Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 261722 AFDILM AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON NC 120 PM EDT WED AUG 26 2015 .SYNOPSIS... A FRONT WILL OSCILLATE ACROSS THE AREA INTO THURSDAY...THEN DRIFT OFFSHORE...REMAINING IN CLOSE PROXIMITY TO THE COAST. HIGH PRESSURE WILL STRUGGLE TO SLOWLY BUILD INTO THE AREA DURING THE WEEKEND. WE WILL BE WATCHING THE PROGRESS OF TROPICAL STORM ERIKA EARLY NEXT WEEK... IT IS TOO EARLY TO SAY WHAT IMPACTS IF ANY WILL BE FELT ACROSS THE EASTERN CAROLINAS. && .NEAR TERM /THROUGH TONIGHT/...
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AS OF 100 PM WEDNESDAY...MORNING ANVIL DEBRIS AND STRATUS HAS CAUSED HEATING TO LAG...BUT THIS IS NOW DISSIPATING. DIFFERENTIAL HEATING AS WELL AS THE OTHER BOUNDARIES MENTIONED BELOW ARE STILL EXPECTED TO SERVE AS A CONVECTIVE FOCUS THIS AFTN. PREVIOUS DISCUSSION BELOW: AS OF 1030 AM WEDNESDAY...ANOTHER COMPLEX PATTERN WILL LEAD TO AN ACTIVE DAY AND DIFFICULT FORECAST ACROSS THE COASTAL CAROLINAS. ANOMALOUSLY AMPLIFIED MID-LEVEL PATTERN CONTINUES TO FEATURE A LARGE RIDGE ACROSS THE WEST WITH A DEEP TROUGH ENGULFING MUCH OF THE EAST. BENEATH THIS TROUGH...A STATIONARY FRONT CONTINUES TO LINGER ALONG THE IMMEDIATE COAST. HARD TO TRULY IDENTIFY THE FRONT SINCE IT IS SO WEAK...BUT IT APPEARS BASED OFF DEWPOINT TEMPERATURES AND THE WIND SHIFT THAT IT IS THROUGH MOST OF THE CWA EXCEPT THE SOUTH COAST. THE EVOLUTION OF THIS BOUNDARY TODAY WILL BE CRITICAL TO HOW CONVECTION EVOLVES THIS AFTN. SHORTWAVE EJECTING OUT OF THE GULF OF MEXICO COMBINED WITH THE EXPECTED SEA BREEZE CIRCULATION THIS AFTN IS FORECAST TO PULL THE FRONT BACK TO THE WEST WHERE IT WILL OSCILLATE TODAY. WEST OF THIS FRONT...THE AIR MASS IS EXPECTED TO REMAIN TOO DRY FOR ANY CONVECTION TODAY SO AREAS WEST OF I-95 SHOULD REMAIN DRY...ALTHOUGH AN ISOLATED SHOWER CANNOT BE RULED OUT. EAST OF THIS FRONT HOWEVER...CONVECTION IS FORECAST TO BECOME WIDESPREAD AS THE SEA BREEZE...THIS FRONT...AND ANY OUTFLOWS SERVE AS CONVERGENT BOUNDARIES. SBCAPE IS FORECAST TO RISE TO AROUND 2000 J/KG...WHICH WILL INCREASE THROUGH THE EVE THANKS TO HEIGHT FALLS ON THE SOUTHERN EDGE OF THE MID-LEVEL TROUGH. WITHIN THIS HIGHLY UNSTABLE ENVIRONMENT...PWATS RISE TO ABOUT 1.9 INCHES...WARM CLOUD DEPTHS APPROACH 12000 FT...AND UPDRAFTS WILL BE AIDED BY INCREASING DIFFLUENCE WITHIN THE STRENGTHENING 300 MB JET STREAK ACROSS THE MID- ATLANTIC AND NORTHEAST. ALTHOUGH STORM MOTION IS EXPECTED TO BE 10- 15 KTS TODAY...BACKBUILDING AND TRAINING OF STORMS IS POSSIBLE AS NOTED BY SHORT CORFIDI VECTORS. ALL OF THIS DESCRIBES AN ENVIRONMENT RIPE FOR CONVECTION WITH TORRENTIAL RAINFALL AND EXCESSIVE LIGHTNING...ASSUMING THE FRONT DOES LIFT BACK NORTH AS EXPECTED AND CLOUD COVER CAN DECREASE...WHICH IS PROGGED ON THE TOTAL CLOUD PRODUCT. A RECENT DEVELOPMENT HAS BEEN THE ADDITION OF A MRGL RISK FROM SPC FOR TODAY. VERY HIGH PWAT AIR MAY ALLOW FOR SOME PRECIP LOADING AND WET DOWNBURSTS THIS AFTN...ALSO AIDED BY 0-3 KM THETA-E DIFFERENCES APPROACHING 30K...SLIGHTLY SHORT OF THE 35K THRESHOLD...BUT CLOSE ENOUGH THAT IT IS A SIGNAL FOR THE POTENTIAL NONETHELESS. HIGH RES GUIDANCE...NAMELY THE NSSL WRF AND ARW WHICH PERFORMED THE BEST ON TUESDAY...SUGGEST CONVECTION WILL PERSIST WELL AFTER DARK...AIDED BY THE SHORTWAVE MOVING OVERHEAD AND WHAT SHOULD BE STEEP LAPSE RATES IN THE RESIDUAL LAYER. WILL MAINTAIN SCATTERED TO NUMEROUS POP THROUGH THE EARLY NIGHTTIME HOURS BEFORE LOSS OF HEATING AND WEAKNING FORCING SHOULD ALLOW CONVECTION TO WANE DURING THE OVERNIGHT PERIOD. HIGHS TODAY WILL BE HIGHLY VARIABLE THANKS TO CLOUDS AND PRECIP...RISING TO AROUND 90 WELL INLAND...BUT STAYING IN THE MID 80S NEAR THE COAST. LOWS WILL AGAIN BE SLIGHTLY ABOVE NORMAL FOR LATE AUGUST...69-70 INLAND AND 72-74 NEAR THE COAST.
