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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KCHS 181134
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
734 AM EDT SAT MAY 18 2013

.SYNOPSIS...
AN UPPER DISTURBANCE WILL MOVE NORTH OF THE AREA THROUGH MONDAY.
ATLANTIC HIGH PRESSURE WILL BE THE DOMINANT FEATURE THROUGH MUCH OF
NEXT WEEK BEFORE A COLD FRONT APPROACHES FRIDAY NIGHT AND SATURDAY.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
-- Changed Discussion --
QUITE A FEW TRICKY ELEMENTS TO OUR FORECAST TODAY...HOWEVER THE
OVERALL SYNOPTIC PATTERN REMAINS SIMILAR WITH THE OFFSHORE ATLC
RIDGE REFUSING TO BUDGE AND THE SURFACE RIDGE AXIS STILL POKING W
THROUGH NORTHERN FLORIDA.

DEEPER MOISTURE BETWEEN 850MB-500MB AND A POCKET OF UPPER FORCING
WITH THE UPSTREAM SHORT WAVE IS EXPECTED TO REMAIN OVER THE
WESTERN CAROLINAS INTO VIRGINIA TODAY. AS THE 925MB-850MB TROUGH
PULLS MORE N THAN E WITH TIME....THERE WILL LIKELY BE A LOW LEVEL
TROUGH/CONVERGENCE ZONE SETTING UP ALONG AND JUST W OF INTERSTATE
95 THIS AFTERNOON. MODEL SOUNDINGS SHOW THE ATMOSPHERE BECOME MORE
CONDUCIVE TO CONVECTIVE DEVELOPMENT LATER TODAY...ESPECIALLY
ANCHORED IN THIS FAIRLY NARROW CORRIDOR OF LOW LEVEL MOISTURE
CONVERGENCE. MID LEVEL INSTABILITY IS NOT VERY IMPRESSIVE WITH MID
LEVEL LAPSE RATES -5.5C TO -6C IN THE 700MB TO 500MB LAYER AND
SHOWALTER INDICES RUNNING SLIGHTLY POSITIVE. SIMILAR TO PREVIOUS
THINKING WE CHANNELED SLIGHT CHANCE TO CHANCE POPS ALONG THE I-95
CORRIDOR. IT STILL LOOKS UNLIKELY WE WILL SEE MANY INTENSE UPDRAFTS
AND MUCH IN THE WAY OF SEVERE WEATHER.

SKY COVER PROGS ARE TOUCH AND GO AS TIME/HEIGHT CROSS SECTIONS
SHOWING COPIOUS HIGH LEVEL MOISTURE STREAMING THROUGH BUT PRE-DAWN
SATELLITE IMAGERY HINTING THAT WE MAY SEE MORE IN THE WAY OF
SUNSHINE AT LEAST OVER THE SE HALF OF THE FORECAST AREA. OF COURSE
CLOUDS WILL HAVE AN IMPACT ON HIGH TEMPS AND OVERALL PERSISTENCE
WAS MAINTAINED WITH MAX TEMPS IN THE MID TO UPPER 80S.
-- End Changed Discussion --

&&

.SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY/...
ANY EARLY EVENING CONVECTION WITH THE SEA BREEZE MAY TEND TO DRIFT
TOWARD THE COAST BUT ALSO LIKELY DISSIPATE QUICKLY WITH LOSS OF
SURFACE HEATING. OVERNIGHT...MODELS DELIVER A BIT MORE UPPER LEVEL
NW FLOW AND DEEPER LAYERED INSTABILITY WHICH COULD LEAD TO ISOLATED
CONVECTIVE RAINS JUST ABOUT ANYWHERE LATE...SLIGHT CHANCE POPS
AFTER MIDNIGHT WERE MAINTAINED. PARTLY TO MOSTLY CLOUDY SKIES ON
TAP WITH TEMPS IN THE 60S ONCE AGAIN.

