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000
FXUS62 KCHS 231517
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1117 AM EDT THU MAY 23 2013

.SYNOPSIS...
A COLD FRONT WILL MOVE THROUGH THE REGION LATE TONIGHT...WITH DRY
HIGH PRESSURE BUILDING IN THROUGH THE MIDDLE OF NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
THE DISTINCT SHORTWAVE PROGRESSING TOWARD THE FORECAST AREA FROM
THE WEST IS EVIDENT IN WATER VAPOR IMAGERY AS A NOTABLE BOUNDARY
BETWEEN DEEP MOISTURE OVER SOUTH CAROLINA/GEORGIA COASTAL AREAS
AND DRIER AIR FURTHER UPSTATE AND INLAND. THE MAIN COLD FRONT
ASSOCIATED WITH THE UPPER TROUGH AXIS IN THE OHIO VALLEY WILL
REMAIN TO THE NORTHWEST THROUGH THE DAYTIME HOURS...HOWEVER A PRE
FRONTAL TROUGH SEEN IN LATEST MESOANALYSIS WILL PROVIDE SOME
ADDITIONAL CONVERGENCE COINCIDENT WITH THE TIMING OF THE SHORTWAVE
ENERGY THIS AFTERNOON. THE ORIENTATION AND MOVEMENT OF THE
SURFACE TROUGH WILL SUPPORT MORE SOLID DOWNSLOPE FLOW ACROSS THE
GEORGIA COUNTIES...WHILE SOUTH CAROLINA ZONES REMAIN WITHIN A MORE
SOUTHWEST FLOW FOR THE NEXT SEVERAL HOURS. THE DOWNSLOPE FLOW
ACROSS SOUTHERN LOCATIONS COULD LIMIT CONVECTIVE DEVELOPMENT LATER
TODAY.

RADAR TRENDS CONFIRM THAT INITIAL CONVECTIVE DEVELOPMENT WILL
OCCUR ACROSS THE SOUTH CAROLINA ZONES...AS ISOLATED SHOWER
ACTIVITY IS ALREADY TRACKING ACROSS THE CHARLESTON TRI COUNTY
REGION. LATEST THINKING IS THAT SHOWERS/THUNDERSTORMS WILL
INCREASE IN COVERAGE OVER THE TRI COUNTY...WITH ISOLATED
CONVECTION SPREADING SOUTHWARD INTO THE GEORGIA COASTAL ZONES
ALONG THE SEABREEZE. HAVE INDICATED 30 PERCENT RAIN CHANCES IN THE
FAVORED NORTHERN COASTAL AREAS THIS AFTERNOON...WITH SLIGHT
CHANCES INLAND SOUTH CAROLINA AND ALONG THE GEORGIA COASTLINE.
HAVE CAPPED RAIN CHANCES BELOW 15 PERCENT FOR THE INLAND GEORGIA
ZONES WHERE THE AFOREMENTIONED DOWNSLOPE FLOW AND EARLIER
INTRUSION OF DRIER AIR WILL SUPPRESS CONVECTIVE DEVELOPMENT.
MODIFYING THE CHS UPPER AIR SOUNDING FOR AFTERNOON TEMPERATURES
AND DEWPOINTS REVEALS ONLY MARGINAL INSTABILITY...AND WITH
CONTINUED WEAK LAPSE RATES AND WIND PROFILES...SEVERE POTENTIAL IS
LOW AGAIN TODAY.

