183
FXUS62 KCHS 200653
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
153 AM EST MON JAN 20 2025
SYNOPSIS
ARCTIC HIGH PRESSURE WILL BUILD IN THROUGH MONDAY NIGHT. A
STORM SYSTEM WILL BRING UNSETTLED WEATHER TO THE AREA TUESDAY
AFTERNOON THROUGH WEDNESDAY MORNING. ANOTHER WEAK STORM SYSTEM
COULD IMPACT THE AREA THURSDAY AND THURSDAY NIGHT.
NEAR TERM /UNTIL 6 AM THIS MORNING/
TONIGHT: DRY AND COLD HIGH PRESSURE WILL BUILD ACROSS THE REGION
THROUGH THE REMAINDER OF THE NIGHT UNDER CLEAR SKIES. WEATHER
CONDITIONS WILL REMAIN QUIET, BUT LOW TEMPS HAVE/WILL BECOME
CONSIDERABLY COLDER THAN THE PREVIOUS NIGHT. TEMPS DIPPING INTO THE
MID 20S FOR MANY AREAS AND UPPER 20S/AROUND 30 NEAR THE COAST ALONG
WITH A PERSISTENT 10-15 MPH NORTHWESTERLY WIND OCCURRING WITH COLD
AIR ADVECTION IN PLACE WILL SUPPORT WIND CHILL TEMPERATURES DIPPING
INTO THE UPPER TEENS TO LOWER 20S (LOWEST ACROSS INLAND GEORGIA).
NOTE: A COLD WEATHER ADVISORY HAS BEEN ISSUED FOR TONIGHT AND
INTO WEDNESDAY EVEN THOUGH CRITERIA WILL ONLY BE MET DURING THE
OVERNIGHT PERIODS. STARTING WEDNESDAY NIGHT, WIND CHILLS MAY
GET INTO EXTREME COLD WARNING TERRITORY (10 ABOVE OR COLDER).
FOR THIS REASON, THE ADVISORY ENDING TIME ENDS AT 6 AM WEDNESDAY.
THIS WILL ALLOW FOR AN EASIER TRANSITION TO EXTREME COLD WATCH/WARNING
PRODUCTS WEDNESDAY NIGHT INTO THURSDAY NIGHT, IF NEEDED. ISSUING
A SINGLE LONG DURATION COLD WEATHER ADVISORY WILL ALSO ALLOW US
TO BETTER HIGHLIGHT AND MESSAGE THE VERY UNUSUAL LONG-DURATION
COLD THAT WILL GRIP THE AREA THIS WEEK. IT CAN NOT BE STRESSED
ENOUGH THE IMPACTS THIS LONG, BITTERLY COLD WEATHER WILL HAVE ON
THE REGION.
LAKE WINDS: WINDY CONDITIONS WILL PERSIST ON LAKE MOULTRIE FOR MUCH
OF THE NIGHT AS STRONG COLD AIR ADVECTION OCCURS ACROSS THE LAKE.
NORTHWEST WINDS SHOULD PEAK AROUND 25 KT FOR THE NEXT FEW HOURS,
THEN GRADUALLY DECREASE APPROACHING DAYBREAK. WAVES WILL BE 2-3 FT
AT TIMES. A LAKE WIND ADVISORY IS IN EFFECT UNTIL 6 AM.
SHORT TERM /6 AM THIS MORNING THROUGH WEDNESDAY/
AN UNSEASONABLY STRONG UPPER TROUGH WILL REMAIN OVER THE UNITED
STATES EARLY TO MID WEEK WITH ARCTIC HIGH PRESSURE EXPANDING
ALL THE WAY INTO THE GULF OF MEXICO AND WESTERN ATLANTIC. A
DEVELOPING SHORTWAVE NOW DIVING SOUTH INTO THE PACIFIC NW WILL
AMPLIFY AS IT ROUNDS THE BASE OF THE TROUGH ON TUESDAY. A WEAK
COASTAL TROUGH IS EXPECTED TO DEVELOP OFF THE SC/GA COAST LATE
MONDAY NIGHT AND TUESDAY BEFORE MOVING NORTHEAST. WEAK
ISENTROPIC ASCENT COULD BRING SOME LIGHT PRECIPITATION TO MAINLY
COASTAL AREAS LATE MONDAY NIGHT INTO TUESDAY MORNING BEFORE
THIS FORCING SHIFTS NORTHEAST. THERE IS LOW MODEL CONSISTENCY
WITH REGARD TO THIS MORNING PRECIP SO WE DON'T CURRENTLY SHOW
ANY QPF TUESDAY MORNING. HOWEVER, IT BEARS WATCHING BECAUSE THE
THERMAL PROFILE WOULD SUPPORT FREEZING RAIN IF WE DO SEE
PRECIPITATION.
