041 FXUS62 KILM 061046 AFDILM AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON NC 644 AM EDT SAT SEP 6 2014 .SYNOPSIS... SHOWERS AND THUNDERSTORMS WILL CONTINUE TO INCREASE IN COVERAGE TODAY AS A COLD FRONT APPROACHES. LOW PRESSURE MAY ENHANCE THE RAINFALL SUNDAY AND MONDAY. A GRADUAL DRYING TREND WILL GET UNDERWAY ON TUESDAY AND PERSIST INTO LATE NEXT WEEK WHILE AFTERNOON HIGHS CLIMB. && .NEAR TERM /THROUGH TONIGHT/... AS OF 600 AM SATURDAY...COLD CLOUD TOPS WERE ORGANIZING OFF THE CAROLINA COAST NEAR DAYBREAK. WATER VAPOR IMAGERY SHOWS A GOOD SLUG OF DEEP MOISTURE ALONG AND JUST OFF THE SOUTH CAROLINA COAST... MOVING NORTH. SHOWERS AND SOME THUNDERSTORMS WERE INCREASING IN NUMBER IN THIS AREA AND MOVING NORTH AT ABOUT 18 MPH. THUS...EXPECT SHOWERS/THUNDERSTORMS TO INCREASE THROUGH THE MORNING AND INTO THE AFTERNOON... ESPECIALLY ALONG THE COAST...BUT EVEN INLAND AS HEATING GETS UNDERWAY. THE COLUMN WILL BE SLIGHTLY MORE MOIST THAN ON FRI WHILE THE INSTABILITY SHOULD BE SLIGHTLY LESS. THERE ARE NO SIGNIFICANT UPPER LEVEL FEATURES TO ENHANCE CONVECTION. HOWEVER... THE RIDGE IS EXPECTED TO GRADUALLY BREAK DOWN WITH MODEST HEIGHT FALLS DEVELOPING ACROSS THE CAROLINAS. THIS SHOULD ALLOW A COLD FRONT TO MAKE SOME DECENT PROGRESS TO THE SOUTHEAST WITH THE FRONT DROPPING INTO THE LEE SIDE TROUGH POSITION TONIGHT. WE EXPECT CONVECTION TO BE LARGELY DRIVEN BY AN ACTIVE SEABREEZE BOUNDARY WITH LITTLE TO NO CONVECTIVE INHIBITION. THE ACTIVITY SHOULD START EARLY ALONG THE COAST AND THEN REDEVELOP ALONG OUTFLOW BOUNDARIES WITH SHOWERS AND THUNDERSTORMS EXPANDING INLAND THROUGH THE DAY. IN FACT OFFSHORE SHOWERS ARE EXPECTED TO MOVE ONTO THE COAST PRIOR TO SUNRISE. THE COVERAGE OF SHOWERS AND THUNDERSTORMS WILL BE GREATER THAN ON FRI...PERHAPS APPROACHING NUMEROUS IN SOME LOCATIONS. THE SOUTHERLY FLOW WILL BE UP THROUGH ABOUT 20 KFT TODAY...SO THE MOISTURE WILL BE A LITTLE DEEPER THAN PREVIOUS DAYS. STORM MOTIONS SHOULD BE PICKING UP THE PACE...ESPECIALLY LATER TODAY AND TONIGHT AS LOW LEVEL WINDS INCREASE AHEAD OF THE APPROACHING FRONT. WILL CONTINUE TO ADVERTISE THE RISK FOR HEAVY RAIN. WILL CONTINUE TO MENTION SHOWERS AND SOME THUNDERSTORMS THROUGH THE EVE AND OVERNIGHT GIVEN A FRONT WILL BE NEARING THE EASTERN CAROLINAS AND WEAK UPSTREAM DISTURBANCES EMBEDDED IN THE FLOW MAY BEGIN TO IMPINGE ON THE AREA. IF NOTHING ELSE TONIGHT...EXPECT SHOWERS TO INCREASE ACROSS THE ATLANTIC WITH SOME OF THIS ACTIVITY MOVING ONTO THE COAST. HIGH TEMPS WILL BE IN THE UPPER 80S TO LOWER 90S...WARMEST ALONG THE INTERSTATE 95 CORRIDOR. TEMPS AT THE BEACHES SHOULD NOT RISE SIGNIFICANTLY TODAY...MAINLY MID 80S THIS AFTERNOON. TEMPS WILL OF COURSE FLUCTUATE WHERE HEAVY RAIN KNOCKS TEMPS DOWN SIGNIFICANTLY FOLLOWED BY A RECOVERY ONCE THE CONVECTION MOVES AWAY. SOUTH WINDS WILL GUST TO 15 TO 20 MPH... HIGHEST AT THE COAST THIS AFTERNOON. LOWS TONIGHT WILL BE SIMILAR TO THE LAST SEVERAL NIGHTS...LOWER TO MID 70S...BUT NEAR 80 ALONG THE OCEAN FRONT WHERE NOCTURNAL MIXING WILL BE LEAST INHIBITED. && .