AP-SC--CHS-SC S Area Forecast Discussion, SC

000

FXUS62 KCHS 151511

AFDCHS

AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE CHARLESTON SC

1111 AM EDT WED JUL 15 2015

.SYNOPSIS...

AN INLAND TROUGH OF LOW PRESSURE WILL PERSIST THROUGH THIS EVENING

BEFORE A WEAK COLD FRONT MOVES INTO SOUTHEAST SOUTH CAROLINA LATE

TONIGHT INTO THURSDAY. THE FRONT WILL THEN STALL AND DISSIPATE

THROUGH THE END OF THE WEEK. LOW PRESSURE SHOULD THEN REDEVELOP

INLAND NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...

A PROGRESSIVE UPPER DISTURBANCE IS CURRENTLY MOVING OFF THE

DELMARVA THIS MORNING WITH CONSIDERABLE SUBSIDENCE DUE TO NEGATIVE

VORTICITY ADVECTION OVER SOUTHERN SC. WE ARE ALSO SEEING DRIER AIR

MOVING INTO SOUTHERN SC WHICH WILL CONTINUE TO MIX DOWN TO THE

SURFACE AS TEMPS RISE. MEANWHILE A WEAK TROUGH AND MOISTURE

GRADIENT EXISTS ACROSS SOUTHEAST GA WITH MOST LOCALES SHOWING MID

70S DEWPOINTS. WE EXPECT LITTLE TO NO UPSTREAM SHORTWAVE ENERGY TO

DRIVE THROUGH THE AREA TODAY. INSTEAD...A SEA BREEZE PINNED NEAR

THE SC COAST AND CONVERGENCE IN THE WEAK TROUGH OVER SOUTHEAST GA

WILL ALLOW ISOLATED TO SCATTERED TSTMS TO DEVELOP THIS AFTERNOON.

WE EXPECT THE BEST COVERAGE TO BE FARTHER SOUTH THOUGH BOUNDARY

INTERACTIONS ACROSS COASTAL SC MAY STILL ALLOW FOR DECENT COVERAGE

BY LATE IN THE DAY.

MID-LEVEL TEMPS AND LAPSE RATES ARE RATHER POOR THOUGH SURFACE-

BASED CAPES INCREASE TO 3000 J/KG PER MODIFIED KCHS 12Z SOUNDING.

850 MB WINDS DECREASE TO AROUND 20 KT THIS AFTERNOON THOUGH THERE

WILL STILL BE ENOUGH FLOW TO SUPPORT SOME MULTI-CELL CONVECTION.

DOWNDRAFT CAPE OF 1000-1500 J/KG BASED ON MODEL GUIDANCE INDICATES

A DAMAGING WIND THREAT WITH THE STRONGEST STORMS. IT IS DIFFICULT

TO PIN DOWN THE EXACT COVERAGE OF SEVERE TSTMS TODAY SINCE WE ARE

NOT WORKING WITH A SYNOPTIC SCALE FEATURE...INSTEAD DEPENDING

MAINLY ON THE SEA BREEZE AND BOUNDARY COLLISIONS. GIVEN THAT THE

SPC DAY 1 SLIGHT RISK STILL INCLUDES THE ENTIRE AREA WE WILL

MAINTAIN MENTION IN THE HAZARDOUS WEATHER OUTLOOK.

TONIGHT...A WEAK COLD FRONT WILL SAG INTO THE NORTHERN HALF OF

SOUTH CAROLINA AND A FEW SHOWERS OR TSTMS COULD LINGER INTO THE

NIGHT SOUTH OF A LINE FROM SYLVANIA TO CHARLESTON AHEAD OF THIS

WEAK BOUNDARY. WE GENERALLY DIMINISHED POPS TO 20 PERCENT OR LESS

AFTER MIDNIGHT WITH PARTLY CLOUDY SKIES.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY/...

THURSDAY...THE BULK OF H5 SHORTWAVE ACTIVITY WILL BE WELL OFFSHORE

ALONG WITH THE PRIMARY AREA OF LOW PRESSURE AT THE SFC. HOWEVER...A

WEAK AREA OF LOW PRESSURE SHOULD LINGER OVER SOUTHEAST GEORGIA NEAR

THE VICINITY OF A STALLED AND/OR DISSIPATING FRONT. SFC HEATING AND

MOISTURE LEVELS NEAR THE LOW SHOULD BE SUFFICIENT TO SUPPORT A

SLIGHT CHANCE TO CHANCE OF SHOWERS/THUNDERSTORMS DURING PEAK

HEATING...WITH GREATEST COVERAGE EXPECTED OVER SOUTHEAST GEORGIA.

HOWEVER...THE THREAT OF STRONGER THUNDERSTORMS WILL BE LOWER THAN

PREVIOUS DAYS GIVEN A LACK OF MID/UPPER LVL FORCING. OVERALL...HIGH

TEMPS SHOULD RANGE IN THE LOW TO MID 90S.

