Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 200532 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 132 AM EDT Sun Aug 20 2017 .SYNOPSIS... A cold front will stall and weaken near the coast this weekend. High pressure will expand across the western Atlantic in the upcoming week, bringing waves of tropical moisture through mid week. A cold front will approach from the northwest Wednesday through Thursday moving off the coast Friday. && .NEAR TERM /THROUGH TODAY/... As of 7 PM Saturday...The last of this afternoons showers are moving offshore and other than the odd sprinkle along the coast expect that will be it for the night as diurnal cooling takes hold. Have allowed the Heat Advisory to expire on time at 6 PM as heat index values are now well below criteria throughout the forecast area. Have updated the forecast and gridded database accordingly. Relative portion of previous discussion follows: Partial clearing and low- level saturation with light wind will support pockets of dense fog from 4 am through sunrise Sunday. Drier mid-level air and lower surface dewpoints Sunday will reduce convective coverage compared to today, while lowering heat indices across the region, and no `heat advisories` are needed for Sunday. The better rain chance will reside near the coast in vicinity of the sea breeze front and its interaction with a decaying frontal boundary. Winds in the lowest several thousand feet remain light Sunday and the severe threat remains minimal, although downdraft CAPES will be higher, so a localized downburst cannot be written off entirely. && .SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/... As of 300 PM Saturday...Eclipse-viewing prospects continue to worsen unfortunately as several ingredients coming into play to increase cloud cover and rain chances. The first `culprit` may be the upper low/surface wave retrograding across the Gulf of Mexico. Locally this leads to an enhanced mid and upper SSE flow of moisture as early as Sunday night. The GFS is much more aggressive than the WRF in its depiction of this moisture. Monday morning even as this upper mositure may wane, models are then showing low and mid level moisture moving ashore as the remnant tropical wave in the Bahamas starts moving around the SW periphery of the Atlantic ridge, possibly even accompanied by weak mid level vorticity centers. Lastly assuming Monday`s airmass is not dissimilar from today`s (barring Sunday`s slight drying trend) thunderstorm initiation will coincide very roughly with the eclipse start time (partiality begins at 119 PM, max eclipse is at 248 PM). Even the seabreeze will likely not represent a clearing line (like today) as it will simply draw in moisture along the coast from the Bahamas system. Assuming the cirrus does not hang tough like the more agressive solutions I`m afraid eclipse viewing will be quite luck-based and be relegated to areas that have holes in the storms and deeper towering cumulus. Locally these lucky spots look to be rather few and far between. && .LONG TERM /TUESDAY THROUGH SATURDAY/... As of 300 PM Saturday...High pressure will reside just off shore extending down from off the coast of the Mid Atlantic region on Tues. At the same time a broad ridge aloft on Tues will be displaced by a trough digging down from the northwest through mid week. This trough will push a cold front into the Carolinas on Wed reaching the Eastern Carolinas late Wed into Thurs and slowly moving off the coast into Fri. The models show it pushing far south and east to bring drier weather on Friday into Fri night across the forecast area. Initially expect moisture convergence along the coast early Tues along periphery of high with some convection along or off shore becoming enhanced by sea breeze front Tues aftn. By Wed, cold front reaches into the Carolinas with gradient tightening ahead of it with moisture pooling over the Eastern Carolinas and dynamics aloft on the increase. Pcp water values will be above 2 inches with convection on the increase ahead of the front as it drops southeast into the area Wed night into Thurs. Drier air with lower temps expected by weeks end as front moves off the coast by Fri. Looks like we may even see a decent northeast surge behind front by late Fri. As it looks now, inland should begin to dry out Thurs night with moisture slow to leave the coast on Fri. Temps will start out warm into mid week ahead of the front, near 90, but will drop off to the mid 80s Thurs into Fri as front pushes south and east. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/...
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As of 06Z...KLTX VWP indicates 15 knots of wind at 1-2 kft which is limiting fog development to this point, but forecast soundings indicate these winds will diminish towards sunrise, increasing the chance for fog during the 09-12Z time frame. Will maintain forecast for IFR visibility, but can`t rule out tempo LIFR, especially at FLO and LBT where winds will be lightest, and at ILM due to precip earlier this aftn. Chance for shower/tstm activity Sunday should be limited to the coast, but widely scattered in nature and won`t include in terminal forecast due to low probability that terminals will be affected. Extended Outlook...Increasing coverage of showers/tstms by Tue through Wed. Flight restrictions will also be possible each early morning due to stratus/fog Wed.
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&& .MARINE... NEAR TERM /THROUGH SUNDAY/... As of 7 PM Saturday...Latest obs show quite variable winds due to convection moving across the waters, with seas in the 3 to 4 ft range. Thunderstorms will move east of the waters, after which winds will settle back into a SW direction of around 10 kts. Forecast in good shape. Have adjusted timing of showers and thunderstorms activity with the latest update. Previous discussion follows: South waves will govern the sea spectrum, running in 5-6 second intervals, around 3 feet, but up to 4 ft outer waters tonight. Isolated to scattered TSTMS will move to the NNE-NE through the weekend. Winds will be of a light character this period as the far western edge of the Bermuda high extends to shore, with a weakening front wavering near the coast. As a result chop will be on the light side through Sunday. Isolated TSTMS will impact the waters through the weekend. SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... As of 300 PM Saturday...Light southwesterly flow Sunday night may get disrupted for a time and go somewhat variable on Monday as poorly defined front/trough moves close to the area. Not much changes Monday night as the boundary remains very weak and possibly retrogrades slightly. Over the marine environment this may allow a southerly wind direction to slightly dominate even as speeds remain capped at 10kt and seas 2ft. LONG TERM /TUESDAY THROUGH THURSDAY/... As of 300 PM Saturday...Southerly winds around high pressure extending down from off the Mid Atlantic coast will become more SE Tues aftn in sea breeze but will remain basically 10 kts or less. Winds will begin to veer and increase out of the southwest Tues night into Wed as a cold front makes its way into the Carolinas tightening the overall pressure gradient. This front will make it into the Eastern Carolinas Wed night into Thurs with stiff SW winds continuing ahead of it. The winds will begin to veer late Thurs into Fri as the front makes its way into and through the waters. Shower and thunderstorm activity will be on the rise ahead of the front through mid week. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...REK NEAR TERM...MJC SHORT TERM...MRR LONG TERM...RGZ AVIATION...CRM MARINE...MJC/REK/RGZ/MRR is the U.S. government's official web portal to all federal, state and local government web resources and services.