Area Forecast Discussion
Issued by NWS Wilmington, NC

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989 FXUS62 KILM 160753 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 253 AM EST Tue Jan 16 2018 .SYNOPSIS... Weak high pressure will dissipate across the Carolinas today. A cold front will move across the area Wednesday bringing a mix of rain and snow with small accumulations possible inland. Cold and dry arctic air will build into area Wednesday night and Thursday. Temperatures should moderate over the weekend as high pressure moves off the Southeast coast. Rain chances could return Monday with the next cold front. && .NEAR TERM /THROUGH TONIGHT/... As of 300 AM Tuesday...A weakening ridge of high pressure extending south into the Carolinas will hold on for most of the period. Warm advection will occur above this surface-based layer allowing for afternoon temperatures to top 50; much milder than yesterday but still a few degrees below climatology. Moisture will increase in the warm advection zone with clear skies this morning giving way to a partly cloudy afternoon. The more pronounced increase increase in moisture is slated to occur from west to east tonight as a cold front approaches ahead of a strong trough and vorticity max. Some very light rain or snow could begin affecting westernmost counties by the end of the period. The ptype is a bit questionable as there could be a late night minor rise in temperature. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... As of 300 AM Tuesday...Virtually all 00Z model guidance is showing more precipitation on Wednesday than was being shown 24 hours ago. The culprit appears to be a sharper mid and upper level trough now being depicted moving across the area. This leads to winds in the 850-500 mb layer backing by maybe 20 degrees compared to yesterday`s model runs, allowing the northern Gulf of Mexico to be briefly tapped as a moisture source and supplementing the meager Pacific moisture that is being routed from the west. Where my QPF values were .02 to .04 yesterday, now a tenth of an inch or more is possible across parts of the Sandhills. Of course the bigger issue is how much of that QPF falls as snow. The GFS is a cooler than the NAM with its low-level thermal profiles which would allow for a more rapid changeover to snow, particularly west of I-95 during the morning hours. The new 00z ECMWF is a compromise solution between the GFS and NAM, and implies rain should change to snow across Hartsville and Bennettsville by 9 AM. Colder air aloft beneath the approaching upper trough will continue to build eastward during the day, offsetting any insolation trying to punch through the clouds and allowing the changeover to occur in Lumberton by noon, and in Elizabethtown and Whiteville by mid afternoon. Given no warm nose aloft, this is likely to be a clean transition from rain to snow without any sleet or freezing rain to deal with. Forecast snowfall accumulations are up to 1 inch from Bennettsville across northern Robeson and Bladen counties, with less than half an inch from Darlington and Dillon to Lumberton and Elizabethtown. Precipitation is not likely to be as significant along the coast as the Gulf of Mexico moisture connection is severed by the time things get going here. Precip should end between 6-9 PM along the coast, but even in Wilmington and Myrtle Beach there could be a brief period of light snow at the tail end of the event. Thinning moisture aloft should preclude any significant snowfall totals here. As skies clear and the core of the cold air aloft moves overhead, lows Wednesday night should fall to 20-23, warmest along the SC coast. Warm advection will begin on westerly winds Thursday with clear, dry weather expected. Highs should reach 40-45. && .LONG TERM /FRIDAY THROUGH MONDAY/... As of 300 PM Monday...Surface high building in from the west Thu is quickly shifted east by zonal flow aloft. Lack of troughing aloft coupled with quick eastward movement of the surface high will limit duration of cold temps to Thu and Thu night. Warm advection begins on Fri as the center of the high slips south and then east of the area as Fri turns into Sat. Southern stream shortwave moving across the Gulf of Mexico this weekend opens up and weakens as it lifts northeast. By the time it reaches the Southeast Sunday, the wave will have weakened considerably. It may bring an increase in mid- level cloud cover to the area but rainfall is unlikely. Best rainfall chances during the period will be next week when a cold front, trailing a surface low over the Great Lakes, moves into the region on Mon. Still a lot of uncertainty, but there should be a period of moisture return ahead of it, compliments of weak 5h ridging over the weekend. The aforementioned 5h ridge coupled with low level warm advection will produce temperatures 10 degrees above climo during the later half of the period. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... As of 06Z...VFR through Tuesday. A ridge of high pressure maintains itself through the period, nudging in from the north-northeast. This will keep winds light and variable and VFR conditions expected. The last few hours of the TAF cycle will usher in rapid changes with the approach of a strong cold front and clouds may increase at FLO/LBT. Extended Outlook...Rain/MVFR/tempo IFR/with a chance for a wintry mix Wed, otherwise VFR with high pressure in control. && .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 300 AM Tuesday...Light northerly winds today will be the result of a ridge of high pressure extending south into the Carolinas. As it weakens this ridge will progress eastward over the coastline and winds may go light and variable early tonight. Towards the end of the period a cold front will approach from the west but its southerly winds appear to fail to overspread the region during the near term. Winds will remain at 10kt or less and may turn westerly. SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... As of 300 AM Tuesday...A cold front will move across the area on Wednesday. While this won`t look like an impressive system on the surface weather maps, it`s got plenty of cold air behind it beneath a very powerful upper level system that will whip across the area Wednesday night. Patchy rain Wednesday afternoon could actually mix with or change to snow before ending Wednesday night, particularly north of Cape Fear. The biggest marine weather impact from this system is likely to be increasing northwesterly winds behind the cold front, anticipated to reach a solid 25 knots Wednesday night. Wind chills could dip as low as 10-15 degrees on the beaches. This will necessitate Small Craft Advisories which might be issued as soon as this afternoon. Wind speeds should diminish during the day Thursday. LONG TERM /FRIDAY THROUGH SATURDAY/... As of 300 PM Monday...High pressure will pass south of the waters Fri night into Sat. Gradient will remain weak Fri and Sat with speeds 10 to 15 kt Fri diminishing to 10 kt or less Sat. Seas trend down to 2 to 3 ft Fri and will remain 2 to 3 ft through the end of the period. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...TRA NEAR TERM...MBB SHORT TERM...TRA LONG TERM...III AVIATION...MBB

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