617
FXUS62 KCHS 201714
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1214 PM EST MON JAN 20 2025
SYNOPSIS
HIGH PRESSURE WILL PREVAIL THROUGH TONIGHT. 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 /THROUGH TONIGHT/
NO MAJOR CHANGES WERE MADE FOR THE NOON UPDATE. TODAY WILL BE
THE FIRST OF SEVERAL COLD DAYS.
UPGRADES TO WINTER STORM WARNING AND/OR WINTER WEATHER
ADVISORIES ARE BEING CONSIDERED FOR THE AFTERNOON FORECAST
PACKAGE. FINAL DETERMINATIONS ON HEADLINE TYPES WILL BE MADE
LATER TODAY AFTER EVALUATING THE 12Z GUIDANCE AND INTERNAL
GUIDANCE TRENDS.
TODAY: A LARGE AND UNSEASONABLY STRONG UPPER TROUGH WILL
ENCOMPASS MUCH OF THE NORTHERN HALF OF THE UNITED STATES,
ALLOWING ARCTIC HIGH PRESSURE TO EXPAND SOUTH TO THE GULF OF
MEXICO AND INTO THE SOUTHEAST UNITED STATES. THE SETUP WILL
FAVOR DRY BUT CONSIDERABLY COLDER TEMPS ACROSS THE REGION
COMPARED TO THE PREVIOUS DAY AS COLD AIR ADVECTION CONTINUES
THROUGHOUT THE DAY AND NORTHWESTERLY SFC WINDS GRADUALLY TURN
MORE NORTHERLY LATE. DESPITE A FULL DAY OF SUNSHINE AFTERNOON
HIGHS WILL STRUGGLE TO WARM INTO THE LOW-MID 40S.
TONIGHT: COLD AND DRY AIR WILL PERSIST THROUGH EVENING HOURS
WITH LITTLE CHANGE IN REGARDS TO THE EXPANSIVE MID-UPPER LVL
TROUGH AND HIGH PRESSURE SPREADING ACROSS THE LOCAL AREA. THIS
WILL BRING ANOTHER NIGHT OF COLD TEMPS WITH LOWS GENERALLY
RANGING IN THE LOWER 20S INLAND TO MID-UPPER 20S CLOSER TO THE
COAST. THE COMBINATION OF THESE TEMPS AND LIGHT NORTHERLY WINDS
WILL PRODUCE WIND CHILL VALUES INTO THE MID-UPPER TEENS ACROSS
MOST OF THE AREA. A COLD WEATHER ADVISORY IS ALREADY IN PLACE
FOR THE ENTIRE AREA TO COVER THESE WIND CHILL TEMPS AT NIGHT.
LATE TONIGHT, SOME GUIDANCE INDICATES WEAK COASTAL TROUGHING
DEVELOPING OFFSHORE, AND POTENTIALLY BRINGING LIGHT PRECIP TO
THE COAST AS IT TRACKS NORTH/NORTHEAST. SOUNDING PROFILES
INDICATE COLD TEMPS, BUT DRY AIR, SUGGESTING PRECIP TO HOLD OFF
UNTIL AT LEAST AFTER SUNRISE. IF PRECIP DID DEVELOP, IT WOULD BE
VERY LIGHT AND A WARM NOSE AROUND 850 MB SUGGESTS MELTING PRIOR
TO REACHING THE SFC. HOWEVER, THERE IS A LOW POTENTIAL OF
REFREEZING WITH COLD SFC TEMPS AT THE COAST. THE SITUATION WILL
CONTINUE TO BE MONITORED.
NOTE: A COLD WEATHER ADVISORY HAS BEEN ISSUED 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 DEGREES OR COLDER). FOR THIS REASON, THE
ADVISORY ENDING TIME ENDS AT NOON 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.
SHORT TERM /TUESDAY THROUGH THURSDAY/
TUESDAY AND WEDNESDAY: THIS WILL BE A VERY IMPACTFUL TIME
PERIOD FOR OUR AREA. THE MID-LEVELS WILL CONSIST OF A VERY LARGE
LONGWAVE TROUGH HOVERING OVER THE EASTERN HALF OF THE CONUS
TUESDAY MORNING, WITH A SHORTWAVE STRETCHING FROM THE GREAT
LAKES REGION TO NEAR THE 4-CORNERS REGION. THIS SHORTWAVE WILL
ROUND THE BASE OF THE TROUGH LATE TUESDAY, PASSING OVER THE
SPINE OF THE APPALACHIANS LATE TUESDAY NIGHT. IT'LL THEN QUICKLY
SHIFT OFFSHORE ON WEDNESDAY, FOLLOWED BY ZONAL FLOW OVER OUR
AREA. ADDITIONALLY, THE RIGHT ENTRANCE REGION OF A 150+ KT JET
STREAK WILL BE LOCATED TO OUR NORTH. THIS WILL PROVIDE PLENTY OF
LIFT TUESDAY EVENING AND OVERNIGHT. AT THE SURFACE, TROUGHING
WILL BE LOCATED JUST SOUTH OF OUR COAST IN THE MORNING.
