000
FXUS62 KCHS 201146
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
746 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/...
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 VERTICALLY 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. MOST OF THE 00Z
HIGH RESOLUTION MODELS HAVE PERFORMED POORLY THROUGH 12 HOURS BUT
SHORT LINES OF HEAVY SHOWERS WERE DEVELOPING E OF I-95 IN SOUTH
CAROLINA AND IT LOOKS LIKE SOME POTENTIAL FOR TRAINING CELLS. THE
TRENDS ARE WORTH WATCHING GIVEN THE 1.8 INCH PWATS LURKING ON THE
LATEST RUC ANALYSIS. WE CONTINUED LIKELY POPS IN PARTS OF THE
CHARLESTON TRI-COUNTY AREA.

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 /12Z MONDAY THROUGH FRIDAY/...
KCHS...A BAND OF SHOWERS WAS DRIFTING TOWARD THE KCHS TERMINAL
THIS MORNING. MODELS CONTINUE TO INDICATE SHOWERS AND ISOLATED
TSTMS INCREASING IN COVERAGE THROUGH MID AFTERNOON WITH THE
SEA BREEZE BECOMING A FOCUS FOR CONVECTION. WE PREVAILED
CONVECTIVE RAINS DURING THE PRIME SEA BREEZE TIME THIS AFTERNOON
WITH VCSH OR TEMPO SHRA UNTIL THEN. TONIGHT...LIKELY VFR BUT
CANNOT RULE OUT MVFR VSBYS LATE IF GROUNDS BECOME WET TODAY.

KSAV...BRIEF MVFR CIGS THIS MORNING BUT CONDITIONS AT DAYBREAK
WERE VFR. THERE COULD BE ADDITIONAL PERIODS OF MVFR CIGS THIS
MORNING OTHERWISE THE MAIN PROBLEM OF THE DAY IS TIMING ANOTHER
BOUT OF DIURNAL CONVECTIVE RAINS. WE MAINTAINED 17Z TO 21Z FROM
PREVIOUS TAFS AS LATEST MODELS ALSO REMAIN CONSISTENT. THERE
COULD BE SOME LOW CLOUDS AND/OR MVFR VSBYS LATE TONIGHT BUT OUR
CONFIDENCE IS LOW AT THIS TIME.

EITHER TERMINAL COULD REPORT THUNDER TODAY AS THE ATMOSPHERE
REMAINS UNSTABLE. WE OPTED TO LEAVE TSRA OUT OF THE PICTURE UNTIL
RADAR TRENDS BECOME BETTER DEFINED.

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