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&& .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... AS OF 330 AM WEDNESDAY...ON THURSDAY...FRONT LOOKS LIKE IT SHOULD BE OFF OR NEAR THE COAST BUT BASICALLY ALIGNED ALONG THE NC/SC COAST WITH SOME DRIER AIR IN PLACE INLAND IN LIGHT NORTHERLY FLOW WHILE ALONG THE COAST AND EASTWARD OVER THE WATERS...WINDS WILL REMAIN MORE SOUTHERLY. THE MID TO UPPER TROUGH WILL REMAIN STRETCHED FROM SW TO NE TO OUR WEST WITH A DEEP SW FLOW WITH BEST UPPER LEVEL DYNAMICS ALIGNED ALONG OR JUST OFF THE COAST TO OUR EAST AND WITH BEST JET ENERGY RIDING OFF TO THE NORTH OF FORECAST AREA. THE ATLANTIC RIDGE BUILDS WESTWARD THROUGH THE PERIOD AS UPPER TROUGH DIGS DOWN TOWARD THE WESTERN GULF AND TRIES TO CUT OFF. THIS MAY ACT TO PULL TROUGH BACK TO THE WEST AND INLAND OVER THE CAROLINAS THROUGH THE PERIOD WITH A GREATER ON SHORE PUSH OF MOISTURE THROUGH THE LOW LEVELS FRI. OVERALL EXPECT A DECENT FLOW OF DRIER AIR FROM THE NORTH ON THURS WITH INCREASING MOISTURE RETURNING ON FRI WITH GREATER ON SHORE E-SE FLOW BY THE WEEKEND. WITH TROUGH DOWN THE EAST COAST AND LOWER HEIGHTS ALONG WITH A SLIGHTLY COOLER NORTHERLY FLOW ...WILL KEEP MAX TEMPS SLIGHTLY BELOW NORMAL THROUGH THE PERIOD. && .LONG TERM /SATURDAY THROUGH TUESDAY/... AS OF 330 AM WEDNESDAY...UPPER LOW PRESSURE OVER THE WESTERN GULF WILL BEGIN TO LIFT OFF TO THE NORTHEAST THROUGH THE WEEKEND AS TROUGH LINGERS OVER THE SOUTHEAST. MAY SEE IT PULLED BACK WEST WITH AN INCREASING ON SHORE TO SOUTHERLY FLOW THROUGH THE LOW LEVELS AROUND THE ATLANTIC RIDGE. AS LOW LIFTS UP INTO THE TENNESSEE VALLEY ANOTHER SHORTWAVE WILL DIG DOWN FROM THE NORTH. THIS SHOULD HELP TO PRODUCE MORE WIDESPREAD COVERAGE OF CLOUDS AND GREATER CHC OF CONVECTION ACROSS THE SOUTHEAST THROUGH EARLY NEXT WEEK WHEN DEEPER MOISTURE AND LIFT OCCURS. MAY ALSO SEE ERIKA OR REMNANTS OF ERIKA COME INTO PLAY BY THE END OF THE PERIOD. FOR NOW IT LOOKS LIKE ERIKA WILL REACH THE BAHAMAS BY EARLY NEXT WEEK BUT MAY GET SUPPRESSED TO THE SOUTH OF THE AREA BY SHORTWAVE DIGGING DOWN FROM THE NORTH. MAX TEMPS REMAIN NEAR CLIMO...MID 80S WITH A CLIMB BACK UP TOWARD 90 EARLY NEXT WEEK. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
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AS OF 18Z...AN OUTFLOW BOUNDARY IS APPROACHING KFLO/KLBT EARLY THIS AFTERNOON BUT THERE IS NO CONVECTION ALONG IT AS IT RUNS INTO DRIER AIR. CONFIDENCE IS LOWERING FOR CONVECTION AT KILM EARLY THIS AFTERNOON DUE TO LACK OF HEATING AND ONSHORE WINDS...BUT THERE IS STILL A CHANCE OF DEVELOPMENT LATER THIS AFTERNOON AS AN UPPER IMPULSE APPROACHES...CLOUD COVER DECREASES AND WINDS BECOME ONSHORE. DO NOT FEEL IT WILL BE AS WIDESPREAD AS EARLIER THOUGHT. WILL MAINTAIN VCSH AT KLBT THIS AFTERNOON. THE BEST CONFIDENCE OF SHOWERS AND THUNDERSTORMS WILL BE AT