301 
FXUS62 KCHS 191758
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1258 PM EST TUE FEB 19 2013

.SYNOPSIS...
A COLD FRONT WILL MOVE THROUGH LATE THIS AFTERNOON...FOLLOWED BY HIGH
PRESSURE WEDNESDAY AND THURSDAY. A FRONTAL SYSTEM WILL MOVE INTO
THE AREA FOR FRIDAY THROUGH AT LEAST SATURDAY...BRINGING A GOOD
CHANCE FOR RAIN LATE IN THE WEEK INTO THE WEEKEND. HIGH PRESSURE
SHOULD BRIEFLY BUILD IN EARLY NEXT WEEK...BEFORE LIKELY GIVING WAY
TO ANOTHER FRONTAL SYSTEM.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
EARLY TUESDAY AFTERNOON...SHOWERS SUPPORTED BY LOW LEVEL
CONVERGENCE...POOLING OF PWATS APPROACHING 1 INCH...ISENTROPIC
ASCENT AND UPPER LEVEL DIVERGENCE AHEAD OF A LONGWAVE UPPER TROUGH
AXIS/ASSOCIATED SURFACE COLD FRONT WERE ADVANCING ACROSS THE FORECAST
AREA. DIMINISHING PRECIPITATION COVERAGE WAS POISED TO ADVANCE
INTO WESTERN COUNTIES. 

PER AREA RADAR TRENDS...COMPLETED MINOR ADJUSTMENTS TO POPS THIS
AFTERNOON/EARLY EVENING. WIDESPREAD SHOWERS WILL PUSH OFF THE COAST
AFTER MID- AFTERNOON...THEN LINGERING/ISOLATED TO SCATTERED
SHOWERS WILL PUSH OFF THE COAST LATE AFTERNOON/EARLY EVENING.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY/...
TONIGHT...THE FRONT WILL PUSH OFFSHORE QUICKLY WITH COOLER AND DRIER 
AIR FILTERING IN. ANY LINGERING SHOWERS SHOULD BE DONE OVER LAND 
AREAS BY THE LATE EVENING AND SKIES WILL CLEAR AS WELL. OVERALL THE 
AIRMASS BEHIND THE FRONT IS NOT INCREDIBLY COLD. LOWS WILL FALL INTO 
THE LOW TO MID 30S INLAND...WITH UPPER 30S TO LOW 40S CLOSER TO THE 
BEACHES.

WEDNESDAY...A DEEP CLOSED LOW WILL SHIFT EAST INTO NEW 
ENGLAND...WITH A STRONG SHORT WAVE TROUGH FOUND IN THE DESERT SW. IN 
BETWEEN A HIGHLY AMPLIFIED RIDGE WILL COVER THE CENTRAL STATES INTO 
SOUTH-CENTRAL CANADA. OUR FORECAST ZONES WILL LIE WITHIN A ZONAL 
FLOW SOUTH OF THE CYCLONIC FLOW ASSOCIATED WITH THE DEEP LOW MOVING 
TOWARD NEW ENGLAND. A SHORT WAVE LOCATED NEAR THE CALIFORNIA BAJA 
TODAY WILL BE EMBEDDED WITHIN THE FAST MOVING FLOW ALOFT AND CROSSES 
THE REGION LATE IN THE DAY. BUT SINCE THERE IS NO MOISTURE AVAILABLE 
FOR IT TO UTILIZE...WITH PWATS NO HIGHER THAN 0.3-0.4 
INCHES...RAIN FREE CONDITIONS WILL BE THE RULE. SUNNY SKIES IN THE 
MORNING WILL GIVE WAY TO SOME JET STREAK CIRRUS IN THE 
AFTERNOON...AS THEY INCREASE AND BECOME A LITTLE MORE OPAQUE LATE. 
MODIFIED CANADIAN HIGH PRESSURE WILL BUILD IN AT THE SURFACE FROM 
THE NW...ACCOMPANIED BY LOW LEVEL THICKNESSES THAT ARE 15-20 METERS 
LOWER THAN TODAY. THIS SUPPORTS AWAY WITHIN A FEW DEGREES EITHER 
SIDE OF 60. COASTAL COMMUNITIES THOUGH WILL BE SOME 5-7 DEGREES 
COOLER.  

