Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 300500 AFDILM AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON NC 100 AM EDT WED JUL 30 2014 .SYNOPSIS... DRIER AND COOLER AIR WILL SETTLE INTO THE REGION AS CANADIAN HIGH PRESSURE MIGRATES INTO THE AREA THIS WEEK. A COASTAL FRONT WILL LIFT BACK NORTHWARD ACROSS OUR AREA THIS WEEKEND...BRINGING INCREASED RAIN CHANCES FRIDAY THROUGH MONDAY. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... AS OF 1030 PM TUESDAY...ACROSS EASTERN PENDER AND NEW HANOVER COUNTIES THIS WAS THE LITTLE AIRMASS THAT COULD! DESPITE SHALLOW INSTABILITY ONLY AMOUNTING TO 1000 J/KG...SHOWERS OVER THE PAST THREE HOURS DROPPED 0.59 INCHES AT THE ILM AIRPORT...0.27 INCHES IN THE KINGS GRANT NEIGHBORHOOD A FEW MILES TO THE EAST...0.25 INCHES IN SURF CITY...AND 0.17 INCHES IN WRIGHTSVILLE BEACH. WET GROUND HAS PRIMED THIS AREA FOR SOME PATCHY FOG OVERNIGHT AS WINDS BECOME CALM. OTHERWISE NO SIGNIFICANT CHANGES ARE NEEDED TO THE FORECAST. PREVIOUS DISCUSSION FROM 730 PM FOLLOWS... AN ANOMALOUSLY DEEP UPPER TROUGH COVERS THE EASTERN THIRD OF NORTH AMERICA. 500 MB HEIGHTS ARE THREE STANDARD DEVIATIONS BELOW THE SEASONAL MEAN WITH 850 MB TEMPS AT -2 STANDARD DEVIATIONS. STEEP LAPSE RATES FROM THE SURFACE UP THROUGH 800 MB PRODUCED A MODERATE CUMULUS FIELD ACROSS THE CAROLINAS THIS AFTERNOON. A SUBSIDENCE INVERSION AROUND 700 EFFECTIVELY CAPPED OFF THESE CUMULUS CLOUDS...AT LEAST UP UNTIL A COUPLE HOURS AGO. WHERE BOUNDARY LAYER MOISTURE HAS BEEN ENHANCED BY SEABREEZE WINDS BLOWING ONSHORE ISOLATED SHOWERS HAVE DEVELOPED ACROSS COASTAL PORTIONS OF SOUTHEAST NC FROM CAPE FEAR NORTHWARD. THE 21Z RUC SHOWS UNCAPPED INSTABILITY ON THE ORDER OF 500-1000 J/KG ALONG AND EAST OF THE SEABREEZE BOUNDARY. THIS CONVECTIVE ACTIVITY SHOULD SETTLE DOWN IN THE NEXT COUPLE OF HOURS AS THE BOUNDARY LAYER COOLS AND INSTABILITY SUBSIDES...HOWEVER WITH STEEP LAPSE RATES REMAINING UNDER THE SUBSIDENCE INVERSION WE WILL PROBABLY KEEP AT LEAST SCATTERED CUMULUS OR LOW ALTOCUMULUS THROUGH THE NIGHT. WEAK LOW PRESSURE HAS DEVELOPED ALONG LAST NIGHT`S COLD FRONT...NOW LOCATED 150 MILES OFFSHORE. HIGH PRESSURE CENTERED OVER THE CENTRAL PLAINS STATES WILL BUILD EASTWARD...WITH LIGHT NORTH WINDS BETWEEN THESE TWO SYSTEMS DRAINING UNSEASONABLY COOL DRY AIR SOUTHWARD INTO THE CAROLINAS. LOWS SHOULD REACH THE MID TO UPPER 60S AWAY FROM THE BEACHES TONIGHT. THIS IS STILL SEVERAL DEGREES ABOVE RECORD LOWS FOR WEDNESDAY MORNING WHICH INCLUDE: 61 IN WILMINGTON...1914 63 IN FLORENCE...1997 62 AT NORTH MYRTLE BEACH...1954. (NOTE: THESE RECORDS ARE CORRECTED FROM THE 300 PM DISCUSSION) && .SHORT TERM /6 AM THIS MORNING THROUGH THURSDAY NIGHT/... AS OF 300 PM TUESDAY...A FLATTENED 500 MB TROUGH WILL REMAIN PARKED OVER THE EASTERN U.S. ON WED...WHILE AT THE SURFACE BROAD HIGH PRESSURE WILL BE POSITIONED TO OUR WEST. FORECAST SOUNDINGS REMAIN FAIRLY DRY FOR WED...ESPECIALLY ABOVE ABOUT 700 MB. AS THE TROUGH AXIS RETROGRADES A BIT ON THU...PWATS INCREASE IN THE AFTN HOURS WITH THE MID