Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 011618
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1118 AM EST SUN FEB 1 2015

.SYNOPSIS...
A COLD FRONT WILL APPROACH FROM THE WEST TODAY AND PASS OFFSHORE
MONDAY MORNING. HIGH PRESSURE WILL THEN RETURN TO THE REGION BY
TUESDAY...BEFORE SHIFTING OFFSHORE AHEAD OF ANOTHER STORM SYSTEM
APPROACHING FROM THE GULF OF MEXICO THURSDAY AND FRIDAY. HIGH
PRESSURE WILL BUILD IN THE WAKE OF THE SYSTEM FOR THE WEEKEND.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
HIGH PRESSURE CENTERED NEAR THE NC COAST WILL SHIFT OFFSHORE WHILE
A COASTAL TROUGH OF LOW PRESSURE OFF THE SC/GA COAST DISSIPATES.
MID LEVEL RIDGING WILL WEAKEN THROUGH THE DAY ALLOWING DEEPER
MOISTURE TO THE WEST TO MOVE CLOSER TO THE AREA. ALSO
STRATOCUMULUS OFFSHORE WILL ADVECT NORTH TOWARD THE SC COAST. THIS
WILL TRANSLATE TO INCREASING CLOUDINESS FOR ALL AREAS WITH THE
MOST CLOUD COVER LIKELY ACROSS FAR INLAND AREAS AND ALONG THE SC
COAST. TEMPS WARMING QUICKLY THIS MORNING GIVEN ABUNDANT SUN IN
MOST AREAS AND INCREASING LOW-LEVEL WARM ADVECTION. SHOULD SEE
HIGHS REACH THE MID TO UPPER 60S...WARMEST SOUTH OF SAVANNAH WHERE
IT COULD REACH 70. THE ONSHORE WINDS WILL KEEP TEMPS DOWN CLOSER
TO THE UPPER 50S AT THE IMMEDIATE COAST. WINDS WILL BE SHIFTING
SOUTHERLY AND INCREASING WITH GUSTS NEAR 25 MPH LATER THIS
AFTERNOON. RAIN CHANCES WERE MAINTAINED LESS THAN 10 PERCENT.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY/...
TONIGHT...THE 01/00Z NAM/GFS/ECMWF ALL CONTINUE TO TREND WITH A
SLOWER PROGRESSION OF APPROACHING STORM SYSTEM TONIGHT...WHICH
NECESSITATES MAKING SOME CHANGES TO THE POP FORECAST FOR THE
OVERNIGHT PERIOD. IT NOW APPEARS VERY LITTLE IN THE WAY OF
MEASURABLE RAINFALL WILL FALL PRIOR TO 06Z...EXCEPT POSSIBLY OVER
PORTIONS OF THE LOWER SOUTH CAROLINA COAST WHERE A STRENGTHENING
ONSHORE FLOW RELATIVE TO THE ORIENTATION OF THE COAST COULD
SUPPORT SOME ISOLATED SHOWER ACTIVITY WITHIN A RESULTING BROAD
LOW-LEVEL CONVERGENCE AXIS. THE BULK OF THE RAINFALL...HOWEVER...
LOOKS TO HOLD OFF UNTIL AFTER 06Z WITH PROBABILITIES RAPIDLY
INCREASING FROM WEST-EAST THROUGH SUNRISE AS A COLD FRONT DRAWS
CLOSER AND LARGE SCALE FORCING FOR ASSENT INTENSIFIES AHEAD OF THE
SUPPORTING UPPER TROUGH.

A 30/30/30 BLEND OF THE NAM/GFS/ECMWF WAS UTILIZED TO CONSTRUCT
HOURLY POPS GIVEN THEIR SIMILAR DEPICTION/TIMING OF THE RAINFALL
OVERNIGHT. THIS YIELDS MAX POPS OF 80-90 PERCENT INLAND AND ALONG
THE LOWER SOUTH CAROLINA COAST TO 60-70 PERCENT ROUGHLY SOUTH OF A
REIDSVILLE-BEAUFORT LINE...INCLUDING THE SAVANNAH METRO AREA. THE
RISK FOR TSTMS LOOK MINIMAL...ALTHOUGH THE LATEST NAM12 SHOWALTER
PROGNOSTICATIONS DO SHOW A VERY NARROW AND TRANSIENT CORRIDOR OF 0
TO -1C UNITS WORKING UP ALONG THE COAST AROUND SUNRISE. THE
OVERALL RISK FOR TSTMS LOOKS TOO LOW TO JUSTIFY A MENTION WITH
THIS FORECAST CYCLE.

