089 FXUS62 KILM 061433 AFDILM AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON NC 1033 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 10 AM SATURDAY...ALTHOUGH CONVECTION CONTINUES TO MOVE ONSHORE COVERAGE HAS BEEN DECREASING AND CLOUD TOPS WARMING. AT THIS POINT THE ONLY NOTEWORTHY CONVECTION IS MOVING NORTH FROM CAPE FEAR AND APPEARS TO BE ASSOCIATED WITH OUTFLOW FROM EARLY MORNING MARINE CONVECTION. MOISTURE CONTINUES TO STREAM NORTH FROM WEAK DISTURBANCE ALONG THE GA COAST...BUT THIS MORNINGS CONVECTION HAS LIKELY WORKED TO TEMPORARILY STABILIZE THE ATMOSPHERE. SHOWERS AND THUNDERSTORMS ALONG THE COAST MAY BE DONE FOR MOST OR ALL OF THE DAY...ONCE THE DIMINISHING CONVECTION MOVING NORTH ACROSS PENDER COUNTY ENDS. MEANWHILE FARTHER WEST ONGOING HEATING WILL RESULT IN AFTERNOON SHOWERS AND THUNDERSTORMS DEVELOPING ACROSS THESE AREAS. GIVEN THE EXPANSIVE MORNING CLOUDS ALONG THE COAST A DIFFERENTIAL HEATING BOUNDARY MAY ALSO SET UP. THIS COULD INITIATE ADDITIONAL AFTERNOON CONVECTION AS WELL AS ENHANCING ANY ONGOING STORMS. HIGH RESOLUTION SHORT RANGE GUIDANCE DOES DEPICT CONVECTION SHIFTING FROM THE COAST THIS MORNING TO INLAND AREAS THIS AFTERNOON...AS HAS BEEN THE CASE THE LAST FEW DAYS. CANNOT RULE OUT ADDITIONAL CONVECTION ALONG THE COAST THIS EVENING ONCE THE ATMOSPHERE RELOADS BUT THE DIURNAL HEATING WINDOW WILL BE LIMITED. BIGGEST CHANGES FOR THE UPDATE WERE TO POP DISTRIBUTION DURING THE DAY BUT OVERALL NUMBERS HAVE NOT CHANGED MUCH. HAVE ONLY MADE SLIGHT CHANGES TO TEMPERATURES FOR TODAY WITH INLAND AREAS STILL EXPECTED TO REACH LOWER 90S. COASTAL AREAS WILL BE A LITTLE MORE DIFFICULT GIVEN LINGERING CLOUD COVER AND SLIGHTLY COOLER ONSHORE FLOW. && .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 /14Z 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 10 AM SATURDAY...BERMUDA HIGH WILL MAINTAIN SOUTHERLY FLOW TODAY ALTHOUGH WEAK COASTAL TROUGH EXTENDING NORTH INTO SC MAY INDUCE SOUTHEAST OR EVEN EAST WINDS ALONG THE COAST. GRADIENT REMAINS WEAK AND SPEEDS WILL NOT CLIMB MUCH ABOVE 10 KT TODAY. GRADIENT MAY BECOME SLIGHTLY BETTER DEFINED TONIGHT AS COLD FRONT TO THE NORTHWEST CREEPS CLOSER. SPEEDS MAY CLIMB INTO THE 10 TO 15 KT RANGE BUT WILL REMAIN WELL BELOW HEADLINE CRITERIA. SEAS 2 TO 3 FT TODAY WITH POTENTIAL FOR ISOLATED 4 FT SEAS OVERNIGHT. 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...III SHORT TERM...MBB LONG TERM...MBB AVIATION...43