STRATOCUMULUS QUICKLY DEVELOPED ACROSS SOUTH CENTRAL GEORGIA AND
IS SHIFTING INTO THE CLEAR AREAS OF SOUTHEAST GEORGIA BY MID
MORNING. AS A RESULT...MOST OF THE FORECAST AREA WILL REMAIN
PARTLY CLOUDY TO MOSTLY CLOUDY THROUGHOUT THE AFTERNOON
HOURS...WITH THICKEST SKY COVER ACROSS THE NORTHERN ZONES. CURRENT
FORECAST TEMPERATURES ARE IN DECENT AGREEMENT WITH LATEST
TEMPERATURES...AND WILL THUS MAINTAIN ONGOING FORECAST HIGHS
RANGING FROM THE UPPER 80S INLAND TO THE LOW TO MID 80S ALONG THE
COAST.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY/...
THE COLD FRONT WILL MOVE THROUGH SHORTLY AFTER MIDNIGHT TONIGHT
WITH SLIGHTLY DRIER AIR BEGINNING TO FILTER INTO THE REGION.
MOSTLY CLEAR SKIES EXPECTED WITH TEMPERATURES IN THE LOWER 60S.

FRIDAY AND FRIDAY NIGHT...AN UPPER LEVEL TROUGH WILL MOVE ACROSS THE
MID-ATLANTIC REGION ON FRIDAY. IN WAKE OF THE DEPARTING COLD
FRONT...A DEEP LAYERED NORTHWEST FLOW WILL PREVAIL THROUGH MUCH OF
THE DAY. THE DOWNSLOPE FLOW WILL RESULT IN DRYING ACROSS THE AREA
AND WILL ALSO NEGATE MOST OF THE INITIAL SURGE OF COLD AIR ADVECTION
AS HIGHS SHOULD STILL BE IN THE MID TO UPPER 80S. UNDER MOSTLY SUNNY
SKIES...BREEZY CONDITIONS ARE ALSO EXPECTED. THEN...AS THE UPPER
TROUGH PASSES OFF THE MID-ATLANTIC COAST FRIDAY EVENING...IT WILL
PUSH A SECONDARY COLD FRONT ACROSS THE AREA ALLOWING HIGH PRESSURE
TO BUILD FROM THE GREAT LAKES REGION. THE AIR MASS WILL BEGIN TO
MODIFY SIGNIFICANTLY FOLLOWING THE SECONDARY COLD FRONT WITH
TEMPERATURES PLUMMETING INTO THE UPPER 40S AND LOWER 50S FRIDAY
NIGHT ON A NORTHERLY FLOW.

SATURDAY AND SATURDAY NIGHT...A VERY DRY AIR MASS WILL SETTLE OVER
THE REGION SATURDAY AS HIGH PRESSURE CONTINUES TO BUILD IN FROM THE
GREAT LAKES REGION. PRECIPITABLE WATER VALUES OF .25 TO .40 INCHES
WILL BE ABOUT AS LOW AS THEY CAN GET FOR THIS TIME OF YEAR...OR MORE
THAN 2 STANDARD DEVIATIONS BELOW NORMAL. FORECAST THICKNESS VALUES
ONLY SUPPORT HIGHS IN THE MID TO UPPER 70S...BUT GIVEN FULL SUNSHINE
AND THE HIGHER SUN ANGLE THIS TIME OF YEAR...WILL INDICATE HIGHS IN
THE UPPER 70S TO LOWER 80S ACROSS THE AREA. ANOTHER UNSEASONABLY
COOL NIGHT IS EXPECTED SATURDAY NIGHT...WITH LOWS IN THE LOWER TO
MID 50S.

