Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 220302
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1002 PM EST SUN DEC 21 2014

.SYNOPSIS...
UNSETTLED WEATHER IS EXPECTED THROUGH TUESDAY NIGHT AS SEVERAL
DISTURBANCES MOVE OVER THE REGION. A STRONG COLD FRONT WILL THEN
MOVE THROUGH THE AREA WEDNESDAY EVENING. DRY HIGH PRESSURE WILL
SETTLE OVER THE SOUTHEAST INTO THE WEEKEND.

&&

.NEAR TERM /THROUGH MONDAY/...
OUR DAMP...COOL AND UNSETTLED WEATHER PATTERN WILL PERSIST TONIGHT
WITH THE STRONG INLAND WEDGE OF HIGH PRESSURE GOING NOWHERE ANY
TIME SOON. IT/LL TRY TO GET NUDGED A LITTLE AS WEAK CYCLOGENESIS
TRANSPIRES OUT NEAR THE GULF STREAM...BUT GIVEN CONSIDERABLE
RAINS EARLY ON THIS WILL ACT TO SHUNT ANY RELAXATION OF THE GRIP
OF THE WEDGE BACK TO THE SOUTH. THE COASTAL WARM FRONT WILL
ATTEMPT TO SWING TOWARD THE COAST BEFORE THE WAVE LIFTS OFF TO THE
NE LATE.

ONE CAN CERTAINLY ASCERTAIN WHERE THE MAIN BAROCLINIC ZONE AND
WARM CONVEYOR BELT IS FOUND...STREAMING FROM SW TO NE ACROSS THE
GULF AND SE PART OF THE NATION. THIS IS ALSO WELL ANALYZED BY THE
BLENDED PW PRODUCT THAT SHOWS THIS DEEPER TROPICAL-LIKE MOISTURE
STREAMING NE ACROSS THE LOCAL AREA.

FIRST BATCH OF RAIN WILL LIFT NORTH OF THE SAVANNAH RIVER LATE
THIS EVENING...COVERING MOST OF OUR SC ZONES. THIS IS IN RESPONSE
TO THE SHORT WAVE RIDING NE FROM OUT OF THE GULF OF MEXICO AND
CONSIDERABLE ISENTROPIC LIFT. THERE IS STEADY PROGRESSION OF THIS
ACTIVITY AND MUCH OF IT WILL BE NORTH/NE OF THE SANTEE RIVER AND
OFFSHORE IN THE ATLANTIC BY 1 OR 2 AM. HOWEVER...ANOTHER SHORT
WAVE NEAR THE FLORIDA PANHANDLE AND ANOTHER DOSE OF ISENTROPIC
ASCENT LATE COULD AGAIN CAUSE ADDITIONAL RAINS TO BREAK OUT FROM
SW TO NE. COMBINED WITH LARGE FORCING FROM THE RIGHT ENTRANCE
REGION OF THE 125 KT UPPER JET...WE ARE CARRYING CATEGORICAL POPS
ACROSS MOST OF SC EARLY ON...WITH CHANCE TO LIKELY CHANCES
SOUTH...THEN CHANCE TO LIKELY ALL SECTIONS LATE. THERE CONTINUES
TO BE AN OCCASIONAL LIGHTNING STRIKE HERE OR THERE WITH STEEP MID
LEVEL LAPSE RATES AND MU CAPES OF 100-200 J/KG...AND THIS WILL
CONTINUE FOR A FEW MORE HOURS.

PWATS OF 1.3-1.5 INCHES WILL ALLOW FOR LIGHT TO MODERATE RAINS AND
PRODUCE AS MUCH AS ANOTHER 1/4 TO 1/2 INCH RAINFALL THE REST OF
THE NIGHT.

WIDESPREAD LOW STRATUS CLOUD DECKS WILL LOWER FURTHER AND THIS
WILL RESULT IN AT LEAST PATCHY FOG SOUTH OF I-16 IN SE GA WHERE
THE LOWEST CONDENSATION PRESSURE DEFICITS WILL OCCUR. HOWEVER...WE
MAY NEED TO EXPAND THE FOG COVERAGE FURTHER NORTH AND NW WITH
LATER UPDATES...AS WELL AS CONSIDERING POSSIBLE PATCHES OF DENSE
FOG.