IT LOOKS TO BE A RATHER BREEZY AND GUSTY NIGHT FOR THE REGION...
ESPECIALLY EASTERN SECTIONS AS STRONG LOW-LEVEL JETTING DEVELOPS
AHEAD OF THE APPROACHING COLD FRONT. THIS WILL KEEP THE BOUNDARY
LAYER WELL MIXED THROUGH THE NIGHT WITH TEMPERATURES ONLY DROPPING
INTO THE MID-UPPER 50S. SUSTAINED WINDS OF 15-25 MPH WILL BE
COMMON WITH GUSTS AS HIGH AS 30-35 MPH AT TIMES. THIS IS JUST
BELOW WIND ADVISORY CRITERIA. POOR MIXING PROFILES OVER LAKE
MOULTRIE SUGGEST SPEEDS WILL ALSO REMAIN BELOW LAKE WIND ADVISORY
THRESHOLDS THERE...MAXING OUT AROUND 15 KT. COULD SEE A BRIEF 2-4
HOUR PERIOD OF SEA FOG AFFECTING THE IMMEDIATE COASTAL AREAS ALONG
THE GEORGIA COAST AND POSSIBLY THE FAR SOUTHERN SOUTH CAROLINA
COAST THIS EVENING AS DEWPOINTS RISE OVER THE COLD ATLANTIC SHELF
WATERS...BUT SUSPECT STRENGTHENING LOW-LEVEL WIND FIELDS WILL BE
TOO HIGH TO SUPPORT ANYTHING SIGNIFICANT AFTER MIDNIGHT.

MONDAY...STRONG SURFACE LOW PRESSURE WILL BE MOVING EAST ACROSS THE
MID ATLANTIC/NORTHERN APPALACHIAN REGIONS AT DAYBREAK...WITH ITS
TRAILING COLD FRONT RAPIDLY APPROACHING THE WEST/NORTHWEST BORDER OF
THE FORECAST AREA. BEST RAIN COVERAGE WILL OCCUR DURING THE EARLY TO
MID MORNING HOURS...WHEN THE FRONT IS PASSING THROUGH THE SOUTHEAST
STATES AT THE SAME TIME THAT A 140 KT UPPER JET AND 40 TO 50 KT LOW
LEVEL JET MOVE INTO THE REGION. HAVE INDICATED 70 TO 90 PERCENT RAIN
CHANCES THROUGH ABOUT 9 AM...BEFORE DEEP MOISTURE DECREASES BEHIND
THE RAPIDLY DEPARTING FRONT THAT WILL LIKELY BE OFFSHORE BY EARLY
AFTERNOON. HAVE DECREASED RAIN CHANCES BELOW 10 PERCENT ALL AREAS NO
LATER THAN 4 PM.

WEST FLOW WILL SURGE IN THE WAKE OF THE FRONT AS THE POTENT LOW
LEVEL JET PASSES OVER THE AREA. DEPENDING ON HOW QUICKLY THICK SKY
COVER CAN SCATTER THROUGH THE AFTERNOON...IMPROVING MIXING PROFILES
COULD TAP INTO IMPRESSIVE 40 TO 50 KT WINDS IN THE BOUNDARY LAYER.
THESE CONDITIONS COULD SUPPORT 20 TO 25 MPH WINDS WITH GUSTS AS HIGH
AS 30 TO 35 MPH. ALTHOUGH THESE CONDITIONS ARE JUST BELOW WIND
ADVISORY CRITERIA...WILL CONTINUE TO MONITOR MODEL TRENDS IN CASE AN
ADVISORY LOOKS MORE POSSIBLE. WILL INCLUDE MENTION OF POTENTIAL
WINDY CONDITIONS IN THE HAZARDOUS WEATHER OUTLOOK.

