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Area Forecast Discussion

074
FXUS62 KCHS 280217
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1017 PM EDT SUN JUL 27 2014

.SYNOPSIS...
A STRONG COLD FRONT WILL CROSS THE REGION LATE MONDAY AND BECOME
STATIONARY SOUTH/SOUTHEAST OF THE AREA THROUGH THE MIDDLE OF THE
WEEK. THE FRONT WILL THEN SLOWLY MOVE BACK TOWARDS THE SOUTHEAST
COAST AS A COASTAL TROUGH LATE IN THE WEEK AND INTO THE FIRST PART
OF THE WEEKEND.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
WATER VAPOR IMAGERY THIS EVENING DEPICTS FLAT UPPER RIDGING
EXTENDING SOUTH OF THE REGION FROM A STRONG RIDGE CENTERED OVER
THE FOUR CORNERS REGION/SOUTHERN PLAINS. MEANWHILE...A SHORT WAVE
TROUGH IS DIGGING ACROSS THE GREAT LAKES REGION AND THIS WILL
AMPLIFY THE LONG WAVE TROUGH IN PLACE OVER MUCH OF THE EASTERN
UNITED STATES LATER TONIGHT. AT THE SURFACE...LOW PRESSURE WILL
MOVE EAST OUT OF THE GREAT LAKES REGION TONIGHT...WHILE ITS
TRAILING COLD FRONT SHIFTS SOUTHEAST TOWARD THE APPALACHIANS
WITHIN THE AMPLIFYING UPPER TROUGH.

HIGHER RESOLUTION MESOSCALE MODES INDICATE THAT THE UPSTREAM
CONVECTION CROSSING INTO THE UPSTATE OF SOUTH CAROLINA LATE THIS
EVENING WILL CONTINUE TO DROP SOUTH AND EAST THROUGH THE
NIGHT...BUT SHOULD DISSIPATE BEFORE REACHING THE FORECAST AREA.
THIS SEEMS REASONABLE GIVEN THE STRONG INVERSION DEPICTED ON THE
00Z KCHS SOUNDING AND THE SOLID WEST/NORTHWEST DEEP LAYER FLOW IN
PLACE. AS A RESULT WILL MAINTAIN A RAIN-FREE FORECAST...BUT WILL
SHOW A NON-ZERO PROBABILITY OF PRECIPITATION OVERNIGHT.
CONSIDERABLE HIGH LEVEL DEBRIS CLOUDINESS FROM THE UPSTREAM
CONVECTION WILL SHIFT ACROSS MUCH OF THE AREA OVERNIGHT...AND HAVE
ADJUSTED THE CLOUD COVER FORECAST ACCORDINGLY.

A VERY MILD NIGHT IS ON TAP...ESPECIALLY NOW WITH SO MUCH IN THE
WAY OF DEBRIS CLOUDINESS EXPECTED. THE FORECAST SHOWS TEMPERATURES
ONLY FALLING TO LOWS IN THE UPPER 70S...WITH LOWER 80S CLOSER TO
THE COAST. THESE TEMPERATURES WILL BE CLOSE TO RECORD HIGH
MINIMUMS FOR JULY 28TH. REFER TO THE CLIMATE SECTION BELOW FOR
DETAILS.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/...
MONDAY...HOT AND HUMID CONDITIONS WILL REMAIN IN PLACE WELL AHEAD
OF A SFC COLD FRONT POSITIONED TO OUR NORTH AND NORTHWEST THROUGHOUT
THE DAY. STRONG SFC HEATING UNDER A WESTERLY FLOW ALOFT IN
ADDITIONAL TO COMPRESSIONAL HEATING ALONG/AHEAD OF THE FRONT WILL
FAVOR SOME OF THE WARMEST TEMPS WE HAVE EXPERIENCED THIS YEAR...WITH
OVERALL HIGH TEMPS EXPECTED TO REACH THE MID/UPPER 90S AWAY FROM
THE IMMEDIATE COAST. WE COULD SEE A FEW LOCATIONS HIT 100 DEGREES WHILE
SKIES REMAIN MOSTLY SUNNY UNDER A MODERATELY STRONG CAPPING INVERSION.
THIS AMOUNT OF HEATING ALONG WITH SFC DEWPTS REMAINING IN THE LOW/MID
70S UNDER THE CAP SUPPORTS HEAT INDEX VALUES BETWEEN 105-110 DEGREES
OVER A LARGE PORTION OF THE CWA. A HEAT ADVISORY WILL THEREFORE BE
IN EFFECT FOR THE AREA BETWEEN 11 AM TO 7 PM. ONCE WE GET INTO MID
AFTERNOON/EARLY EVENING HOURS...THE MAIN CONCERN IN THE FORECAST
WILL SWITCH OVER TO SEVERE THUNDERSTORM POTENTIAL FOR SOUTHEAST
SOUTH CAROLINA AND SOUTHEAST GEORGIA.

