Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 202027
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
427 PM EDT WED AUG 20 2014

.SYNOPSIS...
THE REGION WILL REMAIN BETWEEN ATLANTIC HIGH PRESSURE AND AN INLAND
TROUGH OF LOW PRESSURE THROUGH FRIDAY. A BACKDOOR COLD FRONT WILL
ADVANCE THROUGH THE AREA LATER THIS WEEKEND. HIGH PRESSURE WILL
BUILD FROM THE NORTH INTO THE MIDDLE OF NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
ONGOING THUNDERSTORMS ALONG THE UPPER CHARLESTON COUNTY COAST
SHOULD REMAIN LOCALIZED...BUT WILL MONITOR FOR POSSIBLE
PROPAGATION ALONG THE SEA BREEZE/TOWARD CHARLESTON HARBOR.

OTHERWISE...ISOLATED THUNDERSTORMS COULD DEVELOP AND DISSIPATE
OVER THE REGION INTO EARLY EVENING...BUT COVERAGE SHOULD REMAIN
SPARSE. OUTSIDE LOCALIZED ACTIVITY ALONG THE CHS COUNTY COAST...
CAPPED POPS AT SLIGHT CHANCE INTO EARLY THIS EVENING.

WILL CONTINUE TO MONITOR UPSTREAM TRENDS WHERE A SHORTWAVE TROUGH
CONTINUES TO INTERACT WITH A SURFACE TROUGH AXIS TO PRODUCE
MULTICELL THUNDERSTORMS WHICH WILL PUSH E/SE TOWARD INLAND/NORTHERN
COUNTIES OF THE FORECAST AREA THIS EVENING. HOWEVER...MOST
GUIDANCE SUGGESTS THAT UPSTREAM CONVECTION WILL DISSIPATE BEFORE
REACHING THE AREA.

THROUGH EARLY EVENING...MLCAPES 2500-3500 J/KG AND DOWNDRAFT CAPES
1200-1500 J/KG SUGGEST THAT ANY THUNDERSTORM COULD PRODUCE BRIEF
DAMAGING WINDS.

OVERNIGHT...EXPECT TRANQUIL CONDITIONS UNDER MAINLY CLEAR SKIES.
LOW TEMPERATURES WILL AVERAGE IN THE MID 70S MOST LOCATIONS.
ISOLATED LOWER 70S ARE POSSIBLE WELL INLAND...WHILE TEMPS ON THE
BEACHES COULD REMAIN CLOSE TO 80F THROUGH DAYBREAK.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
LIKELY SOME OF THE HOTTEST TEMPERATURES AND HEAT INDICES SO FAR THIS
SUMMER WILL OCCUR DURING THIS PERIOD. A DEEP LAYER RIDGE WILL BUILD
TO THE WEST OVER THE GULF STATES...KEEPING NORTHWEST UPPER FLOW AND
WEST-SOUTHWEST LOW LEVEL FLOW.

THURSDAY...HAVE RAISED A HEAT ADVISORY FOR THE AFTERNOON...WHICH
MATCHES WELL WITH SURROUNDING OFFICES. EXPECT HEAT INDICES TO BE
106-110...WHICH IS MARGINAL HEAT ADVISORY CRITERIA. THINK THE BEST
CHANCE FOR HEAT INDICES OF 110+ WILL BE CLOSER TO THE COAST...ALONG
THE WESTERN EDGE OF THE SEA BREEZE BOUNDARY.

RELATIVELY LIGHT PRESSURE GRADIENT WITH STRONG AFTERNOON HEATING
WILL CREATE A TROUGH OF LOW PRESSURE INLAND AND A SEA BREEZE
CIRCULATION. THE CONVERGENCE BETWEEN THESE TWO FEATURES WILL RESULT
IN ISOLATED AFTERNOON/EARLY EVENING THUNDERSTORMS. DEEP LAYER
MOISTURE IS MARGINAL...WHICH IS WHY WE ARE KEEPING SLIGHT CHANCE
POPS. HOWEVER...GIVEN HIGH TEMPS IN THE MID TO UPPER 90S...CAPE
VALUES OF 2500-3000 J/KG...WHICH COULD RESULT IN SOME STRONG TO
SEVERE STORMS. ANY CONVECTION SHOULD DIE DOWN IN THE EVENING.

FRIDAY...VERY SIMILAR TO THURSDAY WITH ISOLATED AFTERNOON CONVECTION
BETWEEN THE INLAND TROUGH OF LOW PRESSURE AND SEA BREEZE.
AGAIN...EXPECT TEMPS IN THE MID TO UPPER 90S...AND COUPLED WITH
MODERATE SURFACE HUMIDITY...COULD RESULT IN MAX HEAT INDICES OF NEAR
ADVISORY LEVELS.