LEVEL FLOW BECOMING MORE SOUTHWESTERLY. THE REMNANT FRONT/SFC TROUGH OFFSHORE MAY ALSO DRIFT BACK TOWARD THE COAST LATE THU...FURTHER MOISTENING THE COLUMN WITH INCREASING EASTERLY LOW LEVEL WINDS. A FEW SPRINKLES CANNOT BE RULED OUT DURING THE DAY WED...BUT WILL MAINTAIN INHERITED DRY FORECAST ATTM GIVEN THE LACK OF A SEA BREEZE DUE TO WEAK LAND/SEA TEMP CONTRASTS. THU SEEMS LIKE THE BETTER CANDIDATE FOR ISOLATED SHOWERS/TSTMS...ESPECIALLY LATE IN THE PERIOD. HAVE SLOWLY RAMPED UP POPS THU AFTN INTO THE OVERNIGHT HOURS...GENERALLY SLIGHT CHC WITH SOME CHC POPS ALONG THE COAST. TEMPS WILL REMAIN BELOW NORMAL THANKS TO THE PERSISTENT UPPER TROUGH AND EASTERLY SFC FLOW. HIGHS WILL BE IN THE MID TO UPPER 80S BOTH DAYS. WED NIGHT LOWS WILL FALL INTO THE MID 60S INLAND AND UPPER 60S ALONG THE COAST. INCREASING CLOUDS THU NIGHT WILL KEEP LOWS A FEW DEGREES WARMER...GENERALLY UPPER 60S TO LOWER 70S. && .LONG TERM /FRIDAY THROUGH TUESDAY/... AS OF 3 PM TUESDAY...FRIDAY THROUGH SUNDAY FINALLY SEES THE DEEP CUTOFF NORTH OF THE GREAT LAKES OPEN UP AND RETREAT. DEEP TROUGHINESS LINGERS SOUTH OF THIS FEATURE HOWEVER AS THE FLOW SPLITS WITH SOUTHERN BRANCH TROUGH COVERING MUCH OF THE OHIO AND MID/UPPER MS VALLEY REGIONS. HERE IN THE CAROLINAS THIS LEADS TO A DEEP MOISTURE-LADEN SOUTHWESTERLY FLOW THAT SHOULD LEAVE THE AREA PRONE TO AT LEAST A CLIMATOLOGICAL SCATTERING OF DIURNAL CONVECTION. DURING THIS SAME TIME FRAME A WARM FRONT WILL SLOWLY RETROGRADE FROM A NEARLY COASTAL POSITION ON FRIDAY TO WEST OF THE AREA/CENTRAL CAROLINAS BY SUNDAY. THIS WILL BOLSTER THE LL MOISTURE AND SHOULD YIELD AND UPTICK IN CONVECTIVE COVERAGE AS THE WEEKEND TRANSPIRES. THE SURFACE BOUNDARY BECOMES ILL-DEFINED IF NOT WASHED OUT ALTOGETHER BY MONDAY. THIS COULD LEAD TO A SMALL DOWNWARD TREND IN RAIN CHANCES...BUT WOULD LIKE TO BE CAUTIOUS WITH OPTIMISM AS THERE WILL LIKELY BE OUTFLOW AND DIFFERENTIAL HEATING BOUNDARIES TO STILL SERVE AS CONVECTIVE INITIATION FOCI. THE DEEP LAYER SWRLY FLOW WILL ALSO BE WEAKENING. THE BETTER BET FOR A SLIGHTLY QUIETER FORECAST COMES ON TUESDAY WHEN THE MID LEVEL TROUGHINESS NO LONGER HAS ANY LOCAL EFFECTS AND THE FLOW VEERS TO MORE WESTERLY. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... AS OF 06Z...LEFTOVER DEBRIS CLOUDS FROM EARLIER ROGUE SHRA EARLIER WILL AFFECT MAINLY THE ILM TERMINAL WITH MID-LEVEL CEILINGS...ELSEWHERE...MAINLY SKC. VFR CONDITIONS THROUGH THE FORECAST ISSUANCE PERIOD...WITH BRIEF MVFR CONDITIONS FROM REDUCED VSBY FROM BR ACROSS THE COASTAL TERMS. SFC PRESSURE PATTERN AND RELAXED GRADIENT TO YIELD CALM TO NORTHEAST WINDS 5 KT OR LESS OVERNIGHT. FOR WEDNESDAY...PLENTY OF MOISTURE BELOW 700MB...WITH THE DAYS INSOLATION THE FA WILL OBSERVE SCT/BKN 5K TO 10K FOOT CEILINGS. WINDS DURING DAYTIME WED WILL START OUT NORTHEAST AROUND 5 KT...VEERING TO THE E AND SE ESPECIALLY ACROSS THE COASTAL TERMS DUE TO THE RESULTANT WIND BOUNDARY DEVELOPING AND PUSHING INLAND. ISOLATED CONVECTION REMAINS POSSIBLE ALONG THE RESULTANT WIND BOUNDARY...BUT NOT ENOUGH