HIGH TEMPERATURES ON MONDAY WILL RANGE FROM THE UPPER 50S FAR
INLAND...WHERE COLD ADVECTION WILL INITIATE EARLIEST...TO THE
LOW/MID 60S CENTRAL AND EASTERN ZONES. THE MOST NOTABLE COLD AIR
ARRIVES MONDAY NIGHT...WHEN LOW TEMPERATURES FALL BELOW FREEZING FOR
ALL LOCATIONS EXCEPT THE BEACHES/BARRIER ISLANDS...RANGING FROM THE
UPPER 20S TO LOW 30S. ALTHOUGH WINDS WILL DIMINISH OVERNIGHT...EVEN
SPEEDS IN THE 5 TO 7 MPH RANGE WILL SUPPORT WIND CHILLS IN THE LOW
AND MID 20S BY TUESDAY MORNING.

TUESDAY...CANADIAN HIGH PRESSURE WILL CONTINUE TO MOVE OVER THE
SOUTHEAST AND MID ATLANTIC STATES...AND DESPITE CLEAR SKIES AND
SUNSHINE...EXPECT HIGH TEMPERATURES TO BE SUPPRESSED BELOW SEASONAL
NORMALS AND ONLY REACH THE LOW TO MID 50S. LOW TEMPERATURES WILL
ACTUALLY MODERATE SLIGHTLY FROM THE PREVIOUS NIGHT...AS THE AXIS OF
THE SURFACE HIGH SETTLES ALONG THE COASTLINE AND NORTHEAST FLOW/COLD
ADVECTION ENDS. LOW TEMPERATURES WILL RANGE FROM THE LOW TO MID 30S
AWAY FROM THE COAST.

WEDNESDAY...SURFACE HIGH PRESSURE WILL CONTINUE TO RETREAT INTO THE
ATLANTIC...AS FLOW ALOFT REMAINS NEARLY ZONAL. ANY PRECIPITATION
ALONG THE PERIPHERY OF THE ATLANTIC HIGH LOOKS TO REMAIN WELL BEYOND
THE MARINE ZONES. WILL THUS MAINTAIN A DRY FORECAST THROUGH THE
DAYTIME HOURS...WITH HIGH TEMPERATURES RETURNING TO SEASONAL NORMALS
IN THE UPPER 50S INLAND TO LOWER 60S CLOSER TO THE COAST.

LAKE WINDS...COLD ADVECTION BEHIND A DEPARTING FRONT WILL IMPROVE
MIXING PROFILES OVER LAKE MOULTRIE MONDAY AFTERNOON...AT THE SAME
TIME THAT THE PRESSURE GRADIENT REMAINS TIGHT ALONG BUILDING HIGH
PRESSURE. AS A RESULT...WEST/NORTHWEST WINDS COULD SURGE...AND A
LAKE WIND ADVISORY MAY BE NECESSARY.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
THE FORECAST BECOMES MUCH MORE UNSETTLED DURING THE MID TO LATE WEEK
TIME FRAME...AND THERE CONTINUES TO BE SOME UNCERTAINTY IN DETAILS
DUE TO DIFFERENCES IN MEDIUM RANGE MODEL SOLUTIONS.

