Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 281725 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 125 PM EDT Sun May 28 2017 .SYNOPSIS... High pressure well southeast of the Carolinas will provide hot weather today and Monday. Thunderstorms could become more frequent as a weak front arrives from the north and stalls nearby Wednesday through Friday. && .NEAR TERM /THROUGH TONIGHT/... As of 1030 AM Sunday...Forecast (mostly high resolution) guidance still showing mixed signals for the evolution of expected convection this afternoon. It appears more of a timing issue and if anything the start is a bit later than previously advertised. I still like the GFS solution with a remnant vort in upstate Carolina associated with a previous MCS slated to cross what will be a fertile instability ground later this afternoon at a window between 19-22 UTC. Recalling events of yesterday in Tennessee, thats when things got going and translate that eastward, it all seems reasonable. Long story short, no changes to the forecast with the mid morning update. SPC continues to keep all of our North Carolina counties in a slight risk clipping some of the northern South Carolina counties. Previous discussion follows: Complex situation evolving today creates a more than challenging forecast, with heat and tstms possible across the area. Even before addressing Sunday`s weather, analysis of the ongoing situation must be completed. A complex of tstms moving through the western Carolinas is the last surviving trace of what was once a powerful MCS. This complex has weakened both due to loss of heating, but also advection into drier and more stable air as noted on SPC mesoanalysis. While one moderately sized cluster of storms continues to produce across western/central NC, this will likely remain north of the ILM CWA thanks to 0-6km mean winds on the GSO U/A sounding and KRAX VWP almost directly from 270 degrees. Do not anticipate convection locally overnight, but debris cloudiness will be widespread into daybreak. Synoptic setup for Sunday is quite similar to Saturday, although minor details create a more challenging, and possibly more active, forecast. Elongated high pressure along the Gulf Coast will gradually advect east and amplify, with mid-level heights climbing slowly this evening and tonight. To the north, a belt of enhanced mid-level westerlies will persist between this ridge and a series of troughs moving through southern Canada. Within this belt, vorticity impulses will move quickly from west to east, with each one creating the potential for convection beneath it. The challenge today then, is when will these vort impulses create tstms, and where will they occur. Once again, a mid-level cap will be present today, and as the mid- level ridge amplifies late, it will actually increase in intensity. However, this likely occurs too late to prevent subtle height falls within the flat ridge this aftn/eve, and the 850-700mb thermal ridge is noticeably weaker than what was present on Saturday. This suggests that convection is more likely today, especially as guidance is in good agreement with timing of a vort moving overhead during late aftn/eve /peak heating./ The environment will be very supportive of tstms this aftn, assuming the cap is not stronger than currently progged, and subsidence behind the current vort isn`t too strong to squelch lift. Big caveats of course, but forecast profiles suggest very strong MLCAPE of 2000 J/Kg thanks to highs around 90 with dewpoints around 70, and very steep ML lapse rates. As this vort moves to the north, storms may grow upscale into another tstm complex thanks to 0-6km bulk shear of up to 40 kts, and this is shown in varying degrees on the latest HRRR/ARW/RUC. SPC has placed SE NC into a SLGT risk today, with MRGL across NE SC for this potential. Large hail and damaging winds are the most likely threats. That being said, do NOT expect widespread severe weather today. A cluster of fast moving storms is possible, mostly across NC counties, but total coverage may end up being isolated to widely scattered. Differences in timing, subsidence, and the aforementioned cap all produce enough uncertainty to cap POP at 40 percent well north, with just SCHC south of the state line. Convection that does develop will likely move offshore or dissipate during the evening, leaving slightly drier air and another lull in convection tonight. Debris cloudiness and continued warm WSW winds will keep mins very warm however, falling only into the 70-74 degree range, warmest at the coast. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... As of 300 AM Sunday...A 500 mb ridge centered over Florida Monday will strengthen as it edges offshore Monday night into Tuesday. Although models still have some disagreement with specifics, it appears the seemingly never ending trail of upper level disturbances will remain just north of our portion of the Carolinas Monday through Tuesday, sparing us the worst of what could be multiple periods of severe weather across western South Carolina and most of North Carolina. Monday appears to be the hottest day of the week as 850 mb temps climb as high as +19C. Plenty of sunshine should push highs well into the 90s away from the beaches. Our latest forecast of 94 in Florence is just one degree away from a record of 95 set in 1991. Enough westerly low-level wind should exist to delay the seabreeze by a couple hours and pin the boundary near the coast. Dewpoints in the lower 70s near the coast should push heat indices near 100 degrees in spots. Forecast thunderstorm chances Monday range from around 10 percent in Georgetown to 30 percent in Lumberton. This is due to an increasingly substantial cap of warm mid-level air as you travel southward closer to the upper level ridge, and also increasing distance from the wavetrain of upper disturbances which sets up from central MS/AL across western SC into NC. Although thunderstorms should be only isolated in our portion of the Carolinas, steep lapse rates above the subsidence inversion, mid-level westerly winds of 30-40 knots, and plenty of dry air aloft means any storms that do form could produce damaging winds and hail. On Tuesday the upper ridge nudges just a bit farther off the Florida coast, allowing the wavetrain of disturbances to shift a little eastward as well. High temperatures should run several degrees cooler with a convectively-overturned airmass arriving from the west that should feature 850 mb temps only +15C to +16C, about 3 degrees C cooler than Monday. This should translate to highs mainly upper 80s to near 90. The threat for scattered thunderstorms with strong winds Tuesday afternoon may linger into the night. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... As of 300 PM Saturday...The mid level pattern will show more amplitude across the Eastern U.S. with a broad trough at least initially dipping into the Ohio Valley with ridging off to the southeast. This will keep the pattern somewhat unsettled with ample moisture and several shortwaves. Differences in the global solutions as to timing of course but reconciling the various solutions yields the highest pops, at least for this package occurring Tuesday and once again Friday and Saturday when the mid level flow weakens considerably with an old baroclinic zone providing an impetus for activity oriented east to west. No real fronts pushing through to provide any appreciable airmass change with highs and lows maintaining levels a couple of degrees above average. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/...
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As of 18Z...Expect mostly VFR conditions through the period. There will be an increase in showers and thunderstorms this afternoon and evening but the confidence level does not warrant any prevailing flight restrictions. There should be enough debris cloudiness and wind to prevent any significant fog outbreak after Monday morning. Extended Outlook...MVFR/IFR conditions are possible in showers and thunderstorms Monday Night through Tuesday. More typical summertime scattered showers and thunderstorms are possible Wednesday and Thursday.
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&& .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 1030 AM Sunday...Summertime pattern is steady state and warrants no updates to the forecast with the mid morning update. Previous discussion follows: Elongated high pressure along the Gulf Coast will maintain its local influence across the waters today. Winds from the SW will slowly intensity today, from 10-15 kts this morning, to 15-20 kts this evening and tonight. These persistent and increasing SW winds will create a 5 sec SW chop which will mask the continuing but low-amplitude SE swell, and seas of 2-4 ft are forecast through the period. A cluster of showers and thunderstorms may move in the vicinity of the waters this evening with the potential for gusty winds and hail, but confidence is low attm. SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... As of 300 AM Sunday...High pressure centered south of Bermuda will control our weather through the Monday-Tuesday timeframe with west-southwesterly winds. As it typical this time of year, large inland-to-offshore temperature contrasts should produce well-defined seabreezes both days with wind gusts near the beaches reaching 20 knots from mid-afternoon through early evening. Otherwise wind speeds of 10-15 knots should prevail through the period. Isolated thunderstorms will be possible as a series of weak upper level disturbances move across North Carolina. LONG TERM /WEDNESDAY THROUGH THURSDAY/... As of 300 PM Saturday...Its mostly a show of Bermuda High pressure and a summertime pattern with a south to southwest flow through the period. There may be some local and temporary distortion of wind fields due to expected convection but the overall synoptic pattern should remain the same. Significant seas will be 2-4 feet. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...TRA NEAR TERM...JDW/SHK SHORT TERM...TRA LONG TERM...SHK AVIATION...SHK MARINE... is the U.S. government's official web portal to all federal, state and local government web resources and services.