE ARCTIC HIGH PRESSURE WILL REMAIN ANCHORED OVER THE
CENTRAL APPALACHIANS, MAINTAINING A COLD NORTHERLY FLOW IN
LOW/MID LEVELS. DEEP SYNOPTIC FORCING ASSOCIATED WITH THE
SHORTWAVE WILL SPUR WIDESPREAD PRECIPITATION TUESDAY NIGHT INTO
WEDNESDAY MORNING. MODELS ARE ACTUALLY IN REASONABLY GOOD
AGREEMENT ON THE TOTAL LIQUID PRECIPITATION RANGING FROM
0.25-0.50" FAR INLAND AND 0.5-0.75" ELSEWHERE. HOWEVER,
DETERMINING THE SNOWAMT AND ICEACCUM IS MUCH MORE CHALLENGING
BECAUSE IT DEPENDS ON P-TYPES.
MODEL SOUNDINGS INDICATE A LACK OF ICE NUCLEI ACTIVATION AT THE
ONSET OF THE MAIN FORCING TUESDAY EVENING. HOWEVER, THERE SHOULD
BE AMPLE COLD, DRY AIR IN THE LOW-LEVELS SUCH THAT TEMPS WILL
QUICKLY COOL TO FREEZING AT THE SURFACE. THIS COULD YIELD
FREEZING RAIN FOR MANY AREAS FOR A FEW HOURS AT THE BEGINNING OF
THE EVENT. THEN, GUIDANCE SHOWS THE ENTIRE PROFILE QUICKLY
MOISTENING AND BECOMING MORE OF A SNOW PROFILE FROM LATE TUESDAY
MORNING THROUGH WEDNESDAY MORNING. EVEN AFTER THIS OCCURS, THERE
IS STILL PARTICULARLY HIGH UNCERTAINTY ABOUT HOW THINGS WILL
PLAY OUT ACROSS COASTAL GA. AS FAR AS ACCUMULATIONS, IT IS OF
COURSE ON EVERYONE'S MIND. BEING THAT IT'S MORE THAN 3 DAYS OUT
AT THIS POINT, IT'S STILL A LITTLE EARLY TO CONFIDENTLY FORECAST
ACCUMULATIONS. AT THIS JUNCTURE WE'RE BALLPARKING ONE OR TWO
TENTHS OF AN INCH OF FREEZING RAIN ACCRETION AND 2-4" OF SNOW.
IT STILL APPEARS THE GREATEST ICE ACCRETIONS WOULD PROBABLY BE
IN COASTAL SOUTHEAST GA WHERE THE PRECIPITATION STAYS AS
FREEZING RAIN LONGER THAN ELSEWHERE. ONE THING THAT IS A NEAR
CERTAINTY IS THAT THESE ACCUMULATION FORECASTS WILL CHANGE
BETWEEN NOW AND TUESDAY NIGHT.
THE INITIAL PRECIPITATION SHOULD TAPER OFF WEDNESDAY MORNING.
TEMPS WEDNESDAY AND WEDNESDAY NIGHT WILL BE QUITE COLD,
ESPECIALLY IF WE HAVE SNOWPACK. WE COULD SEE SOME SUNSHINE BY
LATE WEDNESDAY AFTERNOON, BUT PROBABLY NOT ENOUGH TO FULLY MELT
ANY ACCUMULATED PRECIPITATION. HIGHS MIGHT RISE A FEW DEGREES
ABOVE FREEZING. WEDNESDAY NIGHT LOWS WILL BE IN THE MIDDLE
TEENS. WITH A FEW KNOTS OF WIND ON TOP OF THAT, WIND CHILLS MAY
DIP BELOW 10F LATE AT NIGHT, POTENTIALLY REQUIRING AN EXTREME
COLD WARNING.
THE FORECAST FOR WEDNESDAY NIGHT THROUGH SATURDAY IS NOW A LOT
TRICKIER THAN WE PREVIOUSLY THOUGHT. MODELS ARE STARTING TO SHOW
ADDITIONAL SHORTWAVES MOVING THROUGH THE SOUTHEAST DURING THIS
TIME, WITH A POSSIBLE COASTAL TROUGH DEVELOPING THURSDAY OR
THURSDAY NIGHT. QUITE A FEW MODELS ARE NOW SHOWING A FEW TENTHS
OF AN INCH OF QPF THURSDAY THROUGH FRIDAY. WITH ARCTIC HIGH
PRESSURE STILL IN PLACE, SOUNDINGS SHOW THAT SOME OF THIS COULD
FALL AS FREEZING RAIN. WE ADDED ZR TO THE FORECAST DURING THIS
TIME FRAME, THOUGH THERE REMAINS A LOT OF UNCERTAINTY ABOUT WHEN
THIS WOULD OCCUR. IF WE DO GET A PROLONGED PERIOD OF FREEZING
RAIN ON TOP OF ACCUMULATING SNOWFALL, THIS WOULD RESULT IN
SIGNIFICANT IMPACTS THROUGH MUCH OF THE WEEK.
