Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 201943
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
343 PM EDT MON OCT 20 2014

.SYNOPSIS...
HIGH PRESSURE WILL PULL EAST OVER THE ATLANTIC TONIGHT AS A WEAK
TROUGH MOVES OFF THE COAST OVERNIGHT. A COLD FRONT WILL MOVE THROUGH
THE REGION TUESDAY NIGHT...WITH HIGH PRESSURE BUILDING IN ITS WAKE
THROUGH LATE IN THE WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
THROUGH THIS EVENING...WARM CONDITIONS WITH AN EXTENSIVE BUT MOSTLY
FLAT CUMULUS FIELD...AS THE SEA BREEZE CONTINUES ITS SLOW TREK
INLAND AND REACHES NEAR OR WEST OF THE I-95 CORRIDOR BY SUNSET.

TONIGHT...MUCH OF THE DAYTIME CUMULUS CLOUDS WILL FADE WITH SUNSET.
FOR AWHILE WE SHOULD TRANSITION BACK TO PARTLY CLOUDY...BEFORE THE
ARRIVAL OF THE TAIL END OF A LOW TO MID LEVEL SHORT WAVE DURING THE
LATE EVENING AND OVERNIGHT. THIS FEATURE IS UPSTREAM ACROSS
THE OHIO VALLEY TO THE MID MS VALLEY AS OF LATE AFTERNOON AND WILL
TRIGGER THE DEVELOPMENT OF A DIFFUSE SURFACE TROUGH ACROSS THE
NEARBY ATLANTIC WATERS AFTER MIDNIGHT. IN RESPONSE FROM ABOUT 10 PM
TO 3 AM THE FLOW IN THE 850-700 MB LAYER BACKS A LITTLE SOUTH/SW AND
PULLS UP SOME MOISTURE FROM THE ATLANTIC AND OUT OF THE GULF. THIS
ALONG WITH INCREASING ALBEIT WEAK ISENTROPIC UPGLIDE ATOP THE
SURFACE TROUGH...A 80-90 KT UPPER JET MAX AND PVA IN RESPONSE TO THE
SHORT WAVE MAY SPUR A FEW SHOWERS OVER THE COASTAL COUNTIES. THE
BULK OF THE SHOWERS THOUGH WILL STAY OFFSHORE AND THERE WILL BE FINE
LINE BETWEEN WHERE IT DOES RAIN AND WHERE IT DOESN/T...AND LITTLE
QPF IS ANTICIPATED. AS THE PERTURBATION ALOFT AND SURFACE TROUGH
PULL FURTHER INTO THE ATLANTIC LATE TONIGHT ANY SHOWERS WILL
END...AND SKIES WILL CLEAR FROM WEST/SW TO EAST/NE.

WITH SUBTLE WARM TO NEUTRAL ADVECTION THROUGH MUCH OF THE NIGHT WE
DON/T FORESEE TEMPS GETTING ANYWHERE NEAR AS LOW AS THEY WERE THIS
MORNING. BUT ONCE CLOUDS MOVE OUT LATE AND THE SYNOPTIC FLOW BECOMES
NW WE LOOK FOR LOWS TO RANGE FROM AROUND 50 IN ALLENDALE TO PARTS OF
SCREVEN AND JENKINS...LOWER AND MIDDLE 50S MOST ELSEWHERE
INLAND...WITH UPPER 50S AND LOWER 60S ALONG THE BARRIER ISLANDS.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY/...
TUESDAY...LIGHT RAIN/SHOWERS WILL CONTINUE TO LIFT NORTHEAST AND
FURTHER OFFSHORE FROM THE AREA EARLY AS MOISTURE ASSOCIATED WITH A
PARENT LOW PRESSURE SYSTEM SLOWLY SHIFTS OFF THE NORTHEAST COAST.
WEST/NORTHWEST FLOW ALONG THE SOUTHERN PERIPHERY OF THE LOW WILL
HELP PRODUCE FAIRLY WARM TEMPS AHEAD OF A DRY COLD FRONT APPROACHING
THE AREA LATE. LATEST 1000-850MB THICKNESS VALUES SUPPORT OVERALL
HIGH TEMPS NEAR 80S DEGREES AND GIVEN A DOWNSLOPING WIND COMPONENT
ALONG WITH MOSTLY SUNNY SKIES...HAVE MAINTAINED HIGH TEMPS IN THE
LOWER 80S FOR MOST LOCATIONS.

