562
FXUS62 KCHS 200107
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
807 PM EST SUN JAN 19 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 MONDAY MORNING/
COLD FRONT AND ASSOCIATED PRECIP IS NOW WELL OFF THE COAST WITH
DRIER AIR/CLEAR OR CLEARING SKIES TAKING SHAPE. THERE IS A
"TAIL" OF LOWER CLOUD COVER SWINGING INTO THE WESTERN CAROLINAS
AS WELL AS ALABAMA AND GEORGIA. CLOUD COVER IS DWINDLING WITHIN
THE SUBTLE DOWNSLOPING FLOW REGIME, ALTHOUGH SOME LOCATIONS IS
THE FAR W/SW PART OF THE FORECAST AREA MIGHT SEE A PERIOD OF
CLOUD COVER OVER THE NEXT FEW HOURS.
OTHERWISE, TEMPERATURES WILL LOWER INTO THE MIDDLE TO UPPER 20S
FOR MANY AREAS OVERNIGHT. COMBINED WITH A PERSISTENT WIND, WIND
CHILL TEMPS WILL DIP INTO THE HIGH TEENS TO LOWER 20S.
NOTE: THE COLD WEATHER ADVISORY HAS BEEN ISSUED THROUGH THE DAY
WEDNESDAY EVEN THOUGH CRITERIA WILL ONLY BE MET DURING THE
OVERNIGHT PERIOD. 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 PM 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
OVERNIGHT AS STRONG COLD AIR ADVECTION IMPACTS THE LAKES.
NORTHWEST WINDS SHOULD PEAK 20-25 KT WITH GUSTS TO 30 KT DURING
THE PEAK OF THE WIND SURGE. WAVES WILL BE 2-3 FT AT TIMES. A LAKE
WIND ADVISORY IS IN EFFECT UNTIL 6 AM.
SHORT TERM /6 AM MONDAY 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 /00Z MONDAY THROUGH FRIDAY/
20/00Z TAF DISCUSSION:
KCHS/KJZI/KSAV: DRIER AIR CONTINUES TO SPREAD INTO THE REGION
AND WILL RESULT IN VFR CONDITIONS THROUGH 00Z TUESDAY. GUSTY
WINDS WILL PERSIST WELL INTO THE OVERNIGHT.
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 WILL OCCUR OVER ALL WATERS
TONIGHT AS POST-FRONTAL COLD AIR ADVECTION YIELDS A STRONG
SURGE OF WINDS. NORTHWEST WINDS WILL INCREASE TO 25-30 KT WITH
GUSTS POSSIBLY APPROACHING GALES AT TIMES, ALTHOUGH LIKELY
INFREQUENT. OFFSHORE WINDS WILL TEND TO LIMIT SEAS A BIT,
ESPECIALLY WITHIN 10 NM OF THE COAST. SEAS WILL BUILD TO 3-5
FT, EXCEPT 2 TO 3 FT NEAR THE IMMEDIATE COAST WITH UP TO 6 FT
POSSIBLE OVER THE GEORGIA OFFSHORE WATERS AND THE OUTER PORTIONS
OF THE SOUTH SANTEE-EDISTO BEACH NEARSHORE LEG. SMALL CRAFT
ADVISORIES REMAIN IN EFFECT FOR ALL AREAS.
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 FROM MIDNIGHT TONIGHT TO 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 FROM MIDNIGHT TONIGHT TO 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 MONDAY FOR SCZ045.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EST MONDAY FOR AMZ330.
SMALL CRAFT ADVISORY UNTIL 10 AM EST MONDAY FOR AMZ350-352-354-
374.
NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...
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