FRIDAY AND SATURDAY...A LARGE MID LVL RIDGE OF HIGH PRESSURE OVER

THE CENTRAL UNITED STATES WILL EXPAND EASTWARD OVER THE REGION THIS

WEEKEND WHILE WEAK SFC LOW PRESSURE GRADUALLY SHIFTS SOUTH/SOUTHEAST

OF THE AREA. SUBSIDENCE FROM THE DEEP LAYER RIDGE SHOULD LIMIT THE

COVERAGE OF CONVECTION FOR MOST AREAS DESPITE SFC TEMPS HEATING INTO

THE LOW/MID 90S EACH AFTERNOON. HOWEVER...THE FORECAST STILL CALLS

FOR A SLIGHT CHANCE TO CHANCE OF SHOWERS AND THUNDERSTORMS DURING

PEAK HEATING HOURS...WITH GREATEST COVERAGE NEAR AFTERNOON SEABREEZES

AND IN SOUTHEAST GEORGIA CLOSER TO THE VICINITY OF LOW PRESSURE.

&&

.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...

A SLIGHT CHANCE TO CHANCE OF SHOWERS AND THUNDERSTORMS WILL REMAIN

IN THE FORECAST EACH DAY AS A PIEDMONT TROUGH REDEVELOPS INLAND

EARLY NEXT WEEK. GREATER PRECIP CHANCES SHOULD OCCUR BY TUESDAY AS

SOUTHERLY FLOW OCCURS OVER THE AREA WHILE A DEEP LAYERED RIDGE

RETROGRADES WESTWARD IN RESPONSE TO MID LVL TROUGHING OVER THE

EASTERN CONUS. HIGH TEMPS SHOULD RANGE IN THE LOW TO MID 90S EACH

AFTERNOON. OVERNIGHT LOWS SHOULD RANGE IN THE MID TO UPPER 70S.

&&

.AVIATION /15Z WEDNESDAY THROUGH SUNDAY/...

VFR CONDITIONS WILL PREVAIL THROUGH TONIGHT. POTENTIAL FOR AT

LEAST ISOLATED SHOWERS AND TSTMS THROUGH THE TAF CORRIDOR AFTER

MID AFTERNOON TODAY INTO EARLY EVENING. WE HAVE INCLUDED VCTS AT

KSAV AFTER MID AFTERNOON GIVEN THE PROXIMITY TO DEEPER MOISTURE

BUT A FEW TSTMS MAY ALSO BE AROUND THE KCHS TERMINAL AFTER 19-20Z.

EXTENDED AVIATION OUTLOOK...VFR CONDITIONS WILL PREVAIL INTO THE

WEEKEND...BUT BRIEF FLIGHT RESTRICTIONS WILL BE POSSIBLE WITH

AFTERNOON SHOWERS AND/OR THUNDERSTORMS.

&&

.MARINE...

A 25-30 KT LOW LEVEL JET WILL MAINTAIN GUSTY WINDS ACROSS THE

CHARLESTON NEARSHORE WATERS AND GA OFFSHORE THROUGH

TODAY...POTENTIALLY LINGERING INTO THIS EVENING OVER THE SC

WATERS.

OTHERWISE...SW FLOW WILL WEAKEN AS A COLD FRONT APPROACHES LATER

TONIGHT. SEAS THROUGH TONIGHT WILL RANGE FROM 4-5 FT OFFSHORE TO

2-4 FT WITHIN 20 NM.

THURSDAY THROUGH MONDAY...A WEAK COLD FRONT SHOULD SHIFT OVER THE

WATERS EARLY THURSDAY...WITH POSSIBLY A FEW STRONGER THUNDERSTORMS.

HOWEVER...WINDS/SEAS ARE EXPECTED TO REMAIN WELL BELOW SMALL CRAFT

ADVISORY LEVELS OUTSIDE CONVECTION. WINDS/SEAS WILL CONTINUE TO

WEAKEN/SUBSIDE THROUGH THE WEEKEND AS HIGH PRESSURE SETTLES OVER

THE COASTAL WATERS BEFORE GRADUALLY INCREASING AS LOW PRESSURE

DEVELOPS INLAND EARLY NEXT WEEK. IN GENERAL...SOUTHERLY WINDS WILL

BECOME EASTERLY AND REMAIN AT OR BELOW 10 KTS INTO THE

WEEKEND...THEN INCREASE TO 10-15 KTS EARLY NEXT WEEK. SEAS WILL

RANGE BETWEEN 2-4 FT THURSDAY...THEN SUBSIDE TO 1-3 FT THIS

WEEKEND AND EARLY NEXT WEEK.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...

GA...NONE.

SC...NONE.

MARINE...SMALL CRAFT ADVISORY UNTIL 4 PM EDT THIS AFTERNOON FOR AMZ374.

SMALL CRAFT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR AMZ350.

&&

$$

SYNOPSIS...

NEAR TERM...JRL

SHORT TERM...DPB

LONG TERM...DPB

AVIATION...

MARINE...DPB

Delivered by Weather Underground Inc. Wed Jul 15 2015 11:11AM EDT