THURSDAY...THE CLOSED LOW IN THE MID/UPPER TROPOSPHERE WILL MOVE 
INTO THE EASTERN CANADIAN MARITIMES...WITH A NEGATIVELY TILTED 
TROUGH SITUATES IN THE CENTRAL PLAINS. IN BETWEEN THESE TWO 
FEATURES...THE LOCAL AREA WILL BE UNDERNEATH A HIGHLY AMPLIFIED 
RIDGE FROM THE NORTHERN CARIBBEAN SEA TO SOUTH-CENTRAL CANADA. 
SURFACE HIGH PRESSURE REMAINS IN CONTROL...BUT BEGINS TO WEAKEN AS 
THE SOUTHERN PORTION OF IT SLIDES EAST INTO THE ATLANTIC. AN ONSHORE 
RETURN FLOW WITHIN THE COUNTERCLOCKWISE PATTERN AROUND THE HIGH WILL 
BRING WITH A SMALL INFLUX OF ATLANTIC MOISTURE...BUT NOT ENOUGH FOR 
ANYTHING MORE THAN PATCHY STRATOCUMULUS CLOUDINESS. LOW LEVEL 
THICKNESS AND 850 MB TEMPS ARE ON THE RISE...SO A WARMER DAY IS IN 
STORE AWAY FROM THE MUCH COOLER COASTLINE...UNLESS JET STREAM CIRRUS 
ARE THICKER THAN CURRENTLY ANTICIPATED.  

FRIDAY...A SHORT WAVE LIFTING THROUGH THE NORTHERN PLAINS AND UPPER 
MS VALLEY...WILL TAKE IT/S SURFACE LOW ALONG WITH IT AS THEY MOVE 
NORTH AND NE. EXTENDING SE FROM THE LOW WILL BE A TRIPLE POINT 
OCCLUSION IN THE TENNESSEE VALLEY OR IN ALABAMA...A TRAILING COLD 
FRONT TO NEAR NEW ORLEANS...AND WARM FRONTOGENESIS OVER OR NEAR THE 
LOCAL AREA. NORTH OF THE DEVELOPING WARM FRONT WE WILL BE FORMATION 
OF A HIGH PRESSURE WEDGE...WITHIN THE COOL AIR DAMMING EAST OF THE 
APPALACHIAN CHAIN. WITH THE GULF AND ATLANTIC OPENED UP WITHIN THE 
FIRST 8-10K FEET...CONSIDERABLE MOISTURE WILL SPREAD ACROSS THE SE. 
OVER-RUNNING RAINS WILL DEVELOP AS ISENTROPIC UPGLIDE BLOSSOMS AND 
PWATS WILL CLIMB TO NEAR 2 STANDARD DEVIATIONS ABOVE NORMAL. RAIN 
COVERAGE WILL INCREASE...AND DEPENDING UPON WHERE THE WARM FRONT 
ALIGNS ITSELF WE MAY HAVE A SMALL RISK OF THUNDER. RAIN CHANCES WILL 
BE HIGHEST OVER THE NW HALF...IN THE RANGE OF 50-60 PERCENT...AND 
LOWEST SE PORTION...IN THE RANGE OF 20-30 PERCENT. THE TEMP FORECAST 
WILL BE PROBLEMATIC...BUT PRESENT INDICATIONS ARE THAT WITH SOME 
SORT OF WEDGE IN PLACE THAT NW SECTIONS WILL STRUGGLE TO GET OUT OF 
THE 50S...BUT OUR EXTREME SOUTHERN ZONES MIGHT CLIMB NEAR 70.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
A VERY COMPLEX AND HUGE STORM SYSTEM WILL BE IMPACTING THE EASTERN 
HALF OF THE NATION LATE IN THE WEEK...WITH A VERTICALLY STACKED LOW 
OVER THE UPPER MIDWEST REGION INTO THE FIRST PART OF THE WEEKEND. 
CLOSER TO HOME...AN ELONGATED AND NEARLY STATIONARY FRONT WILL 
LINGER OVER OR NEAR THE FORECAST REGION INTO AT LEAST SATURDAY. 
VARIOUS SHORT WAVES WITHIN AN ACTIVE SOUTHERN BRANCH OF THE JET 
STREAM WILL PERIODICALLY PROGRESS THROUGH THE REGION...CAUSING THE 
NEARBY FRONT TO OSCILLATE A LITTLE NORTH AND SOUTH AT TIMES FRIDAY 
NIGHT THROUGH SATURDAY NIGHT. WHEN YOU THROW IN A 120-130 KT UPPER 
LEVEL JET TO PROVIDE ADDITIONAL FORCING FOR ASCENT...AND PWATS THAT 
ARE 2-3 STANDARD DEVIATIONS ABOVE NORMAL...A WET LATE WEEK IS IN 
STORE FOR THE ENTIRE FORECAST AREA. RAINFALL TOTALS OF SEVERAL 
INCHES MAY OCCUR IN MANY LOCALES...ALTHOUGH DUE TO THE SHOWERY 
NATURE OF THE ACTIVITY...ACCUMULATIONS COULD VARY GREATLY FROM ONE 
PLACE TO ANOTHER. THE WEDGE SHOWS INDICATIONS OF BREAKING DOWN BY 
EARLY SATURDAY...WHICH MAY ALLOW FOR MANY AREAS TO MOVE INTO THE 
WARM SECTOR. IF THIS WERE TO OCCUR THEN OUR RISK FOR T-STORMS AND 
MAYBE EVEN MARGINALLY SEVERE WEATHER WILL INCREASE. OUR TEMP 
FORECAST AGAIN WILL BE A CHALLENGE...SINCE ANY SLIGHT DEVIATION IN 
THE FRONTAL POSITION WILL SPELL SIGNIFICANT CHANGES IN OUR LATEST 
FORECAST.

