Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 181046 AFDILM AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON NC 646 AM EDT MON AUG 18 2014 .SYNOPSIS... A COLD FRONT WILL APPROACH THE AREA FROM THE NORTH MONDAY AND TUESDAY BEFORE STALLING OVER THE AREA AND REMAINING THROUGH FRIDAY. THE FRONT COULD DROP SOUTH OF THE AREA FOR THE WEEKEND. HEAT AND HUMIDITY WILL REMAIN OVER THE AREA THROUGH THURSDAY BEFORE TEMPERATURES RETURN TO MORE SEASONABLE VALUES LATE THIS WEEK INTO THE WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... AS OF 630 AM MONDAY...LONGWAVE UPPER PATTERN NOT AS PRONOUNCED LIKE LAST WEEK WHERE THE EASTERN 1/3RD TO 1/2 OF THE U.S. WAS UNDER AN AMPLIFIED UPPER TROF. OVERALL...THE SE STATES WILL REMAIN UNDER A DE-AMPLIFIED UPPER TROF WITH A S/W UPPER RIDGE MOVING ACROSS THE GREAT LAKES TO THE NE STATES. FOR THE SE STATES...2 NOTEWORTHY S/W TROFS EMBEDDED IN THE UPPER FLOW WILL PASS N AND S OF THE FA RESPECTIVELY BUT PARTIALLY AFFECT THE FA WITH THEIR ASSOCIATED DYNAMICS. THE FIRST ONE PASSES JUST N OF THE FA AND OFF THE MID-ATLANTIC COAST TONIGHT...AND THE 2ND MOVES SE TO THE SOUTHERN APPALACHIANS BY TUE MORNING. AT THE SFC...LOW PRESSURE AIDED BY THE 1ST S/W TROF WILL TRAVERSE THE VA-NC BORDER TO OFF THE DELMARVA COAST LATE TONIGHT. SFC BOUNDARY EXTENDING SW FROM THE SFC LOW...WILL BECOME A FOCUS FOR CONVECTION FOR THE ILM CWA LATER TODAY AND TONIGHT. A PINNED SEA BREEZE WILL ALSO BE A FOCUS FOR CONVECTION MIDDAY INTO THIS EVENG. OVERALL LOOKING AT AROUND 40 POPS THIS AFTN AND NIGHT ACROSS THE FA. LATEST SAT IMAGERY AND VARIOUS MODEL TIME HEIGHT DISPLAYS ACROSS THE FA...INDICATE THE FA MAY EXPERIENCE MORE CLOUDINESS THAT COULD LIMIT MAX TEMPS TODAY. WILL ADJUST/TWEAK MAX TEMPS LOWER TODAY WHICH WILL STILL RESULT WITH CONTINUED WIDESPREAD 90S ACROSS THE FA. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... AS OF 300 AM MONDAY...HEAT AND HUMIDITY ANTICIPATED FOR THE SHORT TERM...BUT A WEAK COLD FRONT WILL BRING A GOOD CHANCE FOR THUNDERSTORMS ON TUESDAY. GENERALLY FLAT UPPER FLOW THROUGH TUESDAY MEANS FEATURES WILL MOVE BRISKLY TO THE EAST...AND THUS THE COLD FRONT TRAILING FROM A LOW PRESSURE TO OUR NORTH WILL MOVE INTO THE REGION LATE TUESDAY AND THEN WEAKEN OVER THE AREA ON WEDNESDAY. GUIDANCE HAS GOTTEN STRONGER WITH THIS FRONT IN RECENT RUNS...ENCOURAGED BY A SECONDARY VORT WHICH WILL TRACK NEARLY OVERHEAD THE ILM CWA. FOR THIS REASON WILL BUMP POP TO HIGH CHC CWA-WIDE...STILL HIGHEST NORTH...WITH SOME WIND SHIFT POSSIBLE IN THE NORTHERN ZONES. WHETHER THIS FRONT ACTUALLY CROSSES INTO THE CWA WILL MATTER LITTLE TO THE OVERALL SENSIBLE WEATHER...AS PWATS RISE ABOVE 2 INCHES AHEAD OF IT...AND ONLY MINIMAL AIR MASS CHANGE OCCURS BEHIND IT. EXPECT HIGHS TUESDAY TO SOAR INTO THE LOW 90S AWAY FROM THE BEACHES...WITH MID 90S POSSIBLE IN THE WARMER/SUNNIER LOCATIONS. SHOWERS/STORMS ASSOCIATED WITH THE FRONT WILL WANE AND END BY WEDNESDAY MORNING AS DRIER AIR