TO PLACE IN THE TAFS AT THIS TIME. THE LOWERED CEILINGS WILL BE A REFLECTION OF THIS POSSIBILITY FOR NOW. EXTENDED OUTLOOK...MVFR VSBYS DUE TO MORNING FOG FRIDAY AND SATURDAY...OTHERWISE VFR. CHANCE MAINLY AFTN/EVNG SHRA/ISOLATED TSRA THROUGH THE PERIOD. && .MARINE... NEAR TERM /THROUGH TONIGHT/... AS OF 1030 PM WEDNESDAY...LAST OF THE SHOWERS NORTH OF CAPE FEAR HAVE CLEARED THE COAST AND ARE MOVING OFFSHORE. THIS ACTIVITY BECAME FAIRLY WIDESPREAD AN HOUR AGO BUT TRENDS SUGGEST IT SHOULD DISSIPATE IN THE NEXT HOUR. NORTHEAST WIND DIRECTIONS ARE ALREADY ESTABLISHED DOWN TO CAPE FEAR...AND WINDS SHOULD BACK FROM THE SOUTHEAST TO THE EAST AND NORTHEAST AFTER MIDNIGHT ALONG THE SC COAST. PREVIOUS DISCUSSION FROM 730 PM FOLLOWS... WEAK LOW PRESSURE HAS DEVELOPED ABOUT 150 MILES OFFSHORE ALONG THE COLD FRONT THAT MOVED THROUGH THE AREA LAST NIGHT. THIS LOW IN COMBINATION WITH HIGH PRESSURE IN THE CENTRAL PLAINS SHOULD GIVE US A PREVAILING EAST TO NORTHEAST WIND TONIGHT. THIS AFTERNOON`S SEABREEZE CIRCULATION AND ITS SOUTHEAST WINDS SHOULD DIE AWAY IN THE NEXT FEW HOURS. SEAS CONSIST LARGELY OF A 1-2 FOOT 9 SECOND SOUTHEAST SWELL...PLUS SHORTER PERIOD WIND WAVES PRODUCED BY WINDS CLOSER TO SHORE. COMBINED SEAS ARE AVERAGING 2-3 FEET...HIGHEST NEAR AND NORTH OF CAPE FEAR WHERE THE SWELL IS HAVING THE EASIEST TIME MAKING IT INTO THE NEARSHORE WATERS. RADAR REVEALS SEVERAL SHOWERS NORTH OF CAPE FEAR DEVELOPING NEAR AND JUST EAST OF THE SEABREEZE BOUNDARY. ADDITIONAL SLOW-MOVING SHOWERS MAY DEVELOP THROUGH THE EARLY EVENING HOURS...BUT DRY WEATHER WILL PREVAIL OVERNIGHT. SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... AS OF 300 PM TUESDAY...NORTHEAST TO EAST WINDS AROUND 10 KTS WILL PREVAIL THROUGH THE PERIOD AS SFC HIGH PRESSURE TO OUR NORTHWEST GRADUALLY MOVES OFFSHORE DURING THU. SEAS WILL REMAIN IN THE 2-3 FT RANGE BOTH DAYS...HIGHEST ACROSS AMZ250 WHERE SEAS WILL BECOME AROUND 3 FT ON THU. AS THE REMNANT FRONT/SFC TROUGH OFFSHORE LIFTS BACK TOWARD THE COAST...SHOWER/TSTM CHANCES OVER THE WATERS INCREASE OVERNIGHT THU. LONG TERM /FRIDAY THROUGH SUNDAY/... AS OF 3 PM TUESDAY...WITH A BOUNDARY STALLED VERY CLOSE TO IF NOT RIGHT OVER THE COAST ON FRIDAY THE WATERS WILL EXPERIENCE A LIGHT ONSHORE FLOW. ONSHORE WINDS ACT TO LESSEN THE GRADIENT IN WAVE HEIGHT ACROSS THE 20NM WIDTH OF THE FORECAST ZONES SO A GENERAL 3 FT SEA STATE EXPECTED...A COMBINATION OF THE WIND WAVE AND A LIGHT SOUTHEASTERLY SWELL. OVER THE WEEKEND THE BOUNDARY WILL SLOWLY DRAW INLAND...REACHING THE CENTRAL CAROLINAS BY SUNDAY. THE ONLY REAL LOCAL EFFECT WILL BE A VEERING TO SE OR EVEN S AT TIMES. LAND/SEA TEMPERATURE DIFFERENCES WILL BE MINIMAL FOR THE TIME OF YEAR AND NO APPRECIABLE SEA BREEZE EXPECTED TO PRODUCE THE NORMAL NEARSHORE WIND INCREASE AND CHOP. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...NONE. NC...NONE. MARINE...NONE. && $$ SYNOPSIS...BJR NEAR TERM...TRA SHORT TERM...BJR LONG TERM...MBB AVIATION...DCH MARINE...MJC/MBB

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