Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 220932 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 532 AM EDT Sun Apr 22 2018 .SYNOPSIS...
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Canadian high pressure will continue to extend into the Carolinas today as it migrates slowly east off the Mid-Atlantic coast. A slow moving low pressure system will cross the Southeastern U.S. and produce beneficial rains over a 2 day period, Monday thru Tuesday, in the 2 to 4 inch range across the forecast area. Temperatures below normal thru Tuesday will bounce back to near normal for the rest of the work week with the threat for additional rain Thu into Fri from the next low pressure system.
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&& .NEAR TERM /THROUGH TONIGHT/... As of 3 AM Sunday...Surface high just north of the Outer Banks this morning will gradually retreat northeast today into tonight as stacked low slowly drifts from the southern plains states into the Lower Mississippi Valley. Deep dry air remains over the region into tonight with precipitable water not climbing over half an inch until mid afternoon to early evening. Low level onshore flow gradually helps increase boundary layer moisture, but flow aloft remains west- northwest until very late in the period. This prevents any meaningful moisture return until late tonight, when the mid-level pattern starts to change and deep southwest flow develops. Most areas do not see precipitable water exceed one inch until very late in the period. Expect another dry day today with temperatures running a little below climo. High cloud spreads over the area from the southwest during the day, gradually thickening throughout the day. Increasing cloud cover will limit afternoon heating a bit, especially across inland SC. However, temperatures starting out several degrees warmer than yesterday will lead to highs ranging from the upper 60s along the coast to low to mid 70s inland. As the stacked low moves into the Lower Mississippi Valley tonight it helps pull a weak coastal trough onshore. This aids low level moisture return and leads to increasing/lowering cloud cover. Increased east-southeast winds will also help keep temperatures warmer with lows likely to end up a few degrees above climo, mid 50s for most areas. Latest guidance shows 850/700 mb frontogenesis and increasing divergence aloft moving into the forecast area as the period ends. These features are also near the Theta E ridge, something which suggests heavy rain will be poised to move into the forecast area very late or just after the end of the period. Given guidance does tend to start precip a bit early have slowed down arrival of precip late in the period. && .SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
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As of 400 AM Sunday...The time frame extending from the start of this period, 6am Mon, thru Tuesday daylight morning, the local FA will see nearly a continuous shield of light to moderate stratiform type rains. Embedded in this shield of rainfall, will be a few thunderstorms. For the most part, the tstorm activity will occur over the Atlantic waters and given the trajectory of the swath of pcpn moving onshore, the coastal counties will be the 1st in line to experience a few of these storms. As the pcpn moves further inland, the lack of instability will keep tstorms from further developing or in this case, from progressing too far inland before it`s demise. Models indicate an expansive area of strong UVVs across the FA and surroundings for a good 24 to 36 hrs. This a result of synoptic difluence aloft due to the positioning of the upper closed low as it moves from the lower Mississippi Valley Monday morning, to eastern Tennessee late Tue night before finally opening up to a s/w trof by Wed. Model soundings indicate 50+ kt East to Southeast winds pumping in low level Atlantic moisture across the Carolinas. Gulf of Mexico moisture will have already been and continue to be tapped but by this time the main source will be Atlantic moisture. Forecast rainfall amounts during this 2 day period will range from 2 to 4 inches. Isolated higher amounts are possible mainly along the immediate coast due to the onshore movement of any convection before dying out as it pushes further inland into a more stable atm in the low levels. This modest rainfall amounts over a 2 day period will be extremely beneficial to farmers and local growers. Crops, plants, trees and etc, will literally act like sponges and absorb this water. And given the 2 day period of these rains, we do not expect high runoff problems.
