FXUS62 KCHS 150222
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
922 PM EST MON DEC 14 2009
.SYNOPSIS...
HIGH PRESSURE TO THE NORTH WILL SHIFT OFFSHORE TONIGHT AND
TUESDAY. A COLD FRONT WILL MOVE THROUGH THE AREA TUESDAY
NIGHT...FOLLOWED BY HIGH PRESSURE THROUGH THURSDAY. A SLOW MOVING
STORM SYSTEM WILL THEN LIFT NORTHEAST OFF THE SOUTH CAROLINA AND
GEORGIA COAST FRIDAY THROUGH SATURDAY. HIGH PRESSURE IS THEN
EXPECTED TO BUILD BACK INTO THE AREA FOR THE TAIL END OF THE
WEEKEND INTO EARLY NEXT WEEK.
&&
.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
THE LEADING EDGE OF A LARGE SWATCH OF MODERATE TO HEAVY RAIN HAS
MOVED INTO INTERIOR PORTIONS OF SOUTHEAST GEORGIA. RAIN WILL
CONTINUE TO EXPAND IN BOTH COVERAGE AND INTENSITY TONIGHT AS
INCREASING ISENTROPIC AND SYNOPTIC LIFT OVERSPREAD THE AREA.
EARLY EVENING SURFACE ANALYSIS PLACED THE WARM FRONT RIGHT ALONG
THE ALTAMAHA RIVER WITH TEMPERATURES QUICKLY RISING INTO THE 70S
SOUTH OF THE BOUNDARY. WITH WIDESPREAD HEAVY RAIN FALLING TO THE
NORTH OF THE FRONT WE DO NOT EXPECT THE WARM FRONT TO LIFT NORTH
VERY QUICKLY TONIGHT. HOWEVER...MODELS STILL INSIST THE FRONT WILL
EVENTUALLY PUSH THROUGH THE FORECAST AREA AND BECOMING POSITIONED
ACROSS THE MIDLANDS AND PEE DEE BY TUESDAY MORNING. THINK LOWS
HAVE JUST ABOUT BEEN ACHIEVED FOR MOST LOCATIONS WITH TEMPERATURES
LIKELY TO HOLD STEADY OR SLOWLY RISE OVERNIGHT.
LIGHTNING PLOTS SHOW QUITE A BIT OF TSTM ACTIVITY IN THE WARM
SECTOR WITH SOME ELEVATED TSTMS MOVING ACROSS CENTRAL GEORGIA.
WE UPDATED THE FORECAST EARLIER TO INCLUDE A CHANCE FOR TSTMS AND
THIS STILL LOOKS TO BE THE CASE. IN FACT...SEVERAL BOWING
CONVECTIVE LINE SEGMENTS MOVING ACROSS SOUTHERN ALABAMA AND
GEORGIA HAVE HAD A HISTORY OF PRODUCING WIND DAMAGE AND TORNADOES.
SOME OF THIS ACTIVITY COULD BRUSH THE FAR SOUTHERN AREAS NEAR THE
VICINITY OF THE WARM FRONT OVER THE NEXT SEVERAL HOURS. INCREASED
POPS TO NEAR 100 PERCENT FOR AREAS NORTH OF A REIDSVILLE TO
SAVANNAH LINE WHERE THE AXIS OF HEAVIEST RAINS EXPECTED TO SETUP
WITH POPS TRENDING DOWN TO 50 PERCENT ACROSS THE DARIEN AND SAPELO
ISLAND AREAS.
COUNTY WARNING POINTS...AREA WEBCAMS AND SURFACE OBSERVATIONS
INDICATE AREAS OF DENSE FOG HAVE DEVELOPED ALONG THE NORTH GEORGIA
COAST AND EXTENDING AS FAR NORTH AS BEAUFORT. HAVE ISSUED A DENSE
FOG ADVISORY UNTIL MIDNIGHT TO COVER THIS SITUATION. THE INCOMING
RAIN COULD HELP IMPROVE VISIBILITIES SOMEWHAT AFTER MIDNIGHT SO
THE RISK FOR DENSE FOG SHOULD END AROUND THAT TIME.
