660 FXUS62 KILM 281054 AFDILM AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON NC 654 AM EDT FRI MAR 28 2014 .SYNOPSIS... MUCH MORE MOIST AND WARMER AIR WILL BE IN PLACE AHEAD OF A COLD FRONT APPROACHING FROM THE WEST. THE FRONT WILL MOVE ACROSS THE AREA SATURDAY NIGHT. THE RISK FOR SHOWERS AND THUNDERSTORMS WILL BE ON THE INCREASE UNTIL PASSAGE OF THE COLD FRONT. SOME STORMS MAY BE STRONG TO SEVERE SATURDAY AND SATURDAY NIGHT. A BRIEF COOL DOWN WILL OCCUR BEHIND THE FRONT SUNDAY. HIGH PRESSURE NEXT WEEK WILL BRING DRY WEATHER WITH TEMPERATURES CLIMBING WELL ABOVE NORMAL. A COLD FRONT MAY REACH THE AREA NEXT FRIDAY...BRINGING A RISK FOR SHOWERS. && .NEAR TERM /THROUGH TONIGHT/... AS OF 600 AM FRIDAY...RETURN FLOW AROUND DEPARTING HIGH PRESSURE HAS TAKEN A FIRM HOLD ON THE AREA AND WE ARE BEGINNING TO SEE DEWPOINTS SURGE HIGHER...NOW UP TO THE MID AND UPPER 40S ALONG THE COAST...AND IN THE LOWER 40S FOR MOST INLAND LOCATIONS. TEMPS HAVE ALSO RISEN WITH THE APPROACH OF MORNING...IN THE MID AND UPPER 40S IN MOST LOCATIONS...TOPPING 50 DEGREES IN SOME COASTAL AREAS. DEEP S TO SW FLOW WILL BE IN PLACE THIS PERIOD AND THIS WILL BRING INCREASING MOISTURE AND TEMPERATURE WHICH WILL RESULT IN INCREASED INSTABILITY. PRECIPITABLE WATER VALUES WILL BE NEAR 1 INCH THIS MORNING...CLIMBING TO 1.25 TO 1.5 INCHES LATER TODAY AND TONIGHT. THE COLUMN SUFFICIENTLY SATURATES TO A DEPTH THAT DOES SUPPORT MEASURABLE PRECIPITATION. SHORTWAVE ENERGY IN THE MID LEVELS DOES APPROACH FROM THE W TODAY AND THEN ACROSS THE AREA TONIGHT. THERE IS SOME INDICATION THE ENERGY MAY SPLIT...WITH THE FORECAST AREA LYING IN BETWEEN THE BEST UPPER LEVEL SUPPORT. THERE IS ALSO SOME CONCERN THAT WIDESPREAD CONVECTION ALONG THE GULF COAST MAY SERVE TO ROB OR AT LEAST DELAY DEEPER MOISTURE RETURN. AN EXAMINATION OF INSTABILITY AND MID LEVEL LAPSE RATES DOES SUPPORT INCLUSION OF HIGHER POPS THIS PERIOD. MIXED LAYER CAPE VALUES DO CLIMB TO 300 J/KG WHILE SURFACE BASED VALUES REACH 500 TO 1000 J/KG. MID LEVEL LAPSE RATES DO REACH UP TO 7 DEG C/KM. SO ALTHOUGH WE ARE CONFIDENT MEASURABLE PRECIPITATION WILL OCCUR... THERE IS SOME UNCERTAINTY AS TO WHEN TO INCLUDE THE HIGHEST POPS. LOOKING AT THE MOST RECENT RADAR/SATELLITE DATA...THERE IS A LARGE AREA OF DEEP CONVECTION ONGOING ACROSS THE CENTRAL AND EASTERN GULF COASTAL AREAS. THIS SUGGESTS DEEPEST MOISTURE RETURN MAY BE DELAYED. EXTRAPOLATION FOR TIMING WOULD BRING THE HIGHEST RISK FOR SHOWERS AND THUNDERSTORMS INTO THE AREA TONIGHT...MORE LIKELY LATE TONIGHT WITH THE ARRIVAL OF AN UPPER LEVEL IMPULSE WORKING