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Area Forecast Discussion

397
FXUS62 KCHS 061116
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
616 AM EST FRI MAR 6 2015

...HIGHS 35 TO 40 DEGREES COLDER THAN THURSDAY...

.SYNOPSIS...
COLD HIGH PRESSURE WILL BUILD OVER THE AREA THROUGH SUNDAY. AN
UNSETTLED PATTERN WILL DEVELOP BETWEEN A STATIONARY FRONT SOUTH
AND EAST OF THE REGION AND HIGH PRESSURE CENTERED TO THE NORTH FOR
MUCH OF NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
LOOKS LIKE TEMPERATURES ARE GOING TO BOTTOM OUT JUST ABOVE
FREEZING ACROSS BERKELEY COUNTY. ALL MENTION OF FREEZING DRIZZLE
HAS BEEN REMOVED WITH THE SUNRISE UPDATE.

CONSIDERABLY COLDER TEMPERATURES WILL OCCUR ACROSS SOUTHEAST
SOUTH CAROLINA AND SOUTHEAST GEORGIA TODAY IN THE WAKE OF STRONG
COLD FRONT. HIGHS TODAY WILL GENERALLY RANGE FROM THE LOWER 40S
ACROSS THE FAR NORTHERN ZONES WITH MID-UPPER 40S ELSEWHERE...BUT
STIFF NORTH WINDS WILL KEEP WIND CHILLS IN THE 30S FOR MOST OF THE
DAY. THESE HIGHS ARE ABOUT 35-40 DEGREES COOLER THAN WHAT WAS
OBSERVED THURSDAY WHERE LOWER-MID 80S WERE COMMON AWAY FROM THE
COAST. THERE ARE SOME INDICATIONS THAT HIGHS MAY NOT BREACH 40
DEGREES IN THE CHARLESTON METRO AREA IF DRIZZLE AND RESULTING
DIABATIC COOLING LINGER LONGER THAN EXPECTED SO THIS WILL NEED TO
BE WATCHED CAREFULLY. BECAUSE OF MIDNIGHT HIGHS...THE RECORD LOW
MAXIMUMS FOR THE DATE AT ALL THREE CLIMATE SITES ARE SAFE. WEAK
295-300K ISENTROPIC ASSENT WILL KEEP A RISK FOR DRIZZLE AND
POSSIBLY A FEW SHOWERS IN PLACE THROUGH LATE MORNING...BUT THIS
RISK WILL END LATER THIS AFTERNOON AS DRIER AIR WORKS SOUTH AND
ISENTROPIC DOWNGLIDE ENSUES. CLOUDS LOOK TO HANG TOUGH FOR MUCH OF
THE DAY...POSSIBLY BREAKING BY LATE AFTERNOON... ESPECIALLY ACROSS
THE FAR WESTERN ZONES.

LAKE WINDS...GUSTY CONDITIONS WILL PERSIST ON LAKE MOULTRIE
THROUGH LATE MORNING BEFORE SLOWLY SUBSIDING THROUGH THE
AFTERNOON AS COLD AIR ADVECTION WANES. A LAKE WIND ADVISORY
REMAINS IN FORCE THROUGH LATE MORNING.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH MONDAY/...
TONIGHT...SKIES WILL RAPIDLY CLEAR THIS EVENING AS DRIER AIR WORKS
INTO THE REGION IN THE WAKE OF PASSING SHORTWAVE ENERGY WELL TO
THE NORTH. THERE COULD BE A BAND OF JET ENHANCED CIRRUS THAT
LINGERS THE REGION THROUGH LATE EVENING...BUT MODEL DERIVED
SATELLITE IMAGERY SUGGESTS THE CIRRUS WILL BE QUITE THIN. HIGH
PRESSURE IS PROGGED TO PROPAGATE EAST THROUGH THE NIGHT AND LOOKS
TO BUILD FAR ENOUGH TO THE EAST THAT FULL DECOUPLING OF THE
BOUNDARY LAYER IS LIKELY AS THE PRESSURE GRADIENT RELAXES. CLEAR
SKIES AND CALM/LIGHT WINDS WILL PROMOTE SOLID RADIATIONAL
CONDITIONS SO GENERALLY FAVORED THE COOLER SIDE OF THE GUIDANCE
ENVELOP TO CONSTRUCT OVERNIGHT LOWS.

