Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 160534 AFDILM AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON NC 134 AM EDT THU APR 16 2015 .SYNOPSIS... LOW PRESSURE WILL DEVELOP ALONG A FRONT STALLED ALONG THE GEORGIA COAST TONIGHT...SLOWLY WEAKENING LATE THURSDAY AND FRIDAY. HIGH PRESSURE OVER NEW ENGLAND WILL SHIFT EAST AND OFFSHORE THURSDAY. A WARM FRONT WILL MOVE NORTH THROUGH THE CAROLINAS ON SUNDAY WITH A COLD FRONT TO FOLLOW MONDAY NIGHT INTO TUESDAY. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... AS OF 130 AM THURSDAY...NO CHANGES TO THE FORECAST WITH THE LATEST UPDATE. PREVIOUS DISCUSSION FOLLOWS: THE WEATHER SITUATION IS UNFOLDING PRETTY MUCH AS EXPECTED. THE SOLID MASS OF RAIN HAS CLEARED THE PEE DEE COUNTIES BUT RAIN CONTINUES TO FALL ACROSS WHITEVILLE...SOUTHPORT AND WILMINGTON. THIS AREA SHOULD MOVE OFF THE COAST IN THE NEXT 2 HOURS...LEAVING MUCH WEAKER FORCING FOR THE OVERNIGHT NIGHT. LATEST HRRR AND HRRRMODELS STILL SUGGEST THE BEST POTENTIAL FOR OVERNIGHT RAIN WILL BE NORTH OF A LINE FROM FLORENCE TO DILLON...TO ELIZABETHTOWN AND BURGAW...COINCIDENT WITH THE BETTER 700 MB MOISTURE AND RESIDUAL ISENTROPIC LIFT ON THE SYNOPTIC MODELS. THERE IS ALSO SMALL POSITIVE ELEVATED INSTABILITY ON THE ORDER OF 100 J/KG WHICH COULD HELP SUPPORT SHOWERS GIVEN SUFFICIENT SYNOPTIC TRIGGERING. FEW CHANGES ARE NEEDED TO LOW TEMPERATURE FORECASTS OR WINDS. DISCUSSION FROM 730 PM FOLLOWS... A STALLED FRONT JUST SOUTH OF SAVANNAH WILL DEVELOP AN AREA OF LOW PRESSURE IN THE NEXT FEW HOURS. THIS LOW WILL NOT STRAY TOO FAR OFFSHORE OVER THE NEXT 24 HOURS...BUT WILL MAINTAIN A STEADY NORTHEAST WIND. SURFACE HIGH PRESSURE OVER SOUTHEASTERN CANADA WILL SLIDE SOUTHEAST INTO NEW ENGLAND TONIGHT. THIS HIGH WILL EXTEND A RIDGE AXIS SOUTHWARD INTO THE CAROLINAS...COMPRESSING THE PRESSURE GRADIENT UP AGAINST THE LOW DEVELOPING OFF THE GEORGIA COAST. A COMPLEX UPPER LEVEL PATTERN ACROSS THE WESTERN U.S. HAS THE JET STREAM SPLIT INTO TWO SEGMENTS. THE SOUTHERN STREAM WILL BRING SEVERAL DISTURBANCES ACROSS THE CAROLINAS OVER THE NEXT 36-48 HOURS. ONE OF THESE DISTURBANCES IS MOVING ACROSS INTERSTATE 95 NOW PRODUCING THE LARGE SWATH OF RAIN NOW SEEN ON RADAR. THIS FEATURE SHOULD WORK ITS WAY TO THE COAST AROUND MIDNIGHT...AND I HAVE RAISED FORECAST POPS TO 100 PERCENT AREA-WIDE WITH 0.2 TO 0.4 INCHES OF RAIN EXPECTED OVER THE NEXT 12 HOURS. PLENTY OF MID- LEVEL MOISTURE SHOULD HANG AROUND AFTER MIDNIGHT WITH JUST ENOUGH WEAK ISENTROPIC