ITS WAY UP THE CAROLINA COAST. OF COURSE THIS DOES NOT PRECLUDE SHOWERS AND SOME THUNDERSTORMS TODAY OR THIS EVE AND HIGHER RESOLUTION MODELS ARE SHOWING CONVECTION BREAKING OUT WITH HEATING OF THE DAY WITH PERHAPS THE SEA BREEZE SERVING AS A FOCAL POINT. RAINFALL AMOUNTS WILL BE HIGHLY VARIABLE...BUT SOME LOCATIONS COULD RECEIVE AS MUCH AS THREE-QUARTERS OF AN INCH WITH ONE-QUARTER TO ONE-HALF INCH MORE COMMON...THESE AMOUNTS JUST THROUGH TONIGHT. THICKER CLOUD COVER WILL BE ARRIVING/DEVELOPING THROUGH THE DAY WITH MORE OR LESS CLOUDY SKIES EXPECTED DURING THE AFTERNOON AND TONIGHT. ALSO...AS DEWPOINTS CREEP HIGHER...WE SHOULD BEGIN TO SEE SEA STRATUS/SEA FOG DEVELOP...PERHAPS IMPINGING ONTO THE IMMEDIATE COAST IN SOUTHERLY FLOW LATE DAY AND ESPECIALLY TONIGHT. HIGH TEMPS WILL BE IN THE LOWER TO MID 70S TODAY...BUT THE SEABREEZE WILL KEEP COASTAL AREAS IN THE MID AND UPPER 60S. LOWS TONIGHT WILL BE BALMY AS COMPARED TO RECENT NIGHTS...UPPER 50S TO AROUND 60 DEGREES. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... AS OF 300 AM FRIDAY...SURFACE LOW AND MID LEVEL TROUGH WILL BE WEST OF THE AREA AT THE START OF THE PERIOD WITH THE REGION SOLIDLY IN THE WARM SECTOR. SEVERAL FACTORS APPEAR TO BE IN PLACE SUPPORTING CONVECTION SAT INTO SAT NIGHT. STRENGTHENING MID LEVEL SOUTHWEST FLOW WILL CONTINUE TO PUMP MOISTURE INTO THE REGION. FORECAST SOUNDINGS SHOW PRECIPITABLE WATER VALUES CLOSE TO 1.5 INCH. DIURNAL INSTABILITY WILL ALSO BE PRESENT WITH HIGHS EXPECTED TO CLIMB INTO THE LOWER 70S IN MOST AREAS. LOW LEVEL CONVERGENCE ALONG THE RESULTANT SEA BREEZE MAY INITIATE CONVECTION IN THE AFTERNOON. ALOFT THE APPROACHING 5H TROUGH WILL ENHANCE MID LEVEL LAPSE RATES BUT THE UNKNOWN FACTOR AT THIS POINT REMAINS WHAT IMPACT POTENTIAL CONVECTION IN THE NORTHEAST GULF OF MEXICO WILL HAVE ON INSTABILITY SHOWERS/THUNDERSTORMS. FARTHER WEST A LINE OF CONVECTION SHOULD BE DEVELOPING ASSOCIATED WITH THE ADVANCING COLD FRONT. THIS LINE WILL MOVE INTO WHAT SHOULD BE A MOIST/UNSTABLE ENVIRONMENT LATE SAT AND PUSH OFF THE COAST SAT NIGHT. ALTHOUGH THE FRONT WILL HAVE PLENTY OF LOW LEVEL CONVERGENCE AND MID LEVEL SUPPORT THERE IS SOME QUESTION AS TO THE STATE OF THE ATMOSPHERE IT WILL BE MOVING INTO. THE CONVECTIVE LINE ASSOCIATED WITH THE FRONT MAY END UP WEAKENING AS IT MOVES INTO THE REGION IF EARLIER AFTERNOON CONVECTION IS MORE WIDESPREAD AND USES UP A LOT OF THE AVAILABLE INSTABILITY. ON THE OTHER HAND SHOULD THE GULF CONVECTION BE ABLE TO SUPPRESS MUCH OF THE ACTIVITY DURING THE FIRST HALF OF SAT THE COLD FRONT WOULD HAVE PLENTY OF