THE PRIMARY WEATHER EVENT WILL BE THE APPROACH OF THE STRONG
UPPER SHORTWAVE TUESDAY AFTERNOON AND TUESDAY NIGHT. A 200 KT
H25 JET STREAK WILL SET UP OFF THE MID ATLANTIC COAST TUESDAY
NIGHT, PLACING THE LOCAL AREA SQUARELY WITHIN THE RIGHT ENTRANCE
REGION. MODEST MOISTURE WILL OVERSPREAD THE AREA FROM THE
SOUTHWEST AHEAD OF THE SHORTWAVE. THE BIG QUESTION ALL ALONG
HAS BEEN EXACTLY HOW FAR SOUTH AND EAST THE BEST MOISTURE AND
STRONGEST SYNOPTIC FORCING DEVELOPS. THERE HAS BEEN A NOTABLE
DOWNWARD TREND IN TOTAL QPF WITH THE 12Z GUIDANCE, THOUGH THIS
IS MOST NOTICEABLE IN THE DETERMINISTIC RUNS. THE ENSEMBLE MEANS
HAVE CONTINUED TO RUN HIGHER THAN THE DETERMINISTIC COUNTERPARTS
FOR SEVERAL DAYS NOW, THOUGH WE DID SEE A DOWNWARD TICK IN QPF
WITH THE 12Z ENSEMBLE DATA. OUR LATEST QPF FORECAST STUCK PRETTY
CLOSE TO THE WPC DATA WHICH CLOSELY RESEMBLES THE 13Z NATIONAL
BLEND OF MODELS (NBM). THIS PRINTS OUT A TOTAL QPF OF 0.15-0.25"
FAR INLAND, WITH THE BRUNT OF THE AREA IN A 0.25-0.50" STRIPE.
COASTAL GA SHOWS 0.5-1.0" OF TOTAL LIQUID PRECIP. THE WPC DATA
IS A TAD LOWER THAN SOME OF THE ENSEMBLE MEANS, PARTICULARLY THE
CANADIAN AND EC RUNS.
PRECIPITATION COULD OVERSPREAD THE AREA BY LATE TUESDAY
AFTERNOON WITH THE BRUNT OF THE EVENT OCCURRING TUESDAY NIGHT.
MODEL SOUNDINGS SHOW A NEARLY ENTIRELY SUB-FREEZING PROFILE
EVERYWHERE EXCEPT COASTAL GA TUESDAY AFTERNOON. ANY PRECIP THAT
DOES OCCUR COULD INITIALLY BE RAIN ALONG COASTAL GA WHILE
EVERYWHERE ELSE THERE LOOKS TO BE ENOUGH MOISTURE IN THE
DENDRITIC GROWTH ZONE TO SUPPORT MOSTLY SNOW. TUESDAY NIGHT,
NEARLY THE ENTIRE AREA SHOULD BE PREDOMINANTLY SNOW, THOUGH
THERE COULD STILL BE A TRANSIENT STRIPE OF SOME SLEET DUE TO A
POSSIBLE H85 WARM NOSE. ACROSS COASTAL SOUTHEAST GA, POTENTIALLY
INCLUDING THE SAVANNAH METRO AREA, THERMAL PROFILES SHOW A
PRONOUNCED WARM NOSE AROUND H85 WITH A SUB-FREEZING SURFACE
LAYER THAT IS NOT DEEP ENOUGH TO ALLOW FOR REFREEZING INTO
SLEET. THEREFORE, MUCH OF THE EVENT COULD FALL AS FREEZING RAIN
IN COASTAL SOUTHEAST GA, POTENTIALLY RESULTING IN TOTAL
ACCUMULATIONS AT OR ABOVE 0.25" OF ICE.
BASED ON THE LATEST QPF FORECAST AND WX GRIDS, WE'RE SHOWING A
TOTAL SNOW ACCUMULATION OF 1-2" FAR INLAND SC/GA, WITH 2-3"
ELSEWHERE EXCEPT COASTAL SOUTHEAST GA WHERE TOTALS COULD BE
CLOSER TO 1". FOR ICE ACCUMULATION, WE SHOW A FEW HUNDREDTHS
ALONG THE SC COAST WITH UPWARDS OF 0.25" ALONG THE IMMEDIATE GA
COAST. WE'RE PRETTY CLOSE TO WINTER STORM WARNING CRITERIA FOR
ALL OF OUR AREA, EITHER FROM SNOW/SLEET ACCUMULATION OR ICE
ACCUMULATION. TO PROVIDE ENHANCED LEAD TIME ON A POTENTIALLY
SIGNIFICANT WINTER EVENT FOR OUR AREA, WE HOISTED A WINTER STORM
WATCH FOR THE ENTIRE FORECAST AREA FROM LATE TUESDAY AFTERNOON
THROUGH WEDNESDAY MORNING.
