Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 181159
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
659 AM EST THU DEC 18 2014

.SYNOPSIS...
HIGH PRESSURE WILL PREVAIL THROUGH FRIDAY. LOW PRESSURE WILL
DEVELOP ALONG THE GULF COAST FRIDAY AND TRACK UP THE SOUTHEAST
COAST THIS WEEKEND. UNSETTLED CONDITIONS WILL THEN PREVAIL EARLY
NEXT WEEK AS A MORE SIGNIFICANT AREA OF LOW PRESSURE DEVELOPS WEST
OF THE REGION BY THE MIDDLE OF THE WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
NOT MUCH CHANGE WITH THE WEATHER PATTERN TODAY WITH ZONAL FLOW
ALOFT AND WEAK HIGH PRES AT THE SURFACE. A PASSING SURFACE TROUGH
WILL SHIFT LIGHT WINDS TO NE FOR A BRIEF PERIOD AFTER MID MORNING
AROUND THE CHARLESTON TRI-COUNTY AREA...A VERY SUBTLE FEATURE IN
THE GRAND SCHEME OF THINGS. TEMPS TODAY LOOK TO QUITE SIMILAR TO
WEDNESDAY WITH THE WARMER POTENTIAL READINGS OVER COASTAL SE
GEORGIA WITH A LIGHT OFFSHORE COMPONENT IN THE BOUNDARY LAYER AND
THICKNESS VALUES SOLIDLY IN THE MID 60S RANGE. IF HIGH CLOUDS
REMAIN THIN AND DIMINISH AS MODELS DEPICT THIS AFTERNOON...
SAVANNAH COULD REACH 67 DEGREES ONCE AGAIN.

TONIGHT...MOSTLY CLEAR TO PARTLY CLOUDY SKIES WILL PERSIST WITH
POTENTIAL FOR DECENT RADIATIONAL COOLING PROVIDED ANY HIGH CLOUDS
REMAIN THIN WHICH WHAT BOTH THE NAM AND GEM SKY COVER PROGS SUGGEST.
WE BUMPED LOW TEMPS DOWN A CATEGORY ACROSS NORMALLY COOLER INLAND
AREAS WITH MINOR TWEAKS ALONG THE COASTAL CORRIDOR.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY/...
FRIDAY AND FRIDAY NIGHT...ONE MORE BENIGN DAY IS ON TAP AHEAD OF
APPROACHING SHORTWAVE ENERGY IN THE PROGRESSIVE WESTERLY FLOW ALOFT.
HIGH PRESSURE CENTERED OVER THE UPPER MIDWEST WILL CONTINUE TO
EXTEND INTO THE FORECAST AREA WITH A STILL RELATIVELY DRY ATMOSPHERE
ACROSS THE AREA. IN FACT...OTHER THAN SOME HIGH CLOUDS ASSOCIATED
WITH THE UPPER LEVEL JET...WE SHOULD SEE A GOOD BIT OF SUNSHINE FOR
MUCH OF THE DAY. GIVEN THICKNESS VALUES AND RECENT PERFORMANCE OF
HIGH TEMPERATURES RELATIVE TO GUIDANCE...I HAVE RAISED HIGHS INTO
THE LOW TO MID 60S. THE ARRIVAL OF FORCING FOR ASCENT AND IMPROVED
MOISTURE WILL TAKE PLACE RELATIVELY QUICKLY FROM THE WEST FRIDAY
NIGHT. GIVEN THE FORCING ASSOCIATED WITH THE APPROACHING
SHORTWAVE...JET DYNAMICS...AND AN IMPRESSIVE SHOT OF ISENTROPIC LIFT
THE COVERAGE OF PRECIPITATION WILL RAMP UP QUICKLY LATE FRIDAY
NIGHT. THIS WILL NECESSITATE LIKELY POPS FOR A GOOD PORTION OF THE
AREA BEGINNING IN THE EARLY MORNING HOURS. LOWS WILL DIP INTO THE
LOW TO MID 40S IN MOST AREAS...EXCEPT SOME UPPER 40S RIGHT ALONG THE
COAST.

