Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 250520 AFDILM AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON NC 120 AM EDT SAT APR 25 2015 .SYNOPSIS... A WARM FRONT WILL APPROACH FROM THE SOUTH TODAY AND TONIGHT BRINGING SHOWERS AND POTENTIALLY A FEW STRONG THUNDERSTORMS. THE FRONT WILL STALL BEFORE BEING PUSHED SOUTH AS A COLD FRONT LATE SUNDAY. DRY HIGH PRESSURE WILL RETURN MONDAY INTO TUESDAY BEFORE ANOTHER STORM SYSTEM IMPACTS THE AREA MID TO LATE WEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 120 AM SATURDAY...A LARGE SHIELD OF CLOUDS...GENERATED BY CONVECTION WELL UPSTREAM...WILL CONTINUE TO MOVE ACROSS THE FORECAST AREA OVERNIGHT. THE CENTER OF HIGH PRESSURE TO OUR S AND E WILL CONTINUE TO DRIFT OFFSHORE. THE BRUNT OF THE COOL AND DRY AIRMASS HAS BEGUN TO MOVE OFFSHORE AND WITH THAT...DEWPOINTS HAVE RECOVERED INTO THE 40S UNDER THE INFLUENCE OF A LIGHT SOUTHERLY FLOW. EARLIER TODAY DEWPOINTS WERE COMMONLY IN THE 20S. AN MESOSCALE CONVECTIVE VORTEX IS EXPECTED TO DEVELOP IN ASSOCIATION WITH WIDESPREAD CONVECTION ACROSS THE SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY. MODELS ARE DEPICTING THIS FEATURE DAMPENING AS IT STREAKS ACROSS THE UPPER GULF COASTAL STATES AND TENNESSEE VALLEY OVERNIGHT AND EARLY SAT MORNING. EXAMINATION OF HIGH RESOLUTION MODEL DATA CONFIRMS THAT APPROACHING CONVECTION SAT MORNING WILL REMAIN TO OUR W AND S THROUGH DAYBREAK. HOWEVER... CLOUD COVER WILL CONTINUE TO INCREASE WITH A VERY GRADUAL LOWERING OF THE CEILINGS INTO SAT MORNING. THICKENING CLOUD COVER COUPLED WITH A WEAK SOUTHERLY FLOW AND GREATER LOW LEVEL MOISTURE SHOULD ONLY ALLOW TEMPS TO DROP TO THE UPPER 40S AND LOWER 50S...ALTHOUGH A FEW MID 40S ARE CERTAINLY POSSIBLE. && .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... AS OF 300 PM FRIDAY...ACTIVE WEATHER WEEKEND ON TAP WITH SEVERAL DIFFERENT PERIODS OF CONVECTION LIKELY ACROSS THE AREA. SATURDAY WILL BEGIN DRY BUT CLOUDY...AS A WARM FRONT DRAPED AHEAD OF A LOW PRESSURE SYSTEM APPROACHES FROM THE SW. THIS LOW PRESSURE WILL PUSH EAST FROM THE MIDWEST AND LIKELY TRACK NORTH OF THE CWA...BUT ITS LEADING WARM FRONT WILL LIFT ACROSS THE CAROLINAS ON SATURDAY. AS THIS OCCURS...MOIST ADVECTION INCREASES SIGNIFICANTLY AND A VERY WET COLUMN WILL DEVELOP SATURDAY AFTN THROUGH SATURDAY NIGHT WITH PWATS CLIMBING TOWARDS 1.75 INCHES. AT THE SAME TIME...A SHORTWAVE WILL MOVE OVERHEAD AND DIFFLUENCE WITHIN THE ENTRANCE REGION TO AN UPPER JET WILL TRANSLATE OVERHEAD. INSTABILITY WILL REMAIN RELATIVELY WEAK UNTIL AFTER WARM FRONTAL PASSAGE...BUT 0-3 KM SRH WILL CLIMB ABOVE 500 M2/S2...WHICH IN CONJUNCTION WITH THE OTHER PARAMETERS SUGGESTS A NON-ZERO SEVERE (TORNADO) THREAT LOCALLY. HODOGRAPHS FEATURE LARGE RIGHT-LOOPING STRUCTURES SATURDAY EVENING...AND THIS APPEARS TO BE A SETUP WHERE A LARGE COMPLEX OF CONVECTION WILL EXIST...WITH EMBEDDED TURNING ELEMENTS. AFTER COORDINATION WITH SPC...THE SWODY2 HAS BEEN UPDATED TO INCLUDE A SLIGHT RISK FOR MOST OF THE AREA FOR