000
FXUS62 KCHS 200813
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
413 AM EDT MON MAY 20 2013

.SYNOPSIS...
AN UPPER LEVEL DISTURBANCE OVER THE AREA WILL DISSIPATE THROUGH
MID WEEK WHILE ATLANTIC HIGH PRESSURE PREVAILS UNTIL LATE WEEK. A
COLD FRONT WILL DROP THROUGH THE AREA LATE FRIDAY INTO SATURDAY...
FOLLOWED BY HIGH PRESSURE THROUGH NEXT WEEKEND.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
PRE-DAWN...THROUGH 4 AM IT HAS BEEN A QUIET OVERNIGHT WITH AREAS OF
LAYERED CLOUDS...SOME INLAND STRATUS AND FOG WAS VERY PATCHY IN
NATURE. SUMMER-LIKE TEMPS IN THE 69 TO 73 DEGREE RANGE...WARMEST
ALONG COASTAL SOUTH CAROLINA WHERE STRONG LOW LEVEL MOISTURE
CONVERGENCE WAS ONGOING.

A SHORTWAVE TROUGH ALOFT OVER THE REGION TODAY IS COMPLEX PER LOOPS
OF OVERNIGHT WATER VAPOR SATELLITE IMAGERY. THE MAIN UPPER WAVE
WAS DRIFTING E ALONG THE VA/NC BORDER WHILE A WEAK VORTICITY AXIS
EXTENDED S OVER COASTAL GEORGIA IN NE FLORIDA. AN INTERESTING
FEATURE IS THE IMPULSE OVER THE FLORIDA PANHANDLE...OUR ANALYSIS
DID NOT DETECT THIS FEATURE AT 500 MB...IT MAY BE PART MCV AND IS
FORECAST TO STRETCH THE MID LEVEL TROUGH TODAY.

THE MAIN FORECAST PROBLEMS OF THE DAY ARE TWOFOLD. THERE APPEARS TO
BE HEAVY RAIN POTENTIAL UNTIL MID AFTERNOON ALONG COASTAL SOUTH
CAROLINA AND THEN AN ISOLATED SEVERE WEATHER RISK W OF I-95 IN SE
GEORGIA AND FAR SOUTHERN SOUTH CAROLINA THIS AFTERNOON.

ADDRESSING THE MORNING POTENTIAL FOR DEVELOPING CONVECTIVE RAINS
ALONG THE SOUTH CAROLINA COAST...VERY DEEP MOISTURE IS IN PLAY.
LATEST ANALYSIS INDICATES MOISTURE TRANSPORT CONVERGENCE AND A
INSTABILITY GRADIENT HAS SETUP ALONG THE COAST. A SLEW OF THE 00Z
HIGH RESOLUTION MODELS ERUPT EXCESSIVE QPF OUTPUT SOMEWHERE
BETWEEN EDISTO BEACH AND THE GRAND STRAND. MOST OF THESE MODELS
APPEAR TO HAVE CONVECTIVE FEEDBACK ISSUES BUT THE TREND IS WORTH
WATCHING GIVEN THE 1.8 INCH PWATS LURKING ON THE LATEST RUC
ANALYSIS. WE HAVE BUMPED POPS TO LIKELY IN PARTS OF THE CHARLESTON
TRI-COUNTY AREA CLOSER TO THE COAST.

THE SECOND ISSUE OF THE DAY WILL TURN TO DIURNAL CONVECTIVE
DEVELOPMENT DURING THE AFTERNOON ONCE AGAIN. MODELS INDICATE A 35 KT
700 MB WIND MAX DEVELOPING OVER THE INLAND CAROLINAS AROUND MIDDAY
AND PUNCHING DUE S INTO GEORGIA W OF I-95 LATER TODAY. 300 MB FLOW
ACROSS SE GEORGIA RAPIDLY BACKS FROM SW TO SE TODAY AND A POCKET OF
UPPER DIFLUENCE IS PROGGED...EVEN THOUGH  THE FLOW IS WEAK AT JET
LEVEL. MORNING LOW CLOUDS ARE LIKELY TO DISSIPATE LEAVING A
POTENTIAL FOR SOME INSOLATION LATE MORNING AND EARLY AFTERNOON.
MODEL INSTABILITY PROGS SHOW PARAMETERS A BIT MORE UNSTABLE THAN
ON SUNDAY BACK OVER OUR INLAND ZONES. MUCH OF THIS SCENARIO WILL
DEPEND ONCE AGAIN ON MESOSCALE BOUNDARIES AND SURFACE HEATING.
CANNOT RULE OUT ISOLATED SEVERE THUNDERSTORMS WITH DAMAGING WIND
MARGINALLY SEVERE HAIL OR SOME VERY SMALL SCALE CONVECTIVE
ORGANIZATION. MANY OF THESE STORMS WILL ALSO PRODUCE VERY HEAVY
DOWNPOURS.

THE CONFIDENCE OF EITHER OF THESE SCENARIOS BECOMING REALITY IN
SPACE AND TIME IS NOT GREAT...THUS WE OPTED TO NOT ADD ANY MENTIONS
IN OUR HAZARDOUS WEATHER OUTLOOK UNTIL RADAR TRENDS BECOME MORE
DEFINITIVE AND A 12Z ANALYSIS IS PERFORMED.

