Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 190747 AFDILM AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON NC 347 AM EDT SUN APR 19 2015 .SYNOPSIS... AN APPROACHING FRONTAL SYSTEM WILL BRING SHOWERS AND SCATTERED THUNDERSTORMS TODAY THROUGH MONDAY. A FEW OF THESE STORMS COULD BE STRONG TO SEVERE TODAY AND MONDAY. DRY AND SEASONABLE HIGH PRESSURE WILL BUILD INTO THE AREA TUESDAY AND WEDNESDAY. WARMER TEMPERATURES ARE EXPECTED THURSDAY AHEAD OF THE NEXT COLD FRONT. MUCH COOLER TEMPERATURES ARE POSSIBLE LATE WEEK AND INTO NEXT WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... AS OF 300 AM SUNDAY...SURFACE LOW PRESSURE OVER THE MID-MISSISSIPPI VALLEY WILL DEEPEN AND MOVE NORTH TODAY. THIS IS IN RESPONSE TO AN INCOMING STRONG UPPER DISTURBANCE IN THE CENTRAL PLAINS STATES INTERSECTING A REGION OF LOW-LEVEL BAROCLINICITY. ACROSS THE CAROLINAS THE LOW-LEVEL FLOW WILL BE VEERING TODAY IN RESPONSE TO THE DEEPENING LOW...WITH A DIFFUSE WARM FRONT EXPECTED TO TRANSIT THE REGION FROM SOUTH TO NORTH THIS AFTERNOON. DEEP MOISTURE WILL BE INCREASING RAPIDLY THROUGH THE DAY AND BY THIS EVENING THE 00Z GFS SHOWS PRECIPITABLE WATER IN EXCESS OF 1.8 INCHES ALONG THE COAST...A VALUE TYPICAL OF A SUMMERTIME TROPICAL AIRMASS. A SERIES OF WEAK UPPER DISTURBANCES WILL MOVE OVERHEAD FROM SOUTHWEST TO NORTHEAST TODAY. THE FIRST OF THESE DISTURBANCES SHOULD ARRIVE ACROSS THE CENTRAL CAROLINAS BY MID TO LATE MORNING... SPREADING A ZONE OF RAIN WITH EMBEDDED ELEVATED CONVECTIVE ELEMENTS ACROSS THE AREA. AS THE WARM FRONT ARRIVES DURING THE AFTERNOON MUCAPE VALUES WILL INCREASE TO OVER 1000 J/KG ACROSS SOUTH CAROLINA...WITH 500-750 J/KG EXPECTED ACROSS NORTH CAROLINA. ALONG AND SOUTH OF A LINE FROM DARLINGTON TO FLORENCE TO CONWAY THIS INSTABILITY SHOULD BECOME SURFACE-BASED. BULK SHEAR COMPUTED ACROSS THE 0-6KM LAYER SHOULD REACH 25-30 KT...WITH 0-1 KM HELICITY REACHING 100-150 M^2/S^2. NONE OF THESE VALUES REACH CRITICAL THRESHOLD VALUES FOR SEVERE WEATHER...HOWEVER THE ODDS OF SEVERE WEATHER ARE CERTAINLY NON-ZERO TODAY. IF SEVERE WEATHER WERE TO OCCUR THE TIME OF CONCERN WOULD BE THIS AFTERNOON TO AROUND SUNSET...WITH WIND DAMAGE OR A BRIEF SPIN-UP TORNADO POSSIBLE. HEAVY RAINFALL MAY END UP BEING THE BIGGER THREAT. WITH SUCH HIGH PRECIPITABLE WATER VALUES AND A SECOND UPPER DISTURBANCE MOVING OVERHEAD DURING THE EARLY EVENING...A QUICK 0.5 TO 1.0 INCH OF RAIN CANNOT BE RULED OUT. BEHIND THE LAST DISTURBANCE THE FORCING FOR RAIN OR CONVECTION ENDS...AND I HAVE SHOWN A DIMINISHING TREND IN POPS FROM MIDNIGHT THROUGH DAYBREAK MONDAY MORNING. HIGHS TODAY SHOULD REACH THE MID 70S EXCEPT ~5 DEGREES COOLER AT THE BEACHES. LOWS TONIGHT SHOULD ONLY FALL INTO THE MID TO UPPER 60S WITH MILD SOUTHWEST BREEZES CONTINUING. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... AS OF 300 AM SUNDAY...INTERESTING START TO THE WORK WEEK AS A SHORTWAVE EMBEDDED WITHIN A DEEPENING TROUGH WILL CREATE THE POTENTIAL FOR STRONG THUNDERSTORMS ON MONDAY. WARM FRONT WILL BE WELL NORTH OF THE AREA MONDAY MORNING...AND MOST OF THE HEAVY RAINFALL ANTICIPATED SUNDAY NIGHT WILL BE NORTH/OFFSHORE BY THE BEGINNING OF THE PERIOD. SOME RESIDUAL SHOWERS MAY PERSIST ON THE COAST EARLY...BUT ACTUALLY EXPECT THE MORNING HOURS TO BE DRY FOR THE MOST PART LOCALLY. THE COLUMN WILL DRY CONSIDERABLY FROM SUNDAY AS THE BEST MOISTURE DEPARTS TO THE NE...AND SOME SUBSIDENCE IS EXPECTED BEHIND AN EXITING SHORTWAVE. THIS WILL LEAVE AT LEAST PARTIAL INSOLATION...AND AS WARM/MOIST ADVECTION CONTINUES THE ATMOSPHERE WILL BECOME QUITE UNSTABLE MONDAY AFTN/EVE. FORECAST MLCAPE VALUES RISE TOWARDS 2000 J/KG...WITH THE SREF MEAN AROUND 1500 J/KG. AT THE SAME TIME...A SHORTWAVE WILL RIDE THROUGH THE DEEPENING TROUGH SO PVA COMBINED WITH HEIGHT FALLS /STEEPENING MID-LEVEL LAPSE RATES/ WILL DRIVE AN ENVIRONMENT CONDUCIVE TO STRONG CONVECTION. ADDITIONALLY...LFQ OF A SUBTROPICAL 250MB JET WILL APPROACH FROM THE SW. HOWEVER...SURFACE FORCING IS MOSTLY WEAK AND THE MID-LEVELS REMAIN QUITE DRY DURING THE MOST UNSTABLE PART OF THE DAY. THIS SUGGESTS THAT ACTIVITY WILL BE ISOLATED OR SCATTERED MONDAY AFTN/EVE...BUT ANY STORM WILL HAVE THE POTENTIAL TO BECOME STRONG AND SPC HAS THE AREA IN A SLIGHT RISK FOR MONDAY. DO NOT EXPECT WIDESPREAD STRONG/SEVERE STORMS...AND ATTM THE BEST FOCUS MAY BE ALONG THE PIEDMONT TROUGH AND WESTERN PORTIONS OF THE CWA. COLD FRONT WILL APPROACH SLOWLY FROM THE NW DRIVEN BY THE DEEPENING UPPER TROUGH...AND IS NOW SLATED FOR A CROSSING JUST BEFORE DAWN TUESDAY. THIS FRONT WILL BE ACCOMPANIED BY MORE WIDESPREAD SHOWER ACTIVITY...BUT NOT EXPECTING STRONG CONVECTION WITH ITS PASSAGE. COLD ADVECTION LAGS THE FRONT CONSIDERABLY...SO WHILE TUESDAY WILL BE DRY WITH MUCH MORE SUNSHINE AS HIGH PRESSURE BUILDS ACROSS THE REGION...TEMPS WILL NOT BE SIGNIFICANTLY COOLER THAN MONDAY. ON THE DISCUSSION OF TEMPERATURES...MONDAY WILL LIKELY BE WELL ABOVE NORMAL WITH WIDESPREAD 80S AWAY FROM THE BEACHES ON STRONG WARM ADVECTION AHEAD OF THE FRONT. A RELATIVELY WARM NIGHT EXPECTED MONDAY NIGHT AS FROPA OCCURS LATE...AND LOWS WILL DROP ONLY INTO THE LOW 60S. SLIGHTLY COOLER TUESDAY WITH HIGHS REACHING WELL INTO THE 70S TO NEAR 80...BEFORE COOL DRY HIGH PRESSURE ALLOWS FOR TEMPS TO CRASH TO AROUND 50 TUESDAY NIGHT. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... AS OF 300 AM SUNDAY...MID-LEVELS EVOLVE INTO A DECIDEDLY WINTER-LIKE APPEARANCE THROUGH THE EXTENDED WITH A LARGE VORTEX CUTOFF ACROSS SOUTHEAST CANADA WHICH WILL SLOWLY DROP ACROSS NEW ENGLAND BY THE WKND. INITIALLY THIS PRODUCES BENIGN AND SEASONABLE WEATHER ACROSS THE CAROLINAS...AS THE FLOW BECOMES ZONAL BENEATH THE CUTOFF...SO SURFACE HIGH PRESSURE WILL BECOME THE DOMINANT FEATURE WED/THU. THIS HIGH WILL MOVE OFFSHORE THURSDAY AHEAD OF THE NEXT COLD FRONT...DRIVEN BY A PIECE OF VORT ENERGY ROTATING AROUND THE LARGE MID-LEVEL VORTEX. MID-LEVEL FLOW REMAINS W/NW HOWEVER...SO ALTHOUGH PRECIP CHANCES INCREASE WITH THE COLD FRONT...SIGNIFICANT SHOWER ACTIVITY IS NOT ANTICIPATED. THE BIGGER STORY COULD BE MUCH COOLER TEMPS BEHIND THIS FRONT FRI/SAT THANKS TO 1000-500MB THICKNESSES DROPPING TOWARDS -2 SD`S FROM CLIMO...AND HIGHS/LOWS BY SATURDAY COULD FALL WELL BELOW NORMAL. A LOW PRESSURE SYSTEM MAY BEGIN TO EMERGE FROM THE GULF COAST STATES AND MOVE TOWARDS THE AREA AT THE END OF THE PERIOD...AND WILL MAINTAIN INHERITED LOW-CHC POP FOR SATURDAY. && .AVIATION /08Z SUNDAY THROUGH THURSDAY/... AS OF 06Z...A MIXTURE OF VFR/MVFR THROUGH THE EARLY OVERNIGHT HOURS DUE TO LOW CIGS AND PATCHY FOG...WITH CONDITIONS DETERIORATING TO MVFR/IFR LATE OVERNIGHT AND THROUGH INTO SUNDAY WITH AN APPROACHING FRONTAL SYSTEM. OVERALL...VFR PREVAILS ACROSS THE AREA TONIGHT WITH LIGHT AND VARIABLE WINDS AND INTERMITTENT LOW CIGS...AS WELL AS MID TO HIGH CLOUDS AS SEEN FROM LATEST SATELLITE IMAGERY. OBSERVATIONS ARE ALSO DEPICTING PATCHY FOG INLAND...JUST AT MARGINAL VFR/MVFR STATUS ATTM. WITH ISOLATED LIGHT SHOWERS SLOWLY MOVING ACROSS THE AREA...ANTICIPATE CONDITIONS TO DETERIORATE OVERNIGHT CREATING WIDESPREAD MVFR/IFR DUE TO LOW CIGS AND AREAS OF FOG. AFTER DAYBREAK...EXPECT EASTERLY WINDS AOB 12 KTS IN THE MORNING TO BECOME EAST-SOUTHEAST BY AFTERNOON WITH GUSTS UP NEAR 20 KTS POSSIBLE WITH A FRONTAL SYSTEM TO AFFECT THE AREA. A MIXTURE OF VFR/MVFR/IFR IS ANTICIPATED AS SHOWERS AND ISOLATED THUNDERSTORMS...ALONG WITH LOW CIGS AND PATCHY AREAS OF FOG MOVE THROUGHOUT THE AREA THROUGH THE END OF THE VALID TAF PERIOD. EXTENDED OUTLOOK...MVFR/IFR POSSIBLE INTO MONDAY WITH SHOWERS AND ISOLATED THUNDERSTORMS. A COLD FRONT WILL PUSH THROUGH THE AREA MONDAY NIGHT WITH SHOWERS POSSIBLE FOLLOWED BY MAINLY VFR CONDITIONS TUESDAY. POSSIBLE SHOWERS RETURNING LATER IN THE WEEK. && .MARINE... NEAR TERM /THROUGH TONIGHT/... AS OF 300 AM SUNDAY...LOW PRESSURE OVER THE MID-MISSISSIPPI VALLEY WILL DEEPEN TODAY. THE INCREASING SOUTHERLY WIND AHEAD OF THIS SYSTEM WILL DRAG A WARM FRONT THROUGH THE COASTAL CAROLINAS THIS AFTERNOON. GENERALLY