INSTABILITY TO WORK WITH. SO IT IS NOT SO MUCH A QUESTION OF WILL IT RAIN...BUT MORE OF A QUESTION OF WHEN WILL IT RAIN. SEVERE WEATHER THREAT PERSISTS...ALTHOUGH WITH CAVEATS. LOW LEVEL JETTING WILL BE WEAK FOR MUCH OF THE DAY BEFORE INCREASING TO 30 TO 35 KT JUST AHEAD OF THE FRONT. THE MAIN THREAT WOULD BE DAMAGING WIND...ENHANCED BY STORMS MOVING CLOSE TO 30 MPH. IF STRONG/SEVERE STORMS DEVELOP THEY ARE LIKELY TO DO SO WITH THE LINE OF CONVECTION AHEAD OF THE FRONT...AGAIN ASSUMING DIURNAL DRIVEN CONVECTION IS LIMITED IN SCOPE DURING THE DAY SAT. COLD FRONT PUSHES OFF THE COAST LATE SAT NIGHT WITH THE MID LEVEL TROUGH FOLLOWING ON SUN. COLD ADVECTION BEHIND THE FRONT WILL DROP SUN TEMPS BELOW CLIMO...BUT COLD AIR WILL BE A LITTLE TOO LATE TO HAVE A SIGNIFICANT IMPACT ON SAT NIGHT LOWS WHICH WILL END UP NEAR TO SLIGHTLY ABOVE CLIMO. SUN SHOULD BE DRY WITH DEEP NORTHWEST FLOW BEHIND THE TROUGH DROPPING PWATS UNDER .5 INCH FOR SUN AM AND UNDER .25 INCH BY SUN EVENING. GRADIENT RELAXES SUN NIGHT BUT HIGH REMAINS WEST OF THE AREA THROUGH THE END OF THE PERIOD SO SUN NIGHT WILL NOT BE AN IDEAL RADIATIONAL COOLING NIGHT. STILL LOWS END UP BELOW CLIMO. && .LONG TERM /MONDAY THROUGH THURSDAY/... AS OF 300 AM FRIDAY...LOW AMPLITUDE MID LEVEL RIDGING AND SPRAWLING SURFACE HIGH WILL KEEP THE AREA DRY AND SEASONABLE THROUGH THE PERIOD. COOLEST DAY WILL BE MON WITH SURFACE HIGH DIRECTLY OVERHEAD. HIGH THEN DRIFTS OFFSHORE TUE THROUGH THU BRINGING SEVERAL DAYS OF BEAUTIFUL SPRING WEATHER. PREVIOUSLY MEDIUM RANGE GUIDANCE HAD BEEN MOVING A DRY COLD FRONT ACROSS THE AREA TUE NIGHT INTO WED. NOW THAT GUIDANCE IS SUGGESTING MORE MID LEVEL AMPLIFICATION THIS SEEMS UNLIKELY AND IN FACT THE 00Z GUIDANCE IS BACKING OFF ON THE DRY FRONT. TEMPERATURES NEAR TO SLIGHTLY ABOVE CLIMO MON TRANSITION TO ABOVE CLIMO MON NIGHT THROUGH THE END OF THE PERIOD. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/... AS OF 12Z...RETURN FLOW WILL COMMENCE SHORTLY. HAVE LEANED FAIRLY HEAVILY ON THE HRRR EARLY...WITH SHOWERS POPPING UP ALONG THE MYRTLES BY LATE MORNING. INCREASING SOUTHERLY GRADIENT WILL CAUSE WINDS TO GUSTS OVER 20 KTS AT TIMES...ESPECIALLY ALONG THE COAST. SCATTERED SHOWERS WILL GIVE WAY TO MORE WIDESPREAD RAIN THIS EVENING AS DEEP MOISTURE MOVES INTO THE REGION. RAIN CHANCES WILL BE HIGHEST INLAND THIS EVENING...SPREADING TO THE COAST A FEW HOURS LATER. CEILINGS ARE A BIT PROBLEMATIC...BUT WILL GO FOR MVFR PREDOMINATELY WITH POCKETS OF IFR POSSIBLE. EXTENDED OUTLOOK...SHOWERS AND T-STORMS WITH MVFR/TEMPO IFR CONDITIONS OVERNIGHT AND ON