National Weather Service Weather Forecast Office

Area Forecast Discussion

974
FXUS62 KCHS 031422
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1022 AM EDT THU OCT 3 2013

.SYNOPSIS...
HIGH PRESSURE WILL PREVAIL INTO THE WEEKEND. TROPICAL STORM KAREN
OVER THE GULF OF MEXICO WILL THEN COMBINE WITH AN APPROACHING COLD
FRONT AS IT PROGRESSES TOWARD THE EAST COAST EARLY NEXT WEEK. HIGH
PRESSURE WILL THEN RETURN TO THE REGION BY THE MIDDLE OF NEXT
WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
WEAK HIGH PRESSURE WILL LINGER AT THE SFC TODAY WHILE A MID LVL
RIDGE OF HIGH PRESSURE GRADUALLY FLATTENS AND SLIDES OFF THE
SOUTHEAST COAST. AS THE RIDGE SHIFTS OFFSHORE...A SERIES OF WEAK H5
SHORTWAVES WILL SHIFT OVER THE AREA THIS AFTERNOON/EVENING...AND
SUPPORT A FEW SHOWERS JUST OFFSHORE WHERE A WEAK COASTAL TROUGH
PERSISTS THROUGHOUT THE DAY. A FEW OF THESE SHOWERS MAY APPROACH THE
BEACHES NORTH OF EDISTO SC AS A LIGHT NORTHEAST/EAST FLOW
OCCURS...BUT ANY MEASURABLE PRECIP OVER LAND IS NOT LIKELY AS
ACTIVITY ENCOUNTERS SOME MID LVL DRY AIR.

FORECAST SOUNDINGS ACROSS THE AREA DO INDICATE A POTENTIAL FOR
SCATTERED TO LOCALLY BROKEN CUMULUS/STRATOCU WITH SOME LOW LVL
MOISTURE PRESENT WHILE BROAD DIFLUENCE FROM A 60 KT UPPER LVL JET
SUPPORTS CIRRUS CLOUDS OVER MUCH OF THE AREA. THESE CLOUDS MAY LIMIT
OVERALL HIGH TEMPS TODAY...ESPECIALLY OVER NORTHERN CHARLESTON AND
BERKELEY COUNTIES WHERE MOSTLY CLOUDY SKIES ARE PRESENT. FURTHER
SOUTH...TEMPS WILL REMAIN SOMEWHAT LESS EFFECTED WITH MAINLY CIRRUS
OVER THE AREA. EXPECT OVERALL HIGH TEMPS TO THE MID TO UPPER 80S
OVER MOST LOCATIONS...HIGHEST OVER INLAND AREAS IN SOUTHEAST
GEORGIA.

CLEAR TO PARTLY CLOUDY SKIES TONIGHT WITH DEW POINTS INCREASING
ALONG WITH POTENTIAL FOR AREAS OF FOG LATE. WE TRENDED TOWARD SOME
FOG AROUND FRIDAY MORNING WITH MENTIONS OF PATCHY FOG IN THE FORECAST
TO TREND. LOWS 60-65 WITH NEAR CALM WINDS.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY/...
THE MAJORITY OF NUMERICAL MODEL SOLUTIONS INDICATE A TROPICAL
WAVE IN THE GULF OF MEXICO BY FRIDAY MORNING...DRIFTING NORTHWARD
BENEATH AN AMPLIFYING UPPER RIDGE ALONG THE SOUTHEAST COASTLINE.
THE EVOLUTION OF THIS WAVE THEN BECOMES A MAJOR FORECAST
CONCERN...WITH MODEL REPRESENTATIONS OF ITS STRENGTH AND TRACK IN
NOTABLE DISAGREEMENT. THE GFS SOLUTION REMAINS THE MOST
AGGRESSIVE...INTENSIFYING THE WAVE INTO A DISCRETE TROPICAL
SYSTEM MAKING LANDFALL MIDDAY SATURDAY ALONG THE FLORIDA
PANHANDLE...WELL AHEAD OF AN APPROACHING COLD FRONT FROM THE WEST.
THE ECMWF SOLUTION HAS BEEN CONSISTENTLY WEAKER WITH THE LOW
DEVELOPMENT...KEEPING THE FEATURE AS MORE OF AN OPEN WAVE THROUGH
SATURDAY...BEFORE MERGING IT WITH THE SOUTHERN EXTENT OF THE FRONT
ALONG THE CENTRAL GULF COAST STATES. VARIOUS OTHER MODEL SOLUTIONS
AND AVAILABLE GUIDANCE SHOW THE SYSTEM TRACKING MORE WEST AND
REMAINING RELATIVELY WEAKER THAN THE ROBUST GFS SCENARIO. THE
LOCAL FORECAST WILL THUS LEAN TOWARD A MORE CONSERVATIVE EVOLUTION
OF THIS SYSTEM PER THE ECMWF AND GIVEN WPC GUIDANCE.