SHOWERS AND/OR THUNDERSTORMS CHANCES WILL LIKELY INCREASE OVER THE
AREA AS WE HEAD INTO MID AFTERNOON AND EVENING AS THE CAP BREAKS
OVER THE REGION WELL AHEAD OF THE COLD FRONT. INVERTED-V
SOUNDINGS...SBCAPES BETWEEN 3000-4000 J/KG...LIFTED INDEX VALUES
NEAR -10 C...FAVORABLE LOW AND MID LVL LAPSE RATES...AS WELL AS HAIL
CAPE AND DCAPE VALUES NEAR 1000 J/KG SUPPORT SEVERE THUNDERSTORMS
CAPABLE OF PRODUCING LARGE HAIL AND DAMAGING WINDS BY MONDAY
EVENING. COVERAGE SHOULD REMAIN ISOLATED INITIALLY...BUT IS
EXPECTED TO INCREASE INTO THE EVENING. FURTHER INTENSIFICATION AND
COVERAGE OF THUNDERSTORMS SEEMS APPARENT AS A LARGE MID LVL TROUGH
OF LOW PRESSURE DIGS OVER THE EASTERN CONUS IN RESPONSE TO A H25
JET AND SERIES OF H5 SHORTWAVES ROUNDING ITS BASE. THE DIGGING
TROUGH WILL FORCE THE SFC COLD FRONT SOUTH/SOUTHEAST INTO PORTIONS
OF SOUTHEAST SOUTH CAROLINA NEAR SUNSET...THEN INTO SOUTHEAST
GEORGIA THROUGH MIDNIGHT.

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...THE LARGEST COVERAGE OF SEVERE THUNDERSTORMS
WOULD OCCUR BETWEEN 7 PM AND MIDNIGHT...WITH THE RISK LINGERING THE
LONGEST OVER COASTAL GEORGIA. UNIDIRECTIONAL FLOW/SHEAR PROFILES
ALONG WITH THE MENTIONED PARAMETERS ABOVE SUGGEST PRIMARILY A LARGE
HAIL AND DAMAGING WIND EVENT. BRIEF 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 UPPER 60S INLAND TO LOW/MID
70S...COOLEST BEHIND THE FRONT.

TUESDAY AND WEDNESDAY...THE PATTERN WILL BECOME MUCH MORE QUIET INTO
MIDWEEK AS 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 ON TUESDAY 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 UPPER 80S TO AROUND 90 ON TUESDAY...HIGHEST AWAY FROM
THE COAST. BY WEDNESDAY...WE COULD SEE LIGHT ONSHORE WINDS DEVELOP
NORTH OF LOW PRESSURE OFF THE SOUTHEAST GEORGIA AND NORTHERN FLORIDA
COAST. ALTHOUGH THE SETUP SHOULD FAVOR SLIGHTLY MORE MOISTURE OVER
THE REGION...A DRY FORECAST WILL REMAIN IN PLACE. HOWEVER...A SHOWER
OR ISOLATED THUNDERSTORM CAN NOT BE COMPLETELY RULED OUT ALONG THE
SOUTHEAST SOUTH CAROLINA COAST. OVERALL HIGH TEMPS ON WEDNESDAY SHOULD
REMAIN IN THE UPPER 80S TO AROUND 90...WARMEST IN SOUTHEAST GEORGIA.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
THE DEEP EASTERN CONUS TROUGH WILL REMAIN IN PLACE THROUGH THE END
OF THE WEEK AND INTO THE START OF NEXT WEEKEND. IN FACT SOME OF THE
MODELS SHOW THE TROUGH STRENGTHENING FURTHER AND DEVELOPING A CLOSED
LOW ACROSS THE UPPER MIDWEST. AT THE SURFACE...THE REMNANT COLD
FRONT OFFSHORE MAY ACTUALLY DRIFT BACK WESTWARD AS A COASTAL TROUGH
BY THE END OF THE PERIOD. IF THIS WERE TO OCCUR DEEP MOISTURE WOULD
INCREASE ACROSS THE FORECAST AREA AND AN INCREASE IN CONVECTIVE
COVERAGE APPEARS LIKELY BY THE LATTER PART OF THE FORECAST.
TEMPERATURES WILL REMAIN BELOW CLIMO THROUGH THE PERIOD.