&&
.SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
STRONG WARM ADVECTION TUESDAY AHEAD OF AN APPROACHING COLD FRONT
WILL BRING LOWER TO MIDDLE 60S DEWPOINTS INTO THE REGION AND PUSH
TEMPS CLOSE TO 70. CONSIDERABLE UPPER-LEVEL DIVERGENCE SHOULD
CONTINUE WHILE SHORTWAVE ENERGY MOVES THROUGH. WITH A MOIST
BOUNDARY LAYER AND DEEP-LAYERED FORCING WE SHOULD CONTINUE TO SEE
WIDESPREAD COVERAGE OF RAIN SHOWERS...POSSIBLY HEAVY AT TIMES.
MID-LEVEL LAPSE RATES OF AROUND 6.5C MAY SUPPORT ISOLATED
THUNDERSTORMS SO WE HAVE INCLUDED THOSE IN THE FORECAST.
&&
.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
MEDIUM RANGE GUIDANCE IS IN GOOD AGREEMENT THROUGH THURSDAY...BEFORE
DIVERGING IN A NUMBER OF DIFFERENT DIRECTIONS OVER THE WEEKEND AND
INTO EARLY NEXT WEEK...RESULTING IN PROGRESSIVELY LOWERING
CONFIDENCE THROUGH THE EXTENDED PERIODS.
MODEL SOLUTIONS SHOW A STRONG COLD FRONT MOVING THROUGH THE REGION
TUESDAY NIGHT...AND WITH DECENT SHORTWAVE ENERGY ALONG WITH ENTRANCE
REGION FORCING FROM A 160+ KNOT H25 JET MOVING THROUGH THE REGION AS
WELL AS MID-LEVEL LAPSE RATES STEEPENING TO BETWEEN 6.5 AND 7
C/KM...WILL CARRY HIGH CHANCE/LOW END LIKELY POPS FOR
SHOWERS/THUNDERSTORMS.
HIGH PRESSURE WILL THEN BUILD INTO THE REGION WEDNESDAY THROUGH
THURSDAY...RESULTING IN RAIN FREE CONDITIONS.
GUIDANCE SOLUTIONS THEN BEGINS TO DIVERGE WITH THE HANDLING OF A
STORM SYSTEM PASSING BY TO THE SOUTH AND EAST OF THE FORECAST AREA
DURING THE THURSDAY NIGHT THROUGH SATURDAY TIME FRAME. GUIDANCE IS
TYPICALLY TOO QUICK IN RETURNING DEEP MOISTURE INTO THE REGION...SO
DESPITE THE MODELS SPREADING RAIN BACK INTO THE AREA THURSDAY
NIGHT...WILL KEEP THE FORECAST RAIN FREE FOR NOW. THE MODELS ALL
SHOW A GOOD SHOT FOR RAIN IN THE FRIDAY THROUGH SATURDAY TIME
FRAME...BUT TIMING DETAILS ARE NOT IN THE BEST AGREEMENT. FOR NOW
HAVE INCREASED POPS IN THE FRIDAY THROUGH SATURDAY NIGHT TIME
FRAME...BUT HAVE KEEP THEM IN THE SLIGHT CHANCE/LOW CHANCE RANGE DUE
TO LOW CONFIDENCE ON TIMING DETAILS.
STILL SOME DISAGREEMENT AMONGST THE MODELS WITH RESPECT TO THE EXACT
SYNOPTIC PATTERN EVOLUTION IN THE SUNDAY THROUGH MONDAY TIME
FRAME...BUT GENERALLY HAVE FOLLOWED A SOLUTION BUILDING HIGH
PRESSURE BACK INTO THE AREA. HAVE THEREFORE KEPT THE FORECAST RAIN
FREE SUNDAY THROUGH MONDAY.
