Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 252017
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
417 PM EDT FRI JUL 25 2014

.SYNOPSIS...
AN ATLANTIC RIDGE OF HIGH PRESSURE WILL REMAIN SOUTH OF THE AREA
INTO EARLY NEXT WEEK...WITH A WEAK TROUGH OF LOW PRESSURE PREVAILING
INLAND. A COLD FRONT WILL APPROACH AND CROSS THE REGION LATE MONDAY
AND BECOME STATIONARY SOUTH AND SOUTHEAST OF THE AREA THROUGH THE
MIDDLE OF NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
STRONG CONVECTION HAS LINED UP ALONG THE SOUTH CAROLINA COASTLINE
BY 3 PM EDT...AS THUNDERSTORM ACTIVITY PROGRESSING INTO THE AREA
FROM THE WEST HAS BECOME ENHANCED ALONG THE SEABREEZE. ABUNDANT
MOISTURE EVIDENT BY PRECIPITABLE WATER VALUES ABOVE 2 INCHES...AS
WELL AS MODERATE INSTABILITY...IS SUPPORTING HEAVY RAINFALL AND
EXCESSIVE LIGHTNING WITHIN TRAINING STORM CELLS. THIS LINE OF
CONVECTION COULD CONTINUE TO IMPACT THE CHARLESTON...COLLETON...AND
EVEN NORTHERN BEAUFORT COUNTY COASTLINES FOR THE HOUR OR TWO
BEFORE GRADUALLY DIMINISHING AND/OR SHIFTING OFFSHORE. BOUNDARY
INTERACTIONS AND CELL MERGERS COULD ALLOW ISOLATED STORMS TO
BECOME SEVERE...PRODUCING POTENTIALLY DAMAGING WIND GUSTS AND
LARGE HAIL. THE THREAT FOR LOCALIZED FLOODING WILL ALSO CONTINUE
WHILE THE LINE OF THUNDERSTORMS REMAIN IN THE AREA.

UPSTREAM CONVECTION TRACKING INTO THE AREA THIS AFTERNOON HAS BEEN
INFLUENCED BY A LINGERING SURFACE TROUGH AND STATIONARY FRONT JUST
TO THE WEST/NORTHWEST OF THE FORECAST AREA...AS WELL AS WEAK UPPER
LEVEL ENERGY NEAR THE AXIS OF AN UPPER TROUGH. THESE FEATURES
APPEAR TO CHANGE LITTLE DURING THE OVERNIGHT PERIOD...AND SOME
HIGH RESOLUTION MODELS SUGGEST THAT ISOLATED SHOWERS/THUNDERSTORMS
COULD CONTINUE TO MOVE THROUGH THE REGION FROM WEST TO EAST AFTER
THE ONGOING STRONG COASTAL CONVECTION DIMINISHES/MOVES
OFFSHORE. HAVE THUS MAINTAINED 20 TO 30 PERCENT RAIN CHANCES
THROUGH MIDNIGHT...HIGHEST ALONG THE COAST AND MARINE ZONES...THEN
STEADILY DECREASE COVERAGE FROM WEST TO EAST DURING THE PRE DAWN
HOURS. THESE POP VALUES WILL CERTAINLY NEED TO BE ADJUSTED AS
CONVECTIVE TRENDS BECOME MORE APPARENT IN THE NEXT FEW HOURS. ANY
ISOLATED CONVECTION THAT CAN PERIODICALLY MOVE THROUGH THE AREA
DURING THE EVENING TIME FRAME WILL BE NOTABLY WEAKER DUE TO THE
LOSS OF DIURNAL HEATING AND INSTABILITY.