EXPECT MOST AREAS AWAY FROM THE IMMEDIATE COAST TO DROP BELOW
FREEZING WITH LOWS RANGING FROM THE MID 20S ACROSS INTERIOR
SOUTHEAST SOUTH CAROLINA TO THE LOWER 30S ALONG THE ALTAMAHA RIVER
WITH MID 30S ALONG THE MID-UPPER GEORGIA COAST. THE FREEZE WATCH
WILL THEREFORE BE UPGRADED TO A FREEZE WARNING FOR ALL ZONES
EXCEPT THE GEORGIA COASTAL ZONES WHERE A FROST ADVISORY WILL BE
RAISED. FREEZE DURATIONS WILL RANGE FROM 9-12 HOURS WELL
INLAND...4-8 HOURS LOWER SOUTH CAROLINA COAST AND CENTRAL
SOUTHEAST GEORGIA ZONES WITH 2-4 HOURS FOR AREAS SOUTH OF THE I-16
CORRIDOR.

SATURDAY AND SUNDAY...EXPECT FAIRLY QUIET WEATHER CONDITIONS THIS
WEEKEND...AS THE CENTER OF SURFACE HIGH PRESSURE SHIFTS OVER THE
SOUTHEAST STATES AND THEN SLIPS OFF THE EAST COAST. A STEADY WARMING
TREND WILL OCCUR...WITH AFTERNOON HIGH TEMPERATURES IN THE UPPER 50S
NORTH TO LOW 60S SOUTH SATURDAY AND IN THE UPPER 60S TO AROUND 70
DEGREES SUNDAY. LOW TEMPERATURES SATURDAY NIGHT WILL REMAIN ABOVE
FREEZING IN THE MID TO UPPER 30S INLAND. MID TO HIGH LEVEL CLOUDS
INCREASE LATER SUNDAY DOWNSTREAM OF SHORTWAVE ENERGY LIFTING UP FROM
THE GULF COAST/SOUTHERN PLAINS...HOWEVER RAIN CHANCES WILL BE NEAR
ZERO THROUGH SUNDAY AFTERNOON.

SUNDAY NIGHT INTO MONDAY...SHORTWAVE ENERGY WILL CONTINUE TO LIFT
INTO THE SOUTHEAST STATES...RIDING WITHIN THE UPPER FLOW BETWEEN A
BROAD TROUGH OVER THE CENTRAL AND SOUTHERN STATES AND RIDGING FAR IN
THE ATLANTIC. AT THE SURFACE...A STATIONARY FRONT WILL SET UP JUST
OFF OR ALONG THE SOUTHEAST COAST AND STRETCH BACK THROUGH THE
FLORIDA PENINSULA INTO THE GULF OF MEXICO. ABUNDANT DEEP LAYER
MOISTURE FOLLOWING THE STREAM OF SHORTWAVE ENERGY...WHEN COMBINED
WITH CONVERGENCE ALONG THE DEVELOPING FRONT TO THE SOUTH AND
EAST...WILL SUPPORT INCREASING RAIN CHANCES LATE SUNDAY THROUGH
MONDAY. THERE REMAINS NOTABLE DISAGREEMENT BETWEEN A FEW OF THE
FORECAST MODELS REGARDING THE SPEED WITH WHICH DEEP MOISTURE RETURNS
TO THE SOUTHEAST STATES...AND THUS THERE ARE SOME DISTINCT DRY
VERSUS WET SCENARIOS FOR EARLY NEXT WEEK. PREFER TO LEAN TOWARD
PERSISTENCE AND THE 12Z GFS SOLUTION BY INDICATING RAIN CHANCES
INCREASING FROM SOUTHWEST TO NORTHEAST SUNDAY NIGHT...PEAKING IN THE
30 TO 40 PERCENT RANGE DURING THE DAYTIME HOURS MONDAY. THICK CLOUD
COVER WILL KEEP LOW TEMPERATURES SUNDAY NIGHT IN THE MID TO UPPER
40S INLAND...WHILE A RENEWED NORTHEAST LOW LEVEL FLOW AND THICKENING
CLOUDS COMBINE TO KEEP HIGH TEMPERATURES IN THE LOW 60S MONDAY
AFTERNOON.

