000
FXUS62 KCHS 100254
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
954 PM EST TUE MAR 9 2010

.SYNOPSIS...
A SERIES OF UPPER AIR DISTURBANCES WILL MOVE THROUGH THE AREA LATE
TONIGHT THROUGH FRIDAY. A COMPLEX LOW PRESSURE SYSTEM WILL RESIDE TO
THE NORTH OF THE REGION THIS WEEKEND INTO EARLY NEXT WEEK.

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
MID/HIGH LEVEL CLOUDS WILL CONTINUE TO OVERSPREAD THE REGION
TONIGHT...HOLDING LOW TEMPERATURES IN THE MID 40S NORTH WHERE
CLOUDS WILL INCREASE/THICKEN LATEST TO THE UPPER 40S TO LOWER 50S
ELSEWHERE.

A FEW UPSTREAM SHOWERS COULD PUSH INTO FAR WESTERN/INLAND COUNTIES
AFTER 4 AM...THUS MAINTAINED SLIGHT CHANCE POPS LATE. HOWEVER...
THE 00Z NAM SUGGESTS THAT DRY AIR WILL PERSIST OVER THE
REGION...HOLDING MEASURABLE PRECIPITATION OUT OF WESTERN
COUNTIES UNTIL WEDNESDAY AFTERNOON.

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY NIGHT/...
AN UPPER LEVEL LOW WILL SWING FROM THE SOUTHERN ROCKIES TOWARD
THE MID MISS VALLEY ON WEDNESDAY...BREAKING DOWN THE RIDGING
ACROSS THE EAST COAST. WEAK SHORTWAVE ACTIVITY WILL DEVELOP
AHEAD OF THE MAIN UPPER LOW AND TRACK NORTHEAST FROM THE GULF OF
MEXICO DIRECTLY OVER THE FORECAST AREA. MODELS HINT THAT A WARM
BOUNDARY WILL SET UP ACROSS THE SOUTH CAROLINA
COUNTIES...ENHANCING MOISTURE AND CONVERGENCE WEDNESDAY AFTERNOON.

MODELS SUGGEST THAT THE INITIAL BAND OF PRECIPITATION WILL SKIM
THE WESTERN COUNTIES ON WEDNESDAY...WITH COASTAL LOCATIONS
POSSIBLY AVOIDING MUCH RAINFALL THROUGH THE DAY. HAVE KEPT HIGH
CHANCE POPS CONFINED TO MAINLY THE WESTERN HALF OF THE FORECAST
AREA WITH RAIN CHANCES DECREASING EASTWARD. THIS POP SCHEME WOULD
BEST FOLLOW THE AREA OF STRONGEST WARM ADVECTION BEHIND THE FIRST
SHORTWAVE DEPARTING WEDNESDAY NIGHT.

A STRONGER SHORTWAVE WILL SPIN OFF FROM THE MAIN UPPER LOW
WEDNESDAY NIGHT INTO THURSDAY...POTENTIALLY SUPPORTING A WEAK
WAVE AT THE SURFACE ACROSS SOUTHEAST GEORGIA AND COASTAL SOUTH
CAROLINA. AS A RESULT...EXPECT ANOTHER ROUND OF PRECIPITATION ON
THURSDAY. ALTHOUGH THERE IS SOME UNCERTAINTY AS TO WHERE THE
HEAVIEST AND MOST PERSISTENT RAINFALL WILL OCCUR...LOOKS LIKE
THERE IS ENOUGH CONSISTENCY IN PRECIPITATION POTENTIAL TO
MAINTAIN THE HIGHEST POPS OF THE PERIOD WEDNESDAY NIGHT THROUGH
THURSDAY.

INSTABILITY IS QUITE LIMITED ON WEDNESDAY...AND ONLY THE GFS
INDICATES MARGINAL INSTABILITY ACROSS THE SOUTHEAST GEORGIA
COUNTIES THURSDAY AFTERNOON. HAVE THUS INCLUDED A CHANCE OF
THUNDER MAINLY SOUTH OF THE SAVANNAH ON THURSDAY...WITH A SLIGHT
CHANCE TO THE NORTH.

