Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 171727 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 128 PM EDT Sat Mar 17 2018 .SYNOPSIS... A dry cold front draped over South Carolina today will return north as a warm front this morning and back south as a cold front tonight, wavering across the Carolinas Sunday through Monday. A strong area of low pressure is expected to develop along this front and deepen as it moves east over the Carolinas late Monday into Monday night, bringing a good chance for showers and thunderstorms. A secondary area of low pressure will develop over the Southeast moving up across the off shore waters of the Carolinas through mid week as much colder air funnels in from the north. && .NEAR TERM /THROUGH TONIGHT/... As of 1000 AM SATURDAY...Winds have begun to veer around to the SW as front to the south begins to move back north as a warm front. This will bring warm and moist air back over the local area through this afternoon. An area of showers was just reaching into Darlington and Marlboro and should diminish as it heads east towards the coast this aftn. The main area of pcp will remain over SC as a shortwave moves across the mainly zonal flow to the south, but clouds will increase and stream across the local forecast area through this afternoon. Sounding profiles and time heights show a decent layer of moisture between 4k and 14k ft this afternoon, but diminishing through into early this evening. Therefore expect fewer clouds at the end of the day. As winds come around to the SW, they will increase and become gusty. Temps up near 55 to 60 late this morning will be hampered by clouds and some showers, but WAA should drive temps up near 70 along the northern tier of counties (Robeson, Bladen, and Pender) and mid 70s along the southern tier (Georgetown and Williamsburg). The models are indicating this boundary will lift well north of the area by this afternoon, but a low develops along the front as a potent shortwave drives the boundary back south through Sunday morning. The best chc of pcp tonight will be over NC where better upper level support exists, but a low chc will exist along the actual front as it drops south into early Sun morning. Lows overnight will fall into the upper 40s to the mid 50s to the south. && .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... As of 330 AM Saturday...Somewhat of a noisy wx pattern of features aloft and at the sfc across the U.S. during this short term period of Sunday and Monday. What`s interesting is the models are somewhat similar with one another with this noisy pattern. The strength and positioning of these features are what`s different amongst the models. For Sunday, a mid-level s/w trof will track ESE across the FA and off the coast. It will help drive a sfc cold front across and south of the ILM CWA by late Sun afternoon b4 temporarily stalling. Very limited moisture thru the atm column Sun especially with a WNW downslope trajectory in the wind fields aloft which generally scours moisture out. In essence, could see widely scattered showers early Sun morning, otherwise looking at an overall dry Sun with variable amounts of clouds. Temps will run 5 to 10 degrees below normal if this front is able to clean push across and south of the FA followed by some decent CAA. For Mon thru Mon night, a couple mid-level s/w trofs with Pacific Ocean and Rocky Mountain source regions tapped, are both progged to push eastward and off the SE U.S. Coast. The 1st will occur during Mon whereby it is able to lift the stalled front northward as a warm front, taking it across the ILM CWA late Mon aftn into Mon night. Here, models are having difficulty with the intensification and location of this deepening sfc low. Models should push closer to a uniform decision within the next 2 model runs. At the tail end of this period, some decent CAA is progged to push across the FA as the deepening sfc low drives off the VA Capes. Moisture will likely be thinned out enough and thus have kept any frozen or freezing pcpn out of the fcst. Will still need to monitor partial thickness schemes as next week approaches. && .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 300 PM Friday...Both the GFS and ECMWF develop another cold and deep trough across the eastern U.S. by the end of next week. The particulars of how we get that trough here are different enough to produce sensible weather differences across the Carolinas Monday through Tuesday. A well-defined shortwave will move east across the Ozarks Tuesday. The GFS shows enough ridging off the East Coast to deflect this feature into Indiana/Ohio Tuesday, while the flatter flow shown on the ECMWF allows the shortwave to move into Virginia. Surface high pressure off the East Coast should be lifting a warm front northward along the South Carolina coast. On the ECMWF, the shortwave is close enough geographically to the front to induce surface low pressure to develop along the front. This scenario would lead to better rain chances here on Monday, plus cooler