TEMPERATURES THROUGH THE EXTENDED PERIODS ARE EXPECTED TO RUN NEAR
TO SLIGHTLY BELOW CLIMO.
&&
.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
POOR CONDITIONS WILL CONTINUE AT KCHS/KSAV FOR THE NEXT 24 HOURS.
FOG IS BEGINNING TO REDEVELOP THIS EVENING WITH VSBYS ALREADY
DOWN TO LIFR AT KSAV. VSBYS AND CIGS ARE COMING DOWN QUICKLY AT
THE ADJACENT TERMINALS TO KCHS SO ITS ONLY A MATTER OF TIME
BEFORE IFR OR LIFR CONDITIONS DEVELOP THERE. EXPECT VSBYS TO
IMPROVE A BIT AS RAIN MOVES IN FROM THE WEST BUT STILL EXPECT IFR
CONDITIONS TO PREVAIL ONCE THE RAIN SETTLES IN. HAVE SEEN OCCASIONAL
LIGHTNING STRIKES WITH THE INCOMING RAIN SHIELD SO WILL INCLUDE A
MENTION OF CB/S AT BOTH TERMINALS FROM 07Z ON TO TREND. EXPECT
STEADY AND WIDESPREAD RAINS TO MOVE IN FROM 07Z AT KSAV AND 09Z AT
KCHS ALTHOUGH SOME ISOLATED SHOWER ACTIVITY COULD BRUSH THE KSAV
TERMINAL 02-05Z. INCOMING DATA SUGGESTS THERE COULD BE BRIEF BREAK
IN THE RAIN FROM LATE MORNING INTO THE EARLY AFTERNOON BEFORE
ADDITIONAL RAINS MOVES IN FROM THE WEST WITH AN APPROACHING COLD
FRONT. SINCE THE TAFS ARE ALREADY GETTING FAIRLY LONG AND COMPLEX
WILL LEAVE MENTION OF RAIN OUT OF THE TAFS FROM 18Z ON...ALTHOUGH
RAIN MAY NEED TO BE INCLUDED DURING THE AFTERNOON HOURS WITH LATER
TAF CYCLES.
EXTENDED AVIATION OUTLOOK...MVFR/IFR CONDITIONS ARE EXPECTED
THROUGH TUESDAY EVENING. VFR CONDITIONS ARE EXPECTED WEDNESDAY
THROUGH THURSDAY NIGHT. COULD SEE SOME MVFR OR LOWER CIGS AND/OR
VSBYS FRIDAY THROUGH SATURDAY AS A STORM SYSTEM PASSES BY OFF THE
SOUTHEAST COAST.
&&
.MARINE...
THE MARINE DENSE FOG ADVISORY WILL REMAIN IN PLACE. UNFORTUNATELY
WE HAVE HAD NO OBSERVATIONS OVER THE MARINE AREA SINCE MID
AFTERNOON AND VIEWS FROM COASTAL WEBCAMS ARE INCONCLUSIVE ON HOW
EXTENSIVE THE SEA FOG STILL IS. UNTIL WE CAN GET A BETTER HANDLE
ON HOW MUCH SEA FOG IS STILL OUT OVER THE COASTAL WATERS...THE
ADVISORY WILL BE MAINTAINED. OTHERWISE WINDS WILL REMAIN LESS THAN
10 KT AND SEAS 3-4 FT NEARSHORE WATERS AND 4-5 FT OFFSHORE WATERS.
A COLD FRONT WILL PUSH THROUGH THE WATERS TUESDAY NIGHT...