PRECIPITATION SHOULD BE QUICKLY TAPERING OFF WEDNESDAY MORNING.
HIGHS WILL BE QUITE FRIGID, ESPECIALLY IF MOST AREAS HAVE ANY
SNOW/ICE ACCUMULATIONS. OVERCAST SKIES AND CONTINUED COLD AIR
ADVECTION WILL KEEP HIGH TEMPS IN THE LOW TO MID 30S.
LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/
ANOTHER SHORTWAVE IS FORECAST TO ROUND THE BASE OF THE UPPER
TROUGH MID-WEEK, PROMPTING A COASTAL TROUGH TO DEVELOP OFF THE
SC/GA COAST LATE WEDNESDAY NIGHT AND THURSDAY. THERE ARE VARYING
MODEL SOLUTIONS WITH REGARD TO HOW STRONG THIS TROUGH GETS AND
HOW CLOSE TO THE COAST IT TRACKS. MOST GUIDANCE SHOWS AT LEAST A
FEW HUNDREDTHS OF AN INCH OF QPF FROM LATE WEDNESDAY NIGHT
THROUGH THURSDAY EVENING, MAINLY ACROSS THE EASTERN HALF OF THE
AREA. AT THIS POINT THE ARCTIC HIGH PRESSURE WILL STILL BE
FIRMLY ENTRENCHED ACROSS THE AREA WHILE UPPER LEVELS ARE PRETTY
DRY. THERE PROBABLY WOULDN'T BE ICE NUCLEI ACTIVATION TO SUPPORT
SNOW SO FREEZING RAIN WOULD BE THE DOMINANT P-TYPE. GIVEN THIS,
THE EXACT QPF WILL BE VERY IMPORTANT FOR DETERMINING POTENTIAL
IMPACTS. UNFORTUNATELY, IT'S STILL PRETTY FAR OUT TO BE PINNING
THAT DOWN, THOUGH THE ENSEMBLES RANGE FROM 0.1-0.3" ALONG THE
SC/GA COAST WITH QUICKLY DECREASING VALUES FARTHER INLAND.
THE OTHER MAIN HIGH-IMPACT EVENT WILL BE THE CONTINUED VERY COLD
CONDITIONS. WEDNESDAY NIGHT IS EXPECTED TO BE THE COLDEST NIGHT
IN QUITE A WHILE WITH LOWS IN THE MID TO UPPER TEENS IN MOST
AREAS. COMBINED WITH SUBTLE NORTHERLY WINDS, WIND CHILL VALUES
COULD DIP INTO THE UPPER SINGLE DIGITS, AND WE MAY NEED AN
EXTREME COLD WARNING. THESE VERY COLD TEMPERATURES WEDNESDAY
NIGHT WOULD LIKELY RESULT IN RE-FREEZING OF ANY WATER OR SLUSH
ON AREA ROADWAYS, RESULTING IN A CONTINUATION OF VERY HAZARDOUS
TRAVEL CONDITIONS.
COLD WEATHER ADVISORIES WILL BE POSSIBLE LATE WEEK AS WELL DUE
TO CONTINUED COLD WEATHER AND A BIT OF WIND.
AVIATION /07Z MONDAY THROUGH FRIDAY/
VFR CONDITIONS WILL PREVAIL AT CHS/JZI/SAV TERMINALS THROUGH 06Z
TUESDAY.
EXTENDED AVIATION OUTLOOK: FLIGHT RESTRICTIONS ARE EXPECTED
LATER TUESDAY THROUGH WEDNESDAY MORNING DUE TO WINTER WEATHER.
ADDITIONAL FLIGHT RESTRICTIONS ARE POSSIBLE THURSDAY AND
THURSDAY NIGHT DUE TO ANOTHER ROUND OF WINTER WEATHER.
MARINE
TONIGHT: HAZARDOUS MARINE CONDITIONS REMAIN ACROSS COASTAL
WATERS AS POST-FRONTAL COLD AIR ADVECTION YIELDS SURGING WINDS.
NORTHWEST WINDS TOPPING OUR NEAR 25-30 KT ARE POSSIBLE FOR MUCH
OF THE NIGHT, BUT WILL SHOW SIGNS OF WEAKENING LATE, PARTICULARLY
NEAR THE COAST AND CHARLESTON HARBOR APPROACHING DAYBREAK. OFFSHORE
WINDS WILL LIMIT SEAS A BIT, ESPECIALLY WITHIN 10 NM OF THE COAST.
