Area Forecast Discussion
Issued by NWS Wilmington, NC

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
793 FXUS62 KILM 221506 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 1106 AM EDT Thu Mar 22 2018 .SYNOPSIS... Canadian high pressure will build in from the west today. Well- below normal temperatures will continue for the next several days. Low pressure will move across the Carolinas Saturday night and early Sunday bringing rain, followed by another round of below normal temperatures by early next week. && .NEAR TERM /THROUGH TONIGHT/... As of 11 AM Thursday...Gusty northwest winds expected today as full sun helps mix stronger winds aloft to the surface. Forecast soundings show 25 kt at the top of the mix layer this morning, decreasing to 20 kt in the afternoon. Gusts approaching 25 mph will be possible, especially through midday or so. Gusts should diminish in strength and frequency in the afternoon. Decrease in wind speeds will be welcome as relative humidity will be dropping into the low to mid 20% range in some locations. Temperatures will end up below climo but abundant sunshine will help push high close to the 60 degree mark for many areas. Only a few slight tweaks needed for morning update. && .SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/... As of 220 AM THURSDAY...A winter-like feel will continue into the weekend as this anomalously cool March continues. Friday will likely be a pretty nice day locally despite highs a degree or two either side of 60, as a dry column and dry W/NW flow allow for abundant sunshine through the evening. Things begin to change late on Friday however. Surface high pressure which initially drapes across much of the eastern CONUS will begin to retreat to the north as a warm front lifts north from the Gulf Coast states. This front is extended from a surface low which will be consolidating across the middle of the country in response to a shortwave digging down from western Canada. This shortwave will race SE around the longwave trough over New England through Saturday night, pushing the surface low offshore by Sunday morning. As this evolves, moisture will steadily increase in response to moist advection within the lower portion of the column, forcing thanks to PVA in the vicinity of the shortwave, and Pacific moisture streaming overhead within the cirrus level. Cloud cover will increase Friday night into Saturday, with showers likely developing by Saturday aftn. The surface low will race along the warm front, which will then shift south as a cold front as the low moves offshore. Guidance suggests most of the rainfall will occur behind the cold front, with isentropic lift atop a developing wedge driving much of the precip. This would lead to simply a cold rain, but with deep column saturation QPF could be significant, 0.25 to 0.50 inches is possible. Highs Saturday will struggle only into the low 50s across NC zones, but may climb as high as the mid 60s far SW zones depending on the exact timing of the warm front and WAA racing the advancing cloud cover and showers. Mins both nights should be too warm for any frost concerns, although some mid/upr 30s are possible Friday night across NC zones, depending on how quickly cloud cover develops. Saturday night lows are likely to remain much warmer, falling only into the mid 40s. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... As of 300 PM WEDNESDAY...Model differences with the next shortwave are generally minor, however the ECMWF is stronger and a little slower with the shortwave than the GFS. Although both models show rain developing into Sunday, this probably explains the better developed low-level thermal/moisture advection fields shown on the ECMWF. PoPs have been increased to 50-60 percent for this period, and it`s looking more and more likely we`ll see a widespread 0.20 to 0.30 inch rainfall event. The ECMWF shows a stable airmass through the event. The surface low should jump the Carolinas early Sunday morning, redeveloping just off the coast where low-level baroclinicity is significantly greater than inland. Cold northerly winds should punch southward behind the developing low. Sunday`s high temperature forecast is actually quite difficult since it`s tough to know exactly where the front will be located at 7 AM, and temperatures could actually fall throughout the day in the strong low-level cold advection. A model blend gives mid to upper 50s across SE North Carolina and upper 50s to around 60 in South Carolina, however that could easily be 10 degrees lower if faster cold frontal movement (like shown on the GFS) occurs. Light rain should taper off during the afternoon with skies partially clearing Sunday night as moisture thins from north to south. Dry and unseasonably chilly weather is expected Monday and Tuesday as Canadian high pressure builds down the East Coast. Our 850 mb temps should hover in the +1C to +3C range both days, between the 10th and 20th percentile for late March. Of agricultural concern is a possible frost or even freeze event coming up Monday night as surface winds drop off with the incoming high. On Wednesday the surface high should finally move off the East Coast. A westerly component to the low-level flow will finally bring warm advection and temperatures should pop back to seasonal norms. && .AVIATION /15Z THURSDAY THROUGH MONDAY/... As of 12Z...High confidence in VFR conditions prevailing today and tonight as high pressure builds in from the west. No real aviation concerns except the winds which will become gusty by mid morning. Northwest flow will continue through the afternoon hours, diminishing by sunset. Light winds overnight with little or no fog expected as dewpoints will remain in the 20s. Extended outlook...VFR Friday into Saturday. MVFR/IFR/Rain developing Saturday night and Sunday. Conditions improving again for Monday. && .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 11 AM Thursday...Allowed Small Craft Advisory to expire at 11 EDT but went ahead and put up a short duration Exercise Caution headline. Offshore flow is weakening but seas are mostly running 4 to 5 ft with periods frequently dipping under 5 sec. Gradient will continue to relax and offshore flow will diminish, but to be on the safe side will carry the SCEC until 1500 EDT. Other than the headline update did not see a need to make significant changes to inherited forecast. SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... As of 220 AM THURSDAY...Gusty NW winds greet the period but will wane to 10-15 kts and veer to the N as high pressure ridges down from the Great Lakes through the day. A more convoluted pressure pattern develops Saturday as a warm front lifts into the area and stalls in response to low pressure moving along it. This low will then skirt overhead to become offshore by the end of the period, dragging a cold front with it. The wavering of this boundary combined with the low pressure means that winds will feature a variety of directions Saturday, with a period of gusty SW winds south of the front likely across SC waters in the aftn before NE winds develop late. Speeds should be 10kts or less outside of the narrow winds of SW winds, so seas are expected to be 1-3 ft most of Saturday before amplifying late. After a brief period of 3-4 ft seas early on the stronger NW winds, wave heights fall by Saturday to the aforementioned 1-3 ft. LONG TERM /SUNDAY THROUGH MONDAY/... As of 300 PM WEDNESDAY...Low pressure redevelopment just off our coast early Sunday will drag a front southward again in the morning. Mariners should expect a sudden increase in north- northeasterly winds as the front dives through, with Small Craft Advisory conditions developing and likely persisting through Monday as strong Canadian high pressure builds southward. Our forecast shows 20-25 kt winds Sunday afternoon through Monday, but it`s possible there will be some 30+ knot gusts thrown in there during the period of most rapid thermal advection Sunday afternoon or evening. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ NEAR TERM...III SHORT TERM...JDW LONG TERM...TRA AVIATION...DL is the U.S. government's official web portal to all federal, state and local government web resources and services.