Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 201220 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 820 AM EDT SAT AUG 20 2016 .SYNOPSIS... Showers and thunderstorms are expected through the weekend as an upper trough moves north of the area. Above normal temperatures are expected Sunday with heat index values exceeding 100 degrees. A cold front will cross the Carolinas Sunday night into Monday. Much cooler and drier air will follow this front for much of the upcoming week. && .NEAR TERM /THROUGH TONIGHT/... As of 630 AM Saturday...The Westerlies have dropped into the Carolinas as a trough, currently digging through the Dakotas this morning, moves eastward across the northern United States. The Atlantic ridge has weakened and is now centered near the northern Bahamas at the surface and 500 mb. A stream of deep moisture originating over Texas has been entrained into our westerly flow and will move across the Carolinas today. After 1-2 PM the moderately unstable airmass (CAPE 1500-2000 J/kg) and eroded convective cap should yield scattered showers and t-storms. 700 mb wind speed around 20 knots should push the developing thunderstorms quickly eastward, covering a lot of ground even if a limited number of convective cells develop. Precipitable water values up to 2.25 inches should help feed the potential for heavy rainfall. Forecast PoPs have are 50-70 percent, highest near the coast in the Myrtle Beach-Wilmington-Burgaw corridor between 2-5 PM. This is reduced a bit from the 300 AM forecast package as last night`s storms have developed into an expansive MCS offshore which may induce subsidence over land today, especially if the MCS persists to noon. There is no organized convective risk forecast from SPC, although with such high precipitable water values and the potential for deep convection, a wet microburst cannot be ruled out. Convective activity should diminish quite a bit by sunset as the airmass will have overturned and subsequently stabilizes. A very moist westerly flow aloft will continue, and it`s not impossible for isolated showers and t-storms to linger overnight (elevated instability) along any deeper boundaries left over from daytime activity. && .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... As of 300 AM Saturday...The upper trough will move east across the Great Lakes Sunday and through New England Sunday night. The tail end of the upper disturbance never reaches as far south as the Carolinas, and in fact a careful look at our 500 mb heights show they actually climb a bit through the period as the Atlantic ridge begins to regroup. Surface low pressure moving eastward concurrently with the upper system will push a cold front southward and into the Carolinas Sunday. Models have been bouncing around over the past few days with the anticipated timing of the frontal passage, but the 00z GFS and ECMWF are now targeting Sunday evening as when the front will finally reach the coast. Winds are expected to shift to the north behind the front by midnight Sunday night with drier and cooler air streaming in for Monday and Tuesday. Scattered showers and t-storms may develop Sunday in the warm and humid prefrontal airmass. However once the front pushes through and modified Canadian air begins to stream in, convective chances should plummet Monday. By Monday evening there should be such little moisture present (precip water down to 0.75 inches) that forecast PoPs are below 10 percent. This appears to be the coolest airmass we`ve seen in nearly two months, with lows Monday night and Tuesday night expected to dive into the 60s away from the beaches. && .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 300 AM Saturday...A refreshing break from the heat and humidity is expected for the upcoming week as cool high pressure ridges down the east coast beginning Tuesday. Cold front will be south of the area to start the period, with high pressure becoming centered across the Mid-Atlantic and extending across most of the eastern CONUS. Cool N/NE flow will be reinforced Tuesday night, and although mid-level heights begin to rise quickly, low-level thicknesses remain cool, and the Tue/Wed/Thu timeframe will feature slightly below climo temperatures for the first time in quite a while. It is looking more likely that the streak of consecutive days at Wilmington not dropping below 70 will end on Tuesday, with at least 3 nights next week featuring mins in the 60s, with highs in the mid 80s. Accompanying these cooler temperatures will be some very dry air, PWATS around 1 inch or less, only subtly recovering Friday as the high pressure shifts offshore. The forecast is dry through the period. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
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As of 12Z...Potential for brief MVFR/IFR in any heavy downpours today and again late overnight into the early morning hours due to areas of fog/low cigs. Otherwise expect VFR through the valid TAF period with VCSH/VCTS. Patchy fog and lingering low cigs are creating MVFR at KLBT this morning. Expect these conditions to improve within the next hour or two, allowing for VFR to prevail across the entire forecast area through the rest of this morning. Along with southwest winds increasing to around 10 kts today, anticipate increasing coverage of scattered showers and thunderstorms, which may create brief periods of MVFR/IFR, especially in heavier downpours. Tonight, convection will gradually taper off with winds becoming light for the overnight hours. Latest guidance suggests areas of fog inland, which may create periods of MVFR towards the end of the forecast period. EXTENDED OUTLOOK...Potential for MVFR/IFR due to afternoon showers and thunderstorms and overnight fog/low cigs potential. Otherwise expect VFR.
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&& .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 630 AM Saturday...High pressure located near the northern Bahamas will move very little today. Low pressure moving east across the Dakotas this morning will enter the Great Lakes by this evening. This low will eventually push a cold front into the Carolinas, but for today and tonight a west-southwesterly wind should continue. Overnight thunderstorms have moved into the offshore waters, but a second round of thunderstorms should develop this afternoon and this evening as mid-level winds become quite strong out of the west. Seas are currently 2-3 feet mainly in 4-5 second wind chop. Southwest winds increasing to near 15 knots late tonight may build seas toward a solid 3 feet across open waters late. SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... As of 300 AM Saturday...Surface low pressure will move across the Great Lakes Sunday and into SE Canada Sunday night. This low will push a cold front southward and into the Carolinas. Models have bounced around quite a bit over the past few days with their anticipated timing on the frontal passage. It now appears the front should push out across the coastal waters Sunday evening, with southwesterly winds shifting to the north at 15-18 kt. Behind the front Monday the pressure gradient may be weak enough to still allow the afternoon seabreeze to develop and turn nearshore wind directions onshore. However when the sun goes down Monday Night north-northeasterly surface winds should redevelop. LONG TERM /TUESDAY THROUGH WEDNESDAY/... As of 300 AM Saturday...Cold front will be south of the waters by Tuesday morning, with high pressure expanding down the east coast through mid-week. This creates a long duration of NE winds at 10-15 kts, lasting at least through this extended period. These winds will drive an amplifying wind-wave which will be the dominant wave group, with seas rising from 2-3 ft early Tuesday to 3-4 ft on Wednesday, and would not be surprised if some 5 fters showed up late Wednesday. The exception will be in the typical wave-shadow region SW of Brunswick county in AMZ252/AMZ254 where NE winds get blocked, and seas will remain 1-2 ft. && .CLIMATE... As of 300 AM Saturday...The rain gauge on the North Myrtle Beach ASOS clogged during a thunderstorm on Thursday August 18th. The gauge measured 0.58 inches before the clog occurred. When our technician cleared the blockage Friday morning, an additional 0.30" poured through. This makes the CRE rainfall for August 18th 0.88 inches. (That`s 0.58 + 0.30) The Friday afternoon thunderstorm at CRE only amounted to a trace. Also, the streak of days with low temperatures 70 degrees or warmer in Wilmington is approaching record territory. Counting through midnight Friday August 19th we`re now at 54 days, a streak which began back on June 27th. The all-time record is 56 days set back in 2012. To tie the record our temps will have to stay 70 or warmer all the way through midnight Sunday night, and to break the record we`ll need the same through midnight Monday night. Note: Climate records are kept in local STANDARD time which is actually 1 AM daylight time. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...JDW NEAR TERM...TRA SHORT TERM...TRA LONG TERM...JDW AVIATION...SGL CLIMATE...TRA

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