Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 211414 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 1014 AM EDT Fri Apr 21 2017 .SYNOPSIS... Bermuda High pressure will extend west across the region through early Sunday. A backdoor cold front is expected to stall north of the area during the weekend. Strong low pressure will move slowly through the Carolinas Sunday and Sunday night and then offshore Monday. Widespread rainfall is expected along with the possibility of strong to severe thunderstorms. This system will then move slowly away from the area as high pressure and dry weather builds in for the middle and later portions of next week. && .NEAR TERM /THROUGH TONIGHT/... As of 1000 AM Friday...High pressure has sunk a little farther south over the past 24 hours, increasing the degree of westerly flow across the Carolinas. 12z soundings from both CHS and MHX had 850 mb temps of +14C, near the 90th percentile for the date. Very few changes are needed to the high temperature forecast today which features upper 80s everywhere more than 10 miles inland, with highs close to 80 expected on the beaches. These warm temperatures should help drive a strong seabreeze circulation this afternoon. This is probably the biggest change to the forecast as sustained surface winds should reach 20 mph with gusts near 30 mph during the mid to late afternoon at the beaches. Marine MOS guidance for wind speeds at JMPN7 (Wrightsville Beach) and MROS1 (Myrtle Beach) indicates this potential very well. The initial movement of the seabreeze boundary will probably be quite slow as deep westerly flow holds the boundary close to the beaches from noon through 3 PM. The airmass aloft has dried out a little more than yesterday, and despite very warm temperatures and computed surface-based CAPE as large as 1200 J/kg I don`t expect many of this afternoon`s cumulus will be able to produce showers. If a brief shower does develop the HRRR has been focusing on the Bennettsville to Lumberton corridor for its past few runs. The Piedmont Trough and Sandhills-to-Piedmont differential heating does tend to focus convective activity along this corridor, but the probability of rain is still too low to include today. The dry forecast will continue. Much like last night a moderate low level jet should develop after sunset with 1000 foot winds increasing to 25-30 knots. This mechanically-forced mixing should help keep the boundary layer temperatures from diving too deep, and lows should reach the mid 60s with some upper 60s at the immediate coast. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... As of 300 AM Friday...Warm ridge will get suppressed to our S and E Sat as a cold front struggles to backdoor through North Carolina. This front still looks as though it will get hung up N of our Forecast Area during the first half of the weekend. Upper low across the mid south Sun morning is now expected to take a southeast track and on this path will move across the southern Appalachians late Sun night and Mon morning. The surface low will move slowly across the Carolinas Sun and Sun night and should be moving offshore of the Carolinas Mon morning. Forcing is weak Sat, and moisture is shallow. Mixed layer CAPE values do climb to or just above 500 J/kg and so isolated showers and thunderstorms will be possible with the highest POPs from LBT to Burgaw, in closest proximity to the frontal zone. Attention then turns to system to our W and this promises to be a wetter scenario for the eastern Carolinas with strong lift developing later Sun and Sun night. Precipitable water values will climb to more than one and a quarter inches as the depth of moisture deepens. Mixed layer CAPE values are expected to reach 500 to 1000 J/kg. Thus, the area will have all of the necessary ingredients for showers and thunderstorms. Will show POPs increasing to categorical. At this time, rainfall amounts of one half to one and a half inches seems attainable. There still is some risk for strong to NE...severe thunderstorms and the track of the surface low will be important in determining where this risk will be highest. Bulk shear values and winds within 5 kft of the surface are quite marginal and do not support widespread severe weather. Model consensus would suggest the risk for severe weather will be higher across our southern counties and points S. Temps will be well above normal, warmest Sat and coolest Sun night. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 300 PM Thursday...The sfc low center should be just over or near the Cape Fear coast Mon morning, but the deep upper level trough will still be west. The cutoff low center will track mainly south of the area but the trough will extend up through the Carolinas. The low will move east through the day on Mon and then will travel slowly N to NE parallel to the coast. This will keep clouds and rain chances in the forecast possibly through Tues. Should see drier conditions by mid week as weak high pressure builds in behind departing low. Temps should be a good 10 degrees cooler on Monday in northerly flow on the back end of the low. Clouds and rain will keep smaller diurnal ranges with temps heading back toward normal Tues into Wed as low slowly departs. Overnight lows will probably be 55 to 60 most places. Temps should be back up into the 80s by mid week with increasing sunshine. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/... As of 12Z...High confidence in VFR conditions through the valid TAF period. SW winds will be on the breezy side today with the potential for gusts in excess of 20 kt, especially along the coast. The seabreeze will back winds to SSW at KCRE and KMYR. Cannot rule out an isolated afternoon shower but the chance a terminal would be impacted is extremely low. Any diurnal clouds that manage to develop will dissipate around sunset. Winds above the boundary layer of 25 to 35 kt will preclude any late night fog possibility. Extended outlook...MVFR/IFR conditions possible in showers and TSTMS, mainly Sun through Mon. Otherwise VFR. && .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 1000 AM Friday...Bermuda High Pressure has sunk a little farther south over the past 24 hours, and will continue to control the weather today and tonight. With inland temperatures soaring well into the 80s a strong seabreeze circulation should develop this afternoon with wind speeds by 3 PM increasing to a solid 20 knots near the beaches. The limited area of stronger winds will create very choppy conditions across the nearshore waters, but overall seas should not rise much beyond 3 feet. A low level jet developing again tonight should help keep wind speeds in the 15-20 kt rain almost up through daybreak Saturday. Seas could build to 3-4 feet, particularly away from shore tonight. Dry weather will continue. SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... As of 300 AM Friday...Ridge of high pressure will be offshore at the start of the period. A cold front to our N will be strung out W to E and will struggle to make southward progress. This front is expected to stall out before reaching any of our waters Sat night. A strong area of low pressure and its associated frontal system will approach from the W Sun and move slowly across the waters Sun night into Mon, bringing widespread convection. SW winds will persist Sat into Sun. These winds will be strongest Sat afternoon and Sat night, sustained at 15 to 20 kt. Winds will back slightly on Sun, SSW to S. Late Sun night and Mon morning, the wind direction will back all the way around to NE. Seas will build up to 3 to 5 ft through Sat night with seas holding near this range through Sun night before building further Mon. LONG TERM /MONDAY THROUGH TUESDAY/... As of 300 PM Thursday...Low pressure will be moving across the waters Mon with a sharp shift in wind direction to the N on the back end. The center of the low should be just near or south of the Cape Fear coast Mon morning. The winds may diminish and become quite variable at this time before the low slowly moves east and north through late Mon into Tues. This should allow seas to diminish for a brief period Mon morning before a sharp rise in northerly surge on the back end. Winds may increase up to 15 to 25 kt Mon into Mon night before diminishing through late Tue as the low tracks farther away. Seas may remain above SCA late Mon into Tue, diminishing Tue night in a lighter northerly flow. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...III NEAR TERM...TRA SHORT TERM...RJD LONG TERM...RGZ AVIATION...RJD

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