ISOLATED SUPERCELLS. WHILE TORNADOES ARE NOT TRULY EXPECTED...ONE OR TWO CANNOT BE RULED OUT...AS CONVECTIVE ELEMENTS CROSSING THE HELICITY BOUNDARY OF A WARM FRONT IS HIGHLY FAVORABLE FOR TORNADOES. FORTUNATELY...INSTABILITY WILL BE WEAK AND IS THE LIMITING FACTOR SATURDAY. IN ADDITION TO THIS TORNADO RISK...PERIODS OF VERY HEAVY RAINFALL APPEAR LIKELY THANKS TO ENHANCED LIFT DUE TO UPPER SUPPORT...AND RELATIVELY SLOW UPDRAFTS IN AN ENVIRONMENT WITH AROUND 11 KFT OF WARM CLOUD DEPTH. WPC HAS HIGHLIGHTED THE SC COUNTIES IN AN EXCESSIVE RAINFALL RISK FOR DAY 2 WHICH SUGGESTS THE POTENTIAL FOR FLOODING AS WELL. EVEN THOUGH MUCH OF THE PAST MONTH HAS BEEN PRETTY DRY...WE ARE STILL RUNNING AT EXCESS QPF FOR THE LAST 30 AND 60 DAYS...SO THIS TOO WILL NEED TO MONITORED ON SATURDAY. THIS FRONT WILL CLEAR THE AREA SATURDAY NIGHT BUT THEN STALL NORTH OF THE AREA AS 500MB TROUGH BEGINS TO DIG INTO NEW ENGLAND. SOME OF THE HIGH RES GUIDANCE IS TRYING TO SUGGEST A NOCTURNAL MCS WILL DEVELOP ALONG THE BOUNDARY AND TRY TO PUSH SE INTO THE AREA...BUT WITH THE COLUMN DRYING BEHIND THE SATURDAY SHORTWAVE...WILL NOT SHOW THIS SOLUTION...BUT MAINTAIN THE INHERITED LOW-CHC POP FOR THE NIGHTTIME HOURS. FRONT THEN WAVERS BACK TO THE SOUTH SUNDAY...WITH VERY WARM AND UNSTABLE CONDITIONS DEVELOPING AHEAD OF IT. THIS WILL POSE ANOTHER CONVECTIVE RISK SUNDAY...WITH STRONG TO POSSIBLY SEVERE THUNDERSTORMS ONCE AGAIN POSSIBLE. SPC SWODY3 HAS A MRGL RISK FOR THE SOUTHERN PORTIONS OF THE CWA...AND THE RISK WILL BE DEFINED ALMOST ENTIRELY BY HOW QUICKLY THE FRONT PROGRESSES SOUTH...ESPECIALLY SINCE UPPER AND MID-LEVEL SUPPORT ONCE AGAIN APPEAR FAVORABLE. TORNADO RISK WILL NOT BE THE PRIMARY CONCERN SUNDAY...INSTEAD HAIL/WIND WILL BE POSSIBLE AS SBCAPE CLIMBS TOWARDS 2000 J/KG THANKS TO VERY STEEP LOW AND MID-LEVEL LAPSE RATES. FRONT WILL BE SOUTH OF THE AREA BY THE END OF THE PERIOD...BRINGING MUCH DRIER AIR AND AN END TO ANY CONVECTIVE THREAT. IF THAT ISN`T ENOUGH...A TRICKY TEMPERATURE FORECAST IS ALSO ON TAP DURING THE WEEKEND. HIGHS SATURDAY WILL BE TEMPERED BY CLOUDS AND INCREASING RAINFALL...AND WILL LIKELY STRUGGLE TOWARDS 70 DEGREES. WITH THE WARM FRONT LIFTED NORTH OF THE AREA SATURDAY NIGHT...WARM ADVECTION WILL DRIVE VERY SMALL DIURNAL RANGES...AND LOWS WILL BE ONLY IN THE LOW 60S. MUCH WARMER ON SUNDAY...AND HIGHS WILL POTENTIALLY RISE WELL INTO THE 80S DEPENDING ON HOW QUICKLY THE FRONT SAGS BACK TO THE SOUTH. WHILE SATURDAY FEATURES WEAK DIURNAL RANGES...SUNDAY`S WILL EXCEED 30 DEGREES AS LOWS DROP TO A DEGREE OR TWO EITHER SIDE OF 50. && .LONG TERM /TUESDAY THROUGH FRIDAY/... AS OF 300 PM FRIDAY...AMPLIFIED PATTERN WILL BE THE EMPHASIS FOR THE EXTENDED FORECAST. INITIALLY A CYCLONIC FLOW WILL PREVAIL FOR MONDAY AND TUESDAY WITH DRY AND COOL SURFACE HIGH PRESSURE BUILDING IN FROM THE NORTHWEST. FORECAST BECOMES COMPLEX AND CHALLENGING WEDNESDAY THROUGH FRIDAY AS A MID LEVEL TROUGH MOVES ACROSS THE SOUTHEAST. THE GFS HAS A MORE PROGRESSIVE TROUGH...ALBEIT