HIGH TEMPS TODAY 80 TO 85 DEGREES MOST AREAS WITH LIGHT SOUTH TO
SOUTHEAST WINDS.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY/...
UPPER LEVEL TROUGHING OVER THE AREA IS NOT GOING ANYWHERE TONIGHT
BUT WE DO EXPECT CONVECTION TO DECREASE IN COVERAGE AND INTENSITY
DURING THE EVENING. LOW LEVEL COASTAL MOISTURE CONVERGENCE WILL
INCREASE TOWARD DAYBREAK ON TUE ALONG COASTAL SOUTH CAROLINA AND
CONVECTIVE RAINS MAY BREAK OUT ONCE AGAIN THERE. WILL ALSO NEED TO
WATCH TRENDS FOR FOG DEVELOPMENT TONIGHT IF CLOUDS BREAK. WITH
WIDESPREAD CONVECTIVE RAINS EXPECTED TODAY...THERE SEEMS TO BE
INCREASING CHANCES FOR FOG...ESPECIALLY INLAND.

A MOIST AIRMASS WILL PERSIST DURING THE PERIOD ALTHOUGH WE SHOULD
SEE A SLIGHT DECREASE IN PW VALUES BY THURSDAY. THE UPPER
SHORTWAVE WILL SLOWLY DISSOLVE OVERHEAD ON TUESDAY BUT ANOTHER
WAVE WILL APPROACH LATE WEDNESDAY THROUGH THURSDAY. AT THE SURFACE
ATLANTIC HIGH PRESSURE WILL MAINTAIN ITS CONTROL...KEEPING
SOUTHERLY FLOW IN LOW-LEVELS AND ALLOWING DAILY SEABREEZE
CIRCULATIONS TO DEVELOP. CONVECTIVE COVERAGE WILL VARY SOMEWHAT
BETWEEN THE THREE DAYS WITH WEDNESDAY CURRENTLY LOOKING LIKE THE
LEAST ACTIVE DAY DUE TO A LACK OF APPRECIABLE UPPER ENERGY TO WORK
WITH. HIGH TEMPS WILL CLIMB INTO THE MID TO UPPER 80S WITH LOWS IN
THE MIDDLE 60S.

&&

.LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...
FAIRLY GOOD MODEL CONSISTENCY REGARDING AN UPPER TROUGH SHIFTING
SOUTHEAST AND A COLD FRONTAL PASSAGE FRIDAY OR FRIDAY NIGHT. DRY AND
SLIGHTLY COOLER CANADIAN HIGH PRESSURE LOOKS TO BUILD IN FOR THE
WEEKEND BEFORE SHIFTING OFFSHORE EARLY NEXT WEEK.

&&

.AVIATION /08Z MONDAY THROUGH FRIDAY/...
KCHS...VFR WEATHER TO PREVAIL OVERNIGHT UNTIL LATE. A FEED OF
ABUNDANT MOISTURE AND ASSOCIATED CONVERGENCE WILL PRODUCE
SCATTERED CONVECTION THIS MORNING. WHILE MUCH OF THIS ACTIVITY LOOKS
TO REMAIN EAST OF THE TERMINAL PRIOR TO DAYBREAK...MODELS DEVELOP
CONVECTIVE RAINS AROUND DAWN AND THEN RAIN CHANCES FOR THE REST OF
TODAY LOOK PRETTY GOOD AS DEEP MOISTURE INTERACTS WITH THE UPPER
TROUGH AND THE SEA BREEZE. SHOWERS/TSTMS SHOULD DECREASE LATE DAY
WITH MAINLY VFR CONDITIONS THIS EVENING.

KSAV...VFR OVERNIGHT WEATHER COULD DROP TO THE MVFR RANGE IN
LIGHT FOG/LOW STRATUS LATE. THERE IS THEN A DECENT CHANCE OF
SHRA AND POSSIBLE TSRA FROM 16-22Z MONDAY WITH SEVERAL MESO-SCALE
BOUNDARIES IN PLACE AIDED BY A SHORT WAVE ALOFT. MVFR WEATHER CAN
CERTAINLY OCCUR PERIODICALLY DURING THIS TIME.

EXTENDED AVIATION...THE MAIN CONCERN WILL BE SPORADIC REDUCTIONS
IN CEILINGS AND VISIBILITIES...MAINLY ASSOCIATED WITH SCATTERED
SHOWERS AND THUNDERSTORMS THROUGH THE PERIOD. THE GREATEST CHANCES
WILL BE IN THE AFTERNOON HOURS TUE THROUGH THU...ALTHOUGH EARLY
MORNING FLIGHT RESTRICTIONS CANNOT BE RULED OUT EACH DAY.

&&

.MARINE...
THROUGH TONIGHT...A STRONG RIDGE OF HIGH PRESSURE CENTERED OVER
THE ATLANTIC WILL EXTEND W ACROSS THE COASTAL WATERS...GENERATING
SE AND S WINDS OF 10-15 KT OR LESS AND SEAS IN THE 2-4 FOOT RANGE.

HIGH PRESSURE WILL REMAIN OVER THE WESTERN ATLANTIC THROUGH THURSDAY
NIGHT WITH SEABREEZE CIRCULATIONS DEVELOPING EACH AFTERNOON. A COLD
FRONT WILL DROP THROUGH FRIDAY EVENING OR SATURDAY MORNING WITH A
NORTHEAST FLOW DEVELOPING AS CANADIAN HIGH PRESSURE BUILDS IN. WINDS
AND SEAS WILL LIKELY INCREASE OVER THE WEEKEND IN RESPONSE.

&&

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

&&

$$

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