FOLLOWED BY HIGH PRESSURE BUILDING BACK INTO THE AREA THROUGH
THURSDAY NIGHT. A STORM SYSTEM WILL THEN PASS BY TO THE EAST OF
THE WATERS FRIDAY THROUGH SATURDAY. EXPECT A PRETTY GOOD SURGE IN
THE WINDS FOLLOWING THE COLD FRONT TUESDAY NIGHT AND
WEDNESDAY...AND WILL LIKELY NEED SMALL CRAFT ADVISORIES ACROSS ALL
WATERS. IMPROVING CONDITIONS ARE EXPECTED WEDNESDAY NIGHT...BUT
SEAS MAY LINGER IN THE SMALL CRAFT RANGE THROUGH THURSDAY EVENING
ACROSS THE OUTER GEORGIA WATERS. DEPENDING ON THE STRENGTH AND
PROXIMITY OF THE STORM SYSTEM PASSING BY OFF THE SOUTH CAROLINA
AND GEORGIA COAST FRIDAY THROUGH SATURDAY...SMALL CRAFT ADVISORIES
MAY ONCE AGAIN BE NECESSARY FOR PORTIONS OF THE WATERS.
&&
.HYDROLOGY...
HAVE ISSUED A FLASH FLOOD WATCH FOR MUCH OF THE FORECAST AREA
UNTIL LATE MORNING TUESDAY. INCOMING LINE OF MODERATE TO HEAVY
RAIN WILL IMPACT MUCH OF THE FORECAST AREA TONIGHT. MODELS SHOW
THE AXIS OF HEAVIEST RAIN SETTING UP ALONG A LINE FROM STATESBORO
TO CHARLESTON. THIS IS WHERE THE STRONGEST 850MB MOISTURE FLUX
CONVERGENCE AND PWATS AS HIGH AS 1.7 INCHES WILL BE FOUND. MUCH OF
THIS AREA HAS ALREADY SEEN BETWEEN 3-5 INCHES OF RAIN DURING THE
PAST SEVERAL DAYS AND WITH THE POTENTIAL FOR SEVERAL MORE INCHES
OVERNIGHT WE FELT IT BEST TO GO AHEAD AND RAISE THE FLASH FLOOD
WATCH NOW. HAVING SOME DRY WEATHER FOR THE PAST 24 HOURS HAS
ALLOWED FLASH FLOOD GUIDANCE VALUES TO RECOVER SOMEWHAT...BUT WITH
CONDITIONS FAVORING A CONCENTRATED LINE OF ELEVATED CONVECTION
OVER THE NEXT 6-9 HOURS THESE VALUES COULD EASILY BE EXCEED.
EXPECT ANOTHER 1-3 INCHES THROUGH LATE MORNING TUESDAY...ALTHOUGH
INCOMING HRRR MODEL DATA SUGGEST RAIN AMOUNTS COULD BE HAS HIGH AS
3-4 INCHES IN PLACES.
THE GREATEST RISK FOR FLASH FLOODING WILL BE ACROSS INTERIOR
SOUTHEAST GEORGIA AND THE COUNTIES BORDERING THE SAVANNAH
RIVER WHERE THE HEAVIEST RAINS HAVE FALLEN OVER THE PAST FEW
DAYS...BUT OPTED TO THE INCLUDE OUR SOUTH CAROLINA COASTAL
COUNTIES SINCE HEAVY RAINS COULD FALL DURING A SOMEWHAT ELEVATED
HIGH TIDE CYCLE /6.1 FT IN THE CHARLESTON HARBOR/.
MANY RIVERS REMAIN IN FLOOD THIS EVENING...INCLUDING THE OHOOPEE...
OGEECHEE...CANOOCHEE...SAVANNAH AND SOUTH SANTEE. RIVER FLOOD
WARNINGS REMAIN IN EFFECT.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...FLASH FLOOD WATCH THROUGH TUESDAY MORNING FOR GAZ087-088-
099>101-114>116-118.
DENSE FOG ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR GAZ116>119-
138>141.
SC...FLASH FLOOD WATCH THROUGH TUESDAY MORNING FOR SCZ040-042-043-
047>051.
DENSE FOG ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR SCZ048-049-
051.
MARINE...DENSE FOG ADVISORY UNTIL NOON EST TUESDAY FOR AMZ330-350-352-
354.
&&
$$
