Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 160139
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
939 PM EDT MON SEP 15 2014

.SYNOPSIS...
A STATIONARY FRONT WILL CONTINUE TO DISSIPATE OVER THE AREA
TONIGHT. A STRONG COLD FRONT WILL APPROACH FROM THE NORTHWEST
TUESDAY AND PUSH THROUGH THE REGION LATE WEDNESDAY. A STRONG
INLAND WEDGE OF HIGH PRESSURE WILL THEN PREVAIL IN WAKE OF THE
FRONT INTO NEXT WEEKEND.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
DISCONTINUED THE FLASH FLOOD WATCH FOR SC COUNTIES FROM COLLETON
TO THE SANTEE RIVER.

LATE MONDAY EVENING...ADJUSTED FORECASTS TO ACCOUNT FOR
ONGOING/EXPECTED RADAR TRENDS. FOR THE NEXT FEW HOURS...SCATTERED
SHOWERS/ISOLATED THUNDERSTORMS DEVELOPING/DISSIPATING ALONG VARIOUS
MESOSCALE BOUNDARIES FROM COLLETON COUNTY NE TO THE SANTEE RIVER
SHOULD GRADUALLY DIMINISH IN COVERAGE. ALSO...SCATTERED TO LOCALLY
NUMEROUS SHOWERS/ISOLATED THUNDERSTORMS SHOULD PUSH THROUGH AREAS
MAINLY SOUTH OF I-16. HERE TOO...COVERAGE OF CONVECTION SHOULD
GRADUALLY WIND DOWN OVERNIGHT. ELSEWHERE...EXPECTED NOTHING MORE
THAN ISOLATED SHOWERS/THUNDERSTORMS.

OVERNIGHT...HIGHEST POPS CAPPED AT 30 TO 50 PERCENT SHOULD SHIFT
INTO AREAS ALONG/EAST OF I-95 AND ADJACENT COASTAL WATERS AS LOW
LEVEL WINDS TURN TOWARD THE WEST.

GIVEN PWATS AROUND 2.3 INCHES AS DEPICTED BY THE 00Z KCHS RAOB...
LOCALLY HEAVY RAINFALL IS STILL POSSIBLE IN ANY
SHOWERS/THUNDERSTORMS TONIGHT. HOWEVER...THE THREAT FOR FLASH
FLOODING HAS DIMINISHED.

STRATUS COULD ONCE AGAIN DEVELOP AND LOWER TO THE SURFACE LATE
TONIGHT...THUS FORECASTS INCLUDE AREAS OF FOG.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/...
TUESDAY...THE PATTERN ALOFT WILL FEATURE A BROAD TROUGH OVER THE
EASTERN STATES. A STRONG BUT DAMPENING SHORT WAVE WILL LIFT THROUGH
NEW ENGLAND...WHILE A SECOND AND ALSO WEAKENING SHORT WAVE HEADS
INTO OUR AREA WITHIN THE WEST-NW FLOW. THIS FEATURE LOOKED TO BE
FOUND IN THE MID-MS VALLEY AS OF LATE MONDAY. AT THE SURFACE THE
PRESSURE PATTERN BECOMES RATHER NEBULOUS AS A PRE-FRONTAL TROUGH
ALIGNED MAINLY NE-SW SETS UP ACROSS THE REGION AHEAD OF OUR MID WEEK
COLD FRONT. THERE IS A SLIGHT DECREASE IN MOISTURE PROFILES...WITH
PWATS TO FALL TO AROUND 2 INCHES. ALTHOUGH NOT AS MUCH AS RECENT
DAYS...IT IS STILL ABOVE THE 75TH PERCENTILE FOR MID-SEPTEMBER.
THERE IS LARGE SCALE FORCING ASSOCIATED WITH THE RIGHT ENTRANCE
REGION TO THE UPPER JET AND VARIOUS BOUNDARY INTERACTIONS THAT
DEVELOP FOR THE AFTERNOON HOURS. WE HAVE SCATTERED TO LIKELY POPS
ACROSS THE ENTIRE REGION...WITH THE GREATEST COVERAGE FROM NEAR THE
SAVANNAH AREA TO MCINTOSH AND LONG COUNTIES WHERE THE SEA BREEZE
WILL BE MOST ACTIVE. THERE IS A LITTLE BETTER STORM MOTION THAN
PREVIOUS DAYS...BUT NOT ENOUGH TO PREVENT AT LEAST LOCALLY HEAVY
RAINS FROM DEVELOPING. COVERAGE IS NOT ENOUGH FOR A FLASH FLOOD
WATCH BUT WILL MENTION POTENTIAL FLOODING RAINS IN THE HAZARDOUS
WEATHER OUTLOOK. WITH A LITTLE DRIER AIR ALOFT...SLIGHTLY COOLER MID
LEVEL AIR AND BETTER VERTICAL WIND FIELDS THAN OF LATE...THERE IS A
VERY LOW RISK OF SOME GUSTY WINDS WHERE THE BOUNDARY
MERGERS/INTERACTIONS/COLLISIONS OCCUR. ALTHOUGH THE DAY WILL START
WITH LOW STRATUS AND PATCHY FOG...WHICH WILL LIFT INTO A FAIRLY
EXTENSIVE CUMULUS FIELD...DOWNSLOPE TRAJECTORIES THROUGHOUT MUCH OF
THE TROPOSPHERE WILL BOOST TEMPS INTO THE UPPER 80S PRIOR TO THE
ONSET OF THE CONVECTIVE RAINS.

