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Area Forecast Discussion

045
FXUS62 KCHS 170124
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
924 PM EDT WED APR 16 2014

.SYNOPSIS...
HIGH PRESSURE WILL BUILD NORTH OF THE REGION THROUGH THURSDAY NIGHT.
AN AREA OF LOW PRESSURE MAY AFFECT THE REGION FRIDAY AND SATURDAY
AS IT PASSES BY TO THE EAST OVER THE ATLANTIC. HIGH PRESSURE WILL
THEN RETURN TO THE AREA EARLY NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
THE FORECAST IS ON TRACK. ONLY MINOR ADJUSTMENTS TO HOURLY
PARAMETERS THROUGH MIDNIGHT WERE MADE.

THE HIGH PRESSURE WEDGE WILL STRENGTHEN TONIGHT AS THE CENTER OF
THE PARENT HIGH SHIFTS INTO THE NORTHEAST STATES. MODELS SHOW
MEAGER 290K ISENTROPIC LIFT DEVELOPING FROM MIDNIGHT ON. DESPITE
THE UPTICK IN ASSENT...CONDENSATION PRESSURE DEFICITS LOOK TO
REMAIN ABOVE 100 MB UNTIL EARLY THURSDAY MORNING...WHERE VALUES
DROP BELOW 50 NM ACROSS THE FAR SOUTH A FEW HOURS BEFORE SUNRISE.
THIS WILL RESULT IN A CLEAR CONDITIONS ACROSS THE ENTIRE AREA FOR
MUCH OF THE NIGHT WITH CLOUDS SLOWLY CREEPING INLAND FROM
SOUTHEAST TO NORTHWEST ROUGHLY BETWEEN 3 AM AND SUNRISE. HAVE
ADJUSTED THE GRIDDED SKY FORECASTS TO MATCH EXPECTED
TRENDS...DEPICTING MOSTLY CLEAR WELL INLAND THROUGH 12Z WITH
SKIES BECOMING PARTLY CLOUDY ALONG THE SOUTH CAROLINA COAST AND
MOSTLY CLOUDY ROUGHLY ALONG AND SOUTH OF I-16.

FULL DECOUPLING OF THE BOUNDARY LAYER LOOKS DOUBTFUL TONIGHT GIVEN
THE TIGHTENING PRESSURE GRADIENT. THIS WILL HELP KEEP TEMPERATURES
UP DESPITE THE LACK OF SIGNIFICANT CLOUD COVER...ESPECIALLY ACROSS
THE FAR SOUTHERN AREAS. OPTED TO NUDGE OVERNIGHT LOWS UP A FEW
DEGREES FOR MOST AREAS PER 18Z GUIDANCE AND PATTERN RECOGNITION.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
A LOW-LEVEL RIDGE WILL REMAIN WEDGED DOWN THE EASTERN SEABOARD ON
THURSDAY BUT WILL BE GRADUALLY RETREATING IN RESPONSE TO A DIGGING
UPPER TROUGH FROM THE WEST. MOSTLY SUNNY SKIES WILL PREVAIL IN THE
MORNING...BEFORE CIRRUS STARTS TO INCREASE IN RESPONSE TO A
STRENGTHENING UPPER JET STREAM ACROSS THE SOUTHEAST UNITED STATES.
SCATTERED AFTERNOON CUMULUS IS ALSO POSSIBLE. AS LOW-LEVEL
THICKNESSES WARM...TEMPS SHOULD RESPOND BY RISING INTO THE UPPER 60S
TO AROUND 70.

UPPER VORT ENERGY DEVELOPS THURSDAY NIGHT INTO FRIDAY WITH A SURFACE
LOW FORMING ALONG THE CENTRAL GULF COAST REGION. DEEP LAYERED
MOISTURE WILL INCREASE OVER THE AREA WITH SOME WEAK ISENTROPIC
ASCENT PRODUCING SCATTERED SHOWERS BY DAYBREAK FRIDAY ACROSS
SOUTHERN AREAS. EXTENSIVE CLOUD COVER WILL KEEP HIGHS IN THE
MID/UPPER 60S FRIDAY.

THERE REMAIN MODEL DIFFERENCES REGARDING THE EVENTUAL TRACK OF THE
SURFACE LOW FRIDAY NIGHT AND SATURDAY. THE GFS AND NAM CONTINUE TO
BE THE DRY OUTLIERS WHILE THE CANADIAN AND ECMWF REMAIN QUITE WET
WITH A MORE WESTERN LOW TRACK. WE MAINTAINED SIMILAR POPS TO THE
PREVIOUS PACKAGE BUT INCREASED VALUES A BIT...MAINLY FRIDAY NIGHT
WHEN THE SYSTEM WILL MAKE ITS CLOSEST PASS. THE GREATEST COVERAGE OF
PRECIPITATION WOULD CERTAINLY BE OVER OUR COASTAL WATERS BUT THE
INLAND EXTENT IS QUITE UNCERTAIN AT THIS POINT.

