FXUS62 KILM 091938 AFDILM AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON NC 333 PM EDT SAT MAY 9 2009 .SYNOPSIS... A COLD FRONT WILL DROP SOUTH LATE TONIGHT AND EARLY SUNDAY STALLING ACROSS THE REGION THROUGH MONDAY. THIS WILL BRING A CHANCE OF SHOWERS AND THUNDERSTORMS. THE FRONT WILL MOVE SOUTH OF THE AREA LATE MONDAY...BRINGING COOLER AND DRIER AIR THROUGH MID WEEK...AS HIGH PRESSURE BUILDS INTO THE REGION FROM THE NORTH. ANOTHER COLD FRONT WILL APPROACH THE REGION LATE IN THE UPCOMING WEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 3 PM SATURDAY...THE SYNOPTIC SITUATION IS VERY SIMILAR TO FRIDAY...A VERY ACTIVE ZONAL FLOW ALOFT WITH SEVERAL EMBEDDED SHORT WAVES PRODUCING AREAS OF SHOWERS AND THUNDERSTORMS TO OUR WEST. AT THE SURFACE...A COLD FRONT IS MOVING NORTHWEST TO SOUTHEAST ACROSS THE TENNESSEE VALLEY. ACROSS OUR AREA...A STRONG AREA OF SUBSIDENCE RESIDES AROUND 800MB WHICH IS PRECLUDING ANY SIGNIFICANT CLOUD DEVELOPMENT LET ALONE CONVECTIVE DEVELOPMENT. FORECAST MODELS WERE EARLIER HINTING AT THIS CAP ERODING OVERNIGHT BUT THE 1200 UTC CYCLES NOW MAINTAIN IT FOR THE MOST PART. FOR THIS REASON I HAVE MAINTAINED THE SLIGHT CHANCE POPS FOR THE NORTHWEST CORNER OF THE CWA THIS EVENING FOR ANY ACTIVITY THAT MAY STRAY INTO THESE AREAS FROM THE MCS TO THE WEST...OTHERWISE...NO POPS. LOW LEVEL CONVERGENCE WITH THE COLD FRONT THAT IS SLATED TO MOVE THROUGH IN THE EARLY MORNING HOURS IS WEAK AS WELL. OVERNIGHT LOWS SHOULD BE FAIRLY UNIFORM IN THE MIDDLE 60S WITH SLIGHTLY WARMER CONDITIONS ALONG THE COAST. && .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... AS OF 3 PM SATURDAY...DAYTIME SUNDAY MAY NOT BE A TOTAL WASHOUT GIVEN THE SFC FRONTAL BOUNDARY STALLING ACROSS OR JUST SOUTH OF THE ILM CWA DURING THE DAY. FRONTAL DYNAMICS WILL LIKELY IGNITE WIDELY SCATTERED CONVECTION ALONG ITS BOUNDARY BUT NO UPPER IMPULSE FROM THE WEST TO PINPOINT THAT WOULD FURTHER IGNITE PCPN DURING THE DAY SUNDAY. THE LATTER WILL CHANGE LATER SUNDAY NIGHT THROUGH MONDAY. THE NAM SEEMS SLITELY BETTER IN IDENTIFYING THOSE WEAK S/W TROFS WITHIN WESTERLY FLOW ALOFT. WITH THE STALLED FRONTAL BOUNDARY PROGGED ACROSS THE SOUTHERN PORTIONS OF THE ILM CWA...ISENTROPIC LIFT MAY ALSO BECOME A DRIVING FORCE AS MENTIONED IN PRIOR DISCUSSIONS. THE 1ST UPPER IMPULSE PROGGED TO PUSH THROUGH AFTER MIDNIGHT MONDAY WITH INCREASING POPS IN THE FORECAST. AN EVEN SLITELY STRONGER UPPER IMPULSE MONDAY AFTERNOON