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Area Forecast Discussion

018
FXUS62 KCHS 011536
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1136 AM EDT WED APR 1 2015

.SYNOPSIS...
A COLD FRONT WILL DROP SOUTH THROUGH THE REGION TODAY AS HIGH PRESSURE
BUILDS FROM THE NORTH INTO TONIGHT. HIGH PRESSURE WILL SHIFT OFF
THE EASTERN SEABOARD THURSDAY. A ROBUST COLD FRONT WILL CROSS THE
REGION SATURDAY... FOLLOWED BY COOLER HIGH PRESSURE THROUGH
SUNDAY. THE HIGH WILL SHIFT INTO THE ATLANTIC AND WILL PUSH WARMER
AND MORE HUMID AIR INTO THE REGION THROUGH THE FIRST HALF OF NEXT
WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
A PRONOUNCED UPPER SHORTWAVE AS SEEN ON WATER VAPOR IMAGERY THIS
MORNING IS MAKING ITS WAY THROUGH THE FORECAST AREA. MEANWHILE THE
BACK DOOR COLD FRONT HAS BEEN DRAPED ACROSS THE FAR NORTHERN
REACHES OF OUR FORECAST AREA...ALLOWING A RELATIVELY MOIST AIRMASS
TO RESIDE OVER THE AREA WITH PWATS 1.1-1.3 INCHES. A PRETTY
IMPRESSIVE SLUG OF OMEGA ON THE LEADING EDGE OF THE SHORTWAVE HAS
PRODUCED AN AREA OF SHOWERS THAT IS NOW MOVING OFF THE SC COAST.
WE INCREASED POPS SUBSTANTIALLY ON A 9AM UPDATE. POPS TREND DOWN
QUICKLY THROUGH EARLY AFTERNOON AS THE SHORTWAVE PUSHES OFFSHORE
AND NEGATIVE VORTICITY ADVECTION BEGINS. THE BACK DOOR COLD FRONT
WILL BE SLOW TO MOVE SOUTH TODAY WITH OUR FAR SOUTHERN GA ZONES
REMAINING IN THE WARM SECTOR MUCH OF THE DAY. THOUGH CLOUD COVER
WILL BE FAIRLY EXTENSIVE THROUGH 1 OR 2 PM THERE SHOULD BE ENOUGH
BREAKS IN THE CLOUDS TO ALLOW TEMPS TO QUICKLY RISE INTO THE UPPER
70S FAR SW WITH LOW TO MID 70S FARTHER TO THE NORTH.

MODEL CAPE INCREASES TO AROUND 1000 J/KG DURING THE AFTERNOON
ACROSS FAR SOUTHERN AREAS. ISOLATED SHOWERS OR TSTMS POSSIBLE
ALONG AND SOUTH OF THE SINKING COLD FRONT TODAY BUT THE LOW AND
MID LEVELS ARE GRADUALLY BECOMING LESS CONDUCIVE TO STRONG UPDRAFT
GROWTH. THUS...THE CHANCE FOR SEVERE WEATHER IS QUITE LOW AND
CONVECTIVE COVERAGE WILL BE LIMITED.

TONIGHT WILL BE COOLER ACROSS SOUTHERN SOUTH CAROLINA WHERE
MOSTLY CLEAR SKIES AND DIMINISHING WINDS WILL OCCUR.
ELSEWHERE...INCREASING LAYERED CLOUDS LATE NIGHT WITH DEVELOPING
ONSHORE FLOW WILL KEEP TEMPS A FEW DEGREES WARMER. A MID LEVEL
RIDGE WILL KEEP THE WEATHER DRY ACROSS THE FORECAST AREA.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY/...
THURSDAY...THE UPPER RIDGE WILL SHIFT OFFSHORE AND THE SURFACE HIGH
WILL MOVE INTO THE WESTERN ATLANTIC. LOW LEVEL FLOW BECOMES ONSHORE
AND SURFACE DEWPOINTS INCREASE INTO THE LOWER 60S ACROSS SOUTHEAST
GA. MEANWHILE...A SHORTWAVE TROUGH ALOFT WILL ADVANCE INTO THE
REGION FROM THE WEST/SOUTHWEST DURING THE AFTERNOON...POSSIBLY
TRIGGERING ISOLATED SHOWERS/TSTMS ESPECIALLY DURING THE AFTERNOON
ACROSS WESTERN ZONES. 01/00 UTC GUIDANCE DIFFERS REGARDING THE
STRENGTH OF THE SHORTWAVE AND ASSOCIATED FORCING FOR ASCENT/RESPONSE
OF DEEP LAYERED MOISTURE FIELDS. THUS...CAPPED POPS AT SLIGHT
CHANCE/CHANCE INLAND...BUT ADJUSTMENTS WILL LIKELY BE REQUIRED
WITHIN SUBSEQUENT FORECASTS. OTHERWISE...HIGHS 75-80F WILL BE
COMMON...EXCEPT NEAR THE COAST WHERE A VIGOROUS ONSHORE FLOW WILL
KEEP TEMPS IN THE UPPER 60S.