A FAIRLY ROBUST SHORTWAVE TROUGH WILL BE NORTH OF THE AREA ON SUNDAY
BUT DROP SOUTHEAST INTO CENTRAL SOUTH CAROLINA ON MONDAY. MEANWHILE
WITH ATLANTIC HIGH PRESSURE JUST OFF THE COAST...A SOUTH-SOUTHEAST
FLOW WILL MAINTAIN A FAIRLY JUICY AIRMASS. PW READINGS POTENTIALLY
EXCEED 1.80 INCHES ON MONDAY. SOME MID AND HIGH CLOUDS WILL SOMEWHAT
LIMIT HEATING SUNDAY AND MONDAY BUT HIGHS WILL LIKELY STILL CLIMB
INTO THE UPPER 80S FAR INLAND WITH MIDDLE 80S ELSEWHERE. THE UPPER
HEIGHT FALLS AND STEEPENING MID-LEVEL LAPSE RATES ASSOCIATED WITH
THE SHORTWAVE ENERGY WILL PROVIDE A FAVORABLE ENVIRONMENT FOR
SCATTERED TO NUMEROUS SHOWERS AND TSTMS BOTH DAYS. INSTABILITY
PARAMETERS INDICATE SOME STRONG STORMS WILL BE POSSIBLE EITHER DAY.
IN ADDITION...WITH PW VALUES NEAR THE 99TH PERCENTILE FOR MAY AND
0-6 KM MEAN WINDS LESS THAN 10 KT...LOCALLY HEAVY RAINFALL WILL
ALSO BE A CONCERN.

THE UPPER VORT ENERGY WILL SHIFT OFFSHORE MONDAY NIGHT WITH
SHORTWAVE RIDGING FOR TUESDAY. ONLY ISOLATED AIRMASS CONVECTION
EXPECTED TUESDAY...PRIMARILY DRIVEN BY THE SEABREEZE SO WE HAVE
SLIGHT CHANCE POPS. TEMPS WILL BE A FEW DEGREES WARMER DUE TO MORE
SUN.

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
A RATHER WARM PATTERN PERSISTS IN THE LONG TERM AS THE AREA SITS ON
THE WESTERN SIDE OF AN UPPER RIDGE WITH ATLANTIC HIGH PRESSURE
OFFSHORE. RAIN CHANCES WILL INCREASE A BIT LATE IN THE WEEK AS AN
UPPER TROUGH APPROACHES FROM THE WEST AND A COLD FRONT DROPS INTO
THE AREA FRIDAY NIGHT OR SATURDAY.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
VFR CONDITIONS WILL PREVAIL AT KCHS AND KSAV THROUGH 06Z SUNDAY.
ISOLATED CONVECTION COULD DEVELOP LATER THIS AFTERNOON MAINLY
WEST OF THE I-95 CORRIDOR...PROBABILITIES OF ANY CONVECTION
IMPACTING THE TERMINALS ARE TOO LOW TO INCLUDE IN THE FORECAST AT
THIS TIME. DEEPER MOISTURE MOVES INTO THE TAF CORRIDOR LATER
TONIGHT AND THERE IS A POSSIBILITY FOR MVFR CIGS...ESPECIALLY AT
KSAV. BOTH TERMINALS COULD ALSO SEE AN OVERNIGHT SHOWER BUT FOR
BOTH THESE SCENARIOS...CONFIDENCE IS PRETTY LOW AT THIS TIME.

EXTENDED AVIATION OUTLOOK...PRIMARILY VFR. LOW CHANCES OF DIRECT
IMPACTS FROM ISOLATED TO SCATTERED MAINLY AFTERNOON
SHOWERS/THUNDERSTORMS THROUGH EARLY NEXT WEEK.
-- End Changed Discussion --

&&

.MARINE...
ATLANTIC HIGH PRESSURE WILL PERSIST OFF THE COAST WITH A SOUTH TO
SOUTHEAST FLOW RANGING FROM 10 TO 15 KNOTS PERSISTING. SEAS WILL
AVERAGE 2 TO 4 FEET THROUGH WEDNESDAY WITH SOME BUILDING OF SEAS
LATE WEEK AS THE GRADIENT TIGHTENS A BIT.

&&

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

&&

$$

SYNOPSIS...
NEAR TERM...
SHORT TERM...JRL
LONG TERM...JRL
AVIATION...
MARINE...JRL