TEMPS WON/T CHANGE MUCH WITHIN THIS PATTERN DUE TO THE OVERCAST
SKIES AND EXTENSIVE RAINS. PLUS THE COOLER AIR REMAINS TRAPPED
UNDERNEATH THE WARM ADVECTION...KEEPING MOST OF US IN THE 40S
THROUGH THE NIGHT.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
A FAIRLY PERSISTENT PATTERN WILL CONTINUE ON MONDAY AS A COOL WEDGE
OF HIGH PRESSURE REMAINS ENTRENCHED ACROSS LAND AREAS AND THE
OVERNIGHT COASTAL LOW SHIFTS NORTHEAST AWAY FROM THE AREA. THE BEST
FORCING WILL MOVE AWAY DURING THE MORNING BUT WE WILL STILL SEE
MODERATE ISENTROPIC ASCENT CONTINUING THROUGH EARLY TO MID AFTERNOON
ALONG WITH WEAK UPPER JET DIVERGENCE. WE SHOW LIKELY POPS IN THE
MORNING...TAPERING BACK TO CHANCE POPS IN THE AFTERNOON WITH HIGHEST
VALUES OVER THE WATERS. QPF WILL BE FAIRLY LIGHT BUT SCATTERED RAIN
WILL PERSIST NONETHELESS. CLOUDY SKIES...COLD ADVECTION AND
EVAPORATIONAL COOLING WILL KEEP HIGH TEMPS IN THE 50S.

ON TUESDAY THE WEDGE WILL LIKELY PERSIST AT LEAST THROUGH EARLY
AFTERNOON. SOME EROSION IS POSSIBLE OVER SOUTHERN AND EASTERN AREAS
AS THE UPPER TROUGH DEEPENS TO THE WEST AND THE COASTAL TROUGH
SHIFTS INLAND. INCREASING SHORTWAVE ENERGY WILL LIFT OUT OF THE GULF
COAST REGION DURING THE AFTERNOON...COINCIDENT WITH A BROAD AREA OF
UPPER LEVEL DIVERGENCE ASSOCIATED WITH THE RT ENTRANCE REGION OF A
155 KT JET. PWATS ARE ALSO PROGGED TO INCREASE TO 1.75" OR HIGHER
DURING THE AFTERNOON. WIDESPREAD SHOWERS WILL OVERSPREAD THE AREA
FROM SW TO NE DURING THE DAY. MODELS INDICATE SOME ELEVATED
INSTABILITY ACROSS SOUTHEAST PORTIONS SO WE MAINTAINED SLIGHT CHANCE
THUNDER DURING THE AFTERNOON. SOME TEMPERATURE RECOVERY IS EXPECTED
IN SOUTHERN AND COASTAL AREAS WHERE THE WINDS VEER TO E OR SE. HIGHS
WILL RANGE FROM LOWER 60S INLAND TO UPPER 60S ALONG THE ALTAMAHA
RIVER.