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&& .LONG TERM /TUESDAY THROUGH SATURDAY/... As of 300 PM Saturday...A low pressure system will track off to the NE Tues into Wed. The sfc low will track closer to the coastline while the upper low will move northeast from TN toward the Ohio Valley. As this closed upper low lifts north, another shortwave will rotate down toward the Southern Appalachians by Thurs. Overall, this system remains quite complex, but looks like the heavier rain will move north leaving clouds but some drier air wrapping through mid week. The next shortwave should dig down and push a cold front through on Thurs, but does not look like a big rainmaker. Therefore, expect breaks in the clouds and some clearing late Tues into Wed with increased clouds and potential for pcp again Thurs. Another system will follow in this progressive flow by Fri into Sat, although the GFS keeps most of the weather with this system north of our local forecast area, while the ECMWF remains more pessimistic heading into next weekend. Overall a good amount of clouds and and not much QPF expected through the week. Temps have been trending warmer but remaining near normals through much of the period. && .AVIATION /09Z SUNDAY THROUGH THURSDAY/... As of 06Z...Although low level moisture is slowly increasing, do not expect much in the way of fog this morning. Boundary layer moisture remains on the low side for fog and there appears to be just enough in the way of boundary layer mixing to prevent anything more than fleeting patches of fog. Will carry VFR through the valid TAF period. East winds will be light through the overnight before increasing to 10 to 15 kt later this morning and for the afternoon. Clouds gradually increase today, with ceilings starting to lower from southwest to northeast this evening. Extended outlook...Rain Monday and Tuesday could bring periods of MVFR/IFR conditions in low ceilings and visibility. The worst conditions are expected Monday night. Wed/Thu VFR. && .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 3 AM Sunday...Easterly winds will steadily increase through the period, becoming more southeast late tonight. Surface high north of the Outer Banks this morning will gradually retreat northeast today as low pressure moves east toward the southeastern states. Gradient will slowly become more defined and winds will increase from 10 to 15 kt later today to 15 to 20 kt this evening and overnight. Increase in wind speeds combined with onshore flow helps build seas from 2 to 3 ft this morning to 3 to 5 ft by evening. Seas continue building tonight and it is likely seas will reach 6 ft a few hours prior to the end of the period. Thus the previously raised Small Craft Advisory will remain in effect. SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... As of 400 AM Sunday...SCA conditions will start off this short term period as a well tightened sfc pg settles across the local waters. This sfc pg will tighten some more by mid-afternoon Mon and continue thru Tuesday morning except late morning for the waters north of Cape Fear. Various model soundings indicate 50+ kt sustained winds at only 450 ft to 800 ft above the ocean sfc. With East to Southeast winds pushing offshore Gulf Stream waters toward the coast. With 70+ degree SSTS already lurking just offshore, ie. 41013 at 70.0 degrees F, the thinking is enough of this warm water will be in play for those strong winds just off the deck to mix down to the ocean sfc. Thus a Gale Watch has been issued for all waters from Mon afternoon thru late Tuesday morning. Have left a 3 hr buffer on the ending of the Gale Watch due to closed Lows will at times not follow the latest model fcsts. Significant seas will build rather quickly and primarily will be wind wave driven. A pseudo ground swell, 6 to 8 second periods, in time may develop due to a decent fetch with these onshore winds to operate over. LONG TERM /TUESDAY THROUGH THURSDAY/... As of 300 PM Saturday...Complex low pressure system will track NE parallel and near to the Carolina/VA coast Tues into Wed. A strong onshore flow will persist into Tues , but winds will diminish as they shift around from on shore to off shore by Wed on the back end of the low as it lifts off to the northeast. Another system will follow behind this one, dragging a cold through on Thurs. Therefore expect off shore flow to continue through much fo the period. Overall, expect seas to subside through the period from a peak Tues morning, above 10 ft in outer waters. The on shore flow will shift around to the off shore and decrease with seas down below SCA thresholds by Wed morning and continuing to lower to 2 to 4 ft by Thurs morning. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...Gale Watch from Monday afternoon through Tuesday morning for AMZ250-252-254-256. Small Craft Advisory from 5 AM to 3 PM EDT Monday for AMZ250- 252-254-256. && $$ SYNOPSIS...DCH NEAR TERM...III SHORT TERM...DCH LONG TERM...RGZ AVIATION...III MARINE...

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