Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 290709 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 309 AM EDT Sat Jul 29 2017 .SYNOPSIS... A cold front will bring another chance of showers and thunderstorms to the area before moving offshore this afternoon. High pressure will build into the area Sunday through much of next week. && .NEAR TERM /THROUGH TONIGHT/... As of 3 AM Saturday...Water vapor imagery this morning shows a potent shortwave diving into the southern Appalachians with deep moisture residing to its south. The attendant cold front is now in western North Carolina then draped east to west across the Mississippi Valley. Guidance, both Cam`s and global, continue to insist on development of showers with embedded thunder this morning across the area via a good area of upper level divergence. This "seems" to be occurring at the moment with some development and cooling cloud tops just to our west. However the guidance has been too robust with the convection at least for our area throughout this event, or non event I should say. Long story short, I have walked back pops somewhat from previous values with the highest numbers still centered in and around 12 UTC. The severe risk looks minimal citing the current stable conditions and anticipated cloud cover later this morning. The front and its associated dry air mass will make steady progress through the area this afternoon and evening with all areas being dry by later this evening. Regarding temperatures, leaned heavily toward the cooler MAV numbers for daytime highs and overnight lows Sunday. && .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... As of 3 PM Friday...Cold front will be pushing offshore as the period begins with any lingering convection likely quickly winding down. Forecast soundings show a large amount of mid level dry air spreading over the area in the wake of the cold front. Precipitable water values will have dropped almost an inch across inland areas by Sat evening with coastal sites dropping a few hours later. Cold front pushes off the coast overnight as weak shortwave moves through the 5h trough. A much stronger shortwave drops in from the northwest on Sun and the 5h trough axis moves into the eastern Carolinas. Wave rotates through around 18Z and will be accompanied by an increase in mid level moisture. Anticipate at least some diurnally driven showers and thunderstorms with this feature. Best chances will be across North Carolina counties where mid level moisture is highest and forcing is strongest. Loss of heating and exit of shortwave will help bring a quick end to any convection Sun evening. The biggest factor however will be the return of mid level dry air with pwats dropping under 1 inch. Cooler and drier air mass building in for the start of the week will drop temps below climo with lows in the low to mid 60s and highs in the low to mid 80s. && .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 3 PM Friday...Unseasonably cool Canadian high pressure will start next week with temperatures and absolute humidity below normal for the season, debuting an early but brief offering of an early fall feel across the Carolinas. Cool air advection will linger into Monday as interaction of the high and deepening low pressure offshore tighten the gradient of pressure, sending a gusty N-NE wind flow over the area Monday morning. As the high settles over the region into mid-week and upper troughing lifts north, maximum temperatures will begin to approach normal values, with minimums remaining relatively cool due to low dewpoints and mainly clear nights. A low chance of rain this period, at least until late next week as upstream troughing deepens and draws moisture into the area. && .AVIATION /07Z SATURDAY THROUGH WEDNESDAY/... As of 06Z...Expect mostly VFR conditions through the period. Models have been overestimating the rainfall coverage throughout this event. There is one more period of possible MVFR conditions early this morning as an upper level area of divergence moves across acting on a front and ample moisture in the column. The guidance has been more or less consistent with this feature as well. VFR conditions should develop late this morning and through the afternoon hours (if the MVFR materializes) as dry air moves in. Extended Outlook...VFR expected Sunday thru Tuesday with Sunday possibly seeing brief MVFR from showers and/or ceilings during the aftn. && .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 3 AM Saturday...Winds and seas now increasing across the coastal waters with 41013 near 20 knots sustained with seas nearing five feet. This trend will continue for the next few hours as good low level jetting moves slowly across the region. Expect winds from the southwest at just over twenty knots. Seas should reach a maximum of 5-7 feet. Its probably not the strongest Small Craft Advisory we have seen with some areas barley (if at all) reaching criteria but will maintain the headline as is. The cold front associated with the stronger low level winds will move across the waters late this afternoon and evening with winds acquiring a northerly component across all waters. SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/... As of 3 PM Friday...Southwest flow at the start of the period will be short lived as the front moves off the coast and then east of the waters Sat evening. High pressure over the Upper Midwest Sat will expand southeast Sat night, commencing a period of north to northeast flow across the waters that will continue through Sun night. Speeds Sat night may briefly touch 20 kt before dropping closer to 15 kt on Sun. A secondary surge of colder air Sun night will pick speeds back up to near 20 kt Sun night. Seas will be at their peak at the start of the period, possibly requiring a SCA for the first few hours of Sat evening. Seas will drop to 3 to 5 ft Sat night and remain 3 to 5 ft for much of the period. LONG TERM /MONDAY THROUGH WEDNESDAY/... As of 3 PM Friday...A rough start on the waters early Monday as N-NE winds rip at 15-20 KT and gusty, and a Small Craft Advisory or Caution headline may be in effect Monday morning. After this however a trend in improvement is in the marine cards, as the interaction of low pressure offshore and Canadian high pressure inland weakens late Monday through Wednesday. The position of the high center nearby but north of the waters will allow an E flow TUE/WED, becoming SE during the afternoons. No significant coverage of storms this period. Seas 4-5 feet early Monday will settle to around 3 feet by early Tuesday and hold. NE swell of 2-3 feet every 8 seconds is expected TUE into WED. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...Small Craft Advisory until 6 PM EDT this evening for AMZ250- 252-254-256. && $$ SYNOPSIS...SHK NEAR TERM...SHK SHORT TERM...III LONG TERM...MJC AVIATION...SHK

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