CONVECTION COULD PERSIST INTO THURSDAY EVENING ESPECIALLY ACROSS
INLAND/NORTHERN COUNTIES...BUT OPTED TO MAINTAIN PREVIOUS POPS BELOW
15 PERCENT WITH NO MENTION OF PRECIPITATION. OTHERWISE...AS WINDS
VEER TOWARD THE SOUTH AND DEWPOINTS IN THE 60S ATTAIN A LONGER
TRAJECTORY OVER THE COOL SHELF WATERS...CONDITIONS WILL BECOME
INCREASINGLY FAVORABLE FOR SEA FOG DEVELOPMENT ACROSS NEAR SHORE
WATERS...AND SOME OF THIS FOG COULD PUSH INTO COASTAL COUNTIES.
OTHERWISE...EXPECT A MILD NIGHT WITH LOWS IN THE UPPER 50S/LOWER
60S.

FRIDAY...AHEAD OF AN APPROACHING COLD FRONT...THERMAL RIDGING/
COMPRESSIONAL HEATING SHOULD PUSH TEMPERATURES INTO THE MID 80S. AN
ISOLATED SHOWER/THUNDERSTORM CANNOT BE RULED OUT IF/WHERE LOW LEVEL
CONVERGENCE DEVELOPS EAST OF I-95...BUT CAPPED/FAIRLY DRY MODEL
SOUNDINGS SUGGEST THAT THE POTENTIAL FOR CONVECTION REMAINS TOO
LIMITED TO JUSTIFY A MENTION WITHIN PUBLIC FORECASTS. ALSO OF NOTE...
SEA FOG/STRATUS COULD CONTINUE TO BRUSH THE BEACHES/SEA ISLANDS.

FRIDAY NIGHT...AHEAD OF AN APPROACHING COLD FRONT...TEMPERATURES
WILL HOLD IN THE 60S. 01/00 UTC GUIDANCE HAS COME INTO BETTER
AGREEMENT REGARDING THE PROGRESS OF THE COLD FRONT...SUGGESTING THAT
A SLIGHT CHANCE FOR SHOWERS/THUNDERSTORMS IS IN ORDER ACROSS
NORTHERN/INLAND COUNTIES LATE.

SATURDAY...THE COLD FRONT WILL CROSS THE REGION WITH AN ASSOCIATED
CHANCE FOR SHOWERS/THUNDERSTORMS. MODEL DEPICTIONS OF RATHER MEAGER
SURFACE-BASED INSTABILITY SUGGESTS THAT THE POTENTIAL FOR SEVERE
WEATHER WILL REMAIN LIMITED. OTHERWISE...TEMPERATURES SHOULD RECOVER
INTO THE 70S BEFORE COLD ADVECTION COMMENCES LATER IN THE DAY.

&&

.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
POST FROPA HIGH PRESSURE WILL PROVIDE COOLER AND RAIN-FREE
CONDITIONS SATURDAY NIGHT THROUGH SUNDAY NIGHT. THEN...HIGH PRESSURE
WILL PUSH OFFSHORE AND A RETURN FLOW FEATURING WARMER TEMPERATURES
AND INCREASING MOISTURE WILL PREVAIL MONDAY THROUGH WEDNESDAY. ODDS
FAVOR RAIN-FREE CONDITIONS THROUGH MONDAY. THEN...EVEN THOUGH
SIGNIFICANT MOISTURE/PRECIPITATION SHOULD BE HELD WEST OF THE REGION
BY THE ATLANTIC RIDGE THROUGH MIDWEEK...LOW POPS ARE JUSTIFIED
TUESDAY-WEDNESDAY.

