Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 280007 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 807 PM EDT Thu Jul 27 2017 .SYNOPSIS... Thunderstorms will become more numerous Friday night into Saturday ahead of an unseasonably strong cold front, and a few storms could be severe. Drier and cooler air will follow in the wake of this system Sunday through early next week, with a warming trend to normal summer heat later next week. && .NEAR TERM /THROUGH FRIDAY/... As of 8 PM Thursday...An isolated shower now dissipating over Williamsburg County will be the last of today`s paltry precip and will lead to a dry overnight period. Forecast in good shape with no major adjustments anticipated. Previous discussion follows: Beautiful aftn ongoing across much of the area as one last day of calm weather precedes what could be a very active period beginning late on Friday. GOES-16 water vapor imagery shows the very dry air across the area (PWATs on MHX sounding this morning were less than 1.2 inches), but moisture is increasing from the NW and the S, with widespread cirrus likely tonight. This cirrus may create a nice sunset, and will also at least subtly insulate cooling tonight so combine veering winds to the S/SW, mins tonight will drop only into the mid 70s, and am on the warm side of the guidance envelope. Increasing column moisture may also allow for some stratus development tonight, while a LLJ progged up to 20 kts should preclude much in the way of fog. Things begin to get more interesting on Friday as two features of interest may affect the area. The first is a weak low pressure currently off the GA coast. Guidance is insistent that this feature will eject NE on Friday as the upper trough strengthens to the west. While this makes sense from a synoptic perspective, exactly how strong this will be, and how close to the coast it will pass, is still in question. As the trough amplifies slowly, mid-level winds should become westerly which are likely to push the weak wave far enough out to sea to prevent much shower activity along the coast. However, subtle E/SE winds ahead of the wave may advect a few showers inland and have carried SCHC POP, mostly for the Cape Fear counties, but QPF will be minimal. The more significant feature is a pre-frontal trough ahead of a strong cold front which will cross on Saturday. This pre-frontal trough will move into an area which will feature MLCape of 1100-1500 J/kg thanks to highs a degree or two either side of 90, along with PWATs climbing above 2 inches and 0-6 km shear increasing slowly into the evening. This supports increasing convective coverage as well as storm organization, and have introduced LKLY POP for western zones late Friday, with still just CHC along the coast as the dry air takes a long time to erode. SPC has placed the area in a MRGL risk, SLGT for the far northern counties closer to better upper forcing, but feel any severe potential will occur into Friday night /after this period/. && .SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/... As of 3 PM Thursday...Water vapor imagery this afternoon shows plenty of moisture across the Tennessee and Mississippi Valley`s along with a potent shortwave moving into the Great Lakes Region. The latter will enhance a mid level trough across the eastern U.S. through the period and also allow the moisture rich column to move across the area. Forcing for these elements will be the surface cold front, which should move across Saturday, the Piedmont Trough, which should become active Friday evening, and overall mid level height falls. Overall feel there are three "rounds" of convection possible, one Friday evening, one early Saturday morning and finally with the front and afternoon instability Saturday afternoon. We have maintained the good chance to likely values through the period. The highest severe threat is probably going to be late Friday evening from a somewhat organized cluster or two moving in from the west/northwest. SPC has walked back the slight risk for day two somewhat with it just clipping the northern counties. The threat should be more limited Saturday as the frontal forcing will be competing against mid level drying. Only minor changes to the temperature forecast. && .LONG TERM /SUNDAY THROUGH THURSDAY/... As of 3 PM Wednesday...Chief headline this period `early taste of fall` as both T/Td fall below normal for late July Sunday onward, before a warmup to near normal values by Wednesday or Thursday. Daybreak Sunday a seasonably robust cold front will be positioned offshore, while Canadian high pressure centered over the Great Lakes exerts itself SE into the Carolinas. The air mass change will ring of an early fall feel with dewpoints dipping deep into the 60s, erasing any muggy feel to the air. Lingering low level moisture in wake of the front will result in periods of cloudiness on north winds and many areas could struggle to crack 80 degrees Sunday. Low-level drying should bring plenty sunshine Tuesday onward while a warming trend unfolds. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... As of 00Z...Good confidence VFR through the overnight hours for all terminals, followed by gradually lowering cigs after sunrise. Don`t expect MVFR for cigs until around noon as low level moisture advects in ahead of the next cold front. Have VCTS for FLO and LBT tomorrow afternoon as convection moves in from the NW. High-res guidance does hint at coastal showers in the morning, but confidence not high on this scenario as it is a recent development of the model. Extended Outlook...MVFR/IFR flight restrictions are likely in association with thunderstorms later Fri thru early Sat. Some of the storms may be strong to severe. VFR expected Sunday thru Monday. && .MARINE... NEAR TERM /THROUGH FRIDAY/... As of 8 PM Thursday...Latest obs show light southerly winds of only around 5 kts with seas of 2 ft or less. This is in keeping with the ongoing forecast. No changes needed with the latest update. Previous discussion follows: Dissipating cold front will fall apart south of the waters through tonight as high pressure offshore becomes the dominant feature once again. Winds have already veered to the SE across the waters in response to this high, but speeds have been less than 10 kts. Wind direction will continue to veer to the SW tonight with speeds slowly increasing in response to the gradient tightening ahead of an approaching cold front. Winds on Friday will persist from the SW as a wave of low pressure moves nearby, with speeds increasing towards 20 kts late in the day. The ongoing light winds have kept seas limited today, just 1-2 ft, but as the winds ramp up from the SW tonight, and especially on Friday, wave heights will build to 3-4 ft. SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/... As of 3 PM Thursday...Winds will be mostly from the southwest through the period until late when a front moves across the waters. Preceding the front wind speeds will increase at times to 15-20 knots (mainly Saturday morning) with the higher end of a 10-15 knot range most other times. As mentioned earlier expect a wind shift to the north, northwest after midnight Sunday with similar speeds. Significant seas will be mainly 2-4 feet. A couple of five footers may enter the spectrum briefly early Saturday coinciding with the higher wind speeds. LONG TERM /SUNDAY THROUGH TUESDAY/... As of 3 PM Thursday...Atypical N-NE winds Sunday through a good part of Monday in wake of an unseasonably strong cold frontal passage. Wind direction veers to E-SE Monday afternoon/evening and holds from the SE Tuesday. Because of the unusually strong cell of high pressure pushing in from the NNW, gusts to 20 KT will become common Sunday and Sunday night, veering slightly from N to NE, and an `exercise caution` headline could be needed Sunday, with 4-5 foot seas outer waters probable. A few storms early Sunday may be rumbling near the west wall of the Gulf Stream and around Frying Pan Shoals. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...MJC NEAR TERM...JDW SHORT TERM...SHK LONG TERM...MJC AVIATION...REK MARINE...MJC/REK/JDW/SHK

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