FILTERS INTO THE MID-LEVELS...BUT LOWS TUESDAY NIGHT WILL STAY WELL INTO THE 70S. DRY W/NW MID-LEVEL FLOW COMBINED WITH BULGING THICKNESSES AS A 500MB RIDGE BEGINS TO BLOOM ACROSS THE AREA WILL PUT A CAP ON CONVECTION CHANCES WEDNESDAY. SINCE TEMPS ARE STILL EXPECTED TO RISE INTO THE 90S...AND DEWPOINT TEMPERATURES WILL REMAIN IN THE 70S...ENOUGH INSTABILITY WILL BE PRESENT FOR TYPICAL SEA BREEZE AND PIEDMONT TROUGH CONVECTION...BUT IN A FAR MORE SCATTERED NATURE THAN TUESDAY. LOWS WED NIGHT WILL AGAIN STAY WELL ABOVE NORMAL...MID 70S MOST PLACES. && .LONG TERM /THURSDAY THROUGH SUNDAY/... AS OF 300 AM MONDAY...HOT TEMPERATURES EXPECTED FOR THE BEGINNING OF THE PERIOD...BUT UNCERTAINTY REMAINS INTO THE WEEKEND AS THE MID-LEVEL PATTERN BECOMES VERY AMPLIFIED. GFS CONTINUES TO BE A FAST OUTLIER OF THE DETERMINISTIC MODELS IN BREAKING DOWN THE MID-LEVEL RIDGE AT THE BEGINNING OF THE PERIOD...WHILE OTHER GUIDANCE AND ENSEMBLES ARE SLOWER AND LESS ROBUST IN TROUGH AMPLIFICATION ACROSS THE EAST. AS NOTED BY PREVIOUS FORECASTER...MOS NUMBERS STILL SHOW HOT TEMPS THURSDAY EVEN ON THE LATEST MEX...SEEMINGLY IN CONTRAST WITH THE GFS ITSELF. FOR THIS REASON WILL LEAN ON THE ECMWF WHICH IS MORE MUTED WITH ITS MID-LEVEL AMPLIFICATION...AND CONTINUE TO SHOW A VERY HOT DAY THURSDAY WITH HEAT INDICES APPROACHING 105 ACROSS THE AREA. THEREAFTER...IT DOES APPEAR THAT A TROUGH WILL BEGIN TO DIG INTO NEW ENGLAND AND DOWN THE EASTERN SEABOARD IN RESPONSE TO UPPER RIDGING STRONGLY BLOSSOMING OVER THE CENTER PART OF THE COUNTRY. BENEATH THIS TROUGH...A BACK DOOR COLD FRONT WILL TRY TO PUSH INTO THE AREA FROM THE NORTHEAST...BRINGING A RETURN TO COOLER AND MORE UNSETTLED CONDITIONS FOR THE WEEKEND. STILL A LOT TO RESOLVE IN TERMS OF TIMING AND STRENGTH OF FEATURES...AND WILL FOLLOW THE INHERITED TREND OF A SLOW PATTERN CHANGE INTO THE WEEKEND WITH TEMPS SLOWLY FALLING TO SEASONABLE VALUES...IF NOT SLIGHTLY BELOW BY THE END OF THE PERIOD. IN ADDITION...A BUILDING RIDGE TO THE WEST WITH A SURFACE FRONT IN THE VICINITY AND NW FLOW ENTRENCHED OVERHEAD IS TYPICALLY A SETUP WHICH SUPPORTS NW FLOW TSTM COMPLEX EVENTS. THIS HAS BEEN HINTED FOR SEVERAL RUNS NOW...AND NOTE THAT GUIDANCE HAS SEVERAL MID-LEVEL IMPULSES CRESTING THE RIDGE AND DIVING OVERHEAD AS THIS TROUGH DROPS INTO THE EAST. CANNOT SAY WITH ANY CERTAINTY THAT A NW FLOW EVENT WILL OCCUR LOCALLY...BUT THE SETUP AT LEAST SUPPORTS THE POTENTIAL FRI/SAT. && .AVIATION /12Z MONDAY THROUGH FRIDAY/... AS OF 06Z...EXPECT PATCHY FOG TO DEVELOP. GREATEST CONFIDENCE IS AT THE INLAND TERMINALS AND/OR CRE WHERE WINDS WILL BE LIGHTEST. INCREASING VFR LEVEL CLOUDS SHOULD AID IN PREVENTING ANY IFR OR LOWER VISIBILITIES. TOWARDS MORNING THERE MAY BE ISOLATED...IE. LOW CHANCE...FOR CONVECTION AT KLBT/KFLO. ALTHOUGH CLOUD COVER WILL GREATLY AFFECT WARMING TEMPERATURE AFTER SUNRISE...CONVECTION SHOULD FIRE BETWEEN 16-19Z. BEST CHANCE FOR TSRA WILL BE AT KCRE/KMYR WHERE WESTERLY