SATURDAY THROUGH SUNDAY...DESPITE ONLY A 1027 MB HIGH POSITIONED TO
THE NORTHEAST...COLD AIR DAMMING WILL TAKE SHAPE SATURDAY MORNING AS
A SURFACE LOW MOVES ALONG THE GULF COAST WITH SECONDARY DEVELOPMENT
IN THE EVENING OFF THE SOUTHEAST COAST. THE CAD WILL STRENGTHEN
THANKS TO DIABATIC ENHANCEMENT WITH THE ONGOING PRECIPITATION IN THE
MORNING AND THROUGH THE AFTERNOON. GIVEN THE TRACK OF THE SHORTWAVE
AND ASSOCIATED FORCING...THE BEST PRECIPITATION COVERAGE WILL LIKELY OCCUR
ACROSS THE NORTHERN HALF OF THE FORECAST AREA WHERE CATEGORICAL POPS
ARE IN PLACE. THE CAD WEDGE WILL REMAIN IN PLACE INTO SUNDAY THOUGH
THE LOSS OF LARGER SCALE FORCING WILL DECREASE RAIN CHANCES. THERE
COULD STILL BE POCKETS OF DRIZZLE AND EVEN SOME RAIN APPROACHING
FROM THE SOUTH LATER IN THE DAY ON SUNDAY. REGARDLESS...OVERALL
CONDITIONS WILL BE CLOUDY AND COOL. SOME INLAND AREAS WILL STRUGGLE
TO REACH THE LOW 50S THIS WEEKEND...WHILE EVEN COASTAL SOUTHEAST
GEORGIA WILL BE LIMITED TO THE LOW 60S AT BEST.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
THE LONG TERM PERIOD CONTINUES TO LOOK UNSETTLED AND COMPLEX THROUGH
THE MIDDLE OF NEXT WEEK...LEADING TO A BELOW AVERAGE OVERALL
FORECAST CONFIDENCE CONCERNING THE PERIODS OF HIGHEST RAIN CHANCES.
THE INLAND WEDGE WILL PERSIST AS A WAVE DEVELOPS ALONG THE COAST AND
LIFTS OFF TO THE NORTHEAST THROUGH MONDAY. THIS INLAND WEDGE WILL
LINGER THROUGH TUESDAY BEFORE THE MAIN COLD FRONT AND SURFACE LOW
FINALLY SWEEP THROUGH THE REGION. MODELS STILL DISPLAY NOTABLE
DIFFERENCES IN THE DETAILS IN THIS PERIOD...MAINLY THANKS TO
DISCREPANCIES IN HOW DEEP THE UPPER LOW GETS AND THE OVERALL
AMPLITUDE OF THE MID/UPPER LEVEL TROUGH. MOST AREAS WILL EXPERIENCE
A FEW DAYS OF CLOUD COVER WITH PERIODS OF PRECIPITATION UNTIL THE
COLD FRONT FINALLY SWEEPS THROUGH ON WEDNESDAY. POPS HAVE BEEN KEPT
IN THE CHANCE RANGE FOR NOW...THOUGH IT IS EXPECTED TO PERIODS OF
HIGHER POPS WILL BE NEEDED AS THE FORECAST DETAILS BECOME CLEARER.
TEMPERATURES WILL BE BELOW NORMAL THROUGH MID WEEK.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
VFR.

EXTENDED AVIATION OUTLOOK...SUB-VFR CONDITIONS APPEAR LIKELY AS
EARLY AS FRIDAY NIGHT...CONTINUING THROUGH MONDAY AS HIGH PRESSURE
BUILDS FROM THE NORTH AND SEVERAL LOW PRESSURE SYSTEMS MOVE UP THE
COAST.

&&

.MARINE...
A WEAK PRES PATTERN ACROSS THE LOCAL WATERS THROUGH TONIGHT WITH
LIGHT FLOW MAINLY LESS THAN 10 KT. GIVEN THE WEAK SPEEDS...EXPECT
INHERENT OCCASIONAL PERIODIC VARIABILITIES IN DIRECTION. SEAS 1 TO
2 FT WITH A SMALL 10 SECOND GROUND SWELL.

FRIDAY THROUGH MONDAY...HIGH PRESSURE WILL PREVAIL OVER THE WATERS
ON FRIDAY BEFORE A LOW PRESSURE SYSTEM DEVELOPS OVER THE NORTHERN
GULF OF MEXICO AND SHIFTS NORTHEAST OFF THE SOUTH CAROLINA COAST
SATURDAY. WINDS WILL BE RELATIVELY LIGHT AND VARIABLE ON SATURDAY AS
THE CENTER OF THE LOW PASSES NEARBY BUT WINDS INCREASE OUT OF THE
NORTHEAST ON SUNDAY AS IT SHIFTS NORTHEAST OF THE AREA. OVERALL
CONDITIONS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY
THRESHOLDS.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...NONE.

&&

$$

NEAR TERM...
SHORT TERM...BSH
LONG TERM...BSH
AVIATION...
MARINE...BSH





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