WILL KEEP RAIN CHANCES BELOW 15 PERCENT ACROSS LAND AREAS FRIDAY
AND SATURDAY...AS ATLANTIC SURFACE HIGH PRESSURE AND UPPER LEVEL
RIDGING MAINTAIN LARGE SCALE SUBSIDENCE ACROSS THE REGION. THERE
IS SOME EVIDENCE THAT A COASTAL TROUGH COULD DEVELOP ALONG THE
PERIPHERY OF THE ATLANTIC HIGH...AND HAVE THUS MENTIONED A SLIGHT
CHANCE FOR SHOWERS OVER THE MARINE ZONES THROUGH SATURDAY. AN
ISOLATED SHOWER COULD PUSH LOCALLY ONSHORE WITHIN SOLID EASTERLY
FLOW...HOWEVER TIMING AND COVERAGE ARE TOO UNCERTAIN TO EXPLICITLY
MENTION AT THIS POINT. WITH THE AXIS OF THE UPPER TROUGH
STRENGTHENING ALONG THE EAST COAST...EVEN AS THE SYSTEM IN THE
GULF TAKES SHAPE...TEMPERATURES WILL BE FAIRLY WARM FOR THIS TIME
OF YEAR. AFTERNOON HIGHS WILL REACH THE MID TO UPPER 80S WITHIN
RISING HEIGHTS ALOFT...WHILE DECENT LOW LEVEL MOISTURE SUPPORTS
MILD NIGHTTIME LOWS IN THE LOW/MID 60S FRIDAY NIGHT AND MID/UPPER
60S SATURDAY NIGHT.

A DEEP UPPER TROUGH IN THE MISSISSIPPI VALLEY REGION WILL BREAK DOWN
RIDGING ALONG THE EAST COAST BY SUNDAY. THE ASSOCIATED COLD FRONT
WILL STEADILY PROGRESS INTO THE OHIO/TENNESSEE VALLEY...WHILE THE
GULF WAVE BECOMES SWEPT UP ALONG ITS SOUTHERN PERIPHERY. VEERING
WINDS TO THE SOUTHEAST WILL TAP INTO TROPICAL MOISTURE...AT THE
SAME TIME THAT CONVERGENCE ALONG AND AHEAD OF THE COLD FRONT
SUPPORTS MORE WIDESPREAD CONVECTION JUST UPSTREAM. HAVE RAISED
POPS INTO THE 30 PERCENT RANGE FOR SUNDAY. WILL INDICATE A SLIGHT
COOLING TREND AS HEIGHTS ALOFT FALL AND CLOUD COVER
INCREASES...WITH HIGHS RANGING IN THE MID 80S SUNDAY AFTERNOON.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
THE CUTOFF LOW EMBEDDED WITHIN THE LARGE UPPER TROUGH WILL LIFT
INTO THE GREAT LAKES REGION MONDAY...WHILE THE COLD FRONT SHIFTS
THROUGH THE FORECAST AREA AS THE DAY PROGRESSES. HAVE ADVERTISED
THE BEST POTENTIAL FOR SHOWERS/THUNDERSTORMS ON MONDAY AS A RESULT
OF THE FRONTAL PROGRESSION. AN EXPANSIVE SURFACE HIGH WILL THEN
QUICKLY BUILD EASTWARD IN THE WAKE OF THE FRONT EARLY NEXT
WEEK...EVENTUALLY INTRODUCING A DRIER AIR MASS INTO THE REGION.
HAVE KEPT LOW TO SLIGHT RAIN CHANCES THROUGH MID WEEK TO ACCOUNT
FOR DELAYS IN THE FRONT...HOWEVER MODELS ARE TRENDING WITH A MORE
RAPID PROGRESSION. SUBSEQUENT FORECASTS WILL LIKELY BE ABLE TO
DECREASE PRECIPITATION POTENTIAL FOR TUESDAY THROUGH THURSDAY IF
GUIDANCE CONTINUES WITH THIS TREND.

