Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 261755 AFDILM AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON NC 155 PM EDT SAT JUL 26 2014 .SYNOPSIS... HIGH PRESSURE OVER THE WATERS WILL CIRCULATE HOT AND HUMID AIR ACROSS THE CAROLINAS THROUGH MONDAY. AN UNUSUALLY STRONG COLD FRONT MAY BRING SEVERE THUNDERSTORMS LATE ON MONDAY. COOLER AND DRIER WEATHER WILL RETURN ON TUESDAY...LASTING THROUGH MUCH OF NEXT WEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 10 AM SATURDAY...WARM AND HUMID LATE JULY SATURDAY UNDERWAY AND NOTHING UNCOMMON IN THAT. CONVECTIVE FORECASTS TODAY HOWEVER ARE MURKY...AS OPPOSING ATMOSPHERIC ELEMENTS INTERACT INTO THE AFTERNOON. ALOFT WE ARE SEEING BUILDING HEIGHT RISES AS AN UPPER TROUGH AXIS LIFTS NE OFF OUR COAST. THIS WILL SOON IMPART SLIGHT SINKING OF AIR INTO PRIME SURFACE HEATING. VWP PRESENTLY SHOWS NW DOWNSLOPE TRAJECTORY AIR PARCELS. THIS CAN BE A PROBLEM AT TIMES WHEN CELLS MOVE INTO THE SEA BREEZE FRONT NEARLY DIRECTLY CAUSING SPIKED CONVECTION. RIGHT NOW BASED ON CLOUD COVER WE CAN INFER DIFFERENTIAL HEATING VERTICAL CIRCULATIONS ARE MOVING AND A ROBUST CUMULUS FIELD SHOULD SUSTAIN THE LOW AND MID LEVEL TURBULENCE. 18Z ONWARD DRY AIR INTRUSION ALOFT FROM THE NW DIVES DOWNWARD TO 8 KFT. ESSENTIALLY CONVECTION LOOKS TO BECOME INCREASINGLY THWARTED INTO THE MAXIMUM OF INSOLATION. TO REFLECT THIS IN THE FORECAST WE WILL MAINTAIN ISOLATED TSTMS IN THE FORECAST BUT SHOW A QUICK TREND OF DISSIPATION IN THE LATER AFTERNOON TO VERY EARLY EVENING. EVEN IN DRYING ALOFT PWATS REMAIN AT OR JUST ABOVE 1.5 INCHES THIS AFTERNOON. ZONE OF ENHANCED LOW-LEVEL CONVERGENCE FROM THE SEA BREEZE FRONT WILL DICTATE WHERE INITIAL POPS ARE PLANNED EARLY AFTERNOON THEN EXPANDING THESE MENTIONABLE POPS WEST ACROSS THE EASTERN 1/2 TO 2/3 OF OUR ZONES THROUGH AFTERNOON PRIOR TO DIMINISHING. JULY HEATING AND DEWPOINTS IN THE MIDDLE 70S HAS ALREADY BROUGHT HEAT INDICES TO 90 DEGREES AND WE ARE LOOKING TO TOP OUT AT AN APPARENT MAXIMUM TEMPERATURE OF AROUND 100 DEGREES...WITH MAXIMUM AIR TEMPS OF UPPER 80S NEAR THE OCEAN TO LOWER 90S INLAND. && .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... AS OF 3 AM SATURDAY...START OF NEXT WEEK WILL BE QUITE WARM WITH HIGHS ON BOTH SUN AND MON RUNNING WELL INTO THE 90S. MID LEVEL RIDGE WILL EXTEND EAST FROM THE SOUTHWESTERN CONUS SUN. FORECAST SOUNDINGS SHOW CAPPING AROUND 800 MB...A RESULT OF SUBSIDENCE ON THE PERIPHERY OF THE 5H RIDGE. CAPPING ALONG WITH DEEP WESTERLY FLOW WILL MAKE EVEN ISOLATED CONVECTION HARD TO COME BY. CANNOT RULE OUT AN ISOLATED SHORT LIVED SHOWER ALONG OR JUST BEHIND THE SEA BREEZE BUT NOTHING WORTH CARRYING A POP ABOVE 10%. 