&&

.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
CONFIDENCE IN THE DETAILS OF THE EXTENDED FORECAST REMAIN RATHER LOW
CONSIDERING PERSISTENT MODEL DISCREPANCIES WITHIN A RELATIVELY
CHANGEABLE PATTERN. RAIN CHANCES WILL BE DRIVEN BY THE LOCATION OF A
LINGERING STATIONARY FRONT AND ANY WAVES OF LOW PRESSURE....AS WELL
AS A RIBBON OF DEEP MOISTURE ENHANCED BY CONTINUAL SHORTWAVE ENERGY
MOVING UP FROM THE GULF OF MEXICO. WITH THE SOUTHEAST COAST ALONG
THE PERIPHERY OF THE SUBTROPICAL RIDGE...THE AXIS OF DEEP MOISTURE
WILL LIKELY BE HELD JUST TO THE WEST AND NORTH OF THE FORECAST
AREA...WITH BEST RAIN CHANCES ACROSS INLAND AND NORTHERN ZONES AS A
RESULT. HAVE INCLUDED RAIN CHANCES IN THE FORECAST FOR THE ENTIRE
WEEK...HIGHEST MONDAY NIGHT INTO TUESDAY. OTHERWISE...PREFER TO
REMAIN SOMEWHAT GENERIC AND FLEXIBLE REGARDING THE FORECAST...AS
RAIN POTENTIAL AND COVERAGE EXPECTATIONS FOR THE MID TO LATE WEEK
PERIOD WILL LIKELY CHANGE AS MODELS HOPEFULLY COME INTO BETTER
AGREEMENT.

HIGH TEMPERATURES WILL GENERALLY REACH THE 60S EACH
AFTERNOON...EXCEPT FOR LOW 70S SOUTHEAST GEORGIA ZONES WEDNESDAY AND
THURSDAY. LOW TEMPERATURES WILL BE WARMER THAN NORMAL...MAINLY A
RESULT OF THE INSULATING EFFECTS OF CLOUD COVER THAT IS EXPECTED TO
LINGER THROUGH THE MAJORITY OF THE WEEK.

&&

.AVIATION /11Z FRIDAY THROUGH TUESDAY/...
KCHS...MVFR CIGS WILL BE SLOW TO IMPROVE TO VFR...BUT EXPECT VFR
BY EARLY AFTERNOON...ROUGHLY 20Z. VFR WILL PREVAIL THEREAFTER.
GUSTY WINDS WILL PERSIST THROUGH THE DAY THEN GO VARIABLE THIS
EVENING AS THE BOUNDARY LAYER DECOUPLES. OCCASIONAL BOUTS OF -DZ
WILL CONTINUE...BUT SIGNIFICANT VSBY RESTRICTIONS ARE UNLIKELY.

KSAV...CIGS WILL TEETER IFR/MVFR THROUGH ABOUT 14Z...THEN IMPROVE
TO PREVAILING MVFR. CIGS ARE EXPECTED TO REMAIN ABOVE ALTERNATE
MINIMUMS. VFR WILL RETURN BY 21Z AND PREVAIL THEREAFTER. GUSTY
WINDS WILL PERSIST FOR MUCH OF THE DAY...THEN GO VARIABLE LATE
THIS EVENING AS THE BOUNDARY LAYER DECOUPLES. OCCASIONAL BOUTS
OF -DZ WILL CONTINUE...BUT SIGNIFICANT VSBY RESTRICTIONS ARE
UNLIKELY.

EXTENDED AVIATION OUTLOOK...VFR LIKELY FRIDAY NIGHT THROUGH THIS
WEEKEND. FLIGHT RESTRICTIONS POSSIBLE WITHIN RAIN EARLY NEXT WEEK.