TEMPERATURES HAVE BEEN GREATLY IMPACTED BY THUNDERSTORM
ACTIVITY...WITH RAIN-COOLED AREAS SEEING CONDITIONS DROP 10
DEGREES DURING AND AFTER HEAVIEST RAINFALL. TEMPERATURES WILL
EVENTUALLY FALL INTO THE LOW TO MID 70S ACROSS THE FORECAST AREA
LATE TONIGHT. ALTHOUGH THE LOW LEVELS WILL BE QUITE WET WHERE
RAINFALL HAS OCCURRED THIS AFTERNOON...THERE IS A LOT OF
UNCERTAINTY REGARDING CLOUD COVER AND SUBSEQUENT FOG POTENTIAL.
WILL THUS HOLD OFF ON MENTIONING FOG IN THE FORECAST WITH THE
AFTERNOON PACKAGE...AND ALLOW SUBSEQUENT ISSUANCES TO ADDRESS THE
POTENTIAL.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
SATURDAY AND SATURDAY NIGHT...A MID AND UPPER LEVEL TROUGH WILL
DAMPEN AS ITS AXIS GRADUALLY SHIFTS EAST OF THE AREA AND RIDGING
CENTERED OVER THE SOUTHWEST AND SOUTHERN PLAINS BUILDS EASTWARD. AT
THE SURFACE...ATLANTIC HIGH PRESSURE WILL PREVAIL AS A TROUGH OF LOW
PRESSURE LINGERS INLAND. A WESTERLY FLOW ALOFT WILL REDUCE MOISTURE
AND GRADUAL WARMING/RISING HEIGHTS ALOFT SHOULD AID IN SUPPRESSING
CONVECTION. HOWEVER...WILL CARRY A SLIGHT CHANCE OF SHOWERS/
THUNDERSTORMS DURING THE AFTERNOON/EARLY EVENING AS A FEW ISOLATED
THUNDERSTORMS COULD DEVELOP ALONG ANY LINGERING BOUNDARIES INCLUDING
THE SEA BREEZE. DOWNSLOPE FLOW SHOULD ALLOW TEMPERATURES TO WARM TO
THE MID 90S AWAY FROM THE IMMEDIATE COAST DURING THE AFTERNOON...
WITH LOWS IN THE MID 70S AT NIGHT.

SUNDAY AND SUNDAY NIGHT...MID AND UPPER LEVEL RIDGING WILL CONTINUE
TO EXPAND EASTWARD ACROSS THE REGION FROM THE SOUTHWEST/SOUTHERN
PLAINS. STRONG CAPPING AND A DRIER WESTERLY FLOW ALOFT COULD VERY
WELL RESULT IN RAIN-FREE CONDITIONS...HOWEVER WILL MAINTAIN A SLIGHT
CHANCE OF SHOWERS AND THUNDERSTORMS DURING THE AFTERNOON UNTIL THE
DRIER TREND BECOMES MORE CERTAIN. TEMPERATURES WILL CONTINUE ON THE
WARMING TREND GIVEN DOWNSLOPE FLOW AND RISING HEIGHTS ALOFT...WITH
HIGHS FORECAST TO BE IN THE MID TO UPPER 90S INLAND FROM THE COAST.
LOWS AT NIGHT WILL BE MILD...GENERALLY IN THE MID TO UPPER 70S.

MONDAY...A MORE AMPLIFIED MID AND UPPER LEVEL PATTERN WILL DEVELOP
AS A TROUGH EXPANDS OVER THE EASTERN UNITED STATES. THIS WILL DRIVE
A COLD FRONT AT THE SURFACE TOWARD THE AREA FROM THE NORTHWEST. AN
AXIS OF DEEPER MOISTURE WILL SPREAD OVER THE AREA AHEAD OF THE
FRONT...AND THERE IS A GOOD CHANCE OF SHOWERS AND THUNDERSTORMS
DURING THE AFTERNOON AND EVENING...ESPECIALLY ACROSS
INLAND/NORTHWEST PORTIONS OF THE AREA GIVEN THE ORIENTATION/TIMING
OF THE FRONT. STRENGTHENING SOUTHWEST WINDS IN THE LOW LEVELS OF THE
ATMOSPHERE WILL RESULT IN RATHER MOIST CONDITIONS...WITH DEWPOINTS
SURGING INTO THE LOWER AND MID 70S. THIS MOIST AIR MASS AND STRONG
DIURNAL HEATING WILL RESULT IN A RATHER UNSTABLE AIR MASS WITH SB
CAPE VALUES RISING TO 2000-3000 J/KG...LI/S DOWN TO -7 OR -8C AND
STEEP MID LEVEL LAPSE RATES. IN ADDITION...FALLING HEIGHTS/COOLING
ALOFT AND AN INCREASE OF DEEP LAYER SHEAR COULD SUPPORT STRONG TO
SEVERE THUNDERSTORMS ACROSS THE AREA. DOWNSLOPE FLOW AND STRONG
COMPRESSIONAL HEATING WILL LIKELY RESULT IN HIGHS IN THE UPPER 90S
INLAND FROM THE IMMEDIATE COAST...UNLESS CONVECTION DEVELOPS EARLIER
THAN ANTICIPATED. GIVEN THE HIGH DEWPOINTS...HEAT INDEX VALUES COULD
REACH UPWARDS OF AROUND 110 DEGREES IN SOME AREAS. SINCE THIS IS OUR
CRITERIA FOR A HEAT ADVISORY...HAVE ADDED MENTION TO THE HAZARDOUS
WEATHER OUTLOOK.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
THE COLD FRONT IS PROGGED TO MOVE THROUGH THE AREA MONDAY NIGHT AND
BECOME NEARLY STATIONARY TO THE EAST AND SOUTH. BEHIND THE
FRONT...EXPECT A NOTICEABLE AIR MASS DIFFERENCE AS HEIGHTS FALL
OVERHEAD WITHIN THE AMPLIFYING EASTERN CONUS TROUGH. THIS SETUP WILL
KEEP TEMPERATURES 2-4 DEGREES CLIMO THROUGH THE END OF THE WEEK. THE
BEST CHANCE FOR RAIN...AND RESULTING HIGHEST POPS...WILL BE IN THE
MONDAY NIGHT TIME PERIOD ASSOCIATED WITH THE FRONT.
THEREAFTER...POPS WILL BECOME MORE DIURNAL IN NATURE AS THE LOW
LEVEL FLOW TURNS MORE EAST TO NORTHEAST WITH TIME.