AVIATION /00Z SUNDAY THROUGH THURSDAY/
19/00Z TAF DISCUSSION:
KCHS/KJZI/KSAV: WE HAVE SEEN A BREAK IN THE RAINFALL ALONG WITH
A WINDOW OF OVERALL VFR CONDITIONS AT THE TERMINALS OVER THE
LAST FEW HOURS. HOWEVER, IFR CEILINGS WILL BE DEVELOPING ACROSS
THE REGION THIS EVENING FOLLOWED BY WIDESPREAD LIGHT RAINFALL
SPREADING INTO THE REGION LATE THIS EVENING AND THROUGH THE
OVERNIGHT HOURS.
A RETURN TO MVFR CIGS SHOULD OCCUR BY MID-MORNING SUNDAY AS
RAINFALL COMES TO AN END. VFR CONDITIONS DEVELOP DURING THE
AFTERNOON. GUSTY WESTERLY WINDS DEVELOP ON SUNDAY AS WELL WITH
GUSTS TO AROUND 25 KNOTS COMMON.
EXTENDED AVIATION OUTLOOK: FLIGHT RESTRICTIONS EXPECTED TUESDAY
THROUGH WEDNESDAY AS WINTRY WEATHER MOVES THROUGH. SNOW AND/OR
FREEZING RAIN ARE LOOKING INCREASINGLY LIKELY AT ALL TERMINALS,
PARTICULARLY TUESDAY AFTERNOON THROUGH WEDNESDAY MORNING. FLIGHT
RESTRICTIONS MAY CONTINUE INTO THURSDAY AS A SECONDARY SYSTEM
MOVES THROUGH.
MARINE
TONIGHT: WINDS WILL BECOME SOUTHWEST OVERNIGHT AS A WEAK FRONT
LIFTS NORTH THROUGH THE AREA. SPEEDS WILL BEGIN TO INCREASE
LATER THIS EVENING, REACHING 15 AFTER MIDNIGHT, EXCEPT 15-20 KT
OVER THE SOUTH SANTEE-EDISTO BEACH NEARSHORE AND GEORGIA
OFFSHORE LEG. THERE COULD BE SOME GUSTS TO 25 KT, ESPECIALLY OFF
THE CHARLESTON COUNTY COAST, BUT DURATIONS DO NOT LOOK FREQUENT
ENOUGH FOR A SMALL CRAFT ADVISORY AT THIS TIME. SEAS WILL BUILD
2-4 FT, EXCEPT 3-5 FT OFF THE CHARLESTON COUNTY COAST LATE.
SUNDAY THROUGH THURSDAY: GUSTY NW WINDS WILL DEVELOP SUNDAY
AFTERNOON BEHIND THE ARCTIC COLD FRONT. WE ISSUED SMALL CRAFT
ADVISORIES FOR ALL WATERS EXCEPT CHARLESTON HARBOR STARTING
SUNDAY MORNING, CONTINUING INTO MONDAY MORNING.
ANOTHER SURGE IS EXPECTED TUESDAY THROUGH WEDNESDAY DURING WHICH
STRONG SMALL CRAFT ADVISORY OR POSSIBLE GALES OCCURS. CONDITIONS
SHOULD SLIGHTLY IMPROVE LATER WEDNESDAY, THOUGH WINDS WILL
REMAIN FAIRLY STRONG THROUGH THE WEEK.
CLIMATE
RECORD LOW MAXIMUM TEMPERATURES:
JANUARY 22:
KCHS: 31/1970
KCXM: 31/1970
KSAV: 34/1970
JANUARY 23:
KCHS: 34/1970
KCXM: 38/2016
KSAV: 40/2016
RECORD LOW TEMPERATURES:
THURSDAY, JANUARY 23:
KCHS: 19/1985
KCXM: 24/2003
KSAV: 19/1960
RECORD SNOWFALL:
TUESDAY, JANUARY 21:
KCHS: T/1984*
KSAV: 0.2/1910
WEDNESDAY, JANUARY 22:
KCHS: T/2022*
KSAV: T/2011*
* A TRACE IS NOT CONSIDERED A RECORD IN TERMS OF THE DAILY
CLIMATE. TRACE AMOUNTS SHOWN ABOVE ARE MORE FOR INFORMATION OF
WHEN THE LAST INSTANCE OF SNOW OCCURRED ON THE LISTED DATE.
CHS WATCHES/WARNINGS/ADVISORIES
GA...NONE.
SC...LAKE WIND ADVISORY FROM 10 AM TO 11 PM EST SUNDAY FOR SCZ045.
MARINE...SMALL CRAFT ADVISORY FROM 7 AM SUNDAY TO 10 AM EST MONDAY FOR
AMZ350.
SMALL CRAFT ADVISORY FROM 10 AM SUNDAY TO 10 AM EST MONDAY FOR
AMZ352-354-374.
NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...
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