THERE WILL BE A BRIEF LULL IN SHOWER ACTIVITY THURSDAY NIGHT AS
THE SECONDARY SHORTWAVE LIFTS TO THE NORTH. HOWEVER...THE STRONG
UPPER LOW LINGERING AROUND THE CENTRAL PLAINS/MISS VALLEY WILL
CONTINUE TO SPAWN SHORTWAVE ACTIVITY ALONG ITS SOUTHERN PERIPHERY
AND MAINTAIN UNSETTLED WEATHER INTO FRIDAY. HAVE THUS REINTRODUCED
RAIN CHANCES FROM SOUTH TO NORTH BY FRIDAY MORNING. DETAILS WILL
BE HIGHLY DEPENDENT ON THE SUBSEQUENT SURFACE WAVES...AND THUS
PREFER TO CAP POPS IN THE 40S AT THIS TIME.

OF SOME CONCERN IS THE INSTABILITY PARAMETERS PRODUCED BY THE 12Z
GFS...INDICATING SUFFICIENT THERMODYNAMICS TO SUPPORT STRONG
THUNDERSTORMS AT A TIME WHEN AN IMPRESSIVE UPPER JET IS IDEALLY
LOCATED ACROSS THE SOUTHEAST STATES. HOWEVER...OTHER MODELS DO NOT
ENHANCE INSTABILITY TO THIS DEGREE...SO WILL JUST INCLUDE A CHANCE
FOR THUNDERSTORMS WITHOUT MENTION OF SEVERE POTENTIAL.

EXPECT TEMPERATURES TO RANGE FROM AROUND SEASONAL NORMALS TO A
FEW DEGREES WARMER...BEING HIGHLY DEPENDENT ON CLOUD COVERAGE AND
SPATIAL EXTENT OF SHOWER ACTIVITY. AFTERNOON HIGHS WILL REACH THE
UPPER 60S TO LOWER 70S WEDNESDAY AND THURSDAY...POSSIBLY WARMING
INTO THE MID 70S BY FRIDAY.

SREF VISIBILITY PROBS SUGGEST THAT SEA FOG COULD BECOME AN ISSUE
FOR COASTAL COMMUNITIES LATE WEDNESDAY NIGHT. SURFACE DEWPOINTS
WILL SURGE INTO THE UPPER 50S...WHILE SEA SURFACE TEMPERATURES IN
THE NEARSHORE COASTAL WATERS REMAIN IN THE LOWER 50S. SEA FOG
COULD LINGER THROUGH FRIDAY EVENING AS DEWPOINTS OVER THE WATERS
CONTINUE TO INCREASE INTO THE LOWER 60S.

.LONG TERM /SATURDAY THROUGH TUESDAY/...
MODEL GUIDANCE IS IN GOOD AGREEMENT SHOWING A COLD FRONT SHIFTING
THROUGH THE REGION FRIDAY NIGHT...FOLLOWED BY COLD AIR ADVECTION
AND DEEP CYCLONIC FLOW OVER THE WEEKEND AND INTO EARLY NEXT
WEEK. WILL KEEP SLIGHT CHANCE POPS GOING FOR A FEW SHOWERS IN
ASSOCIATION WITH THE COLD FRONT FRIDAY NIGHT...THEN GO WITH A RAIN
FREE FORECAST SATURDAY THROUGH TUESDAY AS DOWNSLOPE FLOW DRIES THE
BOUNDARY LAYER. TEMPERATURES ARE EXPECTED TO RUN NEAR NORMAL
SATURDAY...THEN DROP TO SLIGHTLY BELOW NORMAL VALUES SUNDAY
THROUGH TUESDAY.

.AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
VFR CONDITIONS ARE EXPECTED AT BOTH CHS AND SAV TERMINALS THROUGH
THE FIRST 24 HOURS. HIGH PRESSURE WILL SHIFT OFFSHORE TONIGHT AS LOW
PRESSURE APPROACHES THE REGION FROM THE WEST. AN INCREASE IN MID LVL
MOISTURE WILL OCCUR AS THIS LOW PRESSURE SYSTEM DEVELOPS PUSHES
TOWARDS THE SOUTHEAST. BKN/OVC VFR CIGS ARE LIKELY BY 14Z WED AT
BOTH TERMINALS AS SOUTHWEST WINDS BECOME SOUTHEAST BETWEEN 10 TO 15
KNOTS. CONFIDENCE REMAINS TOO LOW TO INCLUDE PRECIP AT EITHER
TERMINAL THROUGH 00Z THURSDAY.

EXTENDED AVIATION OUTLOOK...CIGS AND VSBYS WILL OCCASIONALLY DROP
INTO MVFR OR LOWER WED NIGHT THROUGH FRI AS SHOWERS AND TSTMS
AFFECT THE TERMINALS. OTHERWISE VFR CONDITIONS ARE EXPECTED TO
PREVAIL.

.MARINE...
SURFACE HIGH PRESSURE RETREATING E/SE OF THE COAST WILL MAINTAIN
S/SW WINDS 5-15 KNOTS ACROSS THE WATERS OVERNIGHT. THIS TRANQUIL
REGIME WILL SUPPORT SEAS 1-2 FT.

A SERIES OF UPPER LEVEL DISTURBANCES AND WEAK SURFACE BOUNDARIES
WILL MOVE THROUGH THE AREA WEDNESDAY THROUGH FRIDAY. THIS PATTERN
WILL MAKE BOTH WIND SPEED AND DIRECTION FORECASTS QUITE
DIFFICULT...AS WIND FIELDS WILL LIKELY BE DISRUPTED FREQUENTLY
WITHIN CONVECTION MOVING THROUGH THE WATERS.

HAVE MAINTAINED A GENERAL SOUTH TO SOUTHEAST FLOW ACROSS THE
MARINE ZONES THROUGH THURSDAY. THE BEST CHANCE FOR SMALL CRAFT
ADVISORIES WOULD BE THURSDAY AFTERNOON OVER THE OFFSHORE
WATERS...IF A WEAK SURFACE WAVE DEVELOPS ACROSS THE AREA AND
TIGHTENS THE PRESSURE GRADIENT. HAVE OTHERWISE CAPPED WIND SPEEDS
20 KT OR LESS.

VARIABLE WINDS ARE POSSIBLE ON FRIDAY AS A SURFACE LOW SYSTEM
SHIFTS DIRECTLY OVER THE SOUTHEAST STATES AND THE GRADIENT
BECOMES WEAKER. A COLD FRONT WILL THEN MOVE THROUGH THE WATERS
FRIDAY NIGHT WITH COLD AIR ADVECTION EXPECTED TO FOLLOW THROUGH
SUNDAY. DEPENDING ON THE STRENGTH OF THE COLD AIR ADVECTION BEHIND
THE COLD FRONT...THERE IS A CHANCE THAT WINDS COULD REACH SMALL
CRAFT LEVELS ACROSS PORTIONS OF THE WATERS BOTH SATURDAY AND
SUNDAY.

THERE APPEARS TO BE A DECENT CHANCE OF SEA FOG DEVELOPMENT OFF
THE SOUTH CAROLINA AND GEORGIA COAST FROM WEDNESDAY NIGHT THROUGH
FRIDAY EVENING AS WARMER AND MORE HUMID AIR OVERSPREADS THE COOLER
NEARBY ATLANTIC WATERS. THE SREF MODEL HITS THE POTENTIAL FAIRLY
WELL...HOWEVER WILL DELAY INCLUSION IN THE FORECAST UNTIL DETAILS
REGARDING CONVECTIVE SYSTEMS BECOME MORE CLEAR.

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