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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KCHS 182335
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
735 PM EDT SAT MAY 18 2013

.SYNOPSIS...
AN UPPER LEVEL DISTURBANCE WILL GRADUALLY MOVE INTO THE AREA SUNDAY
INTO TUESDAY...THEN WILL STALL AND DISSIPATE AS ATLANTIC HIGH PRESSURE
BECOMES THE DOMINANT FEATURE THROUGH MUCH OF NEXT WEEK. A COLD FRONT
WILL APPROACH THE REGION BY NEXT WEEKEND.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
-- Changed Discussion --
THE CAPE HAS BEEN MOSTLY USED UP NOW...WITH THE EXCEPTION OF THE
FAR SOUTHERN PORTIONS OF THE CWA DOWN BY THE ALTAMAHA RIVER...SO
THE MAJORITY OF THE CONVECTIVE ACTIVITY IS OVER FOR THE EVENING.
HOWEVER...WITH THE SHORTWAVE STILL IN THE VICINITY...THERE REMAINS
A CHANCE OF SHOWERS FOR THE NEXT FEW HOURS. NO SHORT TERM CHANGES
TO THE GRIDS...BUT WILL UPDATE BY 930 OR SO TO ACCOUNT FOR TRENDS.
-- End Changed Discussion --

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/...
THE UPSTREAM SHORTWAVE TROUGH WILL SETTLE INTO THE REGION SUNDAY
THROUGH MONDAY...THEN WILL STALL AND SLOWLY UNRAVEL/WEAKEN OVER THE
REGION BY THE END OF THE FORECAST PERIOD. THE OVERALL REGIME WILL
FAVOR SCATTERED TO NUMEROUS SHOWERS/THUNDERSTORMS...SIGNIFICANT
CLOUD COVER AND TEMPERATURES NOT EXCEEDING THE LOWER TO MID 80S AT
MOST LOCALES. OF GREATEST INTEREST...LOCALLY HEAVY RAINFALL IS
POSSIBLE GIVEN PWATS INCREASING TO BETWEEN 1.5 AND 1.8 INCHES/
1 TO 3 STANDARD DEVIATIONS ABOVE NORMAL FOR MID-MAY AND MULTICELL
CONVECTION WITHIN A RELATIVELY WEAK STEERING FLOW REGIME/MODULATED
BY MESOSCALE BOUNDARIES.

GIVEN THE COMPLEX CONVECTIVE SCENARIO...FORECAST DETAILS WILL REMAIN
VERY DIFFICULT TO PIN DOWN BEYOND THE NEAR TERM FORECAST PERIOD. IN
GENERAL...PRECIPITATION COVERAGE SHOULD GENERALLY INCREASE PER
DIURNAL WARMING/DESTABILIZATION EACH AFTERNOON/EVENING. THE GREATEST
POTENTIAL COVERAGE WILL SUNDAY AND MONDAY PM...THEN DIURNAL
PRECIPITATION COVERAGE SHOULD BE RELATIVELY MORE SPARSE TUESDAY PM
DUE TO BUILDING HEIGHTS ALOFT AND AN ASSOCIATED WEAKENING OF THE
MID/UPPER VORTICITY MAXIMUM. HOWEVER...THE DEGREE OF DIURNAL
WARMING/DESTABILIZATION WILL DEPEND ON CLOUD COVER/ANTECEDENT
PRECIPITATION. INDEED...UPSTREAM/CLOSER TO THE UPPER LOW SATURDAY
AFTERNOON EARLIER PRECIPITATION AND LINGERING CLOUD COVER HELD
TEMPERATURES IN THE 70S AND HAD LIMITED COVERAGE/INTENSITY OF
PRECIPITATION...AND THIS SCENARIO CANNOT BE RULED OUT IN OUR AREA
SUNDAY/MONDAY.

