Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 161036 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 636 AM EDT Thu Aug 16 2018 .SYNOPSIS... Bermuda high pressure will maintain warm and humid weather with mainly isolated thunderstorms through Friday. Rain chances will increase a bit into the weekend, as an upper trough deepens to the west, and a surface front moves into the Carolinas. && .NEAR TERM /THROUGH TONIGHT/... As of 300 AM Thursday...Expect some patchy fog this morning, especially any places that had convection previously, leaving shallow moisture. After sunrise, fog will dissipate leaving sunshine mixing with mainly some high clouds. Ridge axis running back across the Southeast from the Atlantic waters to the east. This will maintain enough dry air and subsidence aloft to keep convection more isolated, basically focused along sea breeze boundary and along inland trough. Models do show a minor perturbation running across mainly NC this evening which may help to push a bit of mid to high clouds or convection into the area from trough to the west, but overall expect isolated convection along sea breeze earlier. HRRR shows main focus along the coast near the Grand Strand this aftn and then along NW bordering counties this eve with pcp water values increasing at that time to 1.8 to 2 inches. Winds become a little stiffer out of the SW heading into Fri morning, with a chc of convection along the Cape Fear coast toward morning. Continued SW flow around Bermuda High pressure will produce warm and humid weather today. Expect temps to reach between 90 and 95 most places combining with dewpoints in the low to mid 70s to generate heat index values near 100 this aftn. Winds will naturally back slightly and spike up in the afternoon sea breeze and slight pinching of the gradient between the high pressure and inland trough. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... As of 300 AM Thursday...A positively tilted upper trough extending from the Great Lakes to the Gulf Coast will slowly advance eastward Friday and Saturday. Deepening moisture ahead of the trough should build precipitable water values toward 2.00 to 2.25 inches. Bermuda high pressure centered about 500 miles off the coast on Friday will begin to move Saturday as the upper trough advances eastward. With the approach of the trough, any residual subsidence inversion aloft with the Bermuda ridge will dissipate during the day Friday. Expect the coverage of thunderstorms to increase versus Wednesday and Thursday, reaching 30-40 percent on Friday and 60-70 percent on Saturday. Shear across the 0-6 km layer should remain only 10-15 knots through the period, favoring only weak storm organization. Lightning, training cells along boundaries, and heavy rainfall may turn out to be the biggest risks with this pattern. Thunderstorms should have diurnal peaks in coverage both Friday and Saturday afternoons, plus models show a secondary peak in coverage late Friday night as a weak shortwave over the northeastern Gulf is pulled across the area. Our airmass will remain seasonably warm and humid. 850 mb temps around +18C both days would yield low to mid 90s for highs, but the increase in clouds and precip should hold us to 90-92 inland and upper 80s near the coast. Overnight lows in the lower to mid 70s, except a little warmer on the beaches. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 300 PM Wednesday...An active period of weather looks likely much of the extended as a series of fronts/troughs impacts the Southeast. The first of these will be driven beneath a mid-level shortwave digging into the area into Sunday. Although the trough axis is progged to shift offshore late Sunday, ahead of this occurrence moisture will stream into the region with PWATs surging towards 2.25 inches. This moisture will work in tandem with convergence near the surface boundary, height falls, and moderate diffluence on the RRQ of an upper jet angling across New England to produce scattered to potentially widespread showers and tstms, especially on Sunday. The surface boundary will linger into Monday but other forcing weakens, so convection chances remain elevated, but lower than during the weekend. A brief period of shortwave ridging on Tuesday which will bring somewhat above normal temps and drier weather, another mid-level trough and cold front will move into the Southeast by the end of the period. Temps through the period will be around to slightly above normal for highs, with above normal mins likely each night. Cloud cover and convection may keep temps a bit cooler than progs for the weekend before subtly warmer conditions develop early next week. && .AVIATION /12Z THURSDAY THROUGH MONDAY/... As of 12Z...Patchy early morning fog inland should burn off quickly this morning with VFR conditions prevailing through the day. Isolated thunderstorms will develop this afternoon between 17-19Z, but coverage is only anticipated to be 20-30 percent, too low for explicit mention in the terminal forecasts at this time. Any storms that do develop should move toward the east around 10 knots and will be efficient lightning producers with gusty winds possible. Extended Outlook...Mainly VFR conditions expected through Friday except for areas of pre-dawn ground fog. The potential for thunderstorms with MVFR/IFR conditions increases by late Friday and becomes even more likely during the weekend. && .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 300 AM Thursday...Southwest flow will continue around Bermuda High basically 10 to 15 kts. Slightly longer period, up between 8 and 9 second SE swell will mix with shorter period wind waves to produce seas just around 3 ft with potential for a few 4 fters in the outer waters tonight. The flow will back slightly and become slightly higher and gustier in aftn sea breeze and slightly pinched gradient between high pressure to the east and trough inland. Also may see some nocturnal jetting helping to boost winds up a bit overnight. Basically expect seas around 3 ft with a few 4 fters possible in outer waters. SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... As of 300 AM Thursday...Bermuda high pressure centered about 500 miles off the Southeast coast Friday will drift farther out to sea on Saturday. Low pressure will move east across New England and drag a cold front into the Mid-Atlantic states by late Saturday. While the front should remain to our north, its proximity should lead to a tighter pressure gradient across the Carolinas with stronger wind speeds expected across the coastal waters. SW winds 10-15 kt Friday could increase to 15-20 kt on Saturday, accompanied by several waves of showers and thunderstorms. Seas should build from 2-3 feet on Friday to 3-4 feet Saturday, unfortunately with most of that increase in the choppy end of the wave spectrum. LONG TERM MARINE /SUNDAY THROUGH MONDAY/... As of 330 PM Wednesday...High pressure offshore will remain in place which will force an approaching cold front to stall and dissipate as it approaches the area late in the weekend into early next week. This will drive SW winds of 15 to 20 kts Saturday, easing a bit to around 15 kts Sunday, before falling off moreso on Monday thanks to the weakening gradient. A low amplitude 1ft/9sec SE swell will persist through the period, but the primary wave group will remain a 5 sec SW wind wave at 3-4 ft. This will produce significant seas of 3-4 ft Sunday, falling to 2-3 ft Monday. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...RGZ NEAR TERM...RGZ SHORT TERM...TRA LONG TERM...JDW AVIATION...TRA

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