ADDITIONAL, A STORM SYSTEM WILL BE DEVELOPING IN THE GULF OF
MEXICO. THIS SYSTEM WILL RAPIDLY SHIFT EAST NORTHEASTWARD INTO
THE AFTERNOON AND COMBINE WITH THE TROUGHING TO FORM A LARGER
SYSTEM ALONG THE SOUTHEAST COAST TUESDAY EVENING AND OVERNIGHT.
HIGH PRESSURE WILL ALSO BE LOCATED TO OUR NORTHWEST, THEN NORTH
DURING THIS SAME TIME PERIOD. THE HIGH WILL BE USHERING
UNSEASONABLY COLD TEMPERATURES INTO OUR AREA, WHILE THE STORM
SYSTEM WILL HAVE ABUNDANT MOISTURE WITH IT, WITH THE HIGHEST
VALUES FURTHER OFFSHORE. THE INTERACTION BETWEEN THESE TWO
FEATURES WILL GENERATE WINTER PRECIPITATION ACROSS OUR AREA.
THERE CONTINUES TO BE VARIATIONS AMONGST THE SYNOPTIC MODELS.
BOTH THE 00Z GFS AND NAM HAVE SIMILAR QPF AMOUNTS OVER OUR AREA,
WITH SLIGHTLY HIGHER VALUES ALONG THE IMMEDIATE COAST AND THE
HIGHEST VALUES AROUND MCINTOSH COUNTY AND VICINITY, AND EVEN
HIGHER SOUTHWARD AND OUT OF OUR AREA. THE 00Z ECMWF HAS A
SIMILAR MOISTURE SPREAD, BUT OVERALL MUCH HIGHER QPF ACROSS OUR
ENTIRE AREA.
WPC LEANED MORE WITH THE NAM AND GFS, TRENDING THEIR QPF MUCH
LOWER ACROSS OUR AREA. WE JUST COULDN'T GO AS LOW AS THEY WERE
FORECASTING, GIVEN A SMALL SHIFT IN THE MOISTURE NORTHWARD AND
INLAND WOULD HAVE A DRASTICALLY DIFFERENT OUTCOME (SIMILAR TO
THE ECMWF). SO WE WENT A LITTLE HIGHER THAN WPC. BUT THE NET
RESULT WAS A LOWER QPF FORECAST RANGING FROM ~0.15" FAR INLAND
TO ~0.25-0.5" ALONG THE IMMEDIATE COAST, WITH A SLIVER OF ~0.75"
ALONG MCINTOSH COUNTY.
THE SYNOPTIC MODELS AND LONG RANGE CAMS GENERALLY HAVE PRECIPITATION
DEVELOPING ALONG THE COAST LATE IN THE MORNING, THEN INCREASING IN
BOTH COVERAGE AND INTENSITY INTO THE LATE AFTERNOON WHILE SPREADING
INLAND. THE HIGHEST POPS WILL BE DURING THE EVENING THROUGH MOST OF
THE NIGHT. THE MODELS STILL HAVE SOME DIFFERENCES REGARDING THE
AMOUNT OF WARM AIR ABOVE THE SURFACE AND THE RESULTING PRECIPITATION
TYPE THAT COMES WITH IT AT THE SURFACE.
DURING THE DAY, MOST LOCATIONS NEAR THE COAST SHOULD BE WARM ENOUGH
FOR RAIN. FURTHER INLAND, POCKETS OF WARMER AND COLDER TEMPERATURES
JUST ABOVE THE SURFACE COULD BRING A RAIN/SNOW MIX.
DURING THE EVENING, SURFACE TEMPERATURES WILL DROP AND TEMPERATURES
JUST ABOVE THE SURFACE WILL LOWER. MOST LOCATIONS NEAR THE COAST
SHOULD GET RAIN TRANSITIONING TO SLEET, EXCEPT FOR MCINTOSH COUNTY
AND VICINITY, WHICH COULD HAVE FREEZING RAIN. LOCATIONS FURTHER
INLAND SHOULD BE MAINLY SNOW.
AROUND AND AFTER MIDNIGHT, AS MORE COLDER AIR COMES IN AT THE
SURFACE AND ALOFT, SNOW IS EXPECTED EVERYWHERE, EXCEPT FOR MCINTOSH
COUNTY AND VICINITY, WHERE THERE COULD BE SLEET.