AT SOME POINT EARLY NEXT WEEK THERE WILL BE A SOUTHERN STREAM SHORT 
WAVE KICKER THAT FINALLY FORCES THE STALLED OUT FRONTAL SYSTEM TO 
EXIT THE REGION. AS HIGH PRESSURE BUILDS FROM THE OHIO AND TENNESSEE 
VALLEYS WE/LL FINALLY DRY THINGS OUT. THIS MIGHT ONLY BE TEMPORARY 
THOUGH...AS THERE MIGHT BE YET ANOTHER RAINMAKER LATE IN THE 
FORECAST PERIOD.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
EXPECT OCCASIONAL MVFR CONDITIONS THIS AFTERNOON/EARLY EVENING...
AND UPSTREAM OBSERVATIONS SUGGEST THAT BRIEF IFR CEILINGS CANNOT BE
RULED OUT. THE POTENTIAL FOR FLIGHT RESTRICTIONS WILL END AS DRIER
AIR SPREADS INTO THE REGION LATER THIS EVENING THROUGH WEDNESDAY
MORNING. 

EXTENDED AVIATION OUTLOOK...PERIODIC FLIGHT RESTRICTIONS ARE LIKELY 
IN SHRA AND POSSIBLY EVEN ISOLATED TSRA FRIDAY THROUGH SATURDAY...AS 
A FRONTAL SYSTEM IMPACTS THE AIRFIELDS. OTHERWISE...VFR CONDITIONS 
WILL PREVAIL.

&&

.MARINE...
MAINTAINED ONGOING SMALL CRAFT ADVISORIES FOR ALL WATERS EXCEPT
FOR AMZ354 WITHOUT CHANGE. 

SW WINDS...GUSTING TO 25 KT N/E OF AMZ354...AND ASSOCIATED
ELEVATED SEAS WILL PERSIST THIS AFTERNOON. AS A COLD FRONT/WEAKER
PRESSURE GRADIENT CROSSES THE WATERS THIS EVENING...WINDS WILL
DIMINISH TO SOME DEGREE. THEN...COLD ADVECTION WILL SUPPORT A
SURGE OF W/NW WINDS OVERNIGHT. THESE POST COLD FROPA WINDS COULD
ATTAIN SCA STRENGTH ESPECIALLY BEYOND 20 NM.

SEAS WILL RANGE FROM 3-5 FT WITHIN NEARSHORE WATERS TO 6-8 FT
BEYOND 20 NM. 

WEDNESDAY...ANY LINGERING SCA CONDITIONS ACROSS THE OUTER GA WATERS 
EARLY ON WILL COME DOWN QUICKLY...AS COLD ADVECTION WANES AND THE 
PRESSURE GRADIENT RELAXES WITH HIGH PRESSURE BUILDING FROM THE NW. 
IN FACT THE PRESSURE PATTERN RELAXES ENOUGH THAT WEAK RESULTANT SEA 
BREEZE CIRCULATIONS LOOK TO DEVELOP IN THE AFTERNOON.

THURSDAY...CONTINENTAL HIGH PRESSURE EARLY WILL SLIDE INTO THE 
WESTERN ATLANTIC...AND VEERING WINDS WILL COMMENCE. WINDS AND SEAS 
WILL BE ON THE RISE...BUT BELOW ANY HEADLINE CONDITIONS. 

FRIDAY THROUGH SATURDAY...WARM FRONTOGENESIS WILL TAKE PLACE ACROSS 
THE WATERS FRIDAY...AND THE FRONT WILL LINGER IN OR NEAR THE 
IMMEDIATE AREA INTO SATURDAY. MOST OF THE WATERS WILL PROBABLY BE ON 
THE SOUTH SIDE OF THE FRONT...BUT WITH A HIGH PRESSURE WEDGE TO BE 
FOUND INLAND AND THE FRONT PERHAPS GETTING STUCK UP ON THE COOLER 
SHELF WATERS...CHANGES MIGHT BE REQUIRED IN SUBSEQUENT COASTAL 
WATERS FORECASTS. BUT SCA CONDITIONS ARE CERTAINLY POSSIBLE AT SOME 
POINT LATE IN THE WEEK.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 7 PM EST THIS EVENING FOR AMZ330.
     SMALL CRAFT ADVISORY UNTIL 1 AM EST WEDNESDAY FOR AMZ350-352.
     SMALL CRAFT ADVISORY UNTIL 7 AM EST WEDNESDAY FOR AMZ374.

&&

$$

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