Area Forecast Discussion
Issued by NWS Wilmington, NC

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778 FXUS62 KILM 210052 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 852 PM EDT Thu Apr 20 2017 .SYNOPSIS... Bermuda High pressure will extend west across the region through early Sunday. A cold front will sag south into North Carolina over the weekend . Low pressure will develop on this front and will further intensify as it slowly drops to the southeast through the Carolinas late Sunday through late Monday. Strong to severe thunderstorms and widespread rain will accompany this slow moving low pressure system. The low will slowly depart out of the area through Tuesday leaving drier high pressure ridging across the area through the middle of next week. && .NEAR TERM /THROUGH FRIDAY/... As of 830 PM Thursday...Low amplitude ridge axis aloft and across the area this evening, will slide eastward and off the coast by early Friday. This will allow thin cirrus clouds to push across the ILM CWA overnight thru Friday. A low level jet and a slow tightening of the sfc pg, will both combine to keep an active sfc SW-WSW winds across the ILM CWA overnight and continuing thru daylight Friday. This will help prevent any fog issues like what occurred Wed night/Thu morning. Could see isolated pockets of fog but at this time not enough coverage to mention in the fcst. Low temps tonight will remain elevated and only drop into the low to mid 60s, which is nearly a good 10 degrees above the normal lows for this time of the year. The same goes with Friday max temps, running up to 10 degrees above the norm. Previous........................................................ As of 300 PM Thursday...The weather pattern is reminiscent of summer with surface high pressure out near Bermuda and sufficient heat and moisture for an expansive cumulus field and a well-defined seabreeze. Dry air aloft has thwarted the potential for showers so far, although I`ll maintain a 20-PoP through about 6 PM in the Cape Fear region for an isolated shower that still may develop. Mid and upper level winds are from the west, so any showers that do develop will be pushed back across the seabreeze front toward the ocean. Clouds should largely dissipate with the loss of heating this evening. With the high off the coast a modest southwesterly low level jet should develop with wind speeds at 1000 feet AGL increasing to 25-30 knots. This frisky wind should help keep the nocturnal inversion from becoming too deep, and my forecast lows are near the warmer GFS MOS numbers: 65-68 along the coast and 62-65 inland. It`s easy to lose sight of the fact those lows are a good 12-15 degrees above normal for this time of the year. The month of April has averaged 3-4 degrees above normal so far with departures over the past week in the +5 to +7 degree range. Heat increases further Friday with highs expected to reach the upper 80s for virtually all areas more than 15 miles from the coast. Conditions aloft will be even drier than today, and with no upper level support I am keeping the forecast dry. && .SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/... As of 300 PM Thursday...Biggest challenge this period involves a southward drifting cold front which will waver to the north before dropping towards the area late Saturday night. Broad mid-level ridging and offshore high pressure will dominate the synoptic flow across the Southeast Friday night through Saturday, creating very warm temperatures and minimal precip chances. Mins Friday night will likely stay in the upper 60s on the coast, mid 60s inland, serving as a launching pad for highs to climb into the mid 80s away from the beaches on Saturday. A strong sea breeze on Saturday will keep the coast cooler, around 80, with mid 70s on the coolest Brunswick County coast. Isolated showers/tstms are possible Saturday aftn, but with dry mid-levels and weak forcing, have capped POP at 20 inland. The forecast becomes muddled Saturday night as a cold front to the north tries to sink southward into the area. The guidance differs greatly in this evolution, with the WRF pushing the front through into SC by Sunday morning, the ECM keeping the front way to the north, and the GFS somewhere in between. The WRF is clearly the outlier, and is ignored for this forecast due to strong impeding SW flow downstream of a deepening upper trough, suggesting the front will struggle to drop south that quickly. A GFS/ECM blend is then preferred which keeps the front just to our north, and while a few showers are possible late in the period, most of the convection should hold off until the extended. With the front forecast to remain north of us Saturday night, warm mins are again expected, dropping only into the mid 60s. && .LONG TERM /SUNDAY THROUGH THURSDAY/... As of 300 PM Thursday...Bermuda high will be losing its grip on the Carolinas as low pressure system moves in from the west on Sunday. Both the GFS and ECMWF show the low center moving east almost directly along the NC/SC