LIFT PLUS ELEVATED INSTABILITY TO MAINTAIN SHOWERS AFTER MIDNIGHT...ESPECIALLY NORTH OF FLORENCE AND MYRTLE BEACH. LOW-LEVEL NORTHEAST WINDS WILL DRAG COOLER AIR SOUTHWARD TONIGHT...WITH LOWS AWAY FROM THE COAST FALLING TO NEAR 50. VARYING DEGREES OF MARINE INFLUENCE WILL KEEP THE IMMEDIATE COAST WARMER WITH LOWS IN THE MID 50S POSSIBLE. && .SHORT TERM /6 AM THIS MORNING THROUGH FRIDAY NIGHT/... AS OF 300 PM WEDNESDAY...THE FORECAST HAS BECOME NO LESS COMPLICATED AND IN FACT...IN SOME RESPECTS...MODELS HAVE DIVERGED EVEN FURTHER IN THE LAST 24 HOURS. THE GFS SOLUTION LOOKS VERY DIFFERENT FROM PREVIOUS RUNS. THE NAM SOLUTION LOOKS SIMILAR TO PREVIOUS THINKING...BUT THE PROGRESSION OF OFFSHORE LOW PRESSURE IS SLOWER AND FURTHER EASTWARD THAN 24 HOURS AGO AND CERTAINLY MUCH STRONGER. THE CANADIAN IS CONSIDERABLY SLOWER AND WEAKER THAN THE NAM AS IS THE EUROPEAN...BUT BOTH DO CLOSE OFF LOW PRESSURE ALONG THE COAST OF SOUTH CAROLINA. SLOWER SEEMS REASONABLE GIVEN THE STRENGTH OF HIGH PRESSURE TO THE NORTH AND RESULTING WEDGE...THUS THE BEST WE CAN DO AT THIS POINT IS TO GO ALONG WITH PERSISTENCE...BUT SLOW PROGRESSION. WILL INCLUDE HIGHEST POPS THU ALONG THE COAST AND UP TO CATEGORICAL THU MORNING ALONG THE CAPE FEAR COAST DUE TO STRENGTH OF ISENTROPIC LIFT COUPLED WITH THE LIFT ASSOCIATED WITH LOW PRESSURE/TROUGH. WILL THEN TREND POPS LOWER THU AFTERNOON AND NIGHT FROM SW TO NE WITH A LINGERING RISK ALONG THE CAPE FEAR COAST FRI MORNING. GIVEN PROXIMITY OF COASTAL TROUGH AND ELEVATED INSTABILITY...WILL INCLUDE MENTION OF THUNDER FOR PORTIONS OF THE FORECAST AREA. THE MOISTURE PROFILES DRY OUT CONSIDERABLY AS A RIDGE OF HIGH PRESSURE ALOFT BUILDS TO THE COAST FROM THE WEST TOWARD THE END OF THE PERIOD. WILL FINALLY DROP POPS BELOW THRESHOLD FRI AFTERNOON AND NIGHT...EVEN ALONG THE SEABREEZE BOUNDARY. BELOW NORMAL HIGH TEMPS ARE EXPECTED AGAIN ON THU AS WEDGE KEEPS LOW- LEVEL MOISTURE TRAPPED BENEATH INVERSION. HIGHS WILL ONLY BE IN THE LOWER TO MID 60S. DEVELOPING SUNSHINE ON FRI SHOULD ALLOW TEMPS TO RETURN TO MORE SEASONABLE LEVELS...LOW AND MID 70S. LOWS THIS PERIOD WILL BE MAINLY IN THE 50S. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... AS OF 300 PM WEDNESDAY...GUIDANCE HAS SHIFTED PRETTY DRAMATICALLY FROM JUST YESTERDAY...LEADING TO ENHANCED UNCERTAINTY DURING THE EXTENDED. LARGE CLOSED LOW ACROSS THE SOUTHWEST WILL ONLY VERY SLOWLY FILL AND EJECT TO THE NORTHEAST THROUGH THE WEEKEND...PHASING WITH A DEEPENING NORTHERN STREAM CUTOFF LOW ACROSS THE GREAT LAKES LATE MONDAY. THIS FEATURE WILL THEN AMPLIFY AND STALL ACROSS THE GREAT LAKES THROUGH THE MIDDLE OF NEXT WEEK...PRODUCING 500MB HEIGHTS OF -2 TO -3 SD`S BELOW CLIMO ACROSS THE NORTHEAST AND INTO THE MID-ATLANTIC. INITIALLY THE EXTENDED WILL BE WARM AND PLEASANT. SATURDAY IS SHAPING UP TO BE A GORGEOUS DAY LOCALLY...WITH HIGHS ABOVE CLIMO AND A LOT OF SUNSHINE. MOISTURE RETURNS SUNDAY IN A PRE-FRONTAL AIR MASS WHICH WILL CONTINUE INTO MONDAY AHEAD OF A COLD FRONT. SUNDAY AND MONDAY WILL BOTH FEATURE ABOVE CLIMO TEMPS...BUT WITH INCREASING RAIN CHANCES AHEAD OF THE COLD FRONT. ATTM THE FRONT DOES NOT LOOK TO BE STRONGLY FORCED SO WIDESPREAD CONVECTION IS NOT ANTICIPATED MONDAY EVENING WITH THE FROPA. COOLER HIGH PRESSURE WILL BUILD IN BEHIND THE FRONT FOR TUE/WED OF NEXT WEEK WITH TEMPS RETURNING TO SEASONABLE LEVELS. && .AVIATION /06Z THURSDAY THROUGH MONDAY/... AS OF 06Z...EXPECTING IFR CONDITIONS MUCH OF THE TAF PERIOD WITH OCCASIONAL RAIN. COULD BE A BREAK IN THE 20 TO 02Z WINDOW WITH MVFR OR VFR CONDITIONS UNTIL THE NEXT BATCH OF PRECIPITATION ARRIVES TOWARD THE END OF THE PERIOD. WITH LOW PRESSURE OFF THE COAST...GUSTY NE WINDS ARE EXPECTED THROUGH MUCH OF THE PERIOD AS WELL WITH SPEEDS IN THE 10 TO 15 KT RANGE WITH WITHS OVER 20 KT...ESPECIALLY COASTAL TERMINALS. EXTENDED OUTLOOK...PREDOMINATELY IFR CONDITIONS ARE EXPECTED INTO EARLY FRIDAY MORNING WITH THE WEDGE. IMPROVING CONDITIONS DURING THE DAY FRI. DETERIORATING CONDITIONS AGAIN SATURDAY NIGHT THROUGH SUNDAY WITH A SLOW MOVING FRONT. SLIGHT CHANCE FOR SHOWERS MONDAY. && .MARINE... NEAR TERM /THROUGH TONIGHT/... AS OF 130 AM THURSDAY...NO CHANGES TO THE FORECAST WITH THE LATEST UPDATE. PREVIOUS DISCUSSION FOLLOWS: STRONG NE WINDS HAVE QUICKLY DEVELOPED THIS EVENING. RECENT WIND GUSTS INCLUDE 31 KNOTS AT SPRINGMAID PIER IN MYRTLE BEACH...24 KNOTS ON BALD HEAD ISLAND...AND 23 KNOTS AT WRIGHTSVILLE BEACH. SEAS OUT AT THE FRYING PAN SHOALS BUOY HAVE ALREADY REACHED 8 FEET...WITH SEAS NOW PASSING 5 FEET AT BOTH NEARSHORE BUOYS NEAR CAPE FEAR. THIS UPDATE BACKED WINDS AROUND MORE NORTHERLY NEARSHORE AND INCREASE SEA HEIGHTS SLIGHTLY...ALL BASED ON CURRENT OBSERVATIONS. DISCUSSION FROM 730 PM FOLLOWS... A FRONT STALLED JUST SOUTH OF SAVANNAH EXTENDS EAST WELL OFF THE COAST. WEAK LOW PRESSURE WILL DEVELOP ALONG THE FRONT TONIGHT...WHILE HIGH PRESSURE OVER NEW ENGLAND RIDGES SOUTHWARD DOWN THE COAST. THE CAROLINAS WILL BE CAUGHT IN BETWEEN THESE