Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 310829
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
429 AM EDT FRI JUL 31 2015

.SYNOPSIS...
A WEAK COLD FRONT WILL SETTLE OVER THE REGION THIS WEEKEND...
SHIFTING SOUTHEAST AS HIGH PRESSURE BUILDS IN EARLY NEXT WEEK. AN
INLAND TROUGH WILL THEN DEVELOP BY LATE WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
PRE-DAWN...DEEP MOISTURE WAS ENTRENCHED ACROSS THE FORECAST AREA
EARLY THIS MORNING WITH RECENT ANALYSIS PAINTING 2.2 TO 2.3 INCH
PWATS. SURFACE MOISTURE CONVERGENCE WAS WEAK AND MOST OF THE
NOCTURNAL CONVECTION WAS CONFINED TO THE WATERS WHERE LOW LEVEL
SPEED CONVERGENCE AND UPPER LEVEL DIFLUENCE RESULTED IN SCATTERED
SHOWERS AND A FEW TSTMS MAINLY NORTH OF THE SAVANNAH RIVER. THERE
HAS BEEN SOME DOWNPOURS ON SOME OF BEACHES OVERNIGHT AS WELL AS IN
COASTAL BEAUFORT COUNTY. A BACKDOOR FRONT IS EXPECTED TO SAG INTO
THE SOUTH CAROLINA MIDLANDS BY DAWN BUT WE HAVE MAINTAINED ONLY
SLIGHT CHANCE POPS MOST AREAS BASED ON LATEST MESOSCALE TRENDS.

DESPITE THE PRESENCE OF THE DEEP MOISTURE AND AN APPROACHING
FRONT EARLY TODAY...PROXIMITY SOUNDINGS ACROSS THE FORECAST AREA
INDICATE A CAP AROUND 2C-3C THROUGH MID MORNING. THERE SHOULD BE
ENOUGH MORNING INSOLATION TO QUICKLY ERODE THIS CAP PRIOR TO
MIDDAY. DURING THE LATE MORNING TO EARLY AFTERNOON HOURS...
SCATTERED CONVECTION SHOULD BEGIN TO DEVELOP IN THE VERY MOIST AND
MODERATELY UNSTABLE ENVIRONMENT. HIGH RESOLUTION OUTPUT SUGGESTS
INITIATION WILL LIKELY BE ALONG THE SEA BREEZE CORRIDOR ALONG AND
NORTH OF THE SAVANNAH RIVER AND PERHAPS WEST ALONG THE I-16
CORRIDOR THROUGH MID AFTERNOON. SUBTLE DIFFERENTIAL HEATING
CHANGES COULD ALTER THESE INITIATION TRENDS. THERE ARE ALSO HINTS
THAT THERE COULD BE LESSER CHANCES OF SHOWERS AND TSTMS ALONG OUR
FAR NW TIER OF ZONES UNTIL PERHAPS LATE AFTERNOON WHEN COVERAGE
INCREASES NEAR THE WEAK FRONTAL SURFACE TROUGH ACROSS THE CSRA AND
EASTERN MIDLANDS. CONVECTIVE TEMPS ARE IN THE LOW 90S AND WE
MAINTAINED HIGH TEMPS TODAY IN THE LOWER TO MID 90S MOST PLACES.

THE MAIN CONVECTIVE HAZARD TODAY WILL LIKELY BE LOCALLY TORRENTIAL
DOWNPOURS AND NOT SO MUCH SEVERE WEATHER. ISOLATED DAMAGING WET
MICROBURSTS ARE CERTAINLY POSSIBLE...HOWEVER THE DEEP MOISTURE
PROFILES LOOK RATHER UNFAVORABLE OVERALL. THERE SHOULD BE PLENTY
OF MULTICELL CONVECTION AROUND BY MID TO LATE AFTERNOON WITH A
WEAK STEERING FLOW. WHILE SOME CONVECTION WILL BE RAINING
OUT/DISSIPATING....OTHER CLUSTERS WILL BE EXPANDING FROM COMPLEX
BOUNDARY INTERACTIONS. WE WILL MENTION A LOCALIZED EXCESSIVE RAIN
POTENTIAL THIS AFTERNOON AND EVENING IN OUR HAZARDOUS WEATHER
OUTLOOK.

UNSETTLED WEATHER COULD LAST INTO THE EVENING AND PERHAPS INTO THE
OVERNIGHT WITH THE INLAND FRONTAL TROUGH AND SPEED CONVERGENCE
ALONG THE SOUTH CAROLINA COAST. WE MAINTAINED CHANCE POPS AND ONCE
AGAIN THERE MAY BE SOME DOWNPOURS FROM WARMER PROCESS CONVECTION
TRENDS OVERNIGHT.