border reaching into the local forecast area right around sunset Sun evening. This will maintain a deep warm and moist southerly return flow with temps into the 80s and dewpoint temps in the mid 60s. Initially expect a fair amount of sunshine early Sunday which should lead to some localized cu and shwr development associated with the sea breeze front as any large scale forcing will be lacking. Once the low moves east, expect increasing clouds and chc of pcp. With the track of the low possibly bisecting the area, there could be potential for severe weather over southern portions mainly east and south of low center, but also could see more in the way of isentropic lift and rain to the north. The loss of heating may diminish the chc of severe convection into the overnight hours but the best upper level support will head east toward the coast by Mon morning. Overall expect fairly widespread coverage of pcp late Sun into Monday. The latest model runs do show a more southern track for the low which could produce more in the way of overrunning pcp for our local area rather than thunderstorms, but that remains to be seen. 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 /01Z FRIDAY THROUGH TUESDAY/... As of 00Z...VFR conditions basically thruout the 24 hr 00Z Taf Issuance period. A low level jetstream, SW 20 to 30 kt, will develop overnight, keeping sfc winds active from the SW-WSW. These sfc winds will help prevent widespread ground fog from developing, but still could see patchy MVFR fog in secluded locations. Any leftover diurnally driven cu will dissipate altogether early this evening, leaving only sct/bkn thin cirrus moving overhead per latest ir sat imagery trends. Diurnal cu will again develop by mid to late morning Fri and persist thru the aftn. Could see isolated convection develop along a somewhat pinned sea breeze, with it`s inland progression being limited due to increasing winds thru the atm column from sfc thru 700mb. Overall winds will be from the SW thru WSW tonight around 5 kt once the sea breeze influence decays. Expect the sea breeze to develop by midday with winds becoming SSW 10 to 15 kt with gusts to 20 kt. Inland terminals will likely hold at WSW around 10 kt by late Fri morning and persisting thru the aftn. Extended outlook...MVFR/IFR conditions possible in showers and TSTMS, mainly Sun through Mon. Otherwise VFR. && .MARINE... NEAR TERM /THROUGH FRIDAY/... As of 830 PM Thursday...Once the sea breeze influence to the winds decays later this evening, winds will become SW-WSW at 10 to 15 kt. A low level Southwesterly jet and a slow tightening of the sfc pg will combine to influence wind speeds across the local waters. This will result in SW winds at a solid 15 kt or possibly a range from 10 to 20 kt. Will decide at press time. Significant seas will run 2 to 4 ft with the 4 footers occurring across the ILM NC Waters where winds in general will run hier than the ILM SC Waters. An easterly pseudo swell at 7 to 8 second periods will dominate the seas spectrum this period. Previous....................................................... As of 300 PM Thursday...High pressure anchored about halfway between the North Carolina coast and Bermuda will maintain a southwesterly wind across the area for the next 24 hours. Although wind speeds are quite light today, a modest increase in wind speeds is expected Friday as the pressure gradient tightens in advance of an approaching cold front over the Ohio Valley. Seas are generally around 2 feet inside 20 miles from shore, the result of at least two sets of 7 to 8 second swells. Seas should build by at least a foot if not a foot and a half by Friday afternoon due to the developing winds. SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/... As of 300 PM Thursday...High pressure offshore and a slow moving cold front to the north will keep SW winds entrenched across the waters through the period. SW winds of 15-20 kts will be common through Saturday, with a slow decrease in speed, especially northern waters, Saturday night as the front sags towards the area. Long period easterly swell from TD one will combine with steepening 5-sec SW wind waves to produce seas of 3-5 ft. LONG TERM /SUNDAY THROUGH TUESDAY/... As of 300 PM Thursday...A southerly flow up to 15 kts or so will persist on Sun between Bermuda High pressure extending over the local waters from the east and an approaching low pressure system to the west. The persistent southerly push could drive seas up from 3 to 5 ft to near SCA thresholds by late Sunday. The low will move across the waters Sun night into 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 kts Mon into Mon night before diminishing through late Tues as low tracks farther away. Seas may remain above SCA late Mon into Tues, diminishing Tues night in a lighter northerly flow. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...DCH/TRA NEAR TERM...DCH/TRA SHORT TERM...JDW LONG TERM...RGZ AVIATION...DCH MARINE...

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