SUNDAY...A WEAK PRESSURE PATTERN WILL PREVAIL OVER THE REGION. AN
INCREASE IN MID AND HIGH LEVEL MOISTURE WILL SUPPORT SOME CLOUD
COVER BUT THE AIR MASS IS TOO DRY STILL FOR ANY SHOWERS TO DEVELOP.
HIGHS SHOULD BE IN THE LOWER TO MID 80S ACROSS MUCH OF THE AREA.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
THE REGION WILL BE SANDWICHED BETWEEN TWO AREAS OF HIGH PRESSURE
EARLY IN THE WEEK...THE STRONGER OF THE TWO PASSING ACROSS THE
MID-ATLANTIC REGION AND THE OTHER OVER THE NORTHEAST GULF OF MEXICO.
DEEPENING MOISTURE WILL RESULT IN AT LEAST AN INCREASE IN CLOUD
COVER...BUT IT APPEARS THE RAIN-FREE CONDITIONS SHOULD PERSIST
THROUGH MEMORIAL DAY. ATLANTIC HIGH PRESSURE WILL THEN BECOME
ESTABLISHED THROUGH THE MIDDLE OF NEXT WEEK...SUPPORTING MAINLY
DIURNAL ISOLATED CONVECTION EACH AFTERNOON ALONG AND AHEAD OF THE
SEA BREEZE TUESDAY THROUGH THURSDAY. TEMPERATURES WILL MODERATE TO
NEAR NORMAL BY EARLY NEXT WEEK AND CONTINUE NEAR SEASONAL NORMS
THROUGH THE END OF THE FORECAST PERIOD.

&&

.AVIATION /15Z THURSDAY THROUGH MONDAY/...
VFR CONDITIONS ARE EXPECTED TO PREVAIL AT BOTH KCHS AND KSAV
THROUGH 12Z FRIDAY. SCATTERED SHOWERS HAVE ALREADY DEVELOPED IN
ASSOCIATION WITH A PRE-FRONTAL TROUGH ACROSS SOUTHEAST SOUTH
CAROLINA. HAVE KEPT MENTION OF ANY PRECIPITATION OUT OF THE KSAV
TAF SINCE COVERAGE WILL BE LIMITED ACROSS SOUTHEAST GEORGIA. ANY
CEILINGS WILL REMAIN VFR OUTSIDE OF CONVECTION...WITH CLEARING
EXPECTED TONIGHT.

EXTENDED AVIATION...VFR CONDITIONS WILL PREVAIL. GUSTY WINDS ARE
POSSIBLE FRIDAY AFTERNOON.

&&

.MARINE...
WINDS AND SEAS WILL BE FAIRLY BENIGN TODAY...BEFORE WINDS
INCREASE OUT OF THE SOUTHWEST AND WEST TONIGHT AS A COLD FRONT
PUSHES THROUGH THE WATERS. WIND SPEEDS WILL INCREASE TO AROUND 15
KT...YET THE OFFSHORE FETCH WILL LIMIT THE BUILDING OF SEAS TO NO
HIGHER THAN 4 FT.

FRIDAY THROUGH TUESDAY...A NORTHWEST FLOW WILL DEVELOP ON FRIDAY IN
WAKE OF A DEPARTING COLD FRONT. A SECONDARY COLD FRONT WILL THEN
MOVE THROUGH BY FRIDAY EVENING...WITH A STRONGER NORTHERLY SURGE
DEVELOPING IN ITS WAKE FRIDAY NIGHT INTO EARLY SATURDAY...POSSIBLY
RESULTING IN SMALL CRAFT ADVISORY CONDITIONS OVER A PORTION OF THE
WATERS.

CONDITIONS WILL THEN IMPROVE LATER IN THE WEEKEND WITH WINDS/SEAS
EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY THRESHOLDS THROUGH
EARLY NEXT WEEK.

&&

.TIDES/COASTAL FLOODING...
HIGH ASTRONOMICAL TIDES AND FAVORABLE NORTH/NORTHEAST WINDS COULD
LEAD TO MINOR SALTWATER INUNDATION NEAR THE COAST DURING THE HIGH
TIDE FRIDAY AND SATURDAY EVENING. BY THE TIME OF THE HIGH TIDE
SUNDAY EVENING AND MONDAY EVENING...WINDS WILL NOT BE AS
CONDUCIVE...YET MINOR SALTWATER FLOODING WILL STILL BE POSSIBLE.

&&

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

&&

$$

NEAR TERM...WMS
SHORT TERM...JAQ/JRL
LONG TERM...JAQ
AVIATION...JAQ
MARINE...JAQ/JRL
TIDES/COASTAL FLOODING...