BY DAYBREAK WEDNESDAY, MAINLY SNOW SHOULD BE FALLING. THE WINTER
PRECIPITATION QUICKLY COMES TO AN END EARLY WEDNESDAY MORNING FAR
INLAND, AND CLOSER TO THE COAST A FEW HOURS LATER.
BY WEDNESDAY AFTERNOON, IT SHOULD BE DRY EVERYWHERE AND THIS WILL
PERSIST INTO THE NIGHT.
TOTAL SNOW AND ICE WILL ALL BE HIGHLY DEPENDENT ON EVERYTHING
MENTIONED ABOVE. AT THIS POINT, WE'RE FORECASTING UP TO 0.25" OF
FREEZING RAIN ACCRETION FOR MCINTOSH COUNTY AND VICINITY, AND 1-2"
OF SNOW EVERYWHERE ELSE.
IN ADDITION TO WINTER WEATHER, BITTERLY COLD TEMPERATURES WILL
OCCUR. TUESDAY, HIGHS SHOULD ONLY PEAK IN THE MID TO UPPER 30S FOR
MOST AREAS, TO THE LOWER 40S ACROSS OUR SOUTHERNMOST GA COUNTIES.
TUESDAY NIGHT, LOWS WILL FALL INTO THE 20S LATE, WITH WIND CHILLS IN
THE TEENS. A COLD WEATHER ADVISORY IS IN EFFECT. WEDNESDAY, HIGHS
SHOULD AGAIN ONLY BE IN THE 30S, AIDED BY AN ARCTIC AIR MASS AND
MADE COLDER BY FROZEN PRECIPITATION THAT'S MELTING. WE CAN'T RULE
OUT SOME PLACES NOT RISING ABOVE FREEZING DURING THE DAY. WEDNESDAY
NIGHT, TEMPERATURES WILL QUICKLY PLUMMET INTO THE TEENS DUE TO
MAINLY CLEAR SKIES EARLY, LIGHT WINDS, AND THE REMNANT SNOW/ICE.
HOWEVER, CLOUD COVER WILL QUICKLY INCREASE OVERNIGHT, WITH IT
BECOMING MOSTLY CLOUDY LATE AT NIGHT. THIS WILL KEEP TEMPERATURES
FROM FALLING AS MUCH AS THEY COULD. IN FACT, WE'LL PROBABLY HIT THE
LOWS IN THE LATE EVENING AND THEN HAVE TEMPERATURES REMAIN NEARLY
CONSTANT OR PERHAPS WARMING SLIGHTLY OVERNIGHT. ANOTHER COLD WEATHER
ADVISORY WILL BE NEEDED AND IT'S POSSIBLE AN EXTREME COLD WATCH MAY
BE NEEDED FOR PORTIONS OF OUR AREA.
THURSDAY: A LONGWAVE TROUGH WILL REMAIN OVER THE EASTERN HALF OF THE
U.S. A SURFACE TROUGH APPEARS TO DEVELOP ALONG THE SOUTHEAST COAST.
THIS WILL USHER SOME MOISTURE INTO THE REGION AND POSSIBLE BRING OUR
AREA SOME SHOWERS. THE NBM POPS SEEMED TO BE TOO HIGH COMPARED TO
THE MAIN MODELS, SO WE TRENDED THEM LOWER. FOR NOW, WE HAVE SLIGHT
CHANCE TO CHANCE POPS. LUCKILY, DAYTIME TEMPERATURES WILL BE WARM
ENOUGH TO SUPPORT ALL RAIN.
LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/
THE SURFACE TROUGH ALONG THE SOUTHEAST COAST THURSDAY NIGHT WILL
SHIFT OFFSHORE. BUT BEFORE IT MOVES AWAY IT COULD GENERATE SOME
PRECIPITATION ALONG THE IMMEDIATE COAST. TEMPERATURES JUST ABOVE THE
SURFACE WILL BE WARM ENOUGH TO SUPPORT RAIN, BUT WILL BE BELOW
FREEZING AT THE SURFACE. SO FREEZING RAIN IS POSSIBLE. BUT ONCE
AGAIN, THE NBM POPS SEEMED TOO HIGH AND HAD TO BE LOWERED. WE WENT
WITH SLIGHT CHANCE POPS IN THE EVENING FOLLOWED BY A DRY OVERNIGHT.
EVEN THESE VALUES MAY BE TOO HIGH. HIGH PRESSURE WILL THEN BUILD
INTO THE REGION AND PREVAIL INTO THE WEEKEND, BRINGING DRY
CONDITIONS. HIGH TEMPERATURES WILL MODERATE, BUT REMAIN WELL BELOW
NORMAL FRIDAY AND SATURDAY. THOUGH, THEY MAY FINALLY RISE TO NEAR
NORMAL ON SUNDAY.
