Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 282057 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 340 PM EDT Wed Sep 28 2016 .SYNOPSIS... A cold front approaching from the west will slow down on Friday and linger near or along the Carolina coast through this weekend. High pressure will build in behind the front through early next week. && .NEAR TERM /THROUGH TONIGHT/... As of 300 PM Wednesday...Convection has broken out along the piedmont as expected, with a few showers/storms along the sea breeze as well. A few of these storms have the potential to become strong, especially far NW zones and just outside of the CWA, where thermodynamics and forcing mechanisms best overlap. These include height falls ahead of the deepening upper low, increasing low-level winds around 850mb, SBCape of 3000 J/kg, and 0-6 km bulk shear around 20 kts. Latest HRRR and 12z NSSL WRF are both modeling the current situation pretty well, and expect most of the activity to remain just outside the CWA border to the west, with the best chance for any severe storms remaining well NW of the ILM CWA. That being said, cannot rule out an isolated strong wind gust along i-95 this aftn/eve, before diurnal heating wanes and storms weaken and dissipate. Tonight, a second round of convection is possible as a vorticity lobe streaks up from the south, embedded in the mean flow between the Atlantic Ridge and deep closed low to the west. Elevated instability will remain, and forcing within this vort will be enough to cause more showers with isolated tstms tonight, and this may affect a larger portion of the CWA than will be impacted through this eve. Do not expect strong or severe overnight, but more showers will be possible and have continued CHC Pop through the overnight. Temperatures overnight will remain above seasonable norms, with mins dropping only to around 70. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... As of 300 PM Wednesday...Synoptic pattern changes very little through the end of the week, although sensible weather will improve through the period. Deep upper low across the OH VLY will remain the dominant feature as flow becomes very slow, keeping the closed low basically stationary through the period. This will cause a cold front to move slowly to the east, but guidance has backed off even further on this motion, and it is now progged to not quite make it to the coast even by Friday night. This will keep unsettled weather with warmer temperatures across at least the eastern third of the CWA, while locations out towards i-95 should still break into the drier and cooler air, especially on Friday. This is noted by much lower RH above 850mb advecting eastward in a dry slot beneath the upper low. However, the large ridge across the Atlantic remains strong, and forces the moist air ahead of the front and the dry slow to remain along the coast, while the pinched flow between these features drives vort impulses and shower chances northward into the region. Friday will overall be a drier and slightly cooler day than Thursday, that will be most felt well inland, while the immediate coast may see little change with above climo temps and scattered aftn convection. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... As of 300 PM Tuesday...Latest model run keeps deep cutoff upper low a bit farther west as it tracks up toward the Great Lakes over the weekend. Therefore the sfc front and deeper moisture should remain aligned parallel, just along the coast rather than off shore. Plenty of dry air will wrap around the upper low into the Carolinas aloft, but the lower dewpoint air behind the sfc boundary may struggle to make it to the coast. Also, the sfc boundary will remain a focal point for convective development and although the air aloft will be drier, there should still be shallow convection possible along and east of the boundary. There will be a sharp gradient between the drier air to the west and moister air to the east, but exactly where that will lie is tough to say. The models are trending on keeping the boundary farther west, along the coast, rather than off shore. This will mean more clouds, showers and more humid air in place over the eastern half or third of our area, but as you move inland there will be greater amounts of sunshine and drier air. The latest pcp water shows values up close to 2 inches from the tip of Cape Fear up to Hatteras while west of I-95 will have PWATS less than an inch with even lower amounts as you head W-SW. Essentially, the drier air will wrap around from the SW aloft and N-NW at the sfc and it will be more of a dewpoint gradient rather than temps. Daytime highs will remain in the 80s most places. The guidance has backed off on the cooler overnight lows due to the lack of lower dewpoint air moving in, but I still think many places inland will get down toward 60 early Sat. As the the mid to upper low lifts north Sunday through early next week, the lingering boundary will be pulled farther back on shore as it dissipates through Monday. The winds should shift around to the NE to E bringing some moister air back inland. Overall, places inland and west of surface boundary will see a greater amount of sunshine while places east of boundary will see a greater amount of clouds and chc of pcp. Heading into the middle of next week, the forecast become further complicated by the differences in the models as to the track and timing of Tropical Cyclone Mathew. For now, this system looks like it will track westward and eventually turn up around the Atlantic Ridge. The GFS is much faster with this system and we will have to see how this evolves to determine how or if this affects the southeast coast. For now, the greatest effects may be over the coastal waters in pulses of swells and increasing gradient winds eventually drive up the seas. && .AVIATION /18Z WEDNESDAY THROUGH SUNDAY/... As of 18Z...VFR conditions this afternoon and evening outside of SCT 3SM TSRA BKN030CB across inland terminals KLBT/KFLO BTWN 22-02z. Isolated showers throughout region aft 02z as disturbance aloft moves north over interior zones and ocean showers move onshore at coastal terminals overnight into very early Thursday. VFR Thursday 13z-18z as drier air spreads into the region with SKC for most locations, TCU at end of TAF cycle. EXTENDED OUTLOOK...Primarily VFR. Isolated to scattered afternoon showers through much the period, although limited in strength and coverage due to dry air aloft. && .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 300 PM Wednesday...Stalled front continues to sit NW of the waters, with a weak pressure gradient remaining in place. Winds will slowly veer from present S/SE to SW overnight, along with a slight increase in speed from 5-10 kts to a more uniform 10 kts. This will create seas of 2-3 ft, with a southerly wind wave and low amplitude SE swell comprising the spectrum. Showers with isolated tstms will be possible across the waters late tonight as well. SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... As of 300 PM Wednesday...Slow moving cold front will drag west to east through the short term, finally approaching or stalling across the waters Friday night. This will keep the waters in the warm sector with S/SW winds of 10-15 kts expected through most of the period, possibly shifting to the W/NW Friday night. These persistent winds combined with the offshore high pressure will keep a 5-6 sec southerly wind wave and 9-10 sec SE swell in the spectrum, creating 2-3 ft seas. LONG TERM/SATURDAY THROUGH MONDAY/... As of 300 PM Tuesday...A cold front will run parallel along or near the Carolina coast...weakening through early next week. Overall expect more northerly winds on west side of front to come around to the NE to E as weakening boundary gets drawn back westward as upper low lifts off to the north through the period, but great variability is possible. Southerly winds should continue to the east of the boundary. Seas will generally remain 2 to 3 ft over most waters but a slight rise will be seen due to some longer period SE swells mixing in through the weekend into early next week. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ NEAR TERM...JDW SHORT TERM...JDW LONG TERM...RGZ AVIATION...MJC

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