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... AS OF 300 AM SATURDAY...VERY ACTIVE WEATHER IS EXPECTED THROUGH THE SHORT TERM PERIOD WITH POTENTIAL FOR SOME HEAVY RAINFALL. THERE IS JUST ENOUGH VARIATION IN MODEL SOLUTIONS TO SAY FOR SURE WHEN THE BEST WINDOW OF OPPORTUNITY FOR THAT WILL BE. PIEDMONT TROUGH NEARLY LINKED WITH NORTHWARD EXTENSION OF CARIBBEAN TROPICAL WAVE EXTENDED JUST WEST OF FL RIGHT NOW. THROUGH SUNDAY THIS MOISTURE IS PROGGED TO ADVECT NORTH AND EASTWARD...SURGING INTO THE COASTAL CAROLINAS. MULTIPLE SOURCES OF LIFT INCLUDE BUT ARE NOT LIMITED TO THE SEA BREEZE, THE PIEDMONT TROUGH, AND PVA ASSOC WITH THE MID LEVEL SYSTEM MOVING NE UP THE COAST. A COLD FRONT WILL ALSO BE APPROACHING FROM THE NORTH TO PROVIDE A SQUEEZE PLAY FOR THIS MOISTURE TRYING TO MOVE NORTHWARD. WHERE THIS ZONE OF SURFACE-BASED OVERRUNNING SETS UP LIKELY STANDS TO SEE THE HEAVIEST RAINFALL ON SUNDAY. WRF IS A BIT NORTH OF THE REGION WHEREAS THE GFS TAKES AIM AT MOST OF THE COASTAL CAROLINAS. THE LATTER HALF OF THE PERIOD GETS TRICKY. THE GFS WOULD IMPLY THAT COPIOUS RAINS CONTINUE THROUGH ABOUT MONDAY MORNING. THEREAFTER THE SURFACE REFLECTION OF THE FL UPPER LOW MOVES NE ALONG THE FRONT AS A FAIRLY FLAT WAVE. THE WRF WHICH WAS INITIALLY A STRONG OUTLIER CONTINUES TO SHOW A SIMILAR SCENARIO. ITS MORE CLOSED OFF LOW IS SLOWER TO ZIPPER ITS WAY UP THE FRONT...BUT IT JUST SEEMS TO BE IMPLYING TOO MUCH BAROTROPIC/LATENT HEATING DRIVEN STRENGTHENING PROCESSES TAKING PLACE...ALL WHILE THE LOW REMAINS OVER LAND. ANY OF THOSE PROCESSES MAY VERY WELL TAKE PLACE BUT PROBABLY WELL AFTER IT HAS PASSED NORTH OF HATTERAS A LA THE CANADIAN GEM MODEL. THE ECMWF IS A RATHER NICE COMPROMISE SHOWING THAT MUCH OF MONDAY IS JUST AS WET FOR MOST AREAS AS SUNDAY...WHICH PERHAPS A MORE DEFINED COASTAL VS INLAND GRADIENT IN QPF...BOTH DAYS WETTEST ALONG THE COAST. && .LONG TERM /TUESDAY THROUGH FRIDAY/... AS OF 300 AM SATURDAY...LOW LEVEL MOISTURE ASSOCIATED WITH DISSIPATING FRONT SHOULD LINGER FOR LOW END CHANCE POPS ESPECIALLY ALONG THE COAST. MID LEVEL ZONAL FLOW WILL BE DRYING OUT MUCH OF THE COLUMN ABOVE THE BOUNDARY LAYER THOUGH. WEDNESDAY LOOKS LIKE A TRANSITION BACK TO A WARM SEASON PATTERN WITH FLAT WEAK RIDGING ACROSS NRN GOMEX AND SRN U.S. WHILE BERMUDA HIGH STRUGGLES TO REASSERT ITSELF. THE LATTER FACT NOT THAT GREAT FOR DIURNAL CONVECTION-INDUCING LOW LEVEL MOISTURE ADVECTION BUT SOME FRONTAL MOISTURE MAY STILL LINGER. ISO POPS AND CLIMO TEMPS APPEAR A GOOD BET. THE MID LEVEL RIDGE INCREASES IN AMPLITUDE ON THURSDAY BRINGING A WARMER AFTERNOON WHILE INCREASING TROUGINESS OVER THE NRN PLAINS DRIVES A STRONG FRONT INTO THE GREAT LAKES. PREFRONTAL TROUGH DEVELOPS ACRS THE PIEDMONT ON FRIDAY WITH A LITTLE EXTRA MOISTURE FLUX INTO THE COASTAL PLAIN AS A RESULT. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/... AS OF 12Z...TROPICAL MOISTURE CONTINUES WITH PRECIPITABLE WATER HOVERING AROUND TWO INCHES AND THE LEVEL OF FREE CONVECTION ONLY 800 METERS. WITH LITTLE CONVECTIVE INHIBITION...EXPECT NUMEROUS SHOWERS AND STORMS ALONG THE COAST WITH SCATTERED CONVECTION INLAND. VISIBILITIES COULD DROP AS LOW AS A MILE...BUT ONLY BRIEFLY. SOUTHERLY FLOW WILL CONTINUE...WITH POSSIBLE GUSTS TO 20 KTS OR SO IN THE CONVECTION. MOST OF THE CONVECTION WILL WANE THIS EVENING...HOWEVER DEEP MOISTURE WILL MOVE IN TOWARDS DAYBREAK WITH NUMEROUS SHOWERS AND STORMS EXPECTED TO RETURN. EXTENDED OUTLOOK...A COLD FRONT WILL DROP INTO THE REGION SUNDAY AND MONDAY... WITH A HIGHER RISK FOR SHOWERS AND STORMS BOTH DAYS. THE FRONT STALLS WITH A CONTINUED CHANCE FOR SHOWERS TUESDAY. && .MARINE... NEAR TERM /THROUGH TONIGHT/... AS OF 600 AM SATURDAY...THE PRESSURE GRADIENT WILL TIGHTEN SLIGHTLY THIS PERIOD AS A TROUGH APPROACHES THE WATERS FROM THE NW. WINDS WILL REMAIN ELEVATED TONIGHT AS LOW LEVEL WINDS INCREASE AHEAD OF THE TROUGH AND MIX MORE EFFICIENTLY DOWN TO THE SURFACE. SUSTAINED WIND SPEEDS WILL INCREASE TO AROUND 15 KT WITH GUSTS TO AROUND 20 KT. THE DIRECTION WILL BE SOUTH. SEAS WILL BUILD SLIGHTLY...WITH MORE 4 FT SEAS EXPECTED TO BE OBSERVED LATER TODAY AND TONIGHT. HEAVY DOWNPOURS ARE EXPECTED IN SHOWERS AND THUNDERSTORMS WHICH WILL CREATE SIGNIFICANT VISIBILITY RESTRICTIONS. CONDITIONS ARE SOMEWHAT FAVORABLE FOR WATERSPOUTS AS WELL. SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... AS OF 300 AM SATURDAY...SWRLY GRADIENT WINDS WILL STILL BE QUITE 'SEASONABLE' DESPITE COLD FRONT PUSHING INTO THE CAROLINAS. THE TEMPORAL PERSISTENCE OF THE FETCH HOWEVER MAY CAUSE THE OCCASIONAL 5 FT WAVE TO APPEAR ALONG OUTER EDGES OF NRN LEGS. HOW THE REMAINDER OF THE PERIOD UNFOLDS IS RATHER UNCERTAIN AS IT WILL INVOLVE LOW PRESSURE TRAVELING NORTH AND EAST ALONG THE STALLED FRONTAL BOUNDARY. SOME GUIDANCE IS PROBLEMATICALLY DEVELOPING A STRONG LOW THAT LOOKS LIKE IT IS BORNE OF TROPICAL STRENGTHENING DESPITE THE LOW REMAINING OVER LAND. THE SLOWER AND WEAKER MODELS ARE THUS PREFERRED AND EVEN THIS MAY PUSH WIND OR SEAS CLOSE TO BUT GENERALLY SHY OF SCEC CRITERIA. FUTURE MODEL RUNS SHOULD CLARIFY THESE UNCERTAINTIES. LONG TERM /TUESDAY THROUGH WEDNESDAY/... AS OF 300 AM SATURDAY...THE DEPARTURE OF THE SURFACE LOW OF THE SHORT TERM AND THE APPARENT RAPID WEAKENING OF ITS ASSOCIATED FRONTAL BOUNDARY AND TUESDAY WINDS AND SEAS MAY FALL TO QUITE MINIMAL LEVELS WITH A GENERALLY OFFSHORE FLOW DIRECTION. A CONTINUED WEAKENING OF THE BOUNDARY ON WEDNESDAY SHOULD ALLOW FOR A GRADUAL TURN TO THE SOUTH WHILE WIND AND SEAS REMAIN MINIMAL. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...NONE. NC...NONE. MARINE...NONE. && $$ NEAR TERM...RJD SHORT TERM...MBB LONG TERM...MBB AVIATION...43