850 TEMPS IN THE 20C TO 22C RANGE AND LACK OF MUCH CLOUD COVER/CONVECTION WILL PUSH HIGHS INTO THE MID TO UPPER 90S AREA WIDE. DESPITE LIMITED CLOUD COVER SUN NIGHT LOWS WILL BE KEPT IN THE UPPER 70S TO AROUND 80 BY STRENGTHENING LOW LEVEL JET. STRONG COLD FRONT WILL CROSS THE AREA ON MON WITH IMPRESSIVE 5H TROUGH THE DRIVING FACTOR. BEST PRECIP CHANCES DURING THE PERIOD WILL BE ON MON...AHEAD OF THE COLD FRONT WHEN PRECIPITABLE WATER VALUES WILL BE AROUND 2 INCHES. MON IS ALSO SHAPING UP TO BE A HOT DAY WITH 850 TEMPS ONCE AGAIN IN THE LOWER 20C RANGE. HIGHS IN THE MID 90S COMBINED WITH DEWPOINTS IN THE LOW 70S WILL NOT ONLY PRODUCE HEAT INDEX VALUES AT OR ABOVE 105F...LIKELY WARRANTING A HEAT ADVISORY...BUT WILL SET THE STAGE FOR AFTERNOON CONVECTION. MID LEVEL COOLING COMBINED WITH STRONG LOW LEVEL CONVERGENCE ALONG THE FRONT AND VERY WARM LOW LEVELS IS LIKELY TO PRODUCE WIDESPREAD SHOWERS AND THUNDERSTORMS. WHILE IT APPEARS THE CORE OF THE UPPER LEVEL JET WILL REMAIN NORTH OF THE AREA STRONG TO SEVERE CONVECTION REMAINS A POSSIBILITY BASED ON THERMODYNAMIC PROFILES MON AFTERNOON/EVENING AND SPC HAS PLACED MUCH OF THE FORECAST AREA WITHIN A SLIGHT RISK AREA FOR DAY 3. && .LONG TERM /TUESDAY THROUGH FRIDAY/... AS OF 3 AM SATURDAY...NOTICEABLE AIR MASS CHANGE FROM MON AFTERNOON TO TUE AFTERNOON AS BOTH HEAT AND HUMIDITY WILL BE LACKING. PRECIPITABLE WATER VALUES DROP DOWN TO AROUND AN INCH TUE WHILE NORTHERLY FLOW USHERS COOLER AIR INTO THE REGION. TROUGH AXIS REMAINS JUST WEST OF THE AREA FOR THE PERIOD WITH GENERALLY DEEP WESTERLY FLOW KEEPING MID LEVELS DRY. GFS/ECMWF BOTH SHOW A SHORTWAVE CROSSING THE AREA TUE NIGHT INTO WED BUT DIFFER ON ITS STRENGTH AND IMPACT. WILL NOT BE ADDING ANY PRECIP CHANCES GIVEN THE UNFAVORABLE ENVIRONMENT AND DIFFICULTY IN ACCURATELY DEPICTING SUCH FEATURES IN THE EXTENDED PERIOD. FORECAST SOUNDINGS DO NOT SHOW MUCH OF AN INCREASE IN DEEP MOISTURE THROUGH THE PERIOD...PWATS BARELY EXCEED 1.25 INCHES DURING THE PERIOD...SO DIURNAL CONVECTION WILL BE SCARCE. CANNOT RULE OUT SOME ISOLATED STORMS ANY GIVEN AFTERNOON BUT DO NOT THINK A MENTIONABLE POP IS WARRANTED. BEST CHANCES WOULD BE NEAR THE COAST...ALONG OR JUST BEHIND THE SEA BREEZE BUT EVEN HERE COVERAGE ABOVE 20% IS UNLIKELY. TEMPERATURES WILL REMAIN BELOW CLIMO THROUGH THE PERIOD WITH POTENTIAL FOR SOME RADIATIONAL COOLING OVERNIGHT DURING THE MIDDLE OF THE WEEK. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... AS OF 18Z...VFR THIS AFTERNOON. WINDS WILL BE SW WITH STRONGEST AVERAGE WINDS OF 8-15 KTS AT THE COASTAL TERMINALS. THROUGH EARLY EVENING TWO SFC BASED FEATURES...THE SEA BREEZE AND THE PIEDMONT TROF...WILL BE THE DRIVING FORCE FOR POSSIBLE CONVECTION. HOWEVER THE ENVIRONMENT WILL BECOME MORE HOSTILE AS THE EVENING APPROACHES. ANY ACTIVITY WILL BE ISOLATED...AND AS SUCH WILL NOT MENTION ANY CONVECTION IN TAFS EXCEPT FOR VCSH AT KILM EARLY THIS AFTERNOON. WINDS DECREASE