Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 292219
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
619 PM EDT FRI AUG 29 2014

.SYNOPSIS...
ATLANTIC HIGH PRESSURE WILL EXPAND WESTWARD THROUGH THE WEEKEND
AND PREVAIL THROUGH AT LEAST THE MIDDLE OF NEXT WEEK. A COLD
FRONT COULD APPROACH OR ADVANCE THROUGH THE REGION LATE NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
MODEST INSTABILITY OVER DORCHESTER AND BERKELEY COUNTIES HAS
TRIGGERED A FEW SHOWERS NEAR AND IN ADVANCE OF THE SEA
BREEZE...WHICH HAS INTERACTED WITH A PRE-EXISTING CONVERGENCE
BOUNDARY ALIGNED EAST-WEST FROM THE ATLANTIC. THIS ACTIVITY WILL
FADE WITH SUNSET AS INCREASING CINH TAKES OVER AND NOCTURNAL
COOLING SETS IN. HOWEVER...WEAK CONVERGENCE OFF THE ATLANTIC
OVERNIGHT WITHIN THE SE TO SOUTH SYNOPTIC FLOW COULD AGAIN SPUR A
FEW COASTAL SHOWERS. BUT POPS HAVE BEEN HELD TO 10 PERCENT OR LESS.

OTHERWISE FOR TONIGHT...DEEP-LAYERED RIDGING AND ITS ASSOCIATED
SUBSIDENCE WILL ALLOW DIURNAL CUMULUS OVER LAND TO DISSIPATE THIS
EVENING. A FEW NOCTURNAL MARINE CUMULUS AND/OR STRATOCUMULUS CAN
ADVECT ONSHORE AFTER MIDNIGHT...AND A LITTLE CONVECTIVE DEBRIS
CLOUDS CAN ARRIVE FROM THE SW. BUT ON AVERAGE MOSTLY CLEAR OR
PARTLY CLOUDY SKIES WILL BE SUFFICIENT.

THE AIR MASS HAS CERTAINLY MOISTEN SINCE YESTERDAY AND LOWS
TONIGHT WON/T BE AS LOW AS RECENT NIGHTS AS A RESULT. LOOK FOR
UPPER 60S AND LOWER 70S INLAND...AND MIDDLE 70S NEAR THE INTRA-
COASTAL AND ON THE BARRIER ISLANDS.

CONFIDENCE ON FOG DEVELOPMENT IS FAR FROM IDEAL GIVEN THE RECENT
SPELL OF DRY CONDITIONS...THE WARM GROUND AND MANY AREAS
STRUGGLING TO ACHIEVE THEIR CROSS-OVER TEMP. BUT FAVORABLE
CONDENSATION PRESSURE DEFICITS...FOG STABILITY INDICES DOWN IN THE
TEENS IN MANY LOCALES...PERSISTENCE FROM THIS MORNING AND THE
INCREASE IN LOW LEVEL MOISTURE SUPPORTS AT LEAST PATCHY FOG INLAND
FROM US-17. WE WILL RE-EVALUATE LATER THIS EVENING TO SEE IF WE
NEED TO HIT THE FOG IN GREATER COVERAGE AND OR AT LEAST SOME
PATCHY DENSE FOG.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
SATURDAY THROUGH MONDAY...THE REGION WILL RESIDE ON THE PERIPHERY OF
SURFACE HIGH PRESSURE CENTERED OVER THE ATLANTIC AND BENEATH DEEP
LAYERED HIGH PRESSURE ALOFT. MOISTURE WILL SLOWLY NUT STEADILY
INCREASE THROUGH THE PERIOD...BEGINNING WITH LOW LEVELS BUT
EVENTUALLY THROUGH THE LOWER TROPOSPHERE. AS A RESULT...THE
POTENTIAL FOR DIURNAL THUNDERSTORMS WILL INCREASE THROUGH THE
HOLIDAY WEEKEND...AND HEAT INDEX VALUES WILL RETURN TO MORE TYPICAL
VALUES FOR LATE AUGUST/EARLY SEPTEMBER.