&&

.MARINE...
TODAY...BUOY AND PILOT BOAT REPORTS INDICATE HAZARDOUS CONDITIONS
ARE IN PROGRESS ACROSS THE COASTAL WATERS EARLY THIS MORNING.
GALES LOOK ON TARGET FOR THE GEORGIA OFFSHORE WATERS AND THE
CHARLESTON COUNTY WATERS WHERE WINDS OF 25-30 KT WITH GUSTS TO 35
KT WILL CONTINUE THROUGH LATE MORNING. OVER THE REMAINING MARINE
LEGS...20-25 KT WITH GUSTS TO 30 KT LOOK GOOD WITH SMALL CRAFT
ADVISORIES. SEAS WILL PEAK SHORTLY AFTER SUNRISE WITH 4-7 FT
NEARSHORE WATERS AND 7-9 FT OFFSHORE WATERS. THE GALE WARNINGS ARE
SET TO EXPIRE BY LATE MORNING/EARLY AFTERNOON AND WILL LIKELY BE
REPLACED WITH SMALL CRAFT ADVISORIES AT THAT TIME. EXPECT ALL
HEADLINES TO BE DROPPED FOR THE NEARSHORE ZONES BY LATE AFTERNOON
AS WINDS AND SEAS CONTINUE TO SUBSIDE.

TONIGHT...GUSTY WINDS WILL PERSIST THROUGH MUCH OF THE NIGHT WITH
A BIT OF PRESSURE GRADIENT FORECAST TO HOLD UNTIL EARLY SATURDAY
MORNING. WINDS WILL GENERALLY AVERAGE 15-20 KT WITH SEAS 2-4 FT
NEARSHORE WATERS AND 4-6 FT OFFSHORE WATERS.

SATURDAY THROUGH TUESDAY...ELEVATED NORTH/NORTHEAST WINDS
AND ASSOCIATED SEAS WILL PERSIST INTO SATURDAY MORNING...BEFORE
CONDITIONS GRADUALLY IMPROVE AS THE DAY PROGRESSES. NO MARINE
CONCERNS FOR THE REMAINDER OF THE WEEKEND AS HIGH PRESSURE SHIFTS
OVER THE WATERS SATURDAY NIGHT THROUGH SUNDAY. FORECAST CONFIDENCE
REMAINS LOW EARLY NEXT WEEK DUE TO THE UNCERTAINTY REGARDING A
FLUCTUATING STATIONARY FRONT AND POSSIBLE WAVES OF LOW PRESSURE
TRACKING ALONG THE FEATURE. WILL CONTINUE TO KEEP WINDS/SEAS BELOW
ADVISORY LEVELS...HOWEVER ANY CHANGES TO THE LOCATION OF THE FRONT
AND/OR THE STRENGTH OF LOW PRESSURE WAVES COULD SUPPORT STRONGER
WINDS AND HIGHER SEAS.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...FREEZE WARNING FROM 11 PM THIS EVENING TO 9 AM EST SATURDAY
     FOR GAZ099>101.
     FREEZE WARNING FROM 2 AM TO 9 AM EST SATURDAY FOR GAZ114>116-
     118-137-138-140.
     FROST ADVISORY FROM 2 AM TO 9 AM EST SATURDAY FOR GAZ117-119-
     139-141.
     FREEZE WARNING FROM 8 PM THIS EVENING TO 9 AM EST SATURDAY FOR
     GAZ087-088.
SC...FREEZE WARNING FROM 11 PM THIS EVENING TO 9 AM EST SATURDAY
     FOR SCZ047>052.
     FREEZE WARNING FROM 8 PM THIS EVENING TO 9 AM EST SATURDAY FOR
     SCZ040-042>045.
     LAKE WIND ADVISORY UNTIL 11 AM EST THIS MORNING FOR SCZ045.
MARINE...SMALL CRAFT ADVISORY UNTIL 4 PM EST THIS AFTERNOON FOR AMZ352-
     354.
     GALE WARNING UNTIL 11 AM EST THIS MORNING FOR AMZ350.
     GALE WARNING UNTIL 2 PM EST THIS AFTERNOON FOR AMZ374.
     SMALL CRAFT ADVISORY UNTIL 11 AM EST THIS MORNING FOR AMZ330.

&&

$$

ST



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