KMYR/KCRE. MVFR LIKELY WITH ANY ACTIVITY...WITH TEMPO IFR IF A CELL MOVES DIRECTLY OVER A TERMINAL. THE PASSAGE OF THE IMPULSE THIS EVENING SHOULD CAUSE SHOWERS TO WANE...BUT AREAS OF RAINFALL MAY PERSIST WELL INTO THE NIGHTTIME HOURS. A MOIST ATMOSPHERE AND SUBSIDENCE SHOULD PROVIDE A FAVORABLE ENVIRONMENT FOR IFR CIGS AT KLBT...LOWER CONFIDENCE AT THE OTHER TERMINALS. SOME SHOWERS MAY RE-DEVELOP IN THE PRE-DAWN HOURS AT THE COASTAL TERMINALS THUS MVFR CIGS WOULD BE MORE LIKELY. WINDS WILL BE LIGHT AND VARIABLE THIS EVENING BECOMING NE OVERNIGHT. VFR CIGS AFTER SUNRISE WITH NE WINDS AND SHOWERS MAINLY NEAR KMYR/KCRE. EXTENDED OUTLOOK...PREDOMINATELY VFR WITH ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS THROUGH THE EXTENDED. BRIEF MORNING FOG/STRATUS IS ALSO EXPECTED EACH DAY.
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&& .MARINE... NEAR TERM /THROUGH TONIGHT/... AS OF 1030 AM MONDAY...COLD FRONT JUST INLAND FROM THE WATERS WILL SLOWLY LIFT BACK TO THE NORTHWEST THIS AFTN. SHOWERS AND THUNDERSTORMS...ALONG WITH ASSOCIATED OUTFLOW BOUNDARIES...WILL DEVELOP AND MOVE ACROSS THE WATERS TODAY...SO THE LIGHT AND VARIABLE WIND WILL AT TIMES FLUCTUATE DIRECTION. OTHERWISE...WINDS SHOULD SETTLE TO A PREDOMINANTLY SOUTHERLY DIRECTION...WITH SPEEDS AROUND 10 KTS EXCEPT WITHIN THE NEAR SHORE SEA BREEZE WHERE SPEEDS WILL RISE TO 10-15 KTS. SEAS WILL REMAIN IN THE 2 TO 3 FT RANGE. AN ESE 9 TO 11 SECOND SWELL WILL BE PRESENT. SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... AS OF 330 AM WEDNESDAY...LINGERING FRONT/TROUGH ALONG THE SOUTHEAST COAST WILL WEAKEN AS IT SLIPS SOUTH AND EAST. N-NE FLOW BEHIND FRONT ON THURS WILL VEER AROUND BECOMING MORE EASTERLY AROUND ATLANTIC RIDGE THROUGH FRI. PREVAILING FLOW WILL REMAIN 10 KT OR LESS THROUGH THE PERIOD BUT THERE WILL BE SLIGHT ENHANCEMENT TO THE ON SHORE FLOW DUE TO SEA BREEZE EACH AFTN. SEAS WILL REMAIN 3 FT OR LESS. A LONGER PERIOD SE SWELL MIXING IN WITH LOW END WIND WAVES WILL DIMINISH THROUGH FRI AFTN BUT WILL JUMP BACK UP TO 11 SEC BY FRI EVE. ON SHORE PUSH WILL GIVE A SLIGHT RISE TO SEAS BY LATE FRI INTO THE WEEKEND. LONG TERM /SATURDAY THROUGH SUNDAY/... AS OF 330 AM WEDNESDAY...ATLANTIC HIGH PRESSURE OFF SHORE WILL KEEP A RELATIVELY WEAK EAST TO OCCASIONALLY NORTHEAST WIND THROUGH SATURDAY. BY SUNDAY THE WINDS MAY TAKE ON MORE OF A SE-S DIRECTION REMAINING BASICALLY 10 KT OR LESS WITH A SLIGHT SPIKE EACH AFTN IN SEA BREEZE. LIGHT ON SHORE PUSH WILL KEEP SEAS AROUND 3 FT THROUGH MUCH OF THE WEEKEND WITH CONTINUED LONGER PERIOD SE SWELL MIXING IN FROM TROPICAL SYSTEM ERIKA IN THE ATLANTIC. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...NONE. NC...NONE. MARINE...NONE. && $$ NEAR TERM...WEISS SHORT TERM...RGZ LONG TERM...RGZ AVIATION...MRR/WEISS

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