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...