TUESDAY NIGHT INTO WEDNESDAY...A DRY COLD FRONT WILL SHIFT THROUGH
THE AREA FROM THE NORTH/NORTHWEST TUESDAY NIGHT...WITH LITTLE TO NO
IMPACT OVER THE SOUTHEAST IN REGARDS TO PRECIP. HOWEVER...COOLER
CONDITIONS ARE ANTICIPATED BEHIND THE FRONT AS A NORTH/NORTHWEST
FLOW DEVELOPS ALONG THE SOUTHEAST SIDE OF HIGH PRESSURE CENTERED
OVER THE MIDWEST. TUESDAY NIGHT TEMPS SHOULD REMAIN IN THE LOW/MID
50S FOR MOST AREAS...BUT TEMPS COULD DIP INTO THE UPPER 40S INLAND
WHERE FROPA OCCURS EARLIEST. HIGH TEMPS WILL BE SOME 5-10 DEGREES
COOLER THAN THE PREVIOUS DAY ON WEDNESDAY AS THE NORTH/NORTHWEST FLOW
PERSISTS BETWEEN HIGH PRESSURE CENTERED OVER THE MIDWEST AND A BROAD
LOW PRESSURE SYSTEM JUST OFF THE NORTHEAST COAST. IN GENERAL...HIGH
TEMPS SHOULD RANGE IN THE LOW/MID 70S...COOLEST OVER SOUTHEAST SOUTH
CAROLINA. WEDNESDAY NIGHT LOWS SHOULD ALSO BE THE COOLEST OF THE
WEEK...WITH PERHAPS A SMALL CONTRIBUTION FROM RADIATIONAL COOLING.
IN GENERAL...LOWS SHOULD DIP INTO THE MID 40S INLAND TO LOW 50S NEAR
THE COAST.

THURSDAY...VERY LITTLE CHANGE IS ANTICIPATED IN REGARDS TO THE DRY
WEATHER PATTERN...BUT SFC WINDS SHOULD GRADUALLY BACK TO NORTHWEST
OVER THE COURSE OF THE DAY. THIS SUPPORTS A GRADUAL MODIFICATION OF
TEMPS...WITH AFTERNOON HIGHS 1-2 DEGREES WARMER THAN WEDNESDAY...BUT
STILL IN THE LOW/MID 70S OVER MOST LOCATIONS.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
GLOBAL MODEL SOLUTIONS NOW VERY DIFFERENT FOR THE MIDDLE TO LATER
PART OF THE PERIOD. THE LATEST SOLUTIONS NOW SHOW THE DEEP/CLOSED
UPPER LOW OFF THE NEW ENGLAND COAST TO CONTINUE SLOWLY MOVING
EASTWARD FRIDAY AS A DEEP LAYER RIDGE DEVELOPS OVER THE SOUTHWESTERN
U.S. STATES BY FRIDAY. BETWEEN THESE TWO FEATURES...A SHORT WAVE UPPER
TROUGH DROPS SOUTHEASTWARD FROM THE GREAT LAKES FRIDAY...TO OFF THE
MID ATLANTIC COAST BY SATURDAY. THEN A DEEP LAYER RIDGE BUILDS EASTWARD
ACROSS THE SOUTH AND SOUTHEAST STATES SUNDAY AND MONDAY. THIS IS
DRASTICALLY DIFFERENT FROM SOLUTIONS 24 HOURS AGO...WHICH
FEATURED AN UPPER LOW OVER THE GULF STATES AND ASSOCIATED SURFACE
LOW MOVING UP FROM THE GULF ACROSS FL THEN INTO THE SOUTHWEST
ATLANTIC. THIS NEWER SOLUTION IS MUCH DRIER AND WARMER THAN
PREVIOUSLY EXPECTED. GIVEN THE EXTREME UNCERTAINTY...MADE ONLY MINOR
CHANGES TO TEMPERATURES THROUGH THE PERIOD...GENERALLY HOLDING THEM
NEAR TO SLIGHTLY ABOVE NORMAL. DID INTRODUCE SLIGHT CHANCE POPS FOR
MONDAY WITH SOME MOISTURE RETURN ON THE EAST SIDE OF THE RIDGE...BUT
CONFIDENCE QUITE LOW FOR POPS GIVEN ABOVE DISCUSSION.

