Area Forecast Discussion
Issued by NWS Wilmington, NC

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883 FXUS62 KILM 171717 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 1217 PM EST Fri Nov 17 2017 .SYNOPSIS... A cooler day today will be followed by a breezy warmup Saturday ahead of a strong cold front. The front may be accompanied by some gusty showers as it sweeps across the area and offshore late Saturday night and early Sunday morning. Much colder and drier air will be ushered in for Sunday and into early next week and we have a reasonable chance of a widespread freeze. Temperatures will moderate Tuesday and Wednesday. Uncertainty increases mid and late next week as another cold front moves into the area and forecast will hinge on the track of developing low pressure in the Gulf of Mexico. && .NEAR TERM /THROUGH TONIGHT/... As of 1100 AM Friday...Cool and dry airmass will remain in place today as Canadian high pressure builds in from the north. The high will migrate south and east through today allowing for the gradient to relax and the gusty northerly winds to weaken and shift to the NE through tonight. The CAA has brought 850 temps a few degrees below yesterdays. This CAA in combination with cool northerly winds and very dry air in place today will make for a much cooler feel to the day than yesterday. Even with bright November sunshine, high temps will remain about 5 degrees below normal with most places remaining in the upper end of 50s to near 60. The center of the high will settle almost directly overhead tonight before shifting off the coast by daybreak Saturday. This will cut out the winds and produce ideal radiational cooling. Once the atmosphere decouples after sunset temps should drop off quite rapidly. The very dry air mass in place will produce a large diurnal swing with temps dropping into the mid to upper 30s most places just inland. Inland Soundings show temps dropping just enough to produce a very shallow saturated layer. There may be just enough very shallow moisture to produce some patchy frost. Places along the coast may see some marine moisture produce some fog or a few lower clouds advecting on shore under subsidence inversion toward morning. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... As of 300 AM Friday...A breezy warmup is in store ahead of a strong cold front which will sweep across the area late Sat night and then offshore around sunrise Sun. Canadian high pressure will then slowly build from the W through Sun night. Wind fields remain impressive with this system. The low-level jet will be on the order of 50 kt overnight Sat, at about 2-2.5 kft and not quite as low to the ground as was indicated 24 hours ago. The environment remains virtually stable during this time with CAPE values barely registering. However, bulk shear values are high and a strong upper level jet favorably, although briefly aligns. Moisture return is also brief and shallow and we are not expecting much in the way of rainfall, a tenth of an inch or less on average still looks in the ballpark. The showers will have the potential to drag down some of the stronger winds aloft, but even without this, it will become breezy later Sat and through Sat night with wind speeds on the order of 15 to 30 mph with higher gusts into early Sun. After collaborating with adjacent weather offices, decided to remove thunder given the almost total lack of instability, brief and shallow moisture return and the best forcing missing our FA to the north. Attention then turns to the magnitude of cold air advection with 850 mb temps flirting with zero by Sun night. The cold air will be enhanced as the pressure gradient weakens and radiational cooling maximizes. Temps will drop well down into the 30s during the wee hours of Mon morning and a freeze is becoming increasingly likely except perhaps along the immediate coast. Highs Sat will be in the lower 70s with the beaches staying near or just under 70 due to the cooling marine influence. We will lob off a good 10 degrees for highs on Sun and a brisk NW wind will make it feel as if it were in the 50s for a good portion of the day. Lows will be above normal Sat night, lower to mid 50s. However, watch for that freeze Sun night as the dry and chilly air maximizes. Did want to briefly highlight the elevated water levels at the beaches and along portions of the lower Cape Fear River with the Sat morning high tide. The new moon is on Sat and with that, we may be near or at minor coastal flood thresholds. The highest risk for reaching these thresholds will be across the Pender and New Hanover County beaches and in downtown Wilmington. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 300 PM Thursday...An amplified upper pattern will exist across North America next week. The forecast is fairly high confidence with two exceptions, owing to increasing model differences in the handling of significant shortwave energy into the southern branch of the jet Tuesday through Thursday. WPC prefers the ECMWF handling of this scenario next week which features a strong slow moving upper level low across the northern Gulf of Mexico by next Thursday, compared to the weaker and more progressive GFS pattern. Canadian high pressure overhead Monday will slip offshore Tuesday, with return flow buckling off the Southeast states as a weak coastal trough develops offshore of the FL/GA/SC coast. The ECMWF shows this feature close enough to the coast that perhaps some showers could push onshore Tuesday. Wednesday and Thursday a strong shortwave should dive into the Gulf. Differences in the handling of this feature between the GFS and ECMWF will determine the position of surface low pressure development and subsequent flux of moisture northward from the Gulf and/or Atlantic. There`s enough uncertainty at this point, and the feature may be far enough south, that differences are relatively minor. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... As of 18Z...High pressure will remain in control for one more day. Winds are a bit more gusty than anticipated, but they will diminish diurnally this evening. Some light fog is possible at all terminals after 08Z, with moderately favorable moisture profiles. Saturday, increasing cloudiness in advance of the next system. Winds will shift to the south as high pressure moves offshore. Extended Outlook...VFR with a chance of showers and possible MVFR/SHRA Saturday night into Sunday. && .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 1100 AM Friday...Allowing Small Craft Exercise Caution headline to end at noon as gusty northerly winds begin to diminish. Frying Pan buoy was showing seas up near 6 ft late this morning, but there remains a tight gradient in a brisk northerly flow holding higher seas just beyond our local waters. Winds will diminish further as high pressure shifts closer overhead through tonight. This will also allow for a veering of winds to the NE through today into tonight, shifting farther to the E by Sat morning as the high begins to shift off the coast of Hatteras. Overall, winds will drop off later today through tonight to under 10 kts before picking up again on Saturday. Seas this morning were mainly in the 3 to 5 ft range in gusty northerly winds will drop off as winds diminish through this afternoon. Seas should be down to 2 to 3 ft by evening. SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... As of 300 AM Friday...A strong cold front will sweep offshore around sunrise Sun with Canadian high pressure to slowly follow Sun night and Mon. The pressure gradient will tighten significantly with a low level jet on the order of 50 kt impinging on the area overnight Sat into early Sun. Water temps have cooled to within a couple degrees of 60 across the near shore waters. Still, such an energetic system will bring strong Small Craft Advisory conditions with SW winds increasing across the waters Sat and peaking in the 25 to 30 kt range late Sat night. Gusts to gale force are possible for about 6 hours late Sat night and it is possible marginal Gale conditions will materialize across the outer northern waters for a short time. In the wake of the front Sun, winds will shift to the W and then NW and then N Sun night as the center of the high nears from the W. Wind speeds will decrease to 15 to 20 kt late on Sun. An increasing cold and dry surge will allow for sustained winds near 20 kt Sun night. Seas will ramp higher late Sat and then peak in the 5 to 8 ft range late Sat night. Developing offshore flow Sun morning will quickly knock seas back to 3 to 5 ft Sun afternoon with similar seas into Sun night. LONG TERM /MONDAY THROUGH TUESDAY/... As of 300 PM Thursday...Canadian high pressure will build strongly across the waters on Mon and will provide much lighter winds as it moves overhead Mon afternoon and evening. The new GFS has come into better agreement with the ECMWF model about a faster veering around to E and SE winds offshore Tue as a weak coastal trough develops along the FL/GA/SC coastline. It remains to be seen how well-defined this coastal trough becomes, and how far west is can move. Our latest forecast does bring a period of E/SE winds into the coastal waters Tue, but with winds veering back to the north late Tue night as the trough is shown by most models to retreat offshore then. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ NEAR TERM...III/RGZ SHORT TERM...RJD LONG TERM...TRA AVIATION...DL

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