SATURDAY. VFR SUNDAY THROUGH TUESDAY. && .MARINE... NEAR TERM /THROUGH TONIGHT/... AS OF 600 AM FRIDAY...THE PRESSURE GRADIENT BETWEEN A LARGE AREA OF HIGH PRESSURE OFFSHORE AND A TROUGH OF LOW PRESSURE TO OUR W WILL BE TIGHTEST TONIGHT...ESPECIALLY LATE TONIGHT AND SAT AS THE TROUGH BEGINS TO MAKE ITS EASTWARD PUSH. THUS THIS IS WHEN THE STRONGEST WINDS ARE EXPECTED ACROSS THE WATERS. THE STRONGEST WINDS ARE EXPECTED ACROSS THE OUTERMOST WATERS AND EASTWARD WHERE SEA SURFACE TEMPS ARE MUCH HIGHER THAN ACROSS THE NEAR SHORE WATERS...THUS ALLOWING FOR THE GREATEST MIXING. WIND SPEEDS WITHIN 20 NM OF THE COAST WILL BE AS HIGH AS 15 TO 20 KT. PERSISTENTLY HIGHER SOUTH WINDS OFFSHORE WILL ALLOW SEAS TO BUILD AND EXPECT THE 6 FT THRESHOLD WILL BE MET ACROSS PORTIONS OF THE OUTER WATERS AS EARLY AS THIS AFTERNOON AND MORESO TONIGHT...NECESSITATING A SMALL CRAFT ADVISORY WHICH WILL BE RAISED AT THIS TIME. FINALLY...HIGHER DEWPOINTS ADVECTING NORTHWARD AHEAD OF AN APPROACHING TROUGH SHOULD ALLOW FOR THE DEVELOPMENT OF SEA FOG...LIKELY MOST PREVALENT OVERNIGHT. SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... AS OF 300 AM FRIDAY...SOUTHERLY FLOW WILL APPROACH 20 KT SAT AS GRADIENT OVER THE WATERS IS PINCHED BETWEEN ADVANCING COLD FRONT AND HIGH PRESSURE. ANTICIPATE A LINE OF CONVECTION AHEAD OF THE FRONT WHICH WILL CROSS THE WATERS SAT EVE/NIGHT. OFFSHORE FLOW DEVELOPS BEHIND THE FRONT WITH GRADIENT AND DEVELOPING COLD ADVECTION KEEPING SPEEDS AROUND 20 KT. LITTLE CHANGE IN THE GRADIENT SUN AS HIGH BUILDS KEEPS NORTHWEST WINDS A SOLID 20 KT FOR MUCH OF THE DAY. OFFSHORE FLOW SLOWLY WEAKENS SUN NIGHT...DROPPING TO 15 KT BY THE END OF THE PERIOD...AS GRADIENT RELAXES. SEAS 4 TO 6 FT EXPECTED SAT INTO SUN WHEN OFFSHORE COMPONENT DROPS SEAS TO 3 TO 5 FT. CONTINUED OFFSHORE FLOW COMBINED WITH REDUCTION IN SPEEDS SUN NIGHT WILL DROP SEAS TO 2 TO 4 FT BY THE END OF THE PERIOD. LONG TERM /MONDAY THROUGH TUESDAY/... AS OF 300 AM FRIDAY...OFFSHORE FLOW AROUND 15 KT AT THE START OF THE PERIOD WILL DECREASE DURING MON AS HIGH PRESSURE MOVES OVER HEAD. SPEEDS WILL DROP UNDER 10 KT BY MON EVENING...BECOMING LIGHT AND VARIABLE MON NIGHT. HIGH SHIFTS OFFSHORE FOR TUE WITH RETURN FLOW SLOWLY RISING INTO THE 10 TO 15 KT RANGE LATE TUE AND TUE NIGHT. SEAS WILL RUN 2 TO 3 FT FOR A MAJORITY OF THE PERIOD. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...NONE. NC...NONE. MARINE...SMALL CRAFT ADVISORY FROM 2 PM THIS AFTERNOON TO 8 AM EDT SATURDAY FOR AMZ250-252-254-256. && $$ NEAR TERM...RJD SHORT TERM...III LONG TERM...III AVIATION...SGL/RJD