WIDESPREAD RAIN...LOCALLY HEAVY...WILL CONTINUE TUESDAY NIGHT INTO
WEDNESDAY AHEAD OF THE COLD FRONT. THE GFS SHOWS IMPRESSIVE PWATS
EXCEEDING 2 INCHES ALONG THE SC COAST AT 12Z WEDNESDAY. NEEDLESS TO
SAY THERE WILL BE NO SHORTAGE OF MOISTURE WITH THIS SYSTEM. THE
WEDGE WILL ERODE AT SOME POINT ON WEDNESDAY WITH STRONG WARM AIR
ADVECTION KICKING IN. TEMPS WILL PUSH INTO THE UPPER 60S TO LOWER
70S DESPITE LITTLE TO NO INSOLATION. LOW-LEVEL WIND FIELDS WILL BE
IMPRESSIVE AHEAD OF THE COLD FRONT. GEOSTROPHIC WINDS WILL INCREASE
TO 35-40 KT DURING THE DAY WHICH WILL EQUATE TO 15-25 MPH SURFACE
WINDS. SEVERE WEATHER POTENTIAL STILL LOOKS LOW DUE TO A LIMITED
OPPORTUNITY FOR BOUNDARY LAYER DESTABILIZATION AHEAD OF THE FROPA.
WE DID MAINTAIN A SLIGHT CHANCE OF TSTMS ON WEDNESDAY DUE TO SOME
ELEVATED INSTABILITY BUT THE HAIL AND DAMAGING WIND THREAT ARE
MARGINAL AT BEST.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
WIDESPREAD SHOWERS ALONG WITH A FEW THUNDERSTORMS WILL BE POSSIBLE
EARLY WEDNESDAY NIGHT BEFORE A COLD FRONT SHIFTS OFFSHORE. STRONG
COLD AIR ADVECTION BEHIND THE FRONT SHOULD RESULT IN SOME GUSTY WIND
CONDITIONS FOR PART OF THE NIGHT BEFORE ENHANCED WIND FIELDS SLIDE
OFFSHORE. CONDITIONS WILL THEN QUICKLY DRY OUT LATE WEDNESDAY NIGHT
INTO EARLY THURSDAY AS HIGH PRESSURE SETTLES OVER THE REGION BEHIND
THE DEPARTING FRONT AND PERSISTS INTO MUCH OF THE WEEKEND. OVERALL
HIGH TEMPS WILL BE COOLER ON THURSDAY...IN THE MID AND UPPER
50S...BEFORE SLIGHTLY WARMING INTO THE LOWER 60S UNDER A SOMEWHAT
ZONAL FLOW ALOFT. OVERNIGHT LOWS SHOULD RANGE IN THE MID/UPPER 30S
THURSDAY NIGHT...BEFORE WARMING INTO THE LOW/MID 40S INTO THE
WEEKEND.

&&

.AVIATION /03Z MONDAY THROUGH FRIDAY/...
KSAV...THE TERMINAL MOST LIKELY WILL REMAIN TANKED AS A STRONG
WEDGE INVERSION PERSISTS JUST OFF THE DECK AND GENERATES IFR OR
LOWER CONDITIONS THROUGH 00Z TUESDAY. IN ADDITION...MID AND UPPER
LEVEL ENERGY AND THE PROXIMITY TO A COASTAL WARM FRONT NEAR THE
GULF STREAM WILL PRODUCE PERIODS OF RAIN OR DRIZZLE.

KCHS...WHILE WE STILL HAVE LOW-END MVFR CONDITIONS EARLY ON...WITH
OVER-RUNNING RAINS TO RE-ENFORCE THE WEDGE INVERSION ATOP THE
TERMINAL...THIS WILL LEAD TO IFR OR LOWER CONDITIONS DURING THE
OVERNIGHT AND THROUGH THE BALANCE OF THE PERIOD.

EXTENDED AVIATION OUTLOOK...PERIODS OF MVFR OR LOWER CONDITIONS ARE
LIKELY WITH RAIN/SHOWERS AND LOW STRATUS THROUGH TUESDAY WHILE A
WEDGE OF HIGH PRESSURE PERSISTS INLAND AND WAVES OF LOW PRESSURE
LIFT NORTHEAST ACROSS THE NEARBY ATLANTIC. ADDITIONAL FLIGHT
RESTRICTIONS APPEAR LIKELY TUESDAY NIGHT INTO WEDNESDAY AFTERNOON AS
A STRONG COLD FRONT APPROACHES FROM THE WEST WITH SHOWERS AND
THUNDERSTORMS. LLWS WILL BE A POSSIBILITY TUESDAY NIGHT AS STRONGER
WIND FIELDS SHIFT OVER THE AREA IN ADVANCE OF THE FRONT. WINDY
CONDITIONS SHOULD ALSO OCCUR NEAR THE TIME OF FRONTAL PASSAGE ON
WEDNESDAY. VFR CONDITIONS SHOULD THEN RETURN ON THURSDAY.