THIS EVENING AS ANY CONVECTION DISSIPATES. ALTHOUGH WINDS DECREASE THEY SHOULD REMAIN SOMEWHAT ELEVATED OVERNIGHT. THIS SHOULD PREVENT ANY DENSE FOG FROM DEVELOPING...BUT SCT IFR STRATUS AND MVFR VSBYS IN BR ARE POSSIBLE IN THE PRE-DAWN HOURS MAINLY AT THE INLAND TERMINALS. OTHERWISE VFR THROUGH THE END OF THE TAF VALID PERIOD. BY 14-16Z WINDS WILL BECOME SSW 10-15 KTS. EXTENDED OUTLOOK...SHOWERS/TSTMS/TEMPO MVFR POSSIBLE SUNDAY AND MONDAY. OTHERWISE EXPECT VFR. && .MARINE... NEAR TERM /THROUGH TONIGHT/... AS OF 1030 AM SATURDAY...THE PIEDMONT TROF ACROSS THE CENTRAL CAROLINAS IS PROGGED TO BECOME STRONGER THRU TONIGHT. RIDGING FROM THE OFFSHORE ATLANTIC HIGH WILL EXTEND WESTWARD JUST SOUTH OF THE AREA WATERS. THE SFC PRESSURE PATTERN AND GRADIENT BETWEEN THESE 2 FEATURES WILL PRODUCE A TIGHTENING GRADIENT THAT YIELDS AT LEAST 15 KT FOR SPEEDS LATER TODAY AND TONIGHT. THE SFC PRESSURE PATTERN WILL TRANSITION INTO A SW FLOW DIRECTION TODAY THRU TONIGHT. SIGNIFICANT SEAS INITIALLY WILL BE DOMINATED BY A 2 FOOT ESE GROUND SWELL. LATER THIS AFTERNOON AND TONIGHT...LOCALLY PRODUCED WIND WAVES WILL INCREASE IN SIZE AND COVERAGE AND LIKELY BECOME THE MORE DOMINATE OF THE 2. SEVEN SECOND DOMINATE PERIODS WILL OCCUR. SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... AS OF 3 AM SATURDAY...INCREASING SOUTHERLY FLOW AHEAD OF STRONG COLD FRONT WILL LIKELY RESULT IN HEADLINES FOR ALL ZONES LATER SUN NIGHT AND MON. NATURE OF THE HEADLINES IS AS OF YET UNDETERMINED. IT MAY END UP THAT SCEC IS NEEDED SUN NIGHT AND THEN SCA MON AND PART OF MON NIGHT. SOUTHWEST FLOW 15 TO 20 KT SUN WILL INCREASE TO A SOLID 20 KT SUN NIGHT AND MON. COMBINATION OF PROLONGED SOUTHWEST FLOW AND INCREASE IN SPEEDS BUILDS SEAS FROM 3 TO 4 FT AT THE START OF THE PERIOD TO 4 TO 6 FT ON MON. OFFSHORE FLOW DEVELOPS IN THE WAKE OF THE FRONT LATER MON NIGHT WITH SPEEDS DROPPING TO 10 KT OR LESS BY TUE MORNING. OFFSHORE COMPONENT AND DECREASE IN SPEEDS LATE MON NIGHT WILL RESULT IN SEAS FALLING TO 3 TO 4 FT BY THE END OF THE PERIOD. LONG TERM /TUESDAY THROUGH WEDNESDAY/... AS OF 3 AM SATURDAY...HIGH PRESSURE WILL BE SLOW TO BUILD IN BEHIND THE DEPARTING COLD FRONT TUE INTO WED...LEAVING A WEAK AND ILL DEFINED GRADIENT OVER THE WATERS DURING THE FIRST HALF OF THE PERIOD. WINDS WILL BE VARIABLE WITH SPEEDS UNDER 10 KT TUE INTO WED. INFLUENCE OF SURFACE HIGH OVER THE MIDWEST BECOMES MORE PRONOUNCED ON WED WITH 10 TO 15 KT NORTHEAST FLOW DEVELOPING BY AFTERNOON. SEAS WILL TREND DOWN TUE AND TUE NIGHT BEFORE INCREASING SLIGHTLY ON WED INTO WED NIGHT AS WIND FIELD BECOMES MORE DEFINED. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...NONE. NC...NONE. MARINE...NONE. && $$ NEAR TERM...MJC SHORT TERM...III LONG TERM...3 AVIATION...MRR/8

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