Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 221737 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 137 PM EDT Thu Jun 22 2017 .SYNOPSIS... Bermuda High pressure will build westward over the Eastern Carolinas through today as Tropical Storm Cindy moves up from the western Gulf coast. The remnants of Tropical Storm Cindy should reach the southern Appalachians Friday night with its associated moisture increasing the risk for showers and thunderstorms through Saturday. A cold front will reach the area but may remain stalled in close proximity Sunday and Monday. Dry High pressure will build in through the middle of next week. && .NEAR TERM /THROUGH TONIGHT/... As of 915 AM Thursday...Analysis of morning sounding data and latest high-res guidance confirms earlier forecast reasoning. High P/W values today at around 2 inches and a moderately unstable airmass will make for isolated to widely scattered convection, mainly this afternoon. Triggers will be few and far between, with the afternoon sea-breeze circulation being the primary and initial one. Extensive cloud cover will limit highs to the upper 80s most places. Previous discussion follows: This will be the last day of the moisture feed from Tropical Storm Cindy as the storm moves on shore over the TX/LA border. Some mid level drying behind trough aloft produced some breaks in the clouds overnight but moisture profiles continue to show moisture just above h70 which was maintaining mostly cloudy skies over the region. Other shallow moisture will produce some low clouds but these should lift into strato cu through the morning. Any nocturnal showers will be steered off to the east and should remain mainly off shore overnight. Atlantic ridge will build back west over the Eastern Carolinas through today into tonight, but some shortwave energy riding around the western periphery of the ridge will move up from the S-SW over the Carolinas. An area of associated clouds and pcp was visible on the Satellite/Radar and although this will mainly remain west of the the local forecast area, there will be some energy riding over the Eastern Carolinas this aftn. Overall the moisture will increase through the mid levels again through today from convection upstream, but also expect some convergence along western periphery of ridge as it builds back in and minor convection focused along sea breeze boundary. Therefore expect a decent amount of clouds once again today, but with a warm start to the day, some breaks in the clouds and westerly downslope flow, temps will reach into the mid 80s most places. The HRRR shows mainly iso to sct showers developing especially along sea breeze in SC. This is where I kept the highest pops in the scattered range. Pcp water values remain up near 2 inches, but a lot of the moisture will remain above h70 with mainly clouds around the forecast area. By tonight any shortwave energy will move north with ridge building over the Carolinas leading to some subsidence and drying. Although expect some mid level clouds to hang on and most of the deep layer drying to occur heading into Fri. Overnight lows will be the mid 70s once again. May see some stratus around again, but will keep pcp out of forecast. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... As of 300 AM Thursday...The 500 mb ridge near the Florida east coast for the past few days will get displaced eastward late this week as the remnants of Tropical Storm Cindy move across Virginia Saturday morning, followed by a pair of shortwave troughs in the Great Lakes which drop 500 mb heights even along the Southeast coast. With the deep flow of Gulf moisture cut off by Cindy`s northward movement out of the Gulf, drier air is expected to advect overhead at and above the 900 mb level Friday. Precipitable water values around 2 inches today should fall to 1.6 to 1.7 inches by Friday afternoon, with forecast soundings showing the tell-tale bump of a weak subsidence inversion from the nearby upper level ridge. There will still be enough surface moisture present Friday for CAPE values near 2000 J/kg, and a slight chance of thunderstorms will remain in the forecast. The remnant circulation of Tropical Storm Cindy will move eastward through Virginia Saturday morning, veering our deep layer wind direction more westerly with time. A pinned seabreeze boundary plus natural differential heating boundaries associated with soil type changes in the Sandhills should be enough to fire scattered showers and storms. Storm motion should be west to east at a rapid 25 mph. The better chance of rainfall might hold off until Saturday night as the surface cold front trailing behind Cindy`s remnants finally dips down into the Carolinas. It`s interesting to note that over the past 20 days there have been some consistent MOS biases evident with high temperatures across