&&

.SHORT TERM /SATURDAY THROUGH MONDAY/...
THERE REMAINS SOME DISAGREEMENT BETWEEN THE GFS AND ECMWF WITH
REGARD TO HOW MUCH PRECIPITATION WILL DEVELOP OVER THE WEEKEND. AN
EAST COAST TROUGH WILL REMAIN IN PLACE WHILE A WEAK FRONT SITS ALONG
OUR COAST. THE 00Z GFS CAME IN DRIER WITH 1.5" PWATS SPREADING
ACROSS SOUTHERN SC AND FAR EASTERN GA BY SATURDAY AFTERNOON. THE
ECMWF RETAINS A BIT MORE LOW-LEVEL MOISTURE OVER COASTAL SECTIONS
WHICH WOULD SUPPORT MORE SEA BREEZE CONVECTION BOTH DAYS. GIVEN OUR
ONGOING WETTER FORECAST...WE TRENDED POPS DOWNWARD WITH THIS PACKAGE
BUT MAINTAINED 50-60 PERCENT ACROSS FAR SOUTHERN GA SATURDAY WITH 40-
50 FARTHER NORTH. SUNDAY DEFINITELY LOOKS DRIER REGARDLESS OF MODEL
SO WE PUSHED VALUES DOWN TO 20-30 PERCENT RANGE. MONDAY COULD BE
COMPLETELY DRY BASED ON THE GFS...BUT SINCE THE ECMWF STILL HANGS
ONTO MORE MOISTURE WE KEPT CHANCE POPS GOING FOR NOW.

HIGH TEMPS WILL BE IN THE LOWER 90S EACH DAY WITH LOWS IN THE LOW TO
MID 70S.

&&

.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
THE UPPER RIDGE BRIEFLY REBUILDS ON TUESDAY BEFORE A WEAK UPPER
TROUGH REDEVELOPS OVER THE EASTERN UNITED STATES MID TO LATE WEEK.
LOW-LEVEL MOISTURE WILL RETURN IN EARNEST LATE WEEK INTO THE WEEKEND
WITH PWATS BACK ABOVE 2 INCHES. UPPER SHORTWAVE ENERGY AND AN
APPROACHING COLD FRONT WILL BRING A RETURN TO HIGHER RAIN CHANCES
DURING THE PERIOD.

&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
VFR CONDITIONS ARE EXPECTED TO PREVAIL OUTSIDE OF CONVECTION THROUGH
06Z SATURDAY. SHOWERS AND THUNDERSTORMS BECOME LIKELY ACROSS THE
AREA THIS AFTERNOON AND HAVE MAINTAINED MENTIONS OF VCTS/CB IN
THE TAF/S AT THIS TIME. SOME OF SHOWERS AND STORMS COULD PRODUCE
LOCALLY HEAVY DOWNPOURS WHICH MAY BRIEFLY RESTRICT VSBYS LATER
TODAY IN THE COASTAL CORRIDOR.

EXTENDED AVIATION OUTLOOK...MOSTLY VFR. MAINLY AFTERNOON/EVENING
SHOWERS AND THUNDERSTORMS WILL IMPACT THE TERMINALS. LOW CHANCES FOR
MVFR CEILINGS OR SHALLOW FOG SUNDAY AND MONDAY MORNINGS AROUND
DAYBREAK.

&&

.MARINE...
THE APPROACHING COLD FRONT WILL LIKELY HANG UP TO THE NORTH OF
THE WATERS THROUGH TONIGHT. A MAINLY SW FLOW WILL SEE SOME
SURGING BY THIS EVENING OVER THE GEORGIA WATERS. WE BUMPED WIND
SPEED CLOSER TO 15 KT WITH 15 TO 20 KT OVER THE OUTER WATERS.
WE DO NOT THINK THE SURGE WILL BE TOO STRONG ALONG THE CHARLESTON
COAST GIVEN THE STALLED FRONT JUST OFF TO THE NORTH. OF
COURSE...CONVECTION COULD SCRAMBLE THE SYNOPTIC FLOW TONIGHT
COMPLICATING THE FORECAST. SEAS WILL AVERAGE 2-3 FT WITH 4 FT SEAS
WELL OFF THE COAST LATER TONIGHT.

MAINLY SOUTH TO SOUTHWEST WINDS WILL PERSIST OVER THE WATERS
SATURDAY THROUGH THE MIDDLE OF NEXT WEEK. THE STRONGEST WINDS WILL
OCCUR AT NIGHT DURING NOCTURNAL SURGING...THOUGH SPEEDS SHOULD
GENERALLY REMAIN AT OR BELOW 20 KT. A SEA BREEZE WILL DEVELOP ALONG
THE COAST EACH AFTERNOON WITH WINDS TOPPING OUT 10-15 KT FOR SEVERAL
HOURS. SEAS WILL BE AT OR BELOW 4 FT THROUGH THE WEEKEND...
INCREASING TO AS HIGH AS 5 FT EARLY NEXT WEEK OVER OUTER PORTIONS.

&&

.TIDES/COASTAL FLOODING...
ELEVATED HIGH TIDE LEVELS WILL CONTINUE TODAY THROUGH THE UPCOMING
WEEKEND THANKS TO THE UPCOMING PERIGEAN SPRING TIDE. SHALLOW
COASTAL FLOODING IS LIKELY INTO EARLY NEXT WEEK ESPECIALLY DURING
EACH EVENING HIGH TIDE. WILL CONTINUE TO HIGHLIGHT THE SHALLOW
COASTAL FLOOD THREAT WITHIN THE HAZARDOUS WEATHER OUTLOOK. ALSO OF
NOTE...THERE IS A CHANCE THAT HEAVY RAIN COULD COINCIDE WITH THE
ELEVATED HIGH TIDES THE NEXT COUPLE OF EVENINGS. IF THIS OCCURS...
MORE SERIOUS LOCALIZED FLOODING WOULD BE POSSIBLE...PARTICULARLY
IN DOWNTOWN CHARLESTON.

&&

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

&&

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


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