SEAS WILL GENERALLY RANGE BETWEEN 3-5 FT, WITH SOME 6 FOOTERS
ACROSS OUTER GEORGIA WATERS. SMALL CRAFT ADVISORIES REMAIN IN
EFFECT FOR ALL AREAS FOR THE NIGHT.
MONDAY: STRONG ARCTIC HIGH PRESSURE WILL BE LOCATED OVER THE
MISSISSIPPI RIVER VALLEY WITH NORTHWEST FLOW OVER THE WATERS.
WINDS WILL BE OUT OF THE NORTHWEST 15 TO 20 KT WITH GUSTS 20 TO
25 KT, OR JUST BELOW SCA CRITERIA. SEAS WILL ALSO BE 2 TO 3
FEET. BY MONDAY NIGHT, ARCTIC HIGH PRESSURE WILL MOVE EAST OF
THE APPALACHIANS ALLOWING WINDS OVER THE WATERS TO VEER AROUND
FROM THE NORTH AND THEN NORTHEAST. WINDS INITIALLY WILL SLACKEN
AS THE PRESSURE GRADIENT TEMPORARILY WEAKENS MONDAY NIGHT, BUT
AS THE WINDS START TO VEER THE PRESSURE GRADIENT AGAIN TIGHTENS
ALLOWING WINDS TO INCREASE IN SPEED AND APPROACH SMALL CRAFT
ADVISORY CRITERIA.
TUESDAY AND WEDNESDAY: A STORM SYSTEM WILL IMPACT THE SOUTHEAST
U.S LATE TUESDAY INTO EARLY WEDNESDAY, WITH THE PRIMARY SURFACE
LOW PASSING WELL OFFSHORE. AT THE SAME TIME, ARCTIC HIGH
PRESSURE WILL BE CENTERED OVER THE DELMARVA. BY TUESDAY MORNING,
NORTHEAST WINDS WILL INCREASE IN SPEED TO 20 TO 25 KT WITH WIND
GUSTS UP TO 34 KT (OR RIGHT AT GALE CRITERIA). AT THIS POINT,
IT LOOKS AS IF WINDS WILL BE A STRONG SMALL CRAFT ADVISORY, BUT
GALES COULD BE WARRANTED (ESPECIALLY FOR THE OFFSHORE GEORGIA
WATERS PAST 20 NM). SEAS WILL ALSO BE 3 TO 5WILL END FEET,
INCREASING TO 6 TO 9 FEET BY WEDNESDAY MORNING. SEAS AND WINDS
WILL THEN REMAIN ELEVATED WEDNESDAY MORNING AND START TO SLOWLY
SLACKEN WEDNESDAY AFTERNOON. FINALLY, MARINERS SHOULD BE ALERT
THAT SOME WINTER PRECIPITATION COULD FALL OVER THE COASTAL
WATERS TUESDAY NIGHT INTO WEDNESDAY MORNING, REDUCING
VISIBILITIES TO 1 NM OR LESS AT TIMES.
THURSDAY: A WEAK COASTAL LOW PRESSURE COULD FORM THURSDAY OR
THURSDAY AFTERNOON ALLOWING SURFACE WINDS TO BACK FROM THE
NORTH/ NORTHWEST. THIS COULD KEEP SEAS AT 6 FT INTO THURSDAY, OR
AT SMALL CRAFT ADVISORY CRITERIA.
CLIMATE
RECORD LOW MAXIMUM TEMPERATURES:
WEDNESDAY, JANUARY 22:
KCHS: 31/1970
KCXM: 31/1970
KSAV: 34/1970
THURSDAY, 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...COLD WEATHER ADVISORY UNTIL 6 AM EST WEDNESDAY FOR GAZ087-088-
099>101-114>119-137>141.
WINTER STORM WATCH FROM TUESDAY AFTERNOON THROUGH WEDNESDAY
MORNING FOR GAZ087-088-099>101-114>119-137>141.
SC...COLD WEATHER ADVISORY UNTIL 6 AM EST WEDNESDAY FOR SCZ040-
042>045-047>052.
WINTER STORM WATCH FROM TUESDAY AFTERNOON THROUGH WEDNESDAY
MORNING FOR SCZ040-042>045-047>052.
LAKE WIND ADVISORY UNTIL 6 AM EST EARLY THIS MORNING FOR
SCZ045.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EST EARLY THIS MORNING FOR
AMZ330.
SMALL CRAFT ADVISORY UNTIL 10 AM EST THIS MORNING FOR AMZ350-
352-354-374.
NEAR TERM...DPB
SHORT TERM...
LONG TERM...
AVIATION...DPB
MARINE...DPB
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