Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 311707
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
107 PM EDT FRI JUL 31 2015

.SYNOPSIS...
A WEAK COLD FRONT WILL APPROACH THE AREA TODAY AND 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/...
NO SIGNIFICANT CHANGES TO THE PREVIOUS FORECAST. SHOWERS AND
THUNDERSTORMS FIRING INLAND ALONG THE WEAK COLD FRONT/TROUGH NEAR
INTERSTATE 16. EXPECT CONVECTION TO CONTINUE TO FIRE THERE AND
NORTHWARD UP THE SC COAST AS THE SEA BREEZE GETS GOING. SO FAR
STORMS HAVE ENOUGH MOTION SO THE FLOOD RISK IS LOW BUT THIS MIGHT
CHANGE LATER AS STORMS TRY TO INTENSIFY AND BECOME MULTI-CELLULAR
AND POSSIBLY TRAIN OVER THE SAME AREAS ALONG BOUNDARIES.

LOW-LEVEL SOUTHERLY FLOW AND UPPER LEVEL NORTHERLY FLOW WILL LEAD
TO SLOW- MOVING STORMS AND WITH PWAT VALUES UNSEASONABLY HIGH OVER
2 INCHES THERE COULD BE SOME HEAVY RAINFALL. MAIN CONCERN THIS
AFTERNOON WILL BE LOCALIZED FLOODING ALTHOUGH CANNOT RULE OUT A
FEW STORMS CAPABLE OF PRODUCING WET MICROBURSTS. A FEW SEVERE
STORMS WILL BE POSSIBLE WITH DAMAGING WINDS THE MAIN HAZARD /OTHER
THAN FREQUENT CLOUD TO GROUND LIGHTNING/ AS THE MODIFIED CHS
SOUNDING FOR A WORST CASE SCENARIO OF TEMPERATURES IN THE MID 90S
AND DEWPOINTS IN THE MID 70S YIELDS OVER 3000 J/KG OF CAPE AND
DOWNDRAFT CAPE OF 1400 J/KG. WE WILL MENTION A LOCALIZED EXCESSIVE
RAIN POTENTIAL THIS AFTERNOON AND EVENING IN OUR HAZARDOUS WEATHER
OUTLOOK AND CONSIDER INCLUDING MENTION IN THE FORECAST.
FORTUNATELY TIDES ARE LOW THIS AFTERNOON SO THAT SHOULD HELP
MINIMIZE FLOODING IN COASTAL URBAN LOCALES LIKE DOWNTOWN
CHARLESTON/SAVANNAH. HIGHS IN THE LOWER TO MID 90S INLAND WITH
UPPER 80S AT THE COAST.

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 /18Z FRIDAY THROUGH WEDNESDAY/...
VFR CONDITIONS ARE EXPECTED TO PREVAIL OUTSIDE OF CONVECTION THROUGH
18Z SATURDAY. SHOWERS AND THUNDERSTORMS LIKELY THROUGH ABOUT
21Z...WHICH WILL BE CAPABLE OF HEAVY RAINFALL AND GUSTY WINDS.
EXPECT SOME SHOWERS AND A FEW TSTMS TO LINGER TONIGHT AS A WEAK
COLD FRONT AND DEEP MOISTURE LINGER OVER THE AREA. CAN/T RULE OUT
SOME STRATUS AND/OR LIGHT FOG AT THE TERMS TOWARD DAYBREAK BUT
CHANCES TOO LOW TO MENTION ATTM.

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...RJB
SHORT TERM...JRL
LONG TERM...JRL
AVIATION...RJB
MARINE...JRL
TIDES/COASTAL FLOODING...



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