000
FXUS62 KCHS 190840
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
440 AM EDT FRI MAR 19 2010
.SYNOPSIS...
HIGH PRESSURE WILL BUILD INTO THE AREA THROUGH SATURDAY. A COLD
FRONT IS EXPECTED TO MOVE THROUGH THE REGION SUNDAY NIGHT...
FOLLOWED BY HIGH PRESSURE THROUGH THE MIDDLE OF NEXT WEEK. ANOTHER
COLD FRONT MAY APPROACH FROM THE WEST LATE NEXT WEEK.
&&
.NEAR TERM /THROUGH TONIGHT/...
WATER VAPOR IMAGERY SHOWS THE PERSISTENT CLOSED UPPER LOW NOW
ABOUT 60 NM SE OF CHARLESTON. A POTENT SHORTWAVE ROUNDING THE BASE
OF THE TROUGH SHOULD HELP TO KICK IT OFF TO THE E AND NE LATER
TODAY. THE ONLY RESIDUAL EFFECT THE LOW WILL HAVE ON OUR WEATHER
WILL BE A SLOWLY RETREATING PATCH OF MID AND HIGH LEVEL CLOUDINESS
ACROSS SOUTHERN SC. THIS CLOUDINESS HAS ALREADY BEGUN TO THIN AND
THE WESTERN EDGE BECOMING BETTER DEFINED. OUR RADAR WAS PICKING UP
SOME LIGHT RETURNS ACROSS BERKELEY COUNTY A FEW HOURS AGO...BUT
THIS WAS PROBABLY ONLY VIRGA GIVEN THE 10 KFT CLOUD HEIGHTS AND
LACK OF SURFACE PRECIP REPORTS.
LARGE-SCALE SUBSIDENCE ASSOCIATED WITH UPPER RIDGING ALONG WITH A
WEAK DOWNSLOPE TRAJECTORY AT LOWER LEVELS WILL SUPPORT SUNNY SKIES
IN MOST LOCATIONS BY LATE THIS MORNING. WE HAVE THE LAST OF THE
MID-CLOUDS SHIFTING OFF THE CHARLESTON COUNTY COAST BY ABOUT 1 PM
BUT EVEN PRIOR TO THIS OCCURRING...THERE SHOULD BE PLENTY OF
BREAKS IN THE CLOUDS TO ALLOW FOR FAIRLY HOMOGENEOUS HEATING.
NUDGED HIGH TEMPS UP ABOUT A DEGREE ACROSS THE INLAND HALF OF THE
FORECAST AREA TO COME IN LINE WITH A BLEND OF GFS/NAM THICKNESS
PROGS. A SEABREEZE WILL PROBABLY DEVELOP BUT NOT SHIFT INLAND
UNTIL AFTER 3 OR 4 PM ONCE THE WESTERLY FLOW WEAKENS SUFFICIENTLY
WITH THE UPPER RIDGE AXIS MOVING OVERHEAD. MOST AREAS SHOULD SEE
TEMPS IN THE LOW TO MID 70S. THE BEACHES WILL PROBABLY TOP OUT IN
THE MID TO UPPER 60S EARLY IN THE AFTERNOON BEFORE THE COOLER
MARINE LAYER BEGINS TO BUILD.
CLEAR SKIES AND LIGHT WINDS SUPPORT STRONG RADIATIONAL COOLING
TONIGHT. THIS WILL ALLOW FOR A LARGE DIURNAL RANGE WITH LOWS
DROPPING BACK INTO THE LOWER TO MIDDLE 40S.
&&
.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
PLENTY OF SUNSHINE TO ACCOMPANY QUITE MILD CONDITIONS ON SAT. AN
UPPER RIDGE WILL BE SLIDING OFFSHORE WITH RETURN FLOW WORKING INTO
THE REGION DURING THE AFTERNOON SEA BREEZE PASSAGE ALONG THE COAST.
WE BUMPED HIGHS UP INTO THE UPPER 70S IN A FEW AREAS. STILL MUCH
COOLER AFTERNOON READINGS AT AREA BEACHES.
THE NEXT SYSTEM WE WILL FACE AT THE END OF THE WEEKEND IS SHAPING
UP TO BE AN ENERGETIC ONE WITH A LARGE AND DEEP MID LEVEL CUT-OFF
LOW PRES AREA MOVING OUT OF THE SOUTHERN PLAINS INTO THE DEEP
SOUTH REGION DURING SUNDAY AFTERNOON. MODELS ARE IN GENERALLY
GOOD AGREEMENT WITH THE THE EVOLUTION...INTENSITY AND TIMING OF THIS
SYSTEM. THE 00Z ECMWF IS FURTHER S THAN THE GFS AND SUGGESTS A MORE
ROBUST POTENTIAL FOR A LOW-TOPPED STRONGLY FORCED SQUALL LINE MOVING
INTO OUR WESTERN AREAS LATE AFTERNOON SUNDAY. IF THE CUT-OFF TAKES
THIS FAR OF A TRACK S OF TENNESSEE WE CERTAINLY COULD SEE A SEVERE
WEATHER EVENT UNFOLD WITH DAMAGING WINDS AND ISOLATED TORNADOES.