HIGH TEMPS ON SATURDAY WILL REALLY DEPEND ON AMOUNT OF CLOUD COVER
AND WHETHER PRECIPITATION LINGERS AS THE ECMWF CURRENTLY SHOWS. FOR
NOW WE ARE SHOWING HIGHS IN THE MIDDLE 70S...A FEW DEGREES BELOW
CLIMO.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
EARLY IN THE PERIOD THERE IS STILL CONSIDERABLE UNCERTAINTY
REGARDING THE SURFACE LOW OFF THE FLORIDA COAST. THE DEEPER MODEL
SOLUTIONS KEEP THE LOW LINGERING AROUND WITH RAIN STILL ONGOING
ALONG THE SOUTHEAST COAST. BY MONDAY OR MONDAY NIGHT...THE LOW IS
EXPECTED TO PULL AWAY AND HIGH PRESSURE WILL RETURN TO THE REGION. A
COLD FRONT MAY ATTEMPT TO SAG IN FROM THE NORTH LATE IN THE PERIOD
WITH SOME MODEST INCREASE IN RAIN CHANCES. OVERALL...TEMPERATURES
ARE EXPECTED TO BE RIGHT AROUND CLIMO...ESPECIALLY BY THE MIDDLE OF
NEXT WEEK.

&&

.AVIATION /02Z THURSDAY THROUGH MONDAY/...
MAINLY VFR. MID-LEVEL CLOUDS WILL INCREASE AFTER 06Z...MAINLY
ACROSS THE SOUTH. LOW PROBABILITIES FOR MVFR CIGS AT BOTH
TERMINALS 09-12Z...BUT CONFIDENCE IS NOT HIGH ENOUGH AT THIS
JUNCTURE TO INCLUDE A MENTION. CAPPED CIGS AT BKN040-050 AT KSAV
AND OPTED NOT TO ESTABLISH CIGS AT KCHS DURING THE ENTIRE TAF
PERIOD.

EXTENDED AVIATION OUTLOOK...LOW CHANCES FOR PERIODIC SUB-VFR
CONDITIONS LATE THURSDAY NIGHT/FRIDAY AS MARINE STRATOCUMULUS
ATTEMPT TO MOVE ONSHORE. BETTER CHANCES FOR FLIGHT RESTRICTIONS
WILL OCCUR FRIDAY NIGHT INTO SATURDAY AS LOW PRESSURE MOVES OUT OF
THE GULF OF MEXICO AND UP THE SOUTHEAST COAST.

&&

.MARINE...
TONIGHT....HIGH PRESSURE WILL STRENGTHEN TO THE NORTH TONIGHT
PRODUCING AN ENHANCED GRADIENT ACROSS THE LOCAL WATERS. THIS MEANS
WINDS WILL INCREASE OVERNIGHT WITH GUSTS NEAR 30 KT AT TIMES...
ESPECIALLY OUTSIDE CHARLESTON HARBOR. SEAS MOSTLY 5 TO 7 FT NEAR
SHORE AND UP TO 9 FT CLOSER TO THE GULF STREAM.

THURSDAY THROUGH SUNDAY...A STRONG RIDGE OF HIGH PRESSURE WILL
REMAIN NORTH OF THE WATERS THROUGH THURSDAY NIGHT BEFORE A GULF
LOW PRESSURE SYSTEM STARTS TAKING SHAPE TO THE SOUTH. THERE ARE
CONSIDERABLE MODEL DIFFERENCES REGARDING THE EVENTUAL TRACK OF THE
LOW...BUT IT WILL AT LEAST INDIRECTLY AFFECT OUR WATERS AS IT
LIFTS NORTHEAST. THE BOTTOM LINE IS THAT A PERSISTENT NORTHEAST
FETCH WITH SOLID SMALL CRAFT ADVISORY WINDS AND/OR SEAS WILL
CONTINUE THROUGH MUCH OF THE UPCOMING WEEKEND. SCA CONDITIONS WILL
LIKELY PERSIST OVER THE OFFSHORE GA WATERS INTO MIDDAY MONDAY DUE
TO LINGERING SEAS.

RIP CURRENTS...MODERATE RISK FOR RIP CURRENTS CONTINUES INTO
THURSDAY DUE TO PERSISTENT SWELL...LINGERING ASTRONOMICAL INFLUENCES
AND GUSTY ONSHORE WINDS. AN ENHANCED RISK MAY PERSIST INTO THE EARLY
WEEKEND.

&&

.TIDES/COASTAL FLOODING...
CURRENT TIDE TRENDS SUGGEST TIDE LEVELS WILL PEAK JUST UNDER 7.0
FT MLLW IN THE CHARLESTON HARBOR WITH HIGH TIDE THIS EVENING.
HOWEVER...STEADY AND PERSISTENT NORTHEAST WINDS WILL LIKELY CAUSE A
FEW PROBLEMS IN DOWNTOWN CHARLESTON DUE TO ONGOING TIDAL LOADING...
DESPITE TIDES OF 6.7-6.9 FT MLLW. WILL ISSUE A COASTAL FLOOD
STATEMENT FOR CHARLESTON COUNTY TO HIGHLIGHT MINOR IMPACTS IN
DOWNTOWN CHARLESTON...MAINLY IN THE NORMAL FLOOD PRONE AREAS. TIDE
TRENDS WILL CONTINUE TO BE MONITORED OVER THE NEXT FEW HOURS AND
THE NEED FOR A COASTAL FLOOD ADVISORY FOR PARTS OF THE LOWER SOUTH
CAROLINA COAST HAS NOT BEEN COMPLETELY RULED OUT.

TIDES WILL CONTINUE TO RUN HIGH THROUGH THE WEEKEND AND COASTAL
FLOOD ADVISORIES COULD BE NEEDED DURING THE NIGHTTIME HIGH TIDE
CYCLES.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 5 PM EDT THURSDAY FOR AMZ330.
     SMALL CRAFT ADVISORY UNTIL 5 PM EDT SUNDAY FOR AMZ350-352-354.
     SMALL CRAFT ADVISORY UNTIL 2 PM EDT MONDAY FOR AMZ374.

&&

$$

ST





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