SLOWER THAN USUAL WHILE THE ECMWF HAS A CLOSED MID LEVEL CYCLONE. REGARDLESS OF WHICH SOLUTION EVENTUALLY VERIFIES...POPS REMAIN IN THE FORECAST FROM EARLY WEDNESDAY MORNING THROUGH THE DAY THURSDAY. LOWEST EARLY AND LATE. I HAVE ELEVATED VALUES TO LIKELY FOR THE DAYTIME HOURS WEDNESDAY. TEMPERATURE FORECAST REMAINS A LITTLE ON THE COOL SIDE VIA THE AIRMASS INITIALLY THEN THE MOISTURE...MORESO FOR DAYTIME HIGHS. && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/... AS OF 06Z...VFR OVERNIGHT...GRADUALLY DETERIORATING TO MVFR AND POSSIBLY IFR THIS AFTERNOON AND EVENING AS A WARM FRONT BRINGS UNSETTLED WEATHER. A FRONTAL BOUNDARY WILL BRING SHOWERS AND THUNDERSTORMS TO THE AREA LATE THIS AFTERNOON AND EVENING...THUNDERSTORM MAY REACH SEVERE LIMITS. ANTICIPATE DETERIORATION OF CONDITIONS TO MVFR AND IFR LATE THIS EVENING. WINDS TODAY WILL REMAIN SOUTHWEST AOB 12 KTS. SHRA/TSRA WILL TAPER OFF LATE TONIGHT...WITH LOW CIGS AND AREAS OF FOG/MIST CREATING MVFR/IFR IN LOCATIONS. EXTENDED OUTLOOK...SHOWERS ALONG WITH TEMPO MVFR CONDITIONS THROUGH SUNDAY. OTHERWISE VFR. && .MARINE... NEAR TERM/THROUGH TONIGHT/... AS OF 120 AM SATURDAY...HIGH PRESSURE ACROSS THE WATERS IS EXPECTED TO CONTINUE TO SHIFT OFFSHORE OVERNIGHT AND SAT MORNING. WINDS WILL BE FROM THE SW AROUND 10 KT OVERNIGHT. SEAS WILL BE 3 FT OR LESS THROUGH SAT MORNING. SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... AS OF 300 PM FRIDAY...BOTH A WARM FRONT AND A COLD FRONT WILL CROSS THE WATERS THIS PERIOD...LEADING TO A VARIETY OF WIND/WAVE CONDITIONS AS WELL AS PERIODS OF THUNDERSTORMS. WARM FRONT WILL LIFT NORTH ACROSS THE WATERS SATURDAY AFTN...SO WINDS WILL VEER SLOWLY FROM SOUTH TO SOUTHWEST BUT WITH INCREASING SPEEDS TO 15-20 KT. THESE WINDS WILL REMAIN FROM THE SW AND PERSIST AROUND 15 KT THE FIRST HALF OF SUNDAY AS THE FRONT STALLS TO OUR NORTH...BUT THEN DROP BACK TO THE SOUTH SUNDAY EVENING TURNING WINDS TO THE NORTH...BUT STILL AROUND 15 KT THROUGH THE END OF THE PERIOD. SEAS WILL BE HIGHEST LATE SATURDAY INTO SUNDAY DUE TO THE ENHANCED SW WINDS...REACHING 3-5 FT. THEY WILL FALL A BIT SUNDAY...AND THEN MORE DRAMATICALLY BEHIND THE COLD FRONT AS THE OFFSHORE WIND COMPONENT PUSHES WAVE HEIGHTS TO 2-3 FT. IN ADDITION...THUNDERSTORMS WILL IMPACT THE WATERS WITH BOTH THE WARM FRONTAL PASSAGE AND THE COLD FRONTAL PASSAGE. SOME OF THESE MAY BE STRONG...ESPECIALLY SATURDAY...WITH GUSTY WINDS AND HEAVY RAINFALL. LONG TERM /MONDAY THROUGH WEDNESDAY/... AS OF 300 PM FRIDAY...WINDS WILL KEEP A MOSTLY NORTHERN COMPONENT THROUGH THE PERIOD AS HIGH PRESSURE MOVES ACROSS THE GREAT LAKES REGION. LATER IN THE PERIOD LOW PRESSURE DEVELOPS OFF THE SOUTHEAST COAST WHICH WILL TURN WINDS TO NORTHEAST. WIND SPEEDS WILL GENERALLY BE 10-15 KNOTS POSSIBLY LIGHTER TUESDAY. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...NONE. NC...NONE. MARINE...NONE. && $$ NEAR TERM...RJD/MJC SHORT TERM...JDW LONG TERM...SHK AVIATION...SGL

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