SATURDAY MORNING...A REPEAT OF THE FRIDAY MORNING SCENARIO IS
POSSIBLE...WITH ENHANCED LOW LEVEL/MARINE MOISTURE POSSIBLY
SUPPORTING A FEW SHALLOW SHOWERS OVER COASTAL COUNTIES/ADJACENT
COASTAL WATERS. THEN...THE FOCUS FOR AFTERNOON SHOWERS/THUNDERSTORMS
WILL SHIFT INTO AREAS ALONG/WEST OF I-95. GIVEN THE CAP STILL
EVIDENT IN MODEL SOUNDINGS...CAPPED POPS AT SLIGHT CHANCE IN THIS
AREA.

SATURDAY NIGHT...THE FOCUS FOR ISOLATED SHOWERS/THUNDERSTORMS WILL
SHIFT OVER COASTAL WATERS...PERHAPS BRUSHING COASTAL COUNTIES. OF
INTEREST...THE 29/12Z NAM DEPICTS INLAND CONVECTION PERSISTING WELL
INTO THE OVERNIGHT HOURS. WHILE WE CANNOT COMPLETELY DISCOUNT THIS
SOLUTION...PER TYPICAL DIURNAL TRENDS POPS TAPER TO LESS THAN 15
PERCENT INLAND WITH NO MENTION OF PRECIPITATION DURING THE OVERNIGHT
HOURS. ALSO OF NOTE...LIGHT WINDS/LOW LEVEL MOISTURE COULD SUPPORT
PATCHY FOG LATE SATURDAY NIGHT INTO EARLY SUNDAY...BUT FORECAST
CONFIDENCE IS INSUFFICIENT TO WARRANT A MENTION WITHIN PUBLIC
FORECASTS.

SUNDAY THROUGH MONDAY...PWATS INCREASE TO AROUND 2 INCHES AND MAX
MLCAPES COULD POTENTIALLY SURGE TO AT LEAST 2500-3500 J/KG...
SUPPORTED BY HIGH TEMPS IN THE LOWER TO MID 90S AND DEWPOINTS IN THE
LOWER TO MID 70S. THIS REGIME SHOULD SUPPORT DIURNAL SHOWERS/
THUNDERSTORMS PERHAPS ACCOMPANIED BY A THREAT FOR LOCALLY HEAVY RAIN
AND A LOW-END THREAT FOR ISOLATED DAMAGING WIND GUSTS. AS THE UPPER
RIDGE BEGINS TO FLATTEN MONDAY...SLIGHTLY STRONGER LOW-MID LEVEL
WINDS COULD SUPPORT MULTICELL THUNDERSTORMS AND A SLIGHTLY GREATER
CHANCE FOR DAMAGING WIND GUSTS.

SUNDAY NIGHT...THE FOCUS FOR SHOWERS/THUNDERSTORMS SHOULD AGAIN
SHIFT OVER COASTAL WATERS.

DUE TO THE SUBTLE CAP PRODUCED BY THE UPPER RIDGE/DEPICTED BY MODEL
SOUNDINGS...CAPPED HIGHEST POPS AT 30-40 PERCENT INLAND SUNDAY AND
MONDAY AFTERNOONS. EVENTUALLY...LOCALLY GREATER POPS COULD BE
REQUIRED.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
THROUGH THE LONG TERM PERIOD...THE LARGE UPPER RIDGE WILL CONTINUE
TO INFLUENCE THE AREA. THE RIDGE WILL UNDERGO A TRANSITION IN THE
MID/LATE WEEK TIME PERIOD AS IT RETROGRADES BACK TO THE WEST ACROSS
THE LOWER MISSISSIPPI VALLY IN RESPONSE TO A TROUGH MOVING ACROSS
CENTRAL AND EASTERN CANADA. THE PATTERN IN THE LOW LEVELS WILL STILL
FEATURE THE INFLUENCE OF THE ATLANTIC HIGH...THOUGH THERE ARE
INDICATIONS THAT AN INLAND TROUGH OF LOW PRESSURE WILL DEVELOP IN
THE TUESDAY/WEDNESDAY TIME FRAME. AS THIS OCCURS...THE COVERAGE OF
AFTERNOON/EVENING SHOWERS AND THUNDERSTORMS MAY TICK UPWARD A BIT.
THE FORECAST FEATURES SLIGHT CHANCE TO CHANCE POPS EACH AFTERNOON
AND EVENING. TEMPERATURES WILL REMAIN ABOVE NORMAL WITH THE RIDGE
ALOFT.