STEERING FLOW WILL SPREAD ACTIVITY ALONG A PINNED SEA BREEZE BACK TOWARDS THE COAST. TSRA WILL ALSO BE MORE LIKELY AT KLBT WHERE GREATER LIFT IS EXPECTED DUE TO ITS CLOSER PROXIMITY TO AN AREA OF LOW PRESSURE PASSING BY TO THE NORTH. DRIER AIR TO MOVE INTO THE MID/UPPER LEVELS DURING LATE THIS AFTERNOON AND EVENING...SUGGESTING CONVECTION WILL DECREASE/BECOME MORE ISOLATED IN COVERAGE. EXTENDED OUTLOOK...CHC AFTERNOON/EVENING SHRA/TSRA THROUGH THE PERIOD. SUB-VFR FOG AND/OR CEILINGS WILL BE POSSIBLE DURING THE EARLY MORNING HOURS EACH DAY. && .MARINE... NEAR TERM /THROUGH TONIGHT/... AS OF 630 AM MONDAY...SFC LOW IS EXPECTED TO DEVELOP ALONG A NE- SW ORIENTED BOUNDARY...THAT MIMICS THE PIEDMONT TROF DUE TO ITS POSITIONING ACROSS THE CENTRAL CAROLINAS. WINDS ACROSS THE AREA WATERS WILL REMAIN SW THROUGHOUT THIS PERIOD. LOOK FOR A TIGHTENING SFC PG LATER THIS AFTN AND TONIGHT WHICH SHOULD YIELD SW WINDS AROUND 15 KT TODAY...AND 15 TO OCCASIONALLY 20 KT TONIGHT. SIGNIFICANT SEAS THRUOUT THIS FORECAST PERIOD WILL BUILD SLOWLY...REACHING 2 TO 4 FT DURING TODAY...AND 3 TO 5 FT DURING TONIGHT. SIG. SEAS WILL MAINLY BE A FUNCTION OF THE LOCALLY PRODUCED WIND DRIVEN WAVES EXHIBITING 4 TO 6 SECOND PERIODS. THE COMBINATION OF THE INCREASING SW WINDS AND RESULTING SIG. SEAS...COULD BREACH SCEC THRESHOLDS LATER THIS AFTN AND TONIGHT. WILL NEED ANOTHER MODEL RUN TO CONFIRM THIS B4 RAISING THE SCEC FLAG. SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... AS OF 300 AM MONDAY...LOW PRESSURE MOVING OFF THE MID-ATLANTIC COAST TUESDAY WILL TRAIL A COLD FRONT TOWARDS THE WATERS ON WEDNESDAY. THIS FRONT WILL BE IMPEDED BY HIGH PRESSURE OFFSHORE...AND EXPECT A MINIMAL WIND SHIFT TO THE WEST...IF AT ALL...WEDNESDAY. OTHERWISE...SW WINDS WILL BE 10-15 KTS THROUGH MID-WEEK. SEAS WILL BE FORMED PRIMARILY THROUGH A 5 SEC SW WIND WAVE...ALTHOUGH A WEAK SE GROUND SWELL WILL EXIST DURING THE PERIOD. WAVE HEIGHTS WILL BE 3-4 FT...WITH SOME ISOLATED 5 FTERS ON TUESDAY...FALLING TO 2-3 FT ON WEDNESDAY. LONG TERM /THURSDAY THROUGH FRIDAY/... AS OF 300 AM MONDAY...HIGH PRESSURE OFFSHORE WILL REMAIN THE DOMINANT INFLUENCE THROUGH THE EXTENDED...BUT SOME UNCERTAINTY EXISTS LATE FRIDAY AS A BACK DOOR COLD FRONT APPROACHES. MUCH OF THE LATE-WEEK PERIOD WILL FEATURE S/SW WINDS OF 10-15 KTS...BUT BY LATE FRIDAY A DECREASE IN WIND SPEEDS AND TURN TO THE NORTH IS POSSIBLE...ESPECIALLY ACROSS THE NORTHERN WATERS. SEAS WILL BE 1-3 FT BOTH DAYS...WITH A SE GROUND SWELL AND SOUTHERLY WIND WAVE CREATING THE SPECTRUM. A CONFUSED SEA STATE MAY DEVELOP AT THE VERY END OF THE PERIOD IF THE WINDS TURN TO THE NORTH...BUT ATTM ANY SIGNIFICANT CHANGES TO THE SPECTRUM ARE EXPECTED TO HOLD OFF UNTIL THE WEEKEND. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...NONE. NC...NONE. MARINE...NONE. && $$ SYNOPSIS...JDW NEAR TERM...DCH SHORT TERM...JDW LONG TERM...JDW AVIATION...DCH/MRR

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