WEDNESDAY THROUGH THURSDAY...OUR NEXT COLD FRONT WILL LIMP TOWARD
THE AREA WEDNESDAY AS IT BECOMES ORIENTED SOMEWHAT PARALLEL TO THE
FLOW ALOFT...AND WAITS FOR THE PUSH FROM CANADIAN HIGH PRESSURE LATE
WEDNESDAY INTO THURSDAY TO KICK THE FRONT THROUGH. MID LEVEL
IMPULSES WILL FORM AT LEAST ONE WAVE OF LOW PRESSURE ALONG THE
FRONT...WHICH ALSO ACTS TO SLOW IT DOWN SOME ON WEDNESDAY. BUT AS
THE MID/UPPER PATTERN AMPLIFIES FURTHER WEDNESDAY NIGHT AND
THURSDAY...THE WAVE AND FRONT WILL PUSH OFFSHORE. IT IS WORTH NOTING
THAT THERE IS NO SIGNS OF ANY TROPICAL CHARACTERISTICS WITH THIS
FEATURE AT THIS TIME. WE NEED TO HOLD ONTO SLIGHT CHANCE AND CHANCE
POPS IN ADVANCE OF THE COLD FRONT WEDNESDAY...WITH PROBABLY NO MORE
THAN SLIGHT CHANCE POPS FOR THURSDAY IN RESPONSE TO WEAK LOW LEVEL
CONVERGENCE OFF THE ATLANTIC. THE COOL AIR LAGS FAR BEHIND THE FRONT
WEDNESDAY...WHICH WILL ALLOW FOR TEMPS TO STILL PEAK IN THE UPPER 80S
TO AROUND 90. COOLER AIR THEN MOVES IN WITH THE BEST COOL ADVECTION
WEDNESDAY NIGHT...WITH LOWS DOWN INTO THE MID AND UPPER 60S AWAY
FROM THE BARRIER ISLANDS. THURSDAY WILL BE A REFRESHING CHANGE IN
AIR MASS WITH LOWER DEW POINTS AND HIGHS ACTUALLY DOWN BELOW
CLIMATOLOGICAL NORMS.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
A WEDGE OF SURFACE HIGH PRESSURE WILL BECOME ESTABLISHED INLAND
LATE WEEK INTO THE WEEKEND. THE UPPER LEVEL PATTERN GRADUALLY
WEAKENS DURING THIS TIME FRAME...AS THE TROUGH ALONG THE EAST
COAST DIMINISHES. THE BEST RAIN CHANCES WILL BECOME INCREASINGLY
CONFINED TO THE IMMEDIATE COASTLINE AND MARINE ZONES...AS DEEPER
MOISTURE AND FORCING REMAIN OFFSHORE ALONG THE PERIPHERY OF THE
INLAND WEDGE. SOLID NORTHEAST FLOW WILL SUPPORT NOTABLY COOLER
CONDITIONS THROUGH THE PERIOD. HIGH TEMPERATURES WILL ONLY REACH
THE LOW 80S FRIDAY AND SATURDAY...WHILE LOW TEMPERATURES FALL INTO
THE LOW TO MID 60S. AS THE WEDGE OF HIGH PRESSURE WEAKENS SUNDAY
AND MONDAY...EXPECT TEMPERATURES TO RETURN TOWARD SEASONAL NORMALS.

&&

.AVIATION /01Z TUESDAY THROUGH SATURDAY/...
MAINLY VFR UNTIL AFTER 06Z. THEN...LOW LEVEL MOISTURE WILL
SUPPORT AT LEAST MVFR/IFR CONDITIONS LATE TONIGHT INTO TUESDAY
MORNING...AND LIFR CONDITIONS ARE POSSIBLE. AS USUAL...THE TIMING
AND DEGREE OF DETERIORATION REMAIN UNCERTAIN... AND AMENDMENTS/
ADJUSTMENTS COULD BE REQUIRED WITHIN SUBSEQUENT FORECASTS
OVERNIGHT. THEN...THUNDERSTORMS ARE AGAIN EXPECTED IN THE VICINITY
OF THE TERMINALS TUESDAY AFTERNOON...AND DIRECT IMPACTS ARE LIKELY
AT KSAV.

