Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 262011
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
411 PM EDT SAT JUL 26 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. THE FRONT WILL THEN SLOWLY DISSIPATE OFF THE
SOUTHEAST COAST THROUGH LATE NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
LATEST WATER VAPOR IMAGERY SHOWS A SWATH OF DRY AIR SWEEPING
TOWARD THE MID ATLANTIC AND SOUTHEAST COASTLINE BEHIND THE AXIS OF
THE DEPARTING UPPER LEVEL TROUGH...EVIDENCE OF MID LEVEL DRYING
TRENDS SEEN IN FORECAST MODEL SOUNDINGS. CONVECTIVE COVERAGE HAS
BEEN LIMITED AS A COMBINED RESULT OF THIS DRY AIR INTRUSION AND
LIKELY SOME ASSOCIATED CAPPING. ONLY ISOLATED SHOWERS AND WEAK
THUNDERSTORMS HAVE INITIATED OVER THE FORECAST AREA BY MID
AFTERNOON...AND ONGOING SLIGHT CHANCE POPS FOR THE REMAINDER OF
THE AFTERNOON SEEMS ON TRACK. EXPECT ANY ISOLATED
SHOWERS/THUNDERSTORMS TO DIMINISH AROUND SUNSET AND CLOUD COVER TO
DISSIPATE WITH THE LOSS OF DIURNAL HEATING/INSTABILITY.
TEMPERATURES PEAKING IN THE LOW TO MID 90S THIS AFTERNOON WILL
STEADILY FALL THROUGH THE EVENING AND OVERNIGHT...YET REMAIN QUITE
MILD IN THE MID 70S INLAND TO THE UPPER 70S ALONG THE COAST UNDER
MOSTLY CLEAR SKIES.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/...
SUNDAY...HOT AND HUMID CONDITIONS WILL START OFF THE WEEK AS THE
AREA REMAINS BETWEEN HIGH PRESSURE OVER THE WESTERN ATLANTIC AND A
TROUGH OF LOW PRESSURE INLAND. LATEST GUIDANCE INDICATES A
WEST/NORTHWEST WINDS OFF THE SFC...RESULTING IN A DOWNSLOPING WIND
COMPONENT DURING STRONG SFC HEATING. LATEST 1000-850 MB THICKNESSES
SUPPORT OVERALL HIGH TEMPS IN THE MID/UPPER 90S...WARMEST INLAND.
THESE TEMPS IN COMBINATION WITH SFC DEWPTS IN THE LOW 70S SUPPORT
HEAT INDEX VALUES BETWEEN 105-108 DEGREES FOR AREAS AWAY FROM THE
COAST...WHICH FALLS JUST SHORT OF HEAT ADVISORY CONDITIONS. SHOULD
SFC TEMPS OR DEWPTS INCREASE A DEGREE OR TWO...HEAT ADVISORIES COULD
BE NEEDED DURING PEAK HEATING SUNDAY AFTERNOON/EVENING. DESPITE
STRONG SFC HEATING DURING THE AFTERNOON...A CAPPING INVERSION WILL
LIMIT OVERALL CONVECTION OVER THE AREA. A DRY FORECAST WILL
THEREFORE REMAIN IN PLACE THROUGH SUNDAY NIGHT. OVERNIGHT TEMPS WILL
REMAIN MILD...IN THE UPPER 70S TO AROUND 80 ALONG THE COAST.

MONDAY...HOT AND HUMID CONDITIONS WILL REMAIN IN PLACE FOR MUCH OF
THE DAY WELL AHEAD OF A SFC COLD FRONT POSITIONED TO OUR
NORTH/NORTHWEST. CHANCES OF SHOWERS AND/OR THUNDERSTORMS SHOULD
INCREASE AS WE HEAD INTO EVENING AS H25 WINDS AND A SERIES OF H5
SHORTWAVES ROUND THE BASE OF THE TROUGH AND CAUSE IT TO DIG
SOUTHWARD OVER THE EASTERN CONUS. THE DIGGING PATTERN IS EXPECTED TO
FORCE THE SFC COLD FRONT TO THE AREA MONDAY EVENING AND
NIGHT...BRINGING EVEN HIGHER CHANCES OF SHOWERS AND THUNDERSTORMS.
CONDITIONS WILL REMAIN QUITE UNSTABLE ALONG AND AHEAD OF THE
ADVANCING FRONT...ESPECIALLY DURING PEAK HEATING HOURS AS LIFTED
INDEX VALUES APPROACH -9.0 C AND SBCAPES RANGE BETWEEN 3000-4000
J/KG. 1000-850 MB THICKNESS VALUES SUPPORT OVERALL HIGH TEMPS IN THE
MID TO PERHAPS UPPER 90S AHEAD OF THE FRONT. HOWEVER...LATEST
GUIDANCE SUGGESTS THAT MOST FORCING ASSOCIATED WITH THE MID LVL
TROUGH OF LOW PRESSURE AND SFC COLD FRONT WILL REMAIN JUST
NORTH/NORTHWEST OF THE AREA THROUGH EARLY EVENING. DESPITE A LATER
ARRIVAL...CONDITIONS WILL LIKELY REMAIN WARM AND MOIST UNTIL COLD
FROPA...AND STRONGER/SEVERE THUNDERSTORMS WILL BE POSSIBLE.

