Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 211945 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 345 PM EDT Sat Apr 21 2018 .SYNOPSIS... Canadian high pressure will continue to extend into the Carolinas as it migrates slowly east off the Mid-Atlantic coast through Sunday. Slow moving low pressure will cross the Southeastern U.S. Monday through Wednesday, bringing widespread rainfall with continued below-normal temperatures. Another system may affect the Carolinas Thursday into Friday. && .NEAR TERM /THROUGH SUNDAY/... As of 300 PM Saturday...A weak 500 mb ridge will move across the area tonight and then offshore Sunday. An upper low dropping southeast across Kansas will make it as far east as Arkansas by Sunday afternoon. Developing southerly flow in the mid and upper levels ahead of the upper low should begin to increase cloud cover across the Carolinas Sunday, with veering low level winds even developing a bit of stratocumulus beneath the upper level moisture plume during the day. A blossoming area of isentropic lift ongoing now across southern Georgia is developing quite a canopy of mid-level clouds between Charleston, SC and Jacksonville, FL. While a little of this moisture may sneak across the Santee River overnight, our skies should remain mainly clear with good radiational cooling expected. The only exception to this will be within a few miles of the beaches where steady onshore winds may prevent a radiational inversion from developing until late tonight, if at all. For this reason I`ve tried to show a large range in forecast lows as you move inland: 53 at MYR, 50 at CRE, and 46 at FLO. The coldest temperatures tonight should be across interior SE North Carolina where lower 40s are expected in the normal cold spots. Despite winds just above the surface veering more southerly during the day Sunday, warm advection goes into lift leading to nearly steady 850 mb temps. This means highs Sunday shouldn`t be appreciably different from today: low 70s inland and mid-upper 60s near the coast. Rain chances should hold off until sunset across the SC Pee Dee region. && .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... As of 300 PM Saturday...A complex weather pattern will unfold during the short term period as low pressure, progged to be near/just E of the MS valley during Monday, promotes strong onshore low-level flow and Theta-E advection. As the upper low drifts ENE across TN and into KY the pattern becomes favorable for strong upward vertical velocities. The upward motion will be enhanced by the increasingly divergent flow aloft, and the convergent flow expected to be present in the low levels. As a result, widespread areas across the ILM CWA may receive 1-3 inches of rainfall. Available instability for thunderstorms is on the low side however strong lift supports carrying isolated thunderstorms in the least. Best chance of rain will occur Monday for southwestern zones, and Monday evening for the remaining areas. Favored a blend of MAV/MET/ECE temperatures all periods. Breezy conditions expected to develop during Monday, especially along the coast. Will have to watch for potential coastal flooding as well each high tide Monday into Monday night given the onshore fetch. && .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 300 PM Saturday...A low pressure system will track off to the NE Tues into Wed. The sfc low will track closer to the coastline while the upper low will move northeast from TN toward the Ohio Valley. As this closed upper low lifts north, another shortwave will rotate down toward the Southern Appalachians by Thurs. Overall, this system remains quite complex, but looks like the heavier rain will move north leaving clouds but some drier air wrapping through mid week. The next shortwave should dig down and push a cold front through on Thurs, but does not look like a big rainmaker. Therefore, expect breaks in the clouds and some clearing late Tues into Wed with increased clouds and potential for pcp again Thurs. Another system will follow in this progressive flow by Fri into Sat, although the GFS keeps most of the weather with this system north of our local forecast area, while the ECMWF remains more pessimistic heading into next weekend. Overall a good amount of clouds and and not much QPF expected through the week. Temps have been trending warmer but remaining near normals through much of the period. && .AVIATION /18Z SATURDAY THROUGH WEDNESDAY/... As of 18Z...VFR conditions expected over the next 24 hours. Easterly winds will reach 12 knots along the coast today, and perhaps again late Sunday morning. Extended outlook...Rain Monday and Tuesday could bring periods of MVFR/IFR conditions in low ceilings and visibility. The worst conditions are expected Monday night. && .MARINE... NEAR TERM /THROUGH SUNDAY/... As of 300 PM Saturday...A ridge of high pressure extending from the Great Lakes to just off the Virginia coast is maintaining an easterly wind across the area. The high will move very little over the next 24 hours as low pressure develops across Louisiana and Arkansas, and this should maintain the easterly wind through Sunday. Wind speeds should average 10-15 knots, perhaps a bit stronger by late Sunday afternoon. Buoys are currently reporting wave heights of 2-3 feet across the coastal waters with the Frying Pan Shoals buoy offshore now up to 4 feet. Dominant wave period has shortened to around 5 seconds with a second peak at 8-9 seconds indicating local wind chop is becoming more dominant. Waves of 4 feet should become more common Sunday afternoon south of Cape Fear. SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... As of 300 PM Saturday...Marine conditions will become hazardous during the short term. High pressure off New England during Monday with low pressure along the MS valley will create a strong onshore fetch with Small Craft thresholds likely. Plan to raise the advisory with the afternoon Coastal Waters Forecast. The strong winds will continue into Monday night, and it`s possible a period of Gales could occur. However, confidence is not high enough to warrant a Gale Watch at this time. The onshore fetch will allow for seas to get above Small Craft thresholds by daybreak Monday, and to exceed 10 ft when winds are strongest later in the day Monday into the evening. Numerous showers and isolated thunderstorms are expected, more-so across the southern waters initially, and all waters by Monday evening. LONG TERM /TUESDAY THROUGH THURSDAY/... As of 300 PM Saturday...Complex low pressure system will track NE parallel and near to the Carolina/VA coast Tues into Wed. A strong onshore flow will persist into Tues , but winds will diminish as they shift around from on shore to off shore by Wed on the back end of the low as it lifts off to the northeast. Another system will follow behind this one, dragging a cold through on Thurs. Therefore expect off shore flow to continue through much fo the period. Overall, expect seas to subside through the period from a peak Tues morning, above 10 ft in outer waters. The on shore flow will shift around to the off shore and decrease with seas down below SCA thresholds by Wed morning and continuing to lower to 2 to 4 ft by Thurs morning. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ NEAR TERM...TRA SHORT TERM...SRP LONG TERM...RGZ AVIATION...TRA is the U.S. government's official web portal to all federal, state and local government web resources and services.