EXTENDED AVIATION OUTLOOK...PERIODIC FLIGHT RESTRICTIONS POSSIBLE
IN OCCASIONAL SHRA AND/OR TSRA DURING THE AFTERNOON AND EARLY
NIGHT TIME PERIODS...AND IN LATE NIGHT/MORNING LOW STRATUS AND/OR
FOG.

&&

.MARINE...
OVERNIGHT...A WEAK PRESSURE GRADIENT WILL SUPPORT WINDS 10 KT
OR LESS. WIND DIRECTION WILL CHANGE FROM EAST TO SOUTH...THEN WILL
TURN TO THE WEST TOWARD DAYBREAK. THUNDERSTORMS AND ASSOCIATED
OUTFLOW WILL ALSO ALTER LOCAL WIND DIRECTION/SPEED. SEAS 1 TO 2 FT
WILL PREVAIL.

TUESDAY...WEAK OFFSHORE FLOW IN THE MORNING WILL SHIFT AROUND TO
ONSHORE WITH THE SEA BREEZE INFLUENCES FOR THE AFTERNOON. SMALL BUT
LONG PERIOD SWELLS AROUND 15-16 SECONDS FROM HURRICANE EDOUARD MAY
ARRIVE BY LATE IN THE DAY...BUT WITH SIGNIFICANT WAVE HEIGHT NO MORE
THAN 2 OR 3 FT. CONDITIONS AGAIN FAVOR WATERSPOUTS DURING THE
MORNING HOURS...ONCE ANY LOW STRATUS AND/OR FOG IN CHARLESTON HARBOR
AND THE NEARBY ATLANTIC WATERS LIFTS/DISSIPATES.

WEDNESDAY THROUGH THURSDAY...A COLD FRONT AND WAVE OF LOW PRESSURE
WILL PROGRESS INTO AND THROUGH THE WATERS DURING THE MID WEEK
PERIOD. LIGHT TO GENTLE BREEZES IN ADVANCE OF THE FRONT WILL GIVE
WAY TO MODERATE BREEZES AFTER BEHIND THE FRONT. SEAS WILL BE
COMPRISED MAINLY OF LONG PERIOD SWELLS FROM DISTANT
EDOUARD...AVERAGING AROUND 2-4 FT WITHIN 20 NM AND 3-5 FT FURTHER
OUT.

FRIDAY THROUGH SUNDAY...THE PRESSURE GRADIENT WILL BECOME QUITE
PINCHED AS THE COLD FRONT STALLS AND BECOMES STATIONARY TO OUR SE
AND A STRONG INLAND WEDGE OF HIGH PRESSURE DEVELOPS. A LONG ONSHORE
FETCH AND STRONGER NE WINDS LOOK TO SUPPORT THE ISSUANCE OF SMALL
CRAFT ADVISORIES.

RIP CURRENTS...LONG PERIOD SWELL FROM TROPICAL CYCLONE EDOUARD COULD
START ARRIVING AT THE BEACHES LATE TUESDAY AND CONTINUE INTO
THURSDAY. FOR NOW THERE DOESN/T APPEAR TO BE MUCH MORE THAN ABOUT 2
FT SWELL THAT MAKES IT TO THE BEACHES BY LATE TUESDAY...SO WILL KEEP
THE RIP CURRENT RISK LOW. HOWEVER...SLIGHTLY LARGER SWELLS AROUND 3
FT MIGHT OCCUR WEDNESDAY INTO THURSDAY...AND THIS MAY LEAD TO AN
ENHANCED RISK OF RIP CURRENTS.

FOR FRIDAY THROUGH SUNDAY WE LOSE THE SWELL FROM EDOUARD...BUT
STRONGER NE WINDS WILL OCCUR AND THIS MAY ALLOW FOR AN ELEVATED RISK
OF RIP CURRENTS TO AGAIN PREVAIL AT AREA BEACHES.

&&

.HYDROLOGY...
ANOTHER ROUND OF SLOW-MOVING SHOWERS AND THUNDERSTORMS WITH A
THREAT FOR LOCALLY EXCESSIVE RAINFALL IS POSSIBLE MAINLY
ALONG/SOUTH OF INTERSTATE 16 TUESDAY.

&&

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

&&

$$

NEAR TERM...SPR
SHORT TERM...
LONG TERM...
AVIATION...SPR
MARINE...SPR
HYDROLOGY...






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