Area Forecast Discussion
Issued by NWS Wilmington, NC

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733 FXUS62 KILM 202243 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 643 PM EDT Sat May 20 2017 .SYNOPSIS... Bermuda High Pressure will start to weaken as a cold front approaches from the west. Showers and thunderstorms will begin to increase Sunday ahead of a cold front that will move in from the west on Monday. Showers and thunderstorms will continue through the middle of the week as the front lingers in the region, then a second cold front should into the area Thursday. High pressure will bring a drying trend for the end of the week. && .NEAR TERM /THROUGH SUNDAY/... As of 630 PM Saturday...A typical summertime pattern exists across our corner of the coastal Carolinas this evening. Warm inland temperatures which reached the lower 90s today contrast with a cooler seabreeze which according to surface obs and radar imagery has pushed a good 30 miles inland from the beaches. Across far-eastern North Carolina a backdoor cold front has ignited a large cluster of thunderstorms which has pushed across the southern Pamlico Sound and is approaching the Crystal Coast region from the north. The cold front itself extends northwestward from the convection and has recently pushed through Greenville, Rocky Mount, and Raleigh. Most models (except for the WRF-NMM and WRF-ARW) have a good handle on the 21Z/5 PM EDT position of the front and show the boundary sinking southward overnight to position just south of Myrtle Beach, Marion, and Florence. This forecast update maintains a 20 PoP for showers with the approaching front, mainly across SE North Carolina. A renegade shower that recently developed along the seabreeze boundary in eastern Williamsburg County is probably not indicative of any significant rain chance there as the overall atmosphere is too dry. No significant changes have been made to temperatures, although I have bumped forecast lows up slightly across SE North Carolina where most of the model guidance is indicating sufficient low-level moisture late tonight to generate some low stratus clouds that will impede radiational cooling some. && .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... As of 300 PM Saturday...Stalled front will be lingering just north of the area as the period begins. Expect there will be some waning sea breeze/diurnal convection Sun evening with more robust storms west of the forecast area, along the slowly advancing cold front. Some of the activity associated with the front may spread over western areas late Sun night, however there are a few negating factors. Low level stability and dry air below 12k ft being the biggest. Also the front`s movement is rather slow with low level convergence being weak and strongest forcing aloft is still west of the area at this time. Will carry low chc pop for western areas with slight chance farther east. Front moves into the region Mon, accompanied by deep moisture and forcing. Forecast precipitable water values exceed 2 inches as deep southwest flow spreads abundant moisture over the region Mon afternoon. All traces of mid level ridging will be gone as broad 5h troughing moves over the region. Surface front ends up laying parallel to flow aloft later Mon and the front ends up stalled in the region Mon night. Weak surface wave develops in GA along the front late Mon. This wave lifts northeast Mon night, resulting in an increase in precip chances late in the period. Best rainfall chances will be Mon afternoon when diurnal heating, surface/frontal convergence and support aloft are present. There is some potential for very heavy rain with the deepest convection. Warm cloud layer depth approaches 12k ft and storm motions of 10 to 13 kt suggest there could be some urban rainfall issues if the heaviest, slow moving storms pass over more urbanized areas. High temps on Mon will be near climo given the abundance of cloud cover and the anticipation of widespread rainfall. Lows will run well above climo mostly due to increased low level moisture and cloud cover. && .LONG TERM /TUESDAY THROUGH SATURDAY/... As of 300 PM Saturday...Southwesterly vorticity-laden flow in place on Tuesday while a weak surface boundary drops into the region. Showers and thunderstorms should spread west to east across the area, becoming more numerous than previously anticipated. Low level wind fields are also stronger than previously progged but this may be related to some apparent convective feedback in guidance, especially the GFS. Assuming this is correct the severe weather threat appears minimal. The next batch of shortwave energy crosses on Wednesday, which should also shape up to be an active day of showers and thunderstorms. The previously anticipated minor severe threat is complicated by the GFS pushing the surface front south of the area. Should the area remain in the warm sector as anticipated then storms could approach severe criteria with damaging winds likely the main threat. The main trough axis swings through either Thursday or Thursday night and this should herald the trend towards dry weather with lower humidity and cooler temperatures especially at night. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/... As of 00Z Saturday...A backdoor cold front that has recently moved through New Bern, Greenville, Rocky Mount, and Raleigh North Carolina should move southward overnight, reaching a position just south of Myrtle Beach and Florence by daybreak Sunday. Ahead of the front VFR conditions will continue with light south-southwesterly winds. When the front arrives isolated showers or t-storms could develop in the ILM vicinity late this evening. The bigger impacts to aircraft operations could develop late tonight into Sunday morning as low stratus could develop affecting ILM and LBT. Any stratus should burn off later Sunday morning after sunrise. Extended Outlook...Reduced flight categories will be possible in periodic showers and thunderstorms Sunday afternoon through Monday, and again on Wednesday. && .MARINE... NEAR TERM /THROUGH SUNDAY/... As of 630 PM Saturday...A backdoor cold front just north of Cape Lookout extends northwestward to near Greenville, Rocky Mount, and Raleigh. Models show this front should sink southward late tonight to a position just south of Myrtle Beach. While there may be a brief gusty surge north of Cape Fear when the front arrives, this should die away south of Cape Fear. Until the front gets here, southwest breezes 10-15 knots should continue through the evening hours with seas mainly around 2 feet. SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... As of 300 PM Saturday...Bermuda High will start retreating east as cold front to the west slowly moves east. This will maintain southerly flow through the period, with the front expected to stall along the coast late Mon or Mon night. Increased gradient will lead to a steady increase in south to southwest flow Sun night and Mon. Surface boundary moves into the area late Mon before stalling along or just off the coast. This helps weaken the gradient late in the period with speeds dropping from a solid 15 kt Mon evening to under 10 kt late Mon night. Seas 2 to 3 ft Sun night build to 3 ft Mon and 3 to 4 ft Mon night. LONG TERM /TUESDAY THROUGH THURSDAY/... As of 300 PM Saturday...Cold front slated to approach Tuesday while a large area of high pressure remains off the coast. Previously there was not to be an area of low pressure along the boundary to strengthen the wind fields and this is still likely though some guidance supports otherwise. The absence of the low should stave off advisory level winds/seas until Wednesday as previously anticipated but Tuesday deterioration not impossible at this point. Cold front approaches Thursday veering the flow and perhaps knocking about 5kt off the wind speeds. These two factors will allow for advisory to be dropped though SCEC may be needed. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...MBB NEAR TERM...TRA SHORT TERM...III LONG TERM...MBB AVIATION...TRA is the U.S. government's official web portal to all federal, state and local government web resources and services.