Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 191419 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 919 AM EST Sun Nov 19 2017 .SYNOPSIS... A strong cold front will move offshore early this morning, ending the risk for showers and bringing very dry and much cooler temperatures on brisk northwest winds. There is the potential for a rather widespread frost away from the immediate coast Monday night with some freezing temperatures possible inland. A coastal trough and approaching cold front may bring some showers late Tuesday and Tuesday night. Low pressure is expected to develop in the eastern Gulf of Mexico mid week and may bring unsettled weather to the eastern Carolinas Thursday and Friday as it moves northeast. High pressure early next weekend will be followed by the passage of a cold front next Sunday. && .NEAR TERM /THROUGH TONIGHT/...
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As of 920 AM Sunday...The cold front is just now moving offshore with all of the showers with it. Clearing line is just in its wake. I did remove all pops which were essentially coming to an end anyway. Otherwise no changes. Previous discussion follows: A strong cold front had barreled through LBT and BBP and will move across EYF and FLO in the 7 o`clock hour before heading offshore between 9 and 10 am. Showers were racing NE ahead of the front and had already ended W of I-95. The remaining light showers will end with frontal passage with winds turning sharply NW. Brisk NW winds and strong cold and dry advection will be the rule behind the front. Cold front rapidly approaching from the west is accompanied by a line of showers, currently approaching the western edge of the CWA. What was once an impressive, albeit low-topped, squall line, has diminished into a broken area of showers. Some of this is due to waning instability, but have also noted a separation between convection the best baroclinicity/fgen forcing, both of which will continue to occur and lead to even further weakening of the convection through daybreak. Timing of the FROPA is well matched by guidance, and expect the front and all showers to be offshore around 9am. While a few locations may receive a brief gusty shower with heavy rainfall, most areas will see just very light showers and total qpf only a few hundredths of an inch. Strong winds ahead of the front, noted on LTX VWP of 40 kt at 1kft, will continue strong gradient winds gusting to 30 mph through FROPA however, veering to the NW behind the front. Once the front crosses offshore, rapid cool and dry advection will occur on gusty NW winds. This will create rapid erosion of the cloud cover and cooling of low-level thermal fields through the day. This will have the two pronged effect of leading to a sunny day, but with temps struggling to warm despite the sunshine. In fact, highs today are likely occurring right now, and although some diurnal warming is forecast, do not expect temps to climb back to current values, and instead afternoon-highs will be in the low to mid 60s. Large area of high pressure will build eastward today and tonight becoming positioned across the western Carolinas tonight. This weakening of the gradient will allow north winds to relax, remaining just a few kts above calm tonight. Cold advection rarely fully decouples at night, so have left a few mph of wind through Monday morning. This will prevent ideal radiational cooling, although a dry column, cool 850mb temps, and light north winds will still permit temps to crash into the low to mid 30s, but no freezing temperatures are currently forecast. Soundings are quite dry at the surface and winds will remain a few mph above calm, but have still introduced patchy frost all zones away from the coast, except Robeson, Bladen, and Inland Pender where the growing season has ended for 2017.
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&& .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... As of 300 AM Sunday...High pressure will be overhead Mon and the atmospheric column will be exceedingly dry with precipitable water values less than two tenths of an inch. Expect bright sunshine and very light winds Mon. 850 mb temps will be increasing Mon, but after such a chilly start, the environment should only support highs in the mid and upper 50s. Dewpoints will be in the 20s for most of the day and this will result in minimum relative humidity values as low as 25 to 30 percent Mon afternoon. The high will move offshore Mon night and Tue and an offshore coastal trough is expected to develop. This trough should then migrate W and may get rather close to the coast Tue night before weak low pressure develops offshore of the Southeast Coast and lifts NE. This weak offshore low will be lifting N of our latitude Wed morning. At the surface, Canadian high pressure will build SE and its expansive center should reach the Mississippi Valley by the end of the period. However, aloft, a very deep trough will be carving out which will lead to the development of low pressure in the eastern Gulf of Mexico later in the week. The forecast gets a little murky later Tue and Tue night and it is unclear how much precipitation will be realized across the Forecast Area. Confidence is a little higher that coastal communities would be most impacted by scattered showers given their proximity to the aforementioned coastal trough. The GFS, and to a lesser extent, the Euro model, are showing several weak perturbations embedded in deep SW flow lifting across the area. These weak features may be able to generate showers further inland as well. Also, as moisture is tapped from the Gulf of Mexico, we will see precipitable water values climb to just over 1 inch Tue night. Thus although confidence is lower than it normally is for this portion of the forecast, will include chance POPs throughout, but favor the coast. We are expecting clouds to fill in, possibly as early as overnight Mon in the form of higher clouds, but more likely during the day Tue when thicker clouds should arrive, with skies becoming mostly cloudy by/during Tue night. Cloud development as early as overnight Mon could impact low temps. At this time, we are forecasting lower to mid 30s across inland areas with upper 30s to near 40 at the coast. This may lead to a frosty night across many areas away from the immediate coast with some locations dropping to freezing inland. Daytime highs in the 60s are expected during this period with lows Tue night in the upper 40s to lower 50s with perhaps some mid 40s well inland. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... As of 300 PM Saturday...A couple of short wave troughs in the southern stream will have some impact on area weather in much of the extended period though confidence is currently low in exactly what those impacts will be due to model divergence. The first upper trough may bring a few showers into Wed with a cold front moving offshore by/during Wed morning. After this fropa, the second upper trough could spawn low development along the front offshore and bring rain to the area Thu into Fri. For now, the forecast reflects slight chance pops Wed and for Wed night into Fri. Temperatures will be near seasonal normals Wed before falling back into the mid to upper 50s for Thu and Fri. Slightly warmer temperatures are expected Sat with highs in the upper 50s to lower 60s. SYNOPSIS...Mins will see a similar trend falling from the mid to upper 40s Tue night to the mid 30s to around 40 Thu night before rebounding to the 40s by Sat night. && .AVIATION /14Z SUNDAY THROUGH THURSDAY/... As of 12Z...The surface cold front will be moving through LBT very close to 12Z, FLO-CRE-MYR around 13Z, and ILM by 14Z. Southwest winds will shift to the west-northwest behind the front. The strong, gusty winds of the past 12 hours are mainly confined to the pre-frontal environment, and behind the front we anticipate gusts no higher than about 20 knots this morning, dying away between 17-19Z as the pressure gradient weakens. Scattered showers along and ahead of the front could be accompanied by ceilings as low as 2,000 feet AGL, however drier air building should erode these lower clouds between 13-15Z. Winds will weaken further tonight and become northerly with VFR conditions expected. Extended Outlook...VFR conditions are expected Sunday through Tuesday morning. Possible MVFR in low clouds and rain Tuesday night through Thursday. && .MARINE...
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NEAR TERM /THROUGH TONIGHT/... As of 920 AM Sunday...No changes to the coastal waters forecast this morning. Previous discussion follows: Cold front approaching from the west will cross the waters this morning and exit the area late this afternoon. This front is creating a pinched gradient locally, and winds across the waters are presently from the SW at 20-25 kt with higher gusts. These winds will persist through FROPA this morning, and then shift rapidly to the NW while remaining at elevated speeds. Along with the wind shift, scattered showers with isolated higher and erratic winds are also likely through late morning. Although winds will begin to ease this aftn as high pressure builds in from the west, strong cool advection will maintain gusty winds through the period, falling only to 15-20 kt from the north late tonight. The ongoing SCA will remain unchanged, and is in effect through 6pm for 20-25 kt of wind (SW early, NW late) and seas 5-8 ft. As the winds shift to the offshore direction, wave heights will fall to 4-5 ft this evening, and 3-5 ft tonight, but a SCEC may be needed once conditions fall below SCA thresholds. SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... As of 300 AM Sunday...High pressure will be overhead Mon. As the high shifts offshore Mon night and Tue, a developing offshore coastal trough will develop and migrate toward the coast. Current thinking is this trough may move into the coastal waters later Tue before shifting back offshore Tue night. In fact, the models are showing a weak offshore low developing on this trough late Tue night which will lift N of our latitude Wed morning. The strongest winds this period will be Mon morning, up to around 15 kt from the N. The wind direction will veer to NE Mon afternoon with speeds decreasing to less than 10 kt late. Wind speeds Mon night will be 10 kt or less, veering from E to ESE. light and generally easterly. The wind direction Tue will be SE at speeds of near 10 kt. The wind direction will back to the N later Tue night, increasing to 10 to 15 kt by Wed morning. Seas will trend lower into Tue, from 3 to 4 ft early Mon to 2 ft or less later Mon afternoon through Tue morning. Seas should then tick about a foot higher Tue afternoon and then back to 3 to 4 ft Tue night. LONG TERM /WEDNESDAY THROUGH THURSDAY/... As of 300 PM Saturday...A coastal trough should retreat back offshore by Wed morning as high pressure advances across the Ohio Valley and shifts our winds to a more north to northeast direction. Light winds and slight seas are expected until Wed night or Thu when NE winds of 15 to 20 kt could build seas to 4 to 5 ft with 6 footers possible at 20 NM.
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&& .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...Small Craft Advisory until 6 PM EST this evening for AMZ250- 252-254-256. && $$ SYNOPSIS... NEAR TERM...RJD/JDW/SHK SHORT TERM...RJD LONG TERM...RAN AVIATION...TRA MARINE...

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