&&

.AVIATION /20Z MONDAY THROUGH SATURDAY/...
VFR AT BOTH KSAV AND KCHS THROUGH TONIGHT. ANY SHOWER ACTIVITY
AND MVFR CEILINGS ASSOCIATED WITH A SURFACE TROUGH AND MID LEVEL
IMPULSE IS TOO LOW TO INCLUDE WITH THE 18Z TAFS...AS THE BULK OF
ANY RAIN AND SUB-VFR WEATHER STAYS TO THE SOUTH AND EAST OF BOTH
TERMINALS. CLEAR SKIES AND SOLID VFR WILL RETURN TUESDAY.

EXTENDED AVIATION OUTLOOK...VFR CONDITIONS ARE EXPECTED AT BOTH CHS
AND SAV TERMINALS THROUGH THIS WEEKEND.

&&

.MARINE...
THROUGH THIS EVENING...LIGHT SEA BREEZE CIRCULATIONS AND CLOCKWISE
FLOW AROUND ATLANTIC HIGH PRESSURE WILL PROVIDE THE WATERS WITH SE
WINDS OF 10 KT OR LESS AND SEAS OF 3 FT OR LOWER.

TONIGHT...A WEAK TROUGH WILL FORM OVER OR NEAR THE MARINE AREA AS A
1021 MB HIGH PRESSURE CORE NEAR 38N AND 88W PULLS FURTHER AWAY TO
THE EAST AND NE. THE TROUGH WILL ALSO FOLLOW BEHIND THE RIDGE AND BY
LATE THERE REMAINS LITTLE IF ANY EVIDENCE OF THE TROUGH AS LAND
BREEZE CIRCULATIONS DEVELOP. THE RESULT WILL BE FOR SE AND SOUTH
WINDS OF 10 KT OR LESS EARLY ON...CLOCKING AROUND TO THE WEST AND NW
OF 15 KT OR LESS LATE. SEAS WILL HOLD AROUND 2 OR 3 FT...GREATEST
ACROSS THE OUTER GA WATERS. ISOLATED TO SCATTERED SHOWERS ARE
FORECAST AFTER 9 OR 10 PM.

TUESDAY AND WEDNESDAY...CONDITIONS ARE EXPECTED TO BE WELL BELOW
SMALL CRAFT ADVISORY LEVELS TUESDAY AS A BROAD TROUGH OF LOW
PRESSURE BEGINS TO SLOWLY SHIFT OFF THE NORTHEAST COAST. IN
GENERAL...WESTERLY FLOW WILL REMAIN AT OR BELOW 15 KTS WITH SEAS NO
HIGHER THAN 3 FT. A DRY COLD FRONT WILL THEN APPROACH THE AREA AND
SHIFT OVER THE COASTAL WATERS FROM NORTH TO SOUTH TUESDAY
NIGHT...RESULTING IN A FAIR AMOUNT OF COLD AIR ADVECTION OVER THE
WATERS WHILE HIGH PRESSURE BUILDS FROM THE NORTHWEST. AS A
RESULT...WINDS/SEAS WILL BE ENHANCED POST FROPA LATE TUESDAY INTO
WEDNESDAY...BUT CONDITIONS SHOULD REMAIN JUST BELOW SMALL CRAFT
ADVISORY LEVELS. IN GENERAL...WEST WINDS WILL BECOME NORTH BETWEEN
15-20 KTS BEHIND THE FRONT WHILE SEAS BUILD TO 3-4 FT...HIGHEST IN
OFFSHORE GEORGIA WATERS.

WEDNESDAY NIGHT THROUGH SATURDAY...WINDS AND SEAS ARE EXPECTED TO
REMAIN BELOW ANY HIGHLIGHTS AS A BROAD AREA OF HIGH PRESSURE REMAINS
TO THE NORTHWEST OF THE REGION. BY SATURDAY...AN UPPER LEVEL
DISTURBANCE WILL MOVE OFF THE NORTH CAROLINA COAST. THIS FEATURE
WILL HELP TO INCREASE THE NORTHWEST WINDS...BUT STILL NOT EXPECTING
WINDS/SEAS TO REACH SMALL CRAFT ADVISORY LEVELS.

&&

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

&&

$$

NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...





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