THE BUILDING SURFACE HIGH WILL HAVE TAKEN A MORE SOUTHERN ROUTE
FROM THE SOUTHERN PLAINS TOWARD THE FORECAST AREA...AND WITH UPPER
RIDGING REBUILDING OVER THE EASTERN HALF OF THE UNITED STATES BY
MID WEEK...DO NOT EXPECT A SIGNIFICANT COOLING TREND BEHIND THE
DEPARTING FRONT. HAVE INDICATED HIGH TEMPERATURES RETURNING BACK
TOWARD SEASONAL NORMALS IN THE LOWER 80S TUESDAY THROUGH THE END
OF THE PERIOD.

&&

.AVIATION /14Z THURSDAY THROUGH MONDAY/...
VFR CONDITIONS WILL PREVAIL AT KCHS AND KSAV THROUGH 06Z FRIDAY.
IN THE LAST 6 HOURS OF THE 12Z TAF CYCLE THERE IS A POTENTIAL FOR
MVFR VSBYS AT THE TERMINALS. LATER TAF RELEASES TODAY MAY NEED TO
CONSIDER ADDITIONS OF REDUCED VSBYS BUT AT THIS TIME CONFIDENCE IS
LOWER END.

EXTENDED AVIATION OUTLOOK...VFR CONDITIONS ARE EXPECTED TO PREVAIL.

&&

.MARINE...
TODAY AND TONIGHT...WINDS/SEAS WILL REMAIN WELL BELOW SMALL CRAFT
ADVISORY LEVELS AS A WEAK COASTAL TROUGH PERSISTS ALONG HIGH
PRESSURE OVER THE WATERS. THE PATTERN WILL RESULT IN NORTHEAST WINDS
AT OR BELOW 15 KTS THROUGHOUT THE DAY...WITH SUBTLE DIURNAL
OSCILLATIONS ALONG LAND/SEA BREEZE CYCLES. SEAS WILL RANGE BETWEEN
1-3 FT...HIGHEST IN OUTER GEORGIA WATERS.

FRIDAY THROUGH MONDAY...RELATIVELY QUIET MARINE CONDITIONS ARE
EXPECTED THROUGH SATURDAY. HIGH PRESSURE WILL BE IN CONTROL
OF THE PATTERN ACROSS THE LOCAL WATERS...RESULTING IN A
PREDOMINANTLY EAST FLOW. WIND SPEEDS WILL BE LESS THAN 15 KT AND
SEAS 1-3 FT...HIGHEST OVER THE OUTER WATERS. SINCE THE FORECAST
FAVORS MODEL SOLUTIONS THAT INDICATE A WAVE OF LOW PRESSURE
BECOMING ABSORBED WITHIN AN APPROACHING FRONT ON SUNDAY...WILL
INDICATE A SLIGHT SURGE IN SOUTHEAST FLOW INTO EARLY NEXT
WEEK...YET KEEP WIND SPEEDS BELOW SMALL CRAFT ADVISORY CONDITIONS.
SEAS WILL BUILD TO 3 TO 5 FT SUNDAY NIGHT INTO MONDAY AFTERNOON.
THE COLD FRONT IS EXPECTED TO SHIFT OFF THE COAST LATE MONDAY.

&&

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

&&

$$

SYNOPSIS...
NEAR TERM...DPB
SHORT TERM...WMS
LONG TERM...WMS
AVIATION...DPB
MARINE...DPB/WMS