&&

.AVIATION /15Z WEDNESDAY THROUGH SUNDAY/...
VFR. RADAR TRENDS WILL DICTATE ANY INCLUSIONS OF SHOWERS THIS
MORNING AND AT KSAV THIS AFTERNOON. WIND SHIFTS TO ONSHORE TODAY
WITH A COLD FRONT PASSAGE FROM N TO S ACROSS THE COASTAL CORRIDOR
FROM MID MORNING N TO MID AFTERNOON S. THE FRONT COULD TANGLE
WITH THE SEA BREEZE AROUND KSAV TO PRODUCE A FEW SHOWERS AND
TSTMS THIS AFTERNOON. TONIGHT...MODEL SOUNDINGS AT KSAV SUGGEST
AN INFUSION OF LOW LEVEL ATLC MOISTURE WHICH COULD PRODUCE MVFR
CIGS AT TIMES.

EXTENDED AVIATION OUTLOOK...SCATTERED SHOWERS AND TSTMS EXPECTED
SATURDAY. OTHERWISE...MAINLY VFR.

&&

.MARINE...
A BACK DOOR COLD FRONT WILL GRADUALLY DROP SOUTH TODAY WITH NE
WINDS DEVELOPING. THE BEST SURGE DURING THE DAYTIME HOURS WILL BE
THE SC NEARSHORE WATERS INCLUDING CHARLESTON HARBOR WHERE SOME
GUSTS TO 20 KT ARE POSSIBLE LATE TODAY.

SEAS SHOULD BUILD TO 4 FT OFF THE SOUTH CAROLINA COAST WITH A
BUILDING WIND WAVE TODAY. ONSHORE FLOW WILL BUMP SEAS UP TO 3-4 FT
TONIGHT WITH SOME 5 FT WAVES OVER OUTER GEORGIA WATERS.

AS HIGHER DEWPOINTS SPREAD ACROSS THE STILL-CHILLY SHELF WATERS...
CONDITIONS WILL BECOME INCREASINGLY FAVORABLE FOR SEA FOG LATER
THURSDAY OR THURSDAY NIGHT THROUGH FRIDAY NIGHT/SATURDAY MORNING.
ADDED A MENTION TO MARINE FORECASTS...AND ALSO ADDRESSED WITHIN
THE HAZARDOUS WEATHER OUTLOOK.

AS SURFACE HIGH PRESSURE SHIFTS OFFSHORE...MODERATE ONSHORE FLOW IS
EXPECTED THURSDAY. AHEAD OF AN APPROACHING COLD FRONT S/SW WINDS
WILL INCREASE FRIDAY/FRIDAY NIGHT...AND SCA CONDITIONS ARE POSSIBLE
ESPECIALLY ACROSS AMZ350 AND AMZ374.

THE COLD FRONT WILL CROSS THE WATERS SATURDAY...AND STRONG HIGH
PRESSURE WILL THEN BUILD INTO THE REGION ENHANCING COLD ADVECTION
AND SUPPORTING A SURGE OF NORTHEAST WINDS AND ELEVATED SEAS DURING
THE LATTER HALF OF THE WEEKEND INTO EARLY NEXT WEEK. SMALL CRAFT
ADVISORIES APPEAR LIKELY WITH THIS EVENT.

THE HIGH PRESSURE WILL SHIFT OFFSHORE NEXT WEEK...AND WINDS WILL
VEER THROUGH THE E/SE TO S/SW. WINDS/SEAS SHOULD REMAIN BELOW SCA
LEVELS THROUGH MID WEEK.

&&

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

&&

$$
SYNOPSIS...
NEAR TERM...JRL
SHORT TERM...SPR
LONG TERM...SPR
AVIATION...
MARINE...JRL/SPR



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