SATURDAY...A WEAK BACKDOOR COLD FRONT IS SHOWN BY ALL MODELS TO
APPROACH THE NORTHERN AREA BY LATER IN THE AFTERNOON/EARLY EVENING.
TIMING IS A BIT DIFFERENT BETWEEN THE MODELS...MAKING THE POP
FORECAST UNCERTAIN. FOR NOW...HAVE GONE LOW END CHANCE NORTHERN
AREAS OF SC...CLOSER TO THE FRONT...AND SLIGHT CHANCE ELSE WHERE.
HIGH TEMPS A TAD COOLER...BUT STILL IN THE MID TO UPPER
90S...ESPECIALLY SOUTH IN THE GA ZONES. THEREFORE...HEAT INDICES
STILL AT LEAST 105-107.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
MEDIUM RANGE GUIDANCE IS IN FAIRLY GOOD AGREEMENT THROUGH MOST OF
THE LONG TERM PERIOD WITH THE OVERALL SYNOPTIC PATTERN. A BACKDOOR
COLD FRONT WILL DROP SOUTH OF THE REGION LATE IN THE WEEKEND...
RESULTING IN A MOIST NORTHEAST FLOW WHICH WILL PREVAIL INTO AT LEAST
EARLY NEXT WEEK AS HIGH PRESSURE BUILDS FROM THE NORTH. THIS WILL
BRING UNSETTLED CONDITIONS TO THE AREA...WITH A SOLID CHANCE OF
SHOWERS AND THUNDERSTORMS EXPECTED ON SUNDAY WITH PROBABILITIES THEN
GRADUALLY LOWERING FROM NORTH TO SOUTH EACH DAY THROUGH WEDNESDAY.
MUCH COOLER TEMPERATURES WILL ALSO OCCUR ONCE THE FRONT MOVES
THROUGH...WITH TEMPERATURES MODERATING CLOSER TO SEASONAL NORMALS.

&&

.AVIATION /20Z WEDNESDAY THROUGH MONDAY/...
VFR THROUGH TONIGHT. THE POTENTIAL FOR THUNDERSTORMS REMAINS LOW
EVENING. WILL AMEND TAFS IF DICTATED BY NEAR TERM CONVECTIVE
TRENDS. ANY THUNDERSTORMS THAT DEVELOP THURSDAY SHOULD HOLD OFF
UNTIL AFTER 18Z.

EXTENDED AVIATION OUTLOOK...MAINLY VFR WILL PREVAIL...WITH ONLY
ISOLATED AFTERNOON THUNDERSTORMS EXPECTED THROUGH FRIDAY WITH
BRIEF FLIGHT RESTRICTIONS POSSIBLE. SATURDAY THROUGH MONDAY BETTER
CHANCES FOR AFTERNOON CONVECTION.

&&

.MARINE...
TONIGHT...S/SW WINDS OVER SC WATERS AND W/SW WINDS OVER GA WATERS
WILL AVERAGE 15 KT OR LESS TONIGHT. AS THE LAND BREEZE DEVELOPS
LATE TONIGHT...WINDS SHOULD VEER TOWARD THE W AND SHOULD DIMINISH
TO 10 KT OR LESS. SEAS WILL RANGE FROM 1-2 FT WITHIN NEARSHORE
WATERS TO 2-4 FT BEYOND 20 NM THROUGH TONIGHT.

THURSDAY THROUGH SATURDAY...THE AREA WILL REMAIN BETWEEN A WEAK
ATLANTIC RIDGE SOUTHEAST OF THE AREA AND AN INLAND TROUGH OF LOW
PRESSURE. THIS WILL RESULT IN SOUTH-SOUTHWEST WINDS OF 15 KTS OR
LESS AND SEAS 3 FT OR LESS. BY SATURDAY...A WEAK BACKDOOR FRONT IS
EXPECTED TO APPROACH FROM THE NORTH LATE...THEN STALL SOUTH OF THE
AREA SUNDAY AND MONDAY. STRONGER NORTHEAST WINDS ARE POSSIBLE BEHIND
THE FRONT...BUT STILL EXPECTED TO REMAIN BELOW ADVISORY LEVELS AT 15 TO
20 KTS.

&&

.CLIMATE...
RECORD MAX TEMPS...

THU 8/21...
KCHS 100 SET IN 1983
KCXM 99 SET IN 1900
KSAV 101 SET IN 1902

FRI 8/22...
KCHS 100 SET IN 1983
KCXM 98 SET IN 1983
KSAV 100 SET IN 1983

LAST TIME 100 DEGREES OR HIGHER...
KCHS JUNE 21 2011
KCXM JUNE 20 2011
KSAV JULY 26 2012

&&

.EQUIPMENT...
THE CHARLESTON SC WSR-88D /KCLX/ REMAINS OUT OF SERVICE DUE TO A
SIGNIFICANT MECHANICAL FAILURE. REPAIR WORK CONTINUES AND THE
RADAR COULD BECOME OPERATIONAL BY LATE THIS WEEK OR EARLY NEXT
WEEK. UNTIL THE CHARLESTON SC RADAR RETURNS TO SERVICE...FOR
DOPPLER RADAR COVERAGE OF SOUTHEAST GEORGIA AND SOUTH COASTAL
SOUTH CAROLINA UTILIZE SURROUNDING RADARS INCLUDING KJAX...KJGX...
KVAX...KCAE AND KLTX.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...HEAT ADVISORY FROM NOON TO 7 PM EDT THURSDAY FOR GAZ087-088-
     099>101-114>119-137>141.
SC...HEAT ADVISORY FROM NOON TO 7 PM EDT THURSDAY FOR SCZ040-
     042>045-047>052.
MARINE...NONE.

&&

$$

NEAR TERM...SPR
SHORT TERM...RFM
LONG TERM...JAQ
AVIATION...RFM/SPR
MARINE...RFM/SPR
CLIMATE...
EQUIPMENT...






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