Area Forecast Discussion
Issued by NWS Wilmington, NC

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378 FXUS62 KILM 161128 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 728 AM EDT Wed Aug 16 2017 .SYNOPSIS... Summertime heat and humidity will build and Heat Advisories will likely be required for at least portions of the area through Friday. Showers and thunderstorms will be on the increase during the weekend as a cold front approaches from the north. This front may stall in close proximity early next week. && .NEAR TERM /THROUGH TONIGHT/... As of 300 AM Wednesday...Synoptic conditions will be very similar to Tuesday across the area through the near term period. For the most part the mid level pattern will be westerly with slight ridging building in tonight. At the surface the Piedmont Trough will once again be the main feature. Guidance is fairly consistent on mostly sea breeze convection today. Temperature guidance seems almost identical to Tuesday which means Heat Advisory criteria will be met in places, mainly in South Carolina and along the coast. The lack of longevity precludes an actual headline however. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... As of 300 AM Wednesday...The center of warm high pressure will be positioned across portions of FL and the Southeast states Thu into Fri. As a longwave trough progressively digs across the eastern third of the nation late Fri and Fri night, it will help drive a surface cold front to the SE. This front should reach central portions of central North Carolina and the upstate of South Carolina by Sat morning. 850 mb temps will be 19-21 deg C during this period. This will allow high temps to rise into the lower to mid 90s. These temps are fairly typical for the later half of Aug. However, dewpoints will be in the mid and upper 70s with perhaps an 80 deg dewpoint for portions of the coast. This will make it uncomfortable to be outdoors as afternoon heat index values will be near or above 105 and as high as 109 deg both Thu and Fri. These conditions will likely require a Heat Advisory. The nights will be in the muggy mid and upper 70s. As for the risk for convection, it will be hit or miss Thu with the seabreeze being the primary impetus for convection along the coast and the Piedmont Trough for areas further inland. Morning and early afternoon convection that does develop along the coast should tend to migrate inland and away from the beaches as the afternoon progresses. Convection should tend to wane and come to an end with loss of heating Thu night. Fri should tend to be more active convectively later in the day and Fri night as a cold front gains proximity. Will cap POPS in the chance category with a likelihood for greater thunderstorm coverage on Sat. && .LONG TERM /SATURDAY THROUGH TUESDAY/... As of 300 PM Tuesday...Vertically stacked high pressure offshore will strengthen into Saturday ahead of a shortwave and associated cold front dropping into the OH VLY. The front will drop into the area and then likely stall as the shortwave hangs back, the front becomes flow-parallel, as ridging persists to the east. Convection chances will ramp up significantly Saturday, with still good chances Sunday as the shortwave digs through the Mid-Atlantic and offshore. Temps for the wknd will remain above climo as well. Concern then shifts to Monday, the day of the total solar eclipse. Guidance has backed off on a clean FROPA, and has the front dissipating overhead during Monday. This is much more typical for late August. While this could create more clouds and unsettled conditions for Monday across the area, mid-level flow does become W/NW behind the aforementioned shortwave which brings some drier air into the mid-levels. At this time a fairly typical August day is expected with aftn CU and convection, especially focused along the stalled boundary wherever that may set up. This does not suggest the eclipse will not be visible, but may be temporarily blocked by convection at times. On Tuesday offshore high pressure re-asserts itself, but yet another weak cold front will approach from the NW creating good convection chances with continuing above climo heat and humidity. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... As of 12Z...VFR is forecast through the period. However, isolated to perhaps scattered showers and thunderstorms that do develop along the seabreeze and Piedmont Trough will have the potential to briefly drop conditions to MVFR or lower. However, the risk that a thunderstorm will move directly over a terminal is low and so flight restrictions are not referenced in any of the TAFs. Afternoon and early eve VCTS was confined to the coastal terminals where the probability for thunderstorms is slightly higher than across KFLO and KLBT. Did include sct stratus below 1kft after 09z at the coastal terminals as model profiles are most supportive of some low cloud development here in very weak onshore flow. However, this low status may very well develop toward the tail end of the valid TAF period across the inland terminals as well. Extended Outlook...A brief period of MVFR or lower conditions can not be ruled out in isolated to scattered showers and thunderstorms through Fri. The risk for flight restrictions due to showers and thunderstorms will increase significantly on Sat and Sun. Low stratus and some fog during the overnight and early morning hours may result in flight restrictions as well each day. && .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 300 AM Wednesday...Winds have a mostly westerly component this morning as a weak trough has pushed across the waters. The weak flow will remain in place through the period with more of a southwest flow developing later this morning then south to southeast with the sea breeze influence. Weak high pressure may build in tonight turning the winds to northeast but once again the flow will be very light, ten knots or less. Regarding seas, the influence of Hurricane Gert will wane as seas will be in a range of 2-4 feet dropping to around two feet by Thursday morning. SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... As of 300 AM Wednesday...A trough will wash out by/during Thu morning and the Piedmont Trough and Bermuda High will be in place for the balance of the forecast period. A cold front will approach the waters from the NW Fri night. Initially, the wind direction may be light E or SE with the direction veering to S Thu afternoon and SW Thu night. SW winds will then persist through the end of the period, increasing to 15 to 20 kt Fri afternoon and night. The strengthening winds will allow seas to build from 2 ft Thu and Thu night to 3 ft Fri afternoon and 3 to 4 ft Fri night. LONG TERM /SATURDAY THROUGH SUNDAY/... As of 300 PM Tuesday...A cold front approaching from the NW will sandwich the waters with a pinched gradient as high pressure spins offshore. This will result in SW winds of around 15 kt into Sunday morning. This front will stall and begin to dissipate inland from the waters on Sunday, causing the gradient to relax and wind speeds to fall to around 10 kt while maintaining a SW direction. Initially seas will be 2 to 4 ft, but will increase thanks to an amplifying SW wind wave, becoming 3-5 ft by Saturday night. Conditions should remain just below any cautionary statements. As the winds begin to ease Sunday, seas will follow, with wave heights falling to around 3 ft at the end of the period. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ NEAR TERM...SHK SHORT TERM...RJD LONG TERM...JDW AVIATION...RJD

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