Area Forecast Discussion
Issued by NWS Wilmington, NC

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798 FXUS62 KILM 040225 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 925 PM EST Sat Dec 3 2016 .SYNOPSIS... High pressure moves off the coast Sunday tonight. Low pressure developing offshore will bring significant rain to the area late Sunday through late Tuesday. Seasonable weather late in the week will give way to Arctic air arriving Thursday night. && .NEAR TERM /THROUGH TONIGHT/... As of 900 PM Saturday...Surface high pressure centered over the Ohio Valley will move into the central Appalachians overnight, maintaining a light north to northeast wind. A very active subtropical jet is spreading thickening mid and high level moisture across the Carolinas. This trend should continue tonight with skies becoming overcast late tonight. Moisture will also lower down to 700 mb/10,000 feet AGL tonight, and there is a slight chance some light rain could sneak down through the residual subcloud dry air to reach the surface from Interstate 95 westward. Thickening clouds should inhibit radiational cooling and provide temperatures a little warmer than what we experienced this morning, generally around 40 for most locations. && .SHORT TERM /SUNDAY MORNING THROUGH MONDAY NIGHT/... As of 300 PM Saturday...A complex weather situation is developing for Sunday and Monday with two waves of substantial rainfall possible. A northern stream trough across the Dakotas Sunday morning will move off the East Coast Sunday night. This system should help sharpen a trough at the surface along the Carolina coast, with surface low pressure developing along the trough Sunday evening then moving out to sea Monday. Low-level moisture obviously will increase with this feature approaching the coastline, and precipitation rates should be helped along with copious mid and upper level moisture pushed out ahead of a strong closed low across northern Mexico. Some very light rain is possible Sunday morning due exclusively to this mid-level moisture advecting overhead, but as isentropic lift strengthens and deepens to include about a 10,000 feet depth of the atmosphere by Sunday evening, look for precipitation coverage and rates to blossom. We`re predicting an inch of rain could fall through Sunday night and our forecast PoPs range from 80 percent near Georgetown to 90-100 percent elsewhere. As this system clears off the coast Monday morning, we`ll have about an 18-hour lull until the big upper low across Mexico gets absorbed into the subtropical jet and accelerates northeastward across the U.S. The surface front should get kicked a couple hundred miles south of the area during the day Monday, but will return northward with a vengeance by late Monday night. Isentropic lift increases rapidly after midnight with PoPs again approaching 100 percent. An additional 0.5 to 1.0 inch of rain could fall Monday night -- quite an event in what is supposed to be a fairly dry La Nina winter! Diurnal temperature ranges should be constricted by all the cloud cover through the period. The GFS model appears quite reasonable with its synoptic fields and my forecast is just a couple degrees cooler than its associated MOS products, accounting for evaporational cooling in the boundary layer. && .LONG TERM /TUESDAY THROUGH SATURDAY/... AS OF 3 PM Saturday...A dual-centered storm system will be affecting the area on Tuesday. One low will lift across the Ohio Valley whilst the other runs along the coast either just onshore or offshore. The exact track of the coastal low could have a significant impact on high temperatures as it will dictate how far inland the warm sector gets, if at all. A wedge of high pressure betwixt will serve as a surface to be overrun by warm advection. The resulting isentropic upglide will yield ample rainfall totals area-wide. Tuesday night the coastal low deepens off the Delmarva and the inland low fills in. This will allow for a good southward surge of dry air into the region. Cold advection is delayed however by upstream troughiness over the nation`s midsection. This next system will drive a mostly moisture-challenged Arctic front through the area Thursday night. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/... As OF 00z...Very good confidence VFR will persist through Sun 18z. Winds will be N-NE tonight aob 5kt, then become NE 5-10 kts, highest at the coastal terminals, a few hours after sunrise for the remainder of the day. Stratiform light rain initially moves in from the west and affects KFLO/KLBT mid-late morning. Rain then spreads NE across the remaining terminals during the afternoon. Sun afternoon there is good confidence of MVFR cigs developing generally from S-N as the rain falls into a cool wedge of high pressure near the surface. Best confidence of MVFR Sun afternoon will be SC terminals. Pretty good confidence vsbys will remain VFR as rain remains light. Extended Outlook...IFR/rain likely Sunday evening through midday Mon, with VFR developing Monday afternoon. IFR/rain likely Tues. MVFR developing Wed. VFR Thur. && .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 900 PM Saturday...High pressure centered across the Ohio Valley will move eastward into the central Appalachians by early Saturday morning. This should maintain north-northeasterly wind across the coastal waters at 10-15 knots, strongest late tonight. Seas are generally 1-2 feet inside 10 miles from shore, 2-3 feet from 10-20 miles from shore. Little change is anticipated through the night. SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... As of 300 PM Saturday...A complex weather situation will develop Sunday into Monday. High pressure across the Mid-Atlantic states Sunday morning will weaken as a wave of low pressure along the Gulf Coast helps sharpen a coastal trough along the Carolina Coast. This trough is expected to move onshore as a warm front Sunday night, then back offshore before daybreak Monday as the low pressure area moves up the boundary and to our east. Although the strongest winds associated with this first wave should remain offshore, winds could still reach 20 knots late Sunday afternoon into Sunday night over the coastal waters, accompanied by seas building to 4-6 feet within 20 miles of shore. The front will sink a couple hundred miles to our south Monday, but Monday night a second wave of low pressure should begin to take shape to our west. This will again tug on the front, causing the boundary to approach to within 20 miles of the coast by early Tuesday morning. Winds may increase to 25 knots Monday night with seas eclipsing 6 feet. Model confidence in this scenario is building, although the precise location of the coastal front is not yet known. LONG TERM /TUESDAY THROUGH THURSDAY/... As OF 3 PM Saturday...The position of a coastal front and flat wave of low pressure on Tuesday is not yet certain. The fairly brisk winds on the warm side of this boundary will likely yield advisory- worthy seas. As this low moves off the the northeast the area will see westerly winds, pushing the larger seas further offshore. Backing winds Wednesday night into Thursday will herald the approach of the next front. This boundary will blast across the waters Thursday night, possibly ramping up a return of advisory late in the period or just beyond. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...MBB NEAR TERM...TRA/31 SHORT TERM...TRA LONG TERM...MBB AVIATION...MRR is the U.S. government's official web portal to all federal, state and local government web resources and services.