AVIATION /17Z MONDAY THROUGH FRIDAY/
20/18Z TAF DISCUSSION:
KCHS/KJZI/KSAV: VFR THROUGH 21/18Z. ANY RISK FOR FREEZING OR
FROZEN PRECIPITATION IMPACTING THE TERMINALS WILL OCCUR AFTER
18Z TUESDAY.
EXTENDED AVIATION OUTLOOK: FLIGHT RESTRICTIONS ARE EXPECTED LATER
TUESDAY THROUGH WEDNESDAY MORNING DUE TO WINTER WEATHER. ADDITIONAL
FLIGHT RESTRICTIONS ARE POSSIBLE THURSDAY, WITH LOW PROBABILITIES OF
FREEZING RAIN ALONG THE COAST THURSDAY EVENING.
MARINE
TODAY AND TONIGHT: ALL REMAINING SMALL CRAFT ADVISORY HEADLINES
WILL BE ALLOWED TO EXPIRE AT 10 PM. SEAS WILL GENERALLY RANGE
BETWEEN 3-5 FT, SLOWLY SUBSIDING TO 2-3 FT THROUGH LATE DAY. THE
PRESSURE GRADIENT WILL BECOME MORE RELAXED DURING THE
AFTERNOON, BUT COLD AIR ADVECTION WILL PERSIST WITH A
NORTHWESTERLY WIND TURNING NORTH. EXPECT CONDITIONS TO REMAIN
BELOW SMALL CRAFT ADVISORY LEVELS FOR ALL WATERS THIS AFTERNOON
INTO LATE NIGHT. HOWEVER, WEAK COASTAL TROUGHING IS ANTICIPATED
TO DEVELOP ACROSS SOUTHERN WATERS LATE TONIGHT, FAVORING A
SLIGHT ENHANCEMENT TO THE PRESSURE GRADIENT AND NORTH/NORTHEAST
WINDS GUSTING UPWARDS TO 15-20 KT DURING THE NIGHT AND PERHAPS
EVEN TOUCHING 25 KT AROUND DAYBREAK. SEAS WILL ALSO BUILD UP TO
3-5 FT LATE. SMALL CRAFT ADVISORIES COULD BE NEEDED ONCE AGAIN
HEADING THROUGH DAYBREAK TUESDAY (EXCEPT FOR THE CHARLESTON
HARBOR).
TUESDAY AND WEDNESDAY: A STORM SYSTEM WILL IMPACT THE SOUTHEAST U.S
LATE TUESDAY INTO EARLY WEDNESDAY WHILE HIGH PRESSURE WILL BE
LOCATED WELL TO OUR NORTH. THE PRESSURE GRADIENT BETWEEN THESE
SYNOPTIC FEATURES WILL BE VERY ELEVATED. EXPECT STRONG AND GUSTY
WINDS RAPIDLY RAMPING UP TUESDAY MORNING AND PERSISTING INTO
WEDNESDAY MORNING. THERE COULD BE A BRIEF PERIOD OF GALE CONDITIONS
TUESDAY NIGHT INTO EARLY WEDNESDAY MORNING, MAINLY FOR THE CHARLESTON
WATERS AND GA WATERS BEYOND 20 NM. AT LEAST SMALL CRAFT ADVISORIES
WILL BE NEEDED FOR ALL OF THE MARINE ZONES, INCLUDING THE
CHARLESTON HARBOR, WITH A POSSIBILITY FOR GALE WATCHES/WARNINGS
FOR THE TWO AFOREMENTIONED ZONES. BOTH WINDS AND SEAS START TO
TREND LOWER WEDNESDAY AFTERNOON, CONTINUING INTO THE OVERNIGHT
HOURS. SEAS LOOK TO PEAK EARLY WEDNESDAY MORNING, 5-7 FT FOR THE
WATERS WITHIN 20 NM AND 7-10 FT FOR THE GA WATERS BEYOND 20 NM.
THOUGH, SEAS WILL BE SLOW TO SUBSIDE INTO WEDNESDAY NIGHT.
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 AND FRIDAY: TROUGHING WILL DEVELOP ALONG THE COAST
THURSDAY, THEN GET PUSHED OFFSHORE ON FRIDAY AS HIGH PRESSURE BUILDS
TOWARDS THE AREA. WINDS WILL STAY SOMEWHAT ELEVATED, WHILE SEAS
SLOWLY SUBSIDE.
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 NOON 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 NOON EST WEDNESDAY FOR SCZ040-
042>045-047>052.
WINTER STORM WATCH FROM TUESDAY AFTERNOON THROUGH WEDNESDAY
MORNING FOR SCZ040-042>045-047>052.
MARINE...NONE.
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