&&

.MARINE...
TONIGHT...THE NE PRESSURE GRADIENT IS STILL PINCHED LATE THIS
EVENING BETWEEN A DEVELOPING WAVE OF LOW PRESSURE OFF THE SE COAST
OUT NEAR THE GULF STREAM AND AN ANCHORED WEDGE OF HIGH PRESSURE
INLAND. AS A RESULT WE HAVE EXTENDED THE SMALL CRAFT ADVISORIES
FOR ALL 0-20 NM WATERS...WHERE NE WINDS WILL PEAK AT 20-25 KT AND
GUSTY AND SEAS WILL HIT 4-6 FT. ACROSS THE OUTER GA WATERS THE
GRADIENT WILL CONTINUE TO SLACKEN AND WINDS WILL BE UNDER 20 KT.
WHILE A FEW 6 FOOTERS WILL OCCUR TO THE NW OF THE LOW...THE BULK
OF THE AMZ374 SEAS WILL BE LIMITED TO 5 FT. IN CHARLESTON HARBOR
WE WILL SHOW 15-20 KT AND 1-2 FT WAVES. AS THE ATLANTIC WAVE
DROPS A COUPLE MILLIBARS AND GATHERS A CLOSED CIRCULATION
OVERNIGHT IT WILL LIFT NE. AS THIS OCCURS WE LOOK FOR A DROP IN
WINDS AND GRADUALLY ALSO IN THE SEAS TOO. LOW STRATUS AND PERIODS
OF RAIN WILL OCCASIONALLY DROP VISIBILITIES UNDER 2 OR 3 NM
THROUGH THE NIGHT. PLUS THERE CAN ALSO BE A LITTLE THUNDER AND
LIGHTNING IN A FEW TALLER CONVECTIVE CLOUD ELEMENTS.

EXTENDED MARINE...A WEAK WEDGE OF HIGH PRESSURE TO THE NORTH WILL
MAINTAIN PERSISTENT NORTHEAST WINDS OVER THE WATERS MONDAY AND
TUESDAY WITH SEAS GENERALLY 3-4 FT BUT NO ADVISORIES ANTICIPATED.

WINDS VEER AROUND TO SOUTHERLY LATE TUESDAY NIGHT INTO WEDNESDAY AS
THE WEDGE SCOURS OUT AND A COLD FRONT APPROACHES FROM THE WEST.
STRONG LOW-LEVEL JETTING AHEAD OF THE FRONT WILL LIKELY RESULT IN
SMALL CRAFT ADVISORY CONDITIONS OVER MOST/ALL OF THE MARINE ZONES BY
DAYBREAK WEDNESDAY.

GALE FORCE WIND GUSTS REMAIN POSSIBLE AS THE COLD FRONT SHIFTS
OFFSHORE WITH STRONG COLD AIR ADVECTION BEHIND IT WEDNESDAY NIGHT. A
GALE WATCH/WARNING COULD EVENTUALLY BE NEEDED FOR A PORTION OF THE
WATERS WEDNESDAY NIGHT AS WINDS GUST TO 30-35 KT AWAY FROM THE COAST.

THURSDAY AND FRIDAY...CONDITIONS WILL IMPROVE QUICKLY OVER ALL WATERS
AS HIGH PRESSURE BECOMES CENTERED JUST SOUTH OF THE WATERS. WINDS/SEAS
SHOULD LOWER BELOW SMALL CRAFT ADVISORY LEVELS FOR ALL WATERS AROUND
DAYBREAK THURSDAY...THEN CONTINUE TO IMPROVE THROUGH LATE WEEK.

SEA FOG...LOW STRATUS AND PERIODS OF RAIN OR DRIZZLE COULD REDUCE
VSBYS OVER THE WATERS AT TIMES. POTENTIAL FOR ACTUAL SEA FOG TO
DEVELOP TUESDAY AND PERSIST INTO WEDNESDAY EVENING AS 60 PLUS
DEW POINTS MOVE OVER THE COOL SHELF WATERS FROM THE SOUTH.

&&

.TIDES/COASTAL FLOODING...
GIVEN THE PERIGEAN SPRING TIDES AND PERSISTENT NORTHEAST WINDS THERE
IS AN INCREASING RISK FOR SHALLOW COASTAL FLOODING WITH THE MORNING
HIGH TIDES MONDAY AND TUESDAY. COASTAL FLOOD ADVISORIES MAY BECOME
NECESSARY.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 4 AM EST MONDAY FOR AMZ350-352.
     SMALL CRAFT ADVISORY UNTIL 1 AM EST MONDAY FOR AMZ354.

&&

$$

NEAR TERM...
SHORT TERM...JRL
LONG TERM...DPB
AVIATION...
MARINE...
TIDES/COASTAL FLOODING...






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