ALONG WITH THE DAYS INSOLATION TO AID IN DESTABILIZATION RESULTING IN POPS REACHING LIKELY THRESHOLDS. FOR MON NITE...THE UPPER LONGWAVE PATTERN WILL BE IN THE PROCESS OF BUCKLING WITH UPPER TROFFINESS BECOMING MORE APPARENT ACROSS THE EASTERN 1/3RD OF THE U.S. AS A RESULT...THE STALLED SFC BNDRY WILL FINALLY GET KICKED FURTHER SOUTH...ENDING THE PCPN FROM NW TO SE AND WITH PARTIAL CLEARING LATE. FOR TEMPS...USED A BLEND OF MODEL MOS GUIDANCE FOR MAX/MIN THRU MON MORNING. THERE-AFTER STAYED CLOSER TO THE GFS MOS WHICH IS SLITELY LOWER...AND EVEN UNDERCUT THAT BY 1 TO 3 DEGREES BASED ON CONTINOUS THICK VEIL OF CLOUDINESS AND PCPN. && .LONG TERM /TUESDAY THROUGH FRIDAY/... AS OF 3 PM SATURDAY...DEPARTING POORLY AMPLIFIED EAST COAST TROUGH WILL ALLOW FOR WEAK UPPER RIDGING TO TAKE HOLD WEDNESDAY NIGHT INTO THURSDAY. A WEAKENING SHORT WAVE WILL PUSH INTO THE EASTERN UNITED STATES BY THURSDAY NIGHT LEAVING NEAR ZONAL FLOW IN ITS WAKE FOR NEXT WEEKEND. AT THE SURFACE...HIGH PRESSURE RIDGING IN FROM THE NORTH TUESDAY WILL SHIFT OFF THE COAST WEDNESDAY WITH GENERALLY WEAK RETURN FLOW DEVELOPING THURSDAY AHEAD OF THE NEXT COLD FRONT. THIS FRONT IS PROGGED TO PUSH INTO THE AREA DURING FRIDAY...AND COULD WASH OUT SOUTH OF THE FORECAST AREA BY THIS WEEKEND. AS A RESULT OF THE PATTERN DISCUSSED IN THE PREVIOUS PARAGRAPH... BELOW NORMAL TEMPERATURES TUE INTO WED WILL WARM TO NEAR NORMALS THE LAST HALF OF THE WEEK. THE AIR-MASS WILL REMAIN ON THE STABLE SIDE TUE AND WED...WITH SOME INSTABILITY RETURNING THURSDAY AND FRIDAY AHEAD OF THE FRONT. THINK CONVECTION WILL REMAIN WIDELY SCATTERED TO SCATTERED THURSDAY AFTERNOON INTO FRIDAY AHEAD OF THE FRONT GIVEN MINIMAL RETURN FLOW TIME. && .AVIATION /18Z SATURDAY THROUGH WEDNESDAY/... MODELS NOT THRILLED AT ALL AT THE PROSPECT FOR CONVECTION...BUT HAVE TO BELIEVE THAT WITH THE WIND SHIFT AND WEAK AIR MASS CHANGE...THERE WILL BE SOME ISOLATED TO SCATTERED CONVECTION AROUND. WILL KEEP THE CONVECTION IN FOR NOW FOR THE OVERNIGHT HOURS...BUT IT IS BECOMING LESS LIKELY. GUSTY SOUTHWEST WINDS THIS AFTERNOON WILL DIMINISH THIS EVENING...BECOMING NORTH AFTER THE FRONTAL BOUNDARY DROPS SOUTH THROUGH THE REGION...FROM 06-08Z. NORTH NORTHEAST WINDS ARE EXPECTED SUNDAY...WITH A POSSIBLE MID CLOUD CEILING. EXTENDED OUTLOOK THROUGH WEDNESDAY... ISOLATED SHOWERS SUNDAY EVENING...WITH A GOOD CHANCE FOR RAIN AND POSSIBLE IFR CEILINGS ON MONDAY. VFR TUESDAY AND WEDNESDAY. && .MARINE... NEAR