&&

.AVIATION /22Z FRIDAY THROUGH WEDNESDAY/...
VFR CONDITIONS ARE EXPECTED TO PREVAIL THROUGH MUCH OF THE VALID
TAF PERIOD. THERE IS A POSSIBILITY FOR FOG/STRATUS TO DEVELOP LATE
TONIGHT AND TOWARDS SUNRISE...SO HAVE MAINTAINED MENTION OF A FEW
STRATUS AND SLIGHT VSBY REDUCTIONS TO TREND INTO THE FORECAST.
PREFER TO WAIT TO INTRODUCE ANY FLIGHT RESTRICTIONS UNTIL CONFIDENCE
IS HIGHER IN TIMING AND COVERAGE...ESPECIALLY SINCE MVFR OR IFR
CONDITIONS ARE NOT TYPICALLY EXPECTED WITH THIS SYNOPTIC PATTERN.
HOWEVER...FOG STABILITY INDICES SUGGEST A FAVORABLE LOW LEVEL WIND
AND MOISTURE PROFILE.

EXTENDED AVIATION OUTLOOK...LOW CHANCES OF DIRECT IMPACTS FROM
ISOLATED SHOWERS/THUNDERSTORMS THIS WEEKEND THROUGH EARLY NEXT
WEEK. ALSO...LOW CHANCES FOR EARLY MORNING FOG/STRATUS THROUGH
EARLY NEXT WEEK. OTHERWISE...MAINLY VFR.

&&

.MARINE...
TONIGHT...A RIDGE OF ATLANTIC HIGH PRESSURE STRETCHED ACROSS THE
COASTAL WATERS WILL BECOME ABSORBED BY A STRONGER 1027 MB HIGH
MOVING OFF NEW ENGLAND LATE. THIS WILL ALLOW FOR SOME FLUCTUATIONS
IN SE AND SOUTH WINDS THROUGH THE NIGHT...BUT ON AVERAGE NO HIGHER
THAN ABOUT 10 OR 12 KT. SEAS WILL BE NO MORE THAN 2 OR 3
FT...MAINLY IN EASTERLY SWELLS.

SATURDAY THROUGH WEDNESDAY...DEEP LAYERED HIGH PRESSURE WILL PREVAIL.
SE WINDS SATURDAY WILL VEER TOWARD THE S/SW SATURDAY NIGHT THROUGH
WEDNESDAY. WINDS WILL GENERALLY REMAIN LESS THAN 15 KT.
HOWEVER...LOCAL WINDS COULD APPROACH 20 KT DUE TO THE DAILY SEA
BREEZE CIRCULATION AND A NOCTURNAL SURGE DEPICTED BY MODELS SUNDAY
NIGHT. SEAS WILL RANGE FROM 1-2 FT WITHIN 20 NM AND 2-3 FT BEYOND.
SUNDAY NIGHT...3 FT SEAS COULD PUSH INTO NEARSHORE WATERS AND SEAS
AS HIGH AS 4-5 FT COULD BRIEFLY DEVELOP BEYOND 20 NM. HOWEVER...ODDS
ARE HIGH THAT SMALL CRAFT ADVISORIES WILL NOT BE REQUIRED THROUGH
MID WEEK.

&&

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

&&

$$

NEAR TERM...
SHORT TERM...SPR
LONG TERM...
AVIATION...SPR/WMS
MARINE...





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