&&

.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
KCHS REMAINS ON THE WESTERN EDGE OF LINE OF STRONG CONVECTION
ALONG THE SEABREEZE AT 330 PM EDT. HAVE CONTINUED A TEMPO GROUP TO
INDICATE MVFR CONDITIONS DURING THE NEXT FEW HOURS AT KCHS
ACCORDINGLY. THERE IS LESS CERTAINTY REGARDING TIMING AND IMPACTS
FARTHER SOUTH TOWARD THE KSAV TERMINAL...AS THESE AREAS ARE
FARTHER AWAY FROM THE FORCING PROVIDED BY A LINGERING TROUGH OF
LOW PRESSURE. WILL JUST MENTION VCTS AT KSAV FROM THROUGH 00Z
UNTIL CONVECTIVE TRENDS BECOME MORE APPARENT. ALTHOUGH HIGH
RESOLUTION MODELS DO HINT AT THE POTENTIAL FOR ISOLATED ACTIVITY
TO LINGER PAST SUNSET...PREFER TO END MENTION OF VCTS AT BOTH TAF
SITES BY 00Z. SINCE AFTERNOON RAIN IMPACTS APPEAR MORE LIKELY AT
KCHS...PATCHY FOG COULD DEVELOP DURING THE PRE-DAWN HOURS. HAVE
INDICATED THIS POTENTIAL USING A TEMPO GROUP WITH 5SM BR
CONDITIONS.

EXTENDED AVIATION OUTLOOK...PRIMARILY VFR. A COLD FRONT IS EXPECTED
TO MOVE THROUGH THE AREA LATE MONDAY. BRIEF CEILING AND VISIBILITY
REDUCTIONS MAY BE POSSIBLE WITH THUNDERSTORMS THAT DEVELOP IN THE
EVENING HOURS.

&&

.MARINE...
TONIGHT...THE WEAKENING INLAND TROUGH WILL LINGER...AND EXPECT ANY
NOCTURNAL WIND SURGE TO RATHER SUBTLE COMPARED TO PREVIOUS NIGHTS.
EXPECT SOUTH/SOUTHWEST WINDS 15 KT OR LESS...VEERING TO THE
SOUTHWEST/WEST LATE AS LAND BREEZE CIRCULATIONS ARRIVE.

SATURDAY THROUGH TUESDAY...THE FIRST PORTION OF THE FORECAST PERIOD
WILL FEATURE HIGH PRESSURE TO THE EAST AND AN INLAND TROUGH OF LOW
PRESSURE. THIS WILL PROMOTE A MODEST SOUTHWEST FLOW THROUGH SUNDAY.
THEN SUNDAY NIGHT ONWARD THE PRESSURE GRADIENT WILL TIGHTEN IN
RESPONSE TO AN APPROACHING COLD FRONT. THIS WILL RESULT IN WINDS
INCREASING INTO THE 15-20 KT RANGE...AND PERHAPS EVEN MARGINALLY
SUPPORTIVE OF SMALL CRAFT ADVISORIES FOR PORTIONS OF THE WATERS
MONDAY AND MONDAY NIGHT. THE GRADIENT AND RESULTING WINDS WILL THEN
DECREASE ON TUESDAY.

&&

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

&&

$$

NEAR TERM...WMS
SHORT TERM...JAQ
LONG TERM...BSH
AVIATION...WMS/JAQ
MARINE...WMS/JAQ





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