OTHERWISE...CANNOT RULE OUT SHOWERS/THUNDERSTORMS AT ANY TIME
THROUGH THE PERIOD. FOR EXAMPLE...18/12Z GUIDANCE GENERALLY
INDICATES AN INCREASE IN DEEP LAYER MOISTURE AND AN ASSOCIATED
INCREASE IN SHOWER COVERAGE OVERNIGHT SUNDAY NIGHT/EARLY
MONDAY...ESPECIALLY ACROSS NORTHERN/EASTERN COUNTIES. WHILE
CONFIDENCE IN THIS SCENARIO IS NOT NECESSARILY HIGH...MODEL TRENDS
JUSTIFY AN INCREASE IN POPS OVERNIGHT SUNDAY NIGHT INTO EARLY
MONDAY. FURTHER...OTHERWISE...HIGHEST POPS ARE CAPPED IN THE HIGH
CHANCE/LOW LIKELY CATEGORY INLAND DURING THE SUNDAY/MONDAY PM
PERIOD...BUT SIGNIFICANT REFINEMENTS WILL BE REQUIRED WITHIN
SUBSEQUENT FORECAST PACKAGES.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
A RATHER WARM PATTERN PERSISTS IN THE LONG TERM AS THE AREA SITS ON
THE WESTERN SIDE OF AN UPPER RIDGE WITH ATLANTIC HIGH PRESSURE
OFFSHORE. RAIN CHANCES WILL INCREASE A BIT LATE IN THE WEEK AS AN
UPPER TROUGH APPROACHES FROM THE WEST AND A COLD FRONT DROPS INTO
THE AREA FRIDAY NIGHT OR SATURDAY.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
-- Changed Discussion --
AT KSAV...THE THUNDERSTORMS HAVE MOVED EAST OF THE FIELD AND
DISSIPATED...ALTHOUGH THERE ARE STILL A FEW SHOWERS UPSTREAM THAT
MAY DRIFT ACROSS THE TERMINAL FOR THE NEXT COUPLE OF HOURS. THEY
SHOULD NOT MAKE MUCH OF AN IMPACT IN TERMS OF VSBYS OR
CIGS...SO VFR CONDITIONS ARE EXPECTED THE REMAINDER OF THE EVENING.

IN THE PRE DAWN HOURS...HOWEVER...I DID ADD IN THE POTENTIAL FOR
SOME MVFR VSBYS. WINDS WILL BE FAIRLY LIGHT...AND THERE WAS SOME
PRETTY HEAVY RAIN FROM THE AIRPORT WESTWARD INTO SOUTHERN
EFFINGHAM COUNTY EARLIER TODAY...SO THE INCREASE IN LOW LEVEL
AVAILABLE MOISTURE HAS LED ME TO BE MORE CONCERNED WITH FOG
DESPITE THE PLENTIFUL HIGH CLOUDS EXPECTED OVERNIGHT.

AT KCHS...OTHER THAN THICK ANVIL CLOUDS PASSING OVERHEAD...I DONT
EXPECT MUCH IN THE WAY OF WEATHER OVERNIGHT. I DO THINK THAT
THUNDERSTORMS WILL BE IN THE VICINITY OF THE TERMINAL AT SOME POINT
TOMORROW...ESPECIALLY IN THE LATER AFTERNOON...BUT I AM NOT
CONFIDENT ENOUGH IN THE TIMING OF THOSE STORMS AT THIS TIME TO
EXPLICITLY INTRODUCE THEM INTO THE TAF.

EXTENDED AVIATION OUTLOOK...PRIMARILY VFR. DIRECT/TRANSIENT IMPACTS
INCLUDING FLIGHT RESTRICTIONS FROM ISOLATED TO SCATTERED
SHOWERS/THUNDERSTORMS WILL LIKELY OCCUR THROUGH EARLY NEXT WEEK.
-- End Changed Discussion --

&&

.MARINE...
TONIGHT...NO CHANGE TO THE SETUP WITH ATLANTIC HIGH PRESSURE DRIVING
PERSISTENT S TO SE FLOW. WIND SPEEDS WILL REMAIN AT OR BELOW 15 KTS
WITH SEAS 2-4 FT.

PERSISTENT ATLANTIC HIGH PRESSURE WILL PRODUCE SOUTH TO SOUTHEAST
WINDS RANGING FROM 10 TO 15 KNOTS...WITH LOCALLY/BRIEFLY STRONGER
ONSHORE WINDS AS HIGH AS 20 KT DUE TO THE DIURNAL SEA BREEZE
CIRCULATION EACH DAY. SEAS WILL AVERAGE 2 TO 4 FEET MUCH OF THE
TIME...ALTHOUGH SEAS AS HIGH AS 5-6 FT COULD BEGIN TO IMPINGE UPON
WATERS BEYOND 20 NM BY MID TO LATE WEEK.

&&

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

&&

$$

SYNOPSIS...
NEAR TERM...FWA
SHORT TERM...SPR
LONG TERM...JRL
AVIATION...FWA
MARINE...BSH/SPR