Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 220140 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 840 PM EST Sun Jan 21 2018 .SYNOPSIS... The risk for showers and perhaps a rumble of thunder will be on the increase ahead of a cold front which will move across the eastern Carolinas on Tuesday. Temperatures will cool to seasonable levels Wednesday through Friday. Weekend temperatures will warm again ahead of a cold front along with the risk for more showers, especially on Sunday. && .NEAR TERM /THROUGH MONDAY/... As of 800 PM Sunday...SKies were clear this eve with nearest cloud cover offshore and not making any inroads closer to the coast. High clouds across GA and AL were increasing and this trend will continue with the clouds expanding across the Carolinas overnight and Mon morning. After a warm day by late January standards, temps have cooled into the 40s and have had to adjust hourly temps down to account for the temp drop this eve. For the remainder of the night, the temp curve will flatten and likely not deviate but a degree or two toward morning as the higher clouds begin to increase and thicken. Forecast lows are within a couple degrees of 40. A challenging forecast develops Monday as the surface high slips further offshore ahead of a cold front approaching from the west. The NAM and Euro indicate a weak coastal trough will develop and lift onshore during the aftn with some showers, while the GFS is dry despite increasing cloudiness. There appears to be a weakness in the pressure field already developing off the FL/GA coast, so this trough seems likely. However, profiles indicate moisture will be quite shallow, below 700mb, even during maximum saturation. Given weak forcing and relatively low PWAT, have kept shower chances to SCHC, favored along the Grand Strand and into Cape Fear during the aftn and into the evening. This enhanced cloud cover combined with southerly winds will keep highs along the coast in the mid 60s, warming to near 70 inland where more sunshine will allow the strong WAA to be realized. Very late in the period the front will approach and may spawn a few showers west of I-95, but the guidance has slowed and expect the bulk of the shower and potential tstm activity to occur overnight Monday into Tuesday. && .SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/... As of 300 PM Sunday...Mid-level low moving from the Upper Mississippi Valley Mon night into Tue will drag a cold front into and across the area Tue morning. Convection ahead of the front is likely to be limited. Deeper moisture and best dynamics pass north of the area and both the GFS and ECMWF suggest the mountains may take a little bit out of convection as it moves east. Also in play will be convection along and south of the FL Panhandle. Convective activity in this area in these kind of setups always seems to lead to reduced coverage in the eastern Carolinas. Convection ahead of and with the front will be associated with some elevated instability. Cannot rule out some isolated thunder, but it may be difficult to get the bulk of the convection that does develop deep enough to generate sufficient charge separation given the abundance of dry air aloft. Still will continue to carry isolated thunder Tue morning. Strong low level jet (50+ kt) does warrant mentioning the low possibility of an isolated damaging wind gust, but overall this is unlikely given the low level stability. If the front/convection were delayed until later in the day strong/severe storms could become more of a concern. Total rainfall will be limited, likely under a quarter of an inch area wide, given the broken coverage and storm motions approaching 50 kt. Front moves off the coast during Tue but a lack of cold advection and clearing skies in the afternoon will keep highs well above climo, especially given Tue morning lows in the mid 50s. Clouds may linger through midday or so, slightly longer at the immediate coast, but then skies should clear out. Combination of sun and deep westerly flow(downslope) in the afternoon will push high into the upper 60s to low 70s (even to the coast). Strong winds just above the surface will likely lead to a breezy day, especially once the sun does come out. Winds start to drop off overnight as surface high builds in from the west. Weakening gradient and lack of cold advection/boundary layer mixing coupled with clear skies will allow for good radiational cooling. This should drop lows back close to climo for late January, mid to upper 30s. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... As of 300 PM Sunday...High pressure will be building in from the west on Wednesday while mid level flow will be zonal and confluent; normally a recipe for sunny and seasonable weather. The surface and upper air pattern will be both progressive and amplifying through Saturday with the ridge developing in the east. Once surface return flow gets established locally we should start to see warmer temperatures. It appears this happens on Saturday. Cloud cover and rain chances then rise quickly on Sunday with the approach of the cold front and strengthening upper trough from the west. && .AVIATION /00Z MONDAY THROUGH FRIDAY/... As of 00Z...Except for tempo MVFR vsbys due to BR around sunrise at KFLO/KLBT, VFR expected all terminals into Monday morning. By mid-morning MVFR cigs are likely to develop. Confidence is low on IFR in the afternoon at KFLO/KLBT due to differences in expected precipitation. There is higher confidence of sea fog/IFR/LIFR at the coastal terminals towards the end of the TAF period, however there is a question whether dewpoints will get high enough above water temperatures in the late afternoon. Extended Outlook...VFR. MVFR/IFR/LIFR Mon evening/early Tue aftn. && .MARINE... NEAR TERM /THROUGH MONDAY/... As of 800 PM Sunday...Large elongated high pressure across the waters was producing an extremely weak gradient as evidenced by winds at the buoys of 5 kt or less, and seas just around 1 ft. The surface high will remain overhead overnight producing light and variable winds, before it shifts offshore during Monday. This will be followed by slowly increasing return flow with winds becoming south at 10-15 kt by the end of the period. Seas will be slow to respond, but a SE swell and subtly amplifying southerly wind wave will push seas up to 2-3 ft late Monday. SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/... As of 300 PM Sunday...Southerly flow will increase Mon night with winds veering to southeast by daybreak as gradient becomes more defined. Cold front moves off the coast and across the waters as Tue morning turns into Tue afternoon. Winds gradually veer to westerly later Tue and Tue night as high pressure expands east. Gradient slowly weakens during the second half of the period as the surface high expands. Weakening gradient coupled with the lack of cold advection will allow for steadily decreasing offshore flow Tue night. Strong southerly flow may create a brief period of SCA seas late Mon night into Tue afternoon before development of offshore flow and weakening wind speeds drops seas under 6 ft late Tue afternoon. LONG TERM /WEDNESDAY THROUGH FRIDAY/... As of 300 PM Sunday...Winds out of the NW on Wednesday as high pressure well to our west approaches. AS the anticyclone approaches Thursday flow veers to N then NE, possibly becoming light and variable for a time Thursday evening or early Thursday night as it moves nearly overhead. E or ESE winds should then increase Friday as this high begins to share a center with one moving off the New England coast. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ NEAR TERM...RJD/JDW SHORT TERM...III LONG TERM...MBB AVIATION...MRR

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