TERM /THROUGH TONIGHT/... AS OF 3 PM SATURDAY...A HEALTHY GRADIENT RESIDES ACROSS THE REGION THIS AFTERNOON WITH WIND SPEEDS RUNNING 15-20 KNOTS ACROSS THE WATERS. THE NAM WINDS INITIALIZED A LITTLE BETTER AS OPPOSED TO THE GFS SO I HAVE USED THEM FOR THE NEAR TERM FORECAST. EXPECT THE GRADIENT TO INCREASE A BIT FOR THE NEXT FEW HOURS AS THE FRONT IN THE TENNESSEE VALLEY INCHES CLOSER. OVERNIGHT WINDS WILL SUBSIDE EVEN AS THE FRONT MOVES CLOSER AS IT WEAKENS AND HIGH PRESSURE WEAKENS WELL OFF TO THE EAST. EXPECT WINDS AROUND 20 KNOTS THIS EVENING DROPPING BACK TO 15-20 KNOTS OVERNIGHT. STILL EXPECTING SMALL CRAFT SEAS TO DEVELOP ACROSS THE NORTHERN WATERS THIS EVENING WITH COINCIDING WITH THE STRONGEST WINDS DROPPING BACK BELOW CRITERIA BY SUNDAY MORNING. SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... AS OF 3 PM SATURDAY...MAIN DILEMMA THIS FCST PACKAGE WILL BE THE POSITION OF THE FRONTAL BOUNDARY ONCE IT BECOMES STATIONARY. INITIAL NW-N SURGE SUNDAY MORNING WILL BECOME LIGHT EASTERLY AS THE SFC PG RELAXES WHILE THE SFC FRONTAL BNDRY STALLS SOUTH OF MURRELLS INLET. WEAK IMPULSES ALOFT TO INTERACT WITH THE SFC BOUNDARY SUNDAY NIGHT THROUGH MONDAY AND PRODUCE WEAK WAVES OF SFC LOW PRESSURE THAT WILL MOVE ENE ALONG THE STALLED BNDRY. ITS DURING THIS TIME THAT A TEMPORARY TIGHTENING OF THE SFC PG WILL OCCUR. HAVE ATLEAST IDENTIFIED MONDAY INTO MONDAY NIGHTS TIMEFRAME WHEN AN INCREASED SFC PG WILL OCCUR FROM 1 OF THE STRONGER ENE MOVING SFC LOWS. SEAS WILL MAINLY BE A FUNCTION OF THE LOCAL WINDS WITH THE EXCEPTION OF THE SE-SSE 2 TO OCCASIONALLY 3 FOOT GROUND SWELL. SCA THRESHOLDS WILL BE CHALLENGED LATE MONDAY AND MONDAY NIGHT AND WILL NEED TO BE MONITORED. FOR THE TIME BEING...NO FLAGS ANTICIPATED. LONG TERM /TUESDAY THROUGH WEDNESDAY/... AS OF 3 PM SATURDAY...NORTHEASTERLY WIND EARLY TUESDAY WILL VEER TO THE EAST DURING THE AFTERNOON...THEN BACK TO A NORTHEASTERLY DIRECTION BY WEDNESDAY MORNING. AS THE SURFACE HIGH SHIFTS OFF THE EAST COAST THE EAST FLOW WEDNESDAY AFTERNOON WILL CONTINUE TO VEER TO THE SOUTH BY THURSDAY AFTERNOON. SEAS WILL BE AT OR ABOUT 3 FT AWAY FROM THE COAST TUESDAY. SEAS WILL BUILD TO 3-5 FT WITH THE EAST WIND WEDNESDAY AND WEDNESDAY NIGHT. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...NONE. NC...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR AMZ250-252. && $$ SYNOPSIS...SHK NEAR TERM...SHK SHORT TERM...11 LONG TERM...SRP AVIATION...SHK