THE GENERAL CONSENSUS IS THAT A SOUTHERN STREAM SHORTWAVE WILL MOVE
INTO THE GULF OF MEXICO WEDNESDAY NIGHT AND SUPPORT THE DEVELOPMENT
OF A SURFACE LOW. NORTHERN STREAM ENERGY MERGES WITH THE DAMPENING
GULF SHORTWAVE LATE THURSDAY INTO FRIDAY MORNING...DRIVING THE
SURFACE LOW EAST/NORTHEAST TOWARD THE FLORIDA PENINSULA AND
EVENTUALLY INTENSIFYING THE SYSTEM OFF THE SOUTHEAST COAST. DETAILS
IN THE EXACT TRACK OF THE LOW PRESSURE CENTER AND THE SUBSEQUENT
COVERAGE OF PRECIPITATION ON ITS BACK SIDE ARE NOT CONSISTENT
BETWEEN MODEL SOLUTIONS. THERE HAS BEEN A TREND FOR THE ECMWF TO
COME MORE IN LINE WITH THE GFS...SUGGESTING SOME PRECIPITATION
POTENTIAL ALONG THE PERIPHERY OF THE COASTAL LOW THURSDAY
NIGHT/EARLY FRIDAY MORNING...AS WELL AS ANOTHER CHANCE FOR
PRECIPITATION ASSOCIATED WITH THE PROGRESSION OF A ROBUST UPPER
TROUGH IN ITS WAKE. AFTER TEMPERATURES PEAK IN THE MID TO UPPER 50S
THURSDAY AFTERNOON...EVEN COLDER AIR WILL MOVE INTO THE REGION
THURSDAY NIGHT INTO FRIDAY WITHIN THE COLD SECTOR OF THE COASTAL
SYSTEM. ALTHOUGH THE POTENTIAL REMAINS QUITE LOW...IF MODELS
CONTINUE TO TREND TOWARD A WETTER AND COLDER SCENARIO FOR THE EARLY
MORNING HOURS ON FRIDAY...FROZEN PRECIPITATION COULD DEVELOP.

THE AMPLIFIED UPPER TROUGH WILL EVENTUALLY PROGRESS ACROSS THE EAST
COAST FRIDAY...AS THE COASTAL LOW SYSTEM DEPARTS TO THE NORTHEAST.
COLD AND DRY HIGH PRESSURE WILL BUILD IN ITS WAKE LATE FRIDAY INTO
THE WEEKEND.

&&

.AVIATION /16Z SUNDAY THROUGH THURSDAY/...
VFR TO PREVAIL...HOWEVER THERE WILL BE INCREASING PROBABILITIES
FOR MVFR CONDITIONS AFTER 09Z AT BOTH TERMINALS AS LIGHT RAIN AND
LOW CLOUDS MOVE IN AHEAD OF AN APPROACHING COLD FRONT. GUSTY SOUTH WINDS
ARE LIKELY AFTER 06Z AS LOW-LEVEL JETTING INTENSIFIES. MARGINAL
LLWS COULD OCCUR THIS EVENING BEFORE SURFACE WINDS REALLY RAMP UP.

EXTENDED AVIATION OUTLOOK...VFR CONDITIONS SHOULD WILL PREVAIL UNTIL
SUNDAY NIGHT INTO MONDAY MORNING...WHEN MVFR OR POSSIBLY LOWER
CONDITIONS WILL OCCUR IN SHRA AND LOWER CLOUD DECKS DUE TO A PASSING
COLD FRONT. BREEZY CONDITIONS AND/OR WIND SHEAR IS ALSO LIKELY
SUNDAY NIGHT/MONDAY. VFR CONDITIONS WILL THEN RETURN FOR THE BALANCE
OF MONDAY INTO THURSDAY.

&&

.MARINE...
TODAY...LIGHT EAST WINDS EARLY THIS MORNING WILL VEER SOUTH LATER
TODAY AND INCREASE AS A WEAK COASTAL TROUGH LIFTS NORTH AND A
STRONGER SOUTHERLY FLOW DEVELOPS BETWEEN DEPARTING HIGH PRESSURE
AND AN APPROACHING COLD FRONT. WINDS LOOK TO INCREASE TO 10-15 KT
THROUGH THE DAY WITH SEAS BUILDING TO 3 FT WITHIN THE NEARSHORE
WATERS AND UP TO 4 FT BEYOND 40 NM. COULD SEE A PERIOD OF GUSTY
WINDS AROUND THE CHARLESTON HARBOR...ESPECIALLY THIS AFTERNOON...
BUT GUSTS LOOK TO REMAIN BELOW 25 KT.