temperatures with a slower northward progression of the front. Strong upper level northwesterly winds across the Rockies and Plains will carve out an increasingly deep trough across the lower Mississippi Valley Monday night into Tuesday. Surface low pressure should intensify across the southern Appalachians in response to this deepening trough, and the warm front should lift northward through North Carolina allowing us one full day in the warm sector Tuesday. Highs should reach well into the 70s Tuesday with breezy SW winds, along with waves of showers and thunderstorms possible. SPC`s day 4 (Monday) severe weather outlook includes a risk area across GA/TN/AL, and we`ll monitor for the potential for strong storms here as this system propagates into the Carolinas Monday night into Tuesday. Tuesday night the strong surface low inland should move eastward and off the Virginia coast. The trailing cold front will move through our area with colder air building in on northwesterly winds. Cold air aloft with the trough won`t allow for quick clearing, and it`s possible we`ll maintain a cloudy/showery pattern through Wednesday, along with much chillier temperatures. Once the upper trough clears offshore Thursday we should dry out, but may also have to deal (yet again) with potential freezing temperatures as the surface high builds in from the west. For now I`ve forecast lows as cold as the mid 30s across much of our area for Thursday night, but with light nighttime winds it`s quite likely there will be some areas below 32 degrees given this pattern. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... As of 17Z...The front is expected to wave northward today with increasing southwest flow. Some precip will try to slide into the area this, but timing and amounts are quite uncertain. Likewise, ceilings are likely to lower, again with uncertainty with respect to timing and height. The models are hinting at sea fog/stratus for the Myrtles but will reevaluate with next set of model runs. Sunday, front drops south again with north winds returning and predominately IFR conditions. Extended outlook...Periods of MVFR Sunday through Wednesday. && .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 1000 AM Saturday...Front to the south has begun its migration north again. This will shift winds around from the E-SE to the SW through early this afternoon. As the boundary shifts northward the winds will become southwest at 10 to 20 knots and the seas of 3 to 4 feet will increase to 3 to 5 feet. A small craft exercise caution may be needed by this evening evening and a Small Craft Advisory may be needed late tonight. SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... As of 330 AM Saturday...Of the 2 days, Sunday will be the better of the 2 for venturing into the local Atlantic waters. Sun starts off with a CFP from north to south b4 finally stalling near the mouth of the Savannah River Sun evening. Weak high pressure, dry conditions, and onshore flow in the wake of the CFP on tap for Sun and Sun evening. Models quickly swing for the worst conditions of the 2 day short term period as the stalled front returns north as a warm front. And, a sfc low on the front across the lower mid-section of the U.S. , is progged to catapult itself to the Eastern Carolinas by Late Mon night/ Tue Morning. It does intensify to sub 1000mb and further tightens the sfc pg across the local waters. Looking at wind speeds likely surpassing SCA thresholds and will have to monitor for possible Gale Conditions by Tue. Significant seas will be at a temporary lull Sun with mainly 3 to 5 second period NE-E wind waves dominating. For Mon into Tue, wind waves will again dominate in the 4 to 7 second period range, but their size will surpass SCEC and even SCA thresholds. If Gales come to be, will have to re-calculate the sig, seas. As for pcpn, looking at liquid RW- with isolated thunder possible aided by mid-level s/w trof energy as well in conjunction with sfc features. LONG TERM /TUESDAY THROUGH WEDNESDAY/... As of 300 PM Friday...It will be a stormy start to next week with a couple areas of low pressure expected to affect the weather across the Carolinas. The first low is expected to develop along a warm front moving north along the South Carolina coast late Monday. This low will slip offshore Monday night. A second much stronger area of low pressure is expected to develop inland Tuesday, drawing the warm front north of our area and allowing breezy southwesterly winds to develop. As this low moves offshore Tuesday night it will push the front back through the area as a cold front, with colder northwesterly winds expected to develop for Wednesday. Given this pattern, there is increasing likelihood we`ll need a Small Craft Advisory for Tuesday and Tuesday night for winds and seas. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ NEAR TERM...RGZ/DRH SHORT TERM...DCH LONG TERM...TRA AVIATION...DL is the U.S. government's official web portal to all federal, state and local government web resources and services.