TWO SYSTEMS...WITH INCREASING EAST-NORTHEAST WINDS THE RESULT. THE 18Z GFS APPEARS TO BE THE BEST INITIALIZED OF OUR MODELS THIS EVENING...AND ITS FORECAST WINDS HAPPEN TO BE THE STRONGEST TONIGHT...INDICATING WINDS NEARSHORE INCREASING TO 20-25 KT AND 25-30 KT AWAY FROM SHORE. THIS IS SLIGHTLY HIGHER THAN THE PREVIOUS FORECAST HAD. LATEST CHECK OF BUOYS INDICATES SEAS ARE INCREASING A BIT FASTER THAN EARLIER THOUGHT. I HAVE ADDED ABOUT ONE FOOT TO THE PREVIOUS FORECAST...WITH SEAS NOW EXPECTED TO BUILD TO 6-8 FEET OUT AT 20 MILES DISTANCE FROM SHORE...WITH 4-7 FEET EXPECTED CLOSER TO SHORE. SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... AS OF 300 PM WEDNESDAY...ONGOING SMALL CRAFT ADVISORY CONDITIONS ARE EXPECTED AT THE BEGINNING OF THE PERIOD AS LOW PRESSURE MOVES UP THE SOUTHEAST COAST. THE PRESSURE GRADIENT BETWEEN DEVELOPING LOW PRESSURE AND THE STRONG HIGH TO THE NORTH WILL ALLOW A TIGHT PRESSURE GRADIENT TO PERSIST INTO THU AND THIS IS WHEN WE EXPECT THE STRONGEST WINDS AND HIGHEST SEAS...UP TO 20 TO 30 KT...HIGHEST NORTHERN WATERS AND SEAS UP TO 5 TO 8 FT THROUGHOUT. AS THE PRESSURE GRADIENT SLACKENS AND LOW PRESSURE MOVES TO OUR N...WINDS AND SEAS WILL SUBSIDE THU NIGHT AND FRI WITH THIS TREND PERSISTING INTO FRI NIGHT. ENE WINDS THU WILL BACK TO NE THU NIGHT WITH NNE TO NE WINDS THEN PERSISTING THROUGH THE END OF THE PERIOD. LONG TERM /SATURDAY THROUGH MONDAY/... AS OF 300 PM WEDNESDAY...HIGH PRESSURE WILL BUILD DOWN THE COAST AND THEN MOVE OFFSHORE SATURDAY...CREATING A WEAK PRESSURE GRADIENT AND WINDS SHIFTING FROM NE EARLY...TO E/SE LATE. WINDS SPEEDS THEN STEADILY INCREASE SUNDAY AS THE GRADIENT STARTS TO PINCH AHEAD OF AN APPROACHING COLD FRONT...BECOMING S/SW AT AROUND 15 KTS MOST OF SUNDAY...AND THEN SW AT 15-20 KTS ON MONDAY DIRECTLY AHEAD OF THE FROPA. COLD FRONT WILL CROSS THE WATERS AT THE VERY END OF THE PERIOD WITH A WIND SHIFT TO THE NW AT 10-15 KTS. ALTHOUGH A WEAK SE GROUND SWELL WILL BE PRESENT IN THE SPECTRUM DURING THE EXTENDED...MUCH OF THE WAVE AMPLITUDE WILL BE FORMED VIA WIND WAVES...AND SEAS WILL BE 2-3 FT SATURDAY...BUILDING TO 3-5 FT SUNDAY AND MONDAY AHEAD OF THE COLD FRONT. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...NONE. NC...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT FRIDAY FOR AMZ250-252-254- 256. && $$ SYNOPSIS...RJD NEAR TERM...REK/TRA SHORT TERM...RJD LONG TERM...JDW AVIATION...RAN MARINE...REK/RJD/TRA/JDW

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