the area. Most notably, both GFS and NAM MOS have been 2-3 degrees too warm at Florence, SC, with a 1 to 1.5 degree warm bias also noted at Lumberton, Whiteville, and Myrtle Beach (MYR). Recent rainfall amounts have not been large enough to produce cool/wet soil anomalies, so I`m not sure what the reason is for this clear bias. However, my forecast highs Friday and Saturday remain on the low side of MOS at these sites. && .LONG TERM /SUNDAY THROUGH THURSDAY/... As of 300 PM Wednesday...Potentially very unsettled through the period but lots of uncertainty exists even in the first part of the extended. A cold front should be just along or off the coast by early Sunday. The caveat to this is that while the front tries to push east, the mid- level pattern features an amplification of the ridge across the east, thus slowing and stalling the front. Where this front stalls will be key to the Sun/Mon forecast. The GFS stalls this front along the coast with continued showers and storms due to deep SW flow and overrunning, and potentially secondary low development. The ECM/CMC push the front far enough offshore to create dry weather the latter half of the wknd. Climatologically the stalled boundary makes sense, and is supported by WPC progs, so will maintain the inherited unsettled forecast into early next week with temps cooling to below climo after a very warm Saturday. Anomalously deep longwave trough then digs into the east clearing the front and bringing much cooler temperatures to the region. 850mb temps may drop towards 10C by the middle of next week, which is below the 10th percentile for late June, suggesting highs and lows several degrees below climo along with a much drier and refreshing airmass. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/...
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As of 18Z...Primary aviation concern will be scattered TSRA/SHRA with a focus on the first few hours this afternoon. Have added the appropriate 3 hour TEMPO groups for all terminals to cover this possibility as confidence is good. Convection has already fired off along the coast with some lesser activity inland. Overnight will be somewhat dryer. Some guidance indicates a sub- 1kft stratus layer in the early morning hours, but confidence is low. Extended Outlook...MVFR ceilings/vsbys Saturday as tropical moisture associated with Cindy remnants traverse the region. Patchy fog and low ceilings possible 08z-13z Friday. More MVFR/IFR conditions possible in SHRA/TSRA with passage of cold front late Saturday into early Sunday.
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&& .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 915 AM Thursday...Latest obs show light southerly winds with seas of 2 to 3 ft. Forecast on track with no changes needed. Previous discussion follows: Benign marine conditions will continue through today as high pressure builds back westward over the waters. A more westerly wind this morning behind low level trough/remnant sfc boundary will come back around to the S-SW as Bermuda High builds westward. Wind speeds generally 10 kt or less will increase by tonight into early tomorrow as gradient tightens between Bermuda High and Cindy moving up from the Gulf. Therefore seas 2 to 3 ft through today will increase up to 3 to 4 ft as winds increase up to to 10 to 15 kts through tonight. SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... As of 300 AM Thursday...Bermuda high pressure anchored well off the Carolina coast will struggle to maintain its grip on our weather as a cold front and the remnants of Tropical Storm Cindy approach from the west. Cindy`s low should link up with the cold front across Arkansas and western Tennessee Friday, accelerating eastward across Virginia Saturday morning. This will help increase our wind speeds here both Friday and Saturday, with an increasing potential of Small Craft Advisory conditions developing before sunrise Saturday morning. After Cindy`s remnant low exits the Mid-Atlantic coast by Saturday afternoon, the trailing cold front should sweep through the Carolinas late Saturday night, likely not reaching the beaches until Sunday morning around daybreak. LONG TERM /SUNDAY THROUGH MONDAY/... As of 300 PM Wednesday...Cold front will waver in the vicinity Sunday and Monday before finally pushing offshore late in the period. This will create a weaker gradient and wind speeds around 10 kts, with direction varying from S to W at times. After the seas will continue to drop to just 2-3 ft late Sunday and remain at these amplitudes on Monday. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...RGZ NEAR TERM...REK/RGZ SHORT TERM...TRA LONG TERM...JDW AVIATION...REK MARINE...REK/TRA/RGZ is the U.S. government's official web portal to all federal, state and local government web resources and services.