&&

.AVIATION /02Z MONDAY THROUGH FRIDAY/...
VFR CONDITIONS WILL PREVAIL AT KCHS AND KSAV THROUGH 00Z TUESDAY.
THE LOW LEVEL JET WILL INCREASE OVERNIGHT AND SUPPORT WINDS
UPWARDS OF 30-35 KT AT 2 KFT BY 06Z. HOWEVER...THESE WINDS APPEAR
TO FALL JUST SHORT OF CRITERIA FOR INCLUDING LOW LEVEL WIND SHEAR
IN THE FORECAST SINCE WINDS AT THE SURFACE WILL NOT DECOUPLE.
THESE STRONGER WINDS ALOFT WILL BEGIN TO MIX TO THE SURFACE IN THE
FORM OF HIGHER GUSTS UPWARDS OF 18-23 KT WITH THE HEATING OF THE
DAY...GENERALLY AFTER 14Z. SCATTERED SHOWERS AND THUNDERSTORMS
WILL DEVELOP AHEAD OF AN APPROACHING COLD FRONT LATE IN THE DAY
MONDAY...AND HAVE INCLUDED VICINITY THUNDERSTORMS AT BOTH
TERMINALS AFTER 21Z.

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 COMBINATION OF AN INTENSIFYING LOW SYSTEM FAR TO THE
NORTH...AND A COLD FRONT APPROACHING THE APPALACHIANS...WILL
SUPPORT A TIGHTENING PRESSURE GRADIENT ACROSS THE COASTAL WATERS.
THE LOW LEVEL JET WILL INCREASE TO 25 TO 30 KT AFTER MIDNIGHT
ACCORDINGLY...HOWEVER EXPECT ONLY A PORTION OF THESE WINDS TO MIX
DOWN TO THE SURFACE WITHIN A STRONG WARM ADVECTION REGIME. HAVE
THUS INDICATED SOUTHWEST WINDS 15 TO 20 KT ACROSS ALL WATERS
TONIGHT...WITH SEAS BUILDING TO 4 TO 5 FT IN THE OFFSHORE ZONES.
ALTHOUGH OCCASIONAL GUSTS UP TO 25 KT ARE POSSIBLE...ESPECIALLY
IN THE CHARLESTON COUNTY WATERS AND OFFSHORE GEORGIA
ZONES...CONFIDENCE IN THE FREQUENCY OF THESE WINDS IS TOO LOW TO
ISSUE A SMALL CRAFT ADVISORY AT THIS TIME.

MONDAY THROUGH THURSDAY...A STRONG COLD FRONT IS EXPECTED TO
APPROACH AND MOVE ACROSS THE LOCAL WATERS MONDAY EVENING THROUGH
MONDAY NIGHT. AHEAD OF THE FRONT...A TIGHT PRESSURE GRADIENT WILL
SUPPORT WINDS BETWEEN 15-20 KTS AND SEAS AS HIGH AS 3-5 FT.
HOWEVER...SMALL CRAFT ADVISORY CONDITIONS ARE NOT EXPECTED AT THIS
TIME. STRONG THUNDERSTORMS WILL LIKELY ACCOMPANY THE FRONT THROUGH
THE EARLY TUESDAY MORNING HOURS...RESULTING IN WHAT WILL LIKELY
BE SPECIAL MARINE WARNINGS OVER THE WATERS. BEHIND THE FRONT...THE
GRADIENT WILL RELAX CONSIDERABLY. WINDS WILL BE 15 KT OR LESS AND
WILL TAKE ON A MORE EASTERLY COMPONENT THROUGH MID WEEK.

&&

.CLIMATE...
RECORD HIGH MINIMUM TEMPS FOR JULY 27TH...
KCHS...79 SET IN 2005.
KCXM...82 SET IN 2005.
KSAV...80 SET IN 1885.

RECORD HIGH MINIMUM TEMPS FOR JULY 28TH...
KCHS...79 SET IN 1981.
KCXM...83 SET IN 1999.
KSAV...81 SET IN 1878.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...HEAT ADVISORY FROM 11 AM TO 7 PM EDT MONDAY FOR GAZ087-088-
     099>101-114>119-137>141.
SC...HEAT ADVISORY FROM 11 AM TO 7 PM EDT MONDAY FOR SCZ040-042>045-
     047>052.
MARINE...NONE.

&&

$$

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






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