TONIGHT...WINDS WILL BE SLOW TO INCREASE THIS EVENING...BUT WILL
INCREASE SUBSTANTIALLY AFTER MIDNIGHT WITH THE ONSET OF STRONG
LOW-LEVEL JETTING. THERE COULD BE ABOUT A 3-6 HOUR PERIOD WHERE
RISING DEWPOINTS ADVECTING OVER THE COOLER SHELF WATERS COULD
SUPPORT SOME PATCHY SEA FOG...BUT CONFIDENCE IN THIS SCENARIO
REMAINS LOW. WILL CONTINUE TO SHOW PATCHY SEA FOG IN THE GRIDDED
AND TEXT FORECASTS THROUGH MIDNIGHT...MAINLY FOR THE BEAUFORT
COUNTY AND GEORGIA NEARSHORE WATERS. WIND GUSTS WILL BE TEMPERED
SOMEWHAT IN THE UNFAVORABLE WARM AIR ADVECTION REGIME OVERNIGHT
WITH UNFAVORABLE MIXING PROFILES NOTED OVER THE NEARSHORE WATERS.
HOWEVER...GUSTS WILL LIKELY STILL BE APPROACHING 35 KT GALES FOR
THE GEORGIA OFFSHORE WATERS AND THE OUTER PORTIONS OF THE
CHARLESTON COUNTY WATERS PRIOR TO SUNRISE MONDAY WHERE WATER
TEMPERATURES ARE CONSIDERABLY WARMER DUE TO THE PROXIMITY TO THE
WEST WALL OF THE GULF STREAM. A GALE WATCH WILL BE POSTED FOR
THESE MARINE ZONES WITH SMALL CRAFT ADVISORIES FOR THE REMAINING
MARINE LEGS...INCLUDING THE CHARLESTON HARBOR. SEAS WILL BUILD 4-6
FT NEARSHORE WATERS AND 6-9 FT OVER THE GEORGIA OFFSHORE WATERS.

MONDAY THROUGH THURSDAY NIGHT...HAZARDOUS MARINE CONDITIONS WILL
CONTINUE INTO MONDAY AS A STRONG COLD FRONT CROSSES THE
REGION...WITH SOLID SMALL CRAFT ADVISORY CONDITIONS AND POSSIBLY
SOME GALE CONDITIONS ONGOING. WINDS/SEAS WILL GRADUALLY IMPROVE
LATE MONDAY/EARLY TUESDAY MORNING...AS SURFACE HIGH PRESSURE
BUILDS INTO THE REGION. MARINE ADVISORIES MAY BE REQUIRED AGAIN
LATE THURSDAY...AS THE GRADIENT TIGHTENS BETWEEN ATLANTIC HIGH
PRESSURE AND A DEVELOPING LOW PRESSURE SYSTEM IN THE GULF OF
MEXICO.

&&

.TIDES/COASTAL FLOODING...
STRONG OFFSHORE WINDS WILL DEVELOP IN WAKE OF THE COLD FRONT
MONDAY AND WILL LIKELY LEAD TO THE DEVELOPMENT OF BLOW-OUT TIDES IN
THE AFTERNOON WITH THE LOW TIDE CYCLE. TIDES COULD RUN AS MUCH AS
1-2 FT BELOW PREDICTED LEVELS WITH LEVELS POSSIBLY DROPPING AS
LOW AS -1 FT MLLW. CURRENTS WILL BE STRONGER THAN NORMAL DURING
THIS TIME AND UNDERWATER STRUCTURES AND SURFACES WILL BECOME
EXPOSED THAT OTHERWISE MIGHT NOT BE A PROBLEM DURING HIGHER TIDE
LEVELS.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 1 AM MONDAY TO 1 AM EST TUESDAY FOR
     AMZ330-352-354.
     GALE WATCH FROM LATE TONIGHT THROUGH MONDAY AFTERNOON FOR
     AMZ350.
     GALE WATCH FROM LATE TONIGHT THROUGH MONDAY EVENING FOR AMZ374.

&&

$$
SYNOPSIS...
NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...
TIDES/COASTAL FLOODING...


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