THE GREATEST CHANCE OF SEVERE WEATHER OVER SOUTHEAST SOUTH CAROLINA
AND SOUTHEAST GEORGIA WILL OCCUR AS THE COLD FRONT SHIFTS OVER THE
REGION LATE MONDAY EVENING INTO MONDAY NIGHT. BASED ON THE LATEST
TIMING OF COLD FROPA...SEVERE THUNDERSTORMS WOULD BE POSSIBLE LATE
MONDAY EVENING UNTIL MIDNIGHT OVER SOUTHEAST SOUTH CAROLINA AND
INLAND GEORGIA...WITH A LINGERING RISK OVER COASTAL GEORGIA BEFORE
DAYBREAK TUESDAY. UNIDIRECTIONAL FLOW/SHEAR PROFILES ALONG WITH THE
MENTIONED PARAMETERS ABOVE SUGGEST PRIMARILY A LARGE HAIL AND
DAMAGING WIND EVENT. HEAVY RAINFALL WILL ALSO BE POSSIBLE AS PWATS
APPROACH 2.0 INCHES ALONG/AHEAD OF THE FRONT. ONCE FROPA
OCCURS...THE OVERALL THREAT OF SEVERE WEATHER SHOULD DIMINISH
QUICKLY. LOW TEMPS SHOULD RANGE IN THE LOW/MID 70S...COOLEST BEHIND
THE FRONT.

TUESDAY...HIGH PRESSURE WILL LIKELY INCREASE OVER THE AREA BEHIND A
SFC COLD FRONT ADVANCING FURTHER SOUTH OF THE REGION. AS A
RESULT...CHANCES OF SHOWERS AND/OR THUNDERSTORMS WILL BE ON THE
DECLINE THROUGH THE DAY AS COOLER AND DRYER AIR SETTLES OVER THE
SOUTHEAST. RAIN-FREE CONDITIONS SHOULD OCCUR OVER ALL AREAS BY
TUESDAY EVENING. LATEST 1000-850 MB THICKNESSES SUPPORT OVERALL HIGH
TEMPS IN THE MID/UPPER 80S...HIGHEST AWAY FROM THE COAST.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
THE PATTERN IN THE LONG TERM WILL BE DOMINATED BY THE ANOMALOUSLY
DEEP MID/UPPER LEVEL TROUGH ACROSS THE EASTERN CONUS. THE LOWERING
HEIGHTS AND THICKNESS VALUES WILL RESULT IN A MUCH COOLER PERIOD
WITH BELOW NORMAL TEMPERATURES THROUGH THE END OF THE WEEK. WEAK
HIGH PRESSURE WILL BE POSITIONED TO THE NORTHEAST WHICH WILL RESULT
IN AN EASTERLY ONSHORE FLOW THROUGH MUCH OF THE PERIOD. CHANCES FOR
CONVECTION WILL START OFF LOWER WEDNESDAY...BUT WILL INCREASE SLOWLY
THROUGH THE END OF THE FORECAST WITH A DEVELOPING COASTAL TROUGH IN
THE VICINITY.

&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
INCREASING DRY AIR AT MID LEVELS HAS LIMITED OVERALL THUNDERSTORM
COVERAGE TODAY. HAVE ADDED VCTS AT KCHS THROUGH 21Z...YET
CONFIDENCE IN DIRECT TSRA OR SHRA IMPACTS AT EITHER TAF SITE IS
TOO LOW TO EXPLICITLY MENTION. VFR CONDITIONS WILL PREVAIL
THROUGH 18Z SUNDAY.

EXTENDED AVIATION OUTLOOK...PRIMARILY VFR. A COLD FRONT IS EXPECTED
TO MOVE THROUGH THE AREA LATE MONDAY...WHICH COULD RESULT IN CEILING
AND VISIBILITY REDUCTIONS AS THUNDERSTORMS PASS OVER THE AREA MONDAY
EVENING AND MONDAY NIGHT.

&&

.MARINE...
TONIGHT...THE MARINE ZONES WILL BE LOCATED WITHIN A FAIRLY WEAK
SURFACE PATTERN...WITH THE MAIN FEATURE A DEVELOPING TROUGH OF LOW
PRESSURE WELL INLAND. SOUTH/SOUTHWEST WINDS THIS AFTERNOON WILL
VEER MORE WEST/SOUTHWEST OVERNIGHT...WITH PREVAILING WIND SPEEDS
GENERALLY 15 KT OR LESS. SEAS WILL RANGE FROM 2 TO 3 FT...EXCEPT
4 FT IN THE FAR OUTER WATERS.

SUNDAY THROUGH WEDNESDAY...EARLY IN THE PERIOD THE SETUP WILL
FEATURE A TIGHTENING SOUTHWEST GRADIENT ACROSS THE WATERS AS A COLD
FRONT APPROACHES FROM THE NORTHWEST. THE STRONG COLD FRONT WILL
CROSS THE WATERS MONDAY NIGHT...LIKELY ACCOMPANIED WITH STRONG
THUNDERSTORMS. DURING THIS SUNDAY/MONDAY TIME PERIOD...THE GRADIENT
WILL SUPPORT SOUTHWEST WINDS IN THE 15-20 KT RANGE AT TIMES.
MARGINAL SMALL CRAFT ADVISORY CONDITIONS WILL BE POSSIBLE
PERIODICALLY...ESPECIALLY FOR THE OUTER GEORGIA WATERS SUNDAY NIGHT.
THEN FOR THE LATTER PART OF THE FORECAST PERIOD...THE GRADIENT WILL
SLACKEN AND WINDS WILL BECOME MORE NORTHEASTERLY WITH TIME. WINDS
AND SEAS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY
THRESHOLDS TUESDAY AND WEDNESDAY.

&&

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

&&

$$

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






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