EASTERLY WINDS THIS MORNING WILL VEER SOUTHEASTERLY THIS AFTERNOON...THEN SOUTHERLY TONIGHT. WINDS WILL INCREASE BUT NOT EXCESSIVELY SO GIVEN THE PRETTY LARGE DISTANCE FROM HERE BACK TO THE LOW...AND ALSO THE FACT THAT THE INCOMING AIRMASS WILL BE SIGNIFICANTLY WARMER THAN THE OCEAN SURFACE LEADING TO MOST OF THE WIND ENERGY RIDING UP AND OVER A COOL AND STABLE LAYER OF AIR AT THE SURFACE. WIDESPREAD SHOWERS AND EMBEDDED T-STORMS SHOULD AFFECT THE COASTAL WATERS THIS AFTERNOON AND TONIGHT. REDUCED VISIBILITY IN HEAVY RAINFALL AND ALSO OCCASIONAL LIGHTNING STRIKES WILL BE THE MOST SIGNIFICANT IMPACTS. SEAS WILL GRADUALLY BUILD DUE TO THE ONSHORE FLOW...WITH THE WORST CONDITIONS EXPECTED NORTH OF CAPE FEAR. THERE IS A 4-6 HOUR WINDOW LATE THIS EVENING INTO EARLY MONDAY MORNING WHERE A SMALL CRAFT ADVISORY MAY BE NEEDED NORTH OF CAPE FEAR DUE TO 6 FOOT SEAS...BUT GIVEN SOME REMAINING UNCERTAINTY ABOUT HOW LONG SOUTHERLY WINDS BLOW BEFORE VEERING SOUTHWESTERLY AND WEAKENING...I WILL DELAY RAISING THE ADVISORY JUST YET. SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... AS OF 300 AM SUNDAY...COLD FRONT APPROACHING FROM THE WEST WILL PINCH THE GRADIENT MONDAY...AND GUSTY SW WINDS WILL REACH 15-20 KTS WITH SLIGHTLY HIGHER GUSTS. THIS WILL PERSIST ALL OF MONDAY SINCE THE COLD FRONT IS NOT EXPECTED TO CROSS OFFSHORE UNTIL FIRST LIGHT TUESDAY...AND THUS A CHOPPY SEA STATE IS EXPECTED. WAVE HEIGHTS WILL RISE TO 4-5 FT...AND A SCEC MAY BE NEEDED MUCH OF MONDAY. WINDS WILL SHIFT QUICKLY TO THE W AND THEN NW BEHIND THE FRONT TUESDAY MORNING...AND THEN SLOWLY DECREASE IN SPEED FROM 10-15 KTS...TO AROUND 5 KTS AS HIGH PRESSURE BUILDS TOWARDS THE AREA REDUCING THE PRESSURE GRADIENT. SEAS WILL FALL INITIALLY ON THE OFFSHORE WIND TO 2-4 FT...BEFORE DROPPING FURTHER TO 1-2 FT TUESDAY NIGHT. LONG TERM /WEDNESDAY THROUGH THURSDAY/... AS OF 300 AM SUNDAY...BROAD HIGH PRESSURE WILL SKIRT ACROSS THE WATERS AND OFFSHORE WEDNESDAY...SO LIGHT AND VARIABLE WINDS WILL GRADUALLY TRANSITION TO A SW DIRECTION WEDNESDAY NIGHT AS RETURN FLOW DEVELOPS. THIS SW FLOW WILL PERSIST MOST OF THURSDAY BUT WITH SPEEDS INCREASING TO 10-15 KTS AHEAD OF A COLD FRONT WHICH WILL CROSS THE WATERS AT THE END OF THE PERIOD. WAVE HEIGHTS OF 1-2 FT WILL BUILD SLOWLY ONCE THE WIND BECOMES PREDOMINANTLY FROM THE SW LATE WEDNESDAY...AND THEN CONTINUE TO SLOWLY RISE THURSDAY TO 3-4 FT BEFORE THE COLD FRONTAL PASSAGE. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...NONE. NC...NONE. MARINE...NONE. && $$ SYNOPSIS...JDW NEAR TERM...TRA SHORT TERM...JDW LONG TERM...JDW AVIATION...TRA MARINE...TRA/JDW

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