SINCE THE GFS REMAINS FAIRLY CONSISTENT FROM RUN TO RUN...IT WAS
GENERALLY THE MODEL OF CHOICE THIS MORNING. IT IS INTERESTING TO
NOTE THAT THE GFS HAS BEEN TRENDING SLOWLY HIGHER ON SURFACE DEW
POINTS ACROSS OUR REGION AHEAD OF THE FRONT WITH EACH MODEL RUN. WE
INCREASED POPS INLAND IN OUR WESTERN ZONES SUNDAY AFTERNOON AND E OF
I-95 ON SUNDAY NIGHT AS THE DYNAMICS AND SURFACE FRONT SWING
THROUGH. HIGHS SHOULD REACH THE LOWER TO MID 70S ON SUNDAY BEFORE
CONVECTIVE RAINS MOVE IN. S WINDS WILL ALSO BEGIN TO INCREASE IN THE
AFTERNOON AND EVENING AHEAD OF THE COLD FRONT.
&&
.LONG TERM /MONDAY THROUGH THURSDAY/...
MON WILL BE A DAY DETERMINED BY THE TRACK OF A DEEP MID LEVEL
CUT-OFF LOW PRES SYSTEM WOBBLING TOWARD THE SOUTHERN MID ATLC
REGION BY LATE DAY. INITIALLY WE APPEAR TO BE DRY-SLOTTED WITH
COLD AIR ADVECTION LAGGING BACK. THE SURFACE COLD FRONT WILL
LIKELY BE JUST THROUGH FOR SOUTH CAROLINA FORECAST AREA BY DAWN
BUT CLOUDS SHOULD DEVELOP DURING THE DAY WITH GOOD UPPER
HEIGHT FALLS AND STEEP LAPSE RATES DEVELOPING AS MID LEVELS
TEMPERATURES COOL. DECENT MODEL AGREEMENT THAT THE CORE OF THIS
SYSTEMS WORKS JUST OFF TO THE N AND SHOWERS WITH GRAUPEL POTENTIAL
MISSING OUR REGION JUST TO THE N AND WE MAINTAINED A FORECAST DRY
FOR NOW.
THE UPPER LOW WILL MOVE OUT OF THE PICTURE TUE INTO WED WITH A
RIDGE BUILDING OVER THE AREA AND TEMPERATURES WARMING BACK TO
SLIGHTLY ABOVE CLIMO READINGS BY MID WEEK. A COLD FRONT WILL
APPROACH LATE WEEK AND MAY BRING SCATTERED CONVECTIVE RAINS
LATE WEEK...POSSIBLY SHIFTING E OF OUR REGION BY SAT. MILD
TEMPERATURES AT OR ABOVE CLIMO VALUES ARE EXPECTED MID TO LATE
WEEK.
&&
.AVIATION /09Z FRIDAY THROUGH TUESDAY/...
VFR CONDITIONS WILL PREVAIL AT BOTH AT KCHS AND KSAV THROUGH 06Z
SATURDAY. LIGHT NORTHWEST WINDS WILL SHIFT TO SW LATE THIS
AFTERNOON WITH A WEAK SEABREEZE.
EXTENDED AVIATION OUTLOOK...VFR CONDITIONS ARE EXPECTED THROUGH
SUNDAY MORNING. COULD SEE SOME MVFR CIGS/VSBYS SUNDAY AFTERNOON AND
SUNDAY NIGHT ALONG WITH A RISK FOR LLWS SUNDAY NIGHT. VFR CONDITIONS
ARE THEN EXPECTED MON THROUGH TUE.
&&
.MARINE...
TRANQUIL CONDITIONS WILL PREVAIL THROUGH TONIGHT ACROSS OUR MARINE
JURISDICTION AS SURFACE HIGH PRESSURE BUILDS OVERHEAD. A WEAK
SEABREEZE IS EXPECTED TO DEVELOP LATE THIS AFTERNOON ALONG THE
COAST WITH WINDS BACKING TO SSE. HOWEVER SPEEDS NOT EXPECTED TO
INCREASE MUCH ABOVE 10 KT. THE ATLANTIC WATERS CONTINUE TO BE
AFFECTED BY A 2-3 FT SWELL WHICH WILL CONTINUE THROUGH TONIGHT.
OVERALL SEA STATE SHOULD IMPROVE SLIGHTLY THROUGH THE PERIOD AS
THE WIND WAVE COMPONENT BECOMES NEGLIGIBLE.
RELATIVELY TRANQUIL CONDITIONS ARE EXPECTED ON SAT WITH DECENT
SEA BREEZE ENHANCEMENTS ALONG THE LAND/SEA INTERFACE DURING THE
AFTERNOON. SE TO S FLOW WILL INCREASE ON SUNDAY AHEAD OF A COLD
FRONT AND SEAS COULD BUILD FAIRLY QUICKLY SUNDAY AFTERNOON WITH
THIS PATTERN.
SMALL CRAFT ADVISORY CONDITIONS ARE LIKELY SUNDAY NIGHT INTO
EARLY MON WITH THE STRONG FRONTAL ZONE SWINGING THROUGH THE
COASTAL WATERS. GUSTY OFFSHORE FLOW IS ANTICIPATED EARLY NEXT
WEEK WITH JETTING CONDITIONS AWAY FROM THE COAST AND POSSIBLE
SCA CONDITIONS ALONG THE LAND/SEA INTERFACE EACH AFTERNOON MON
AND TUE GIVEN FORECAST MIXING PROFILES AND STEEP LOW LEVEL
LAPSE RATES.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...NONE.
&&
$$
JRL/
