Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 151554 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 1154 AM EDT Sat Jul 15 2017 .SYNOPSIS... Hot and humid weather will continue through today, but clouds and thunderstorms should increase with slightly cooler temperatures expected Sunday into Monday as a cold front approaches from the north. This front should dissipate to our north by Tuesday. Hot temperatures should redevelop for the second half of next week as high pressure expands eastward from the Central Plains states. && .NEAR TERM /THROUGH TONIGHT/...
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As of 1130 AM Saturday...A Heat Advisory has been issued for all zones between 17z to 23Z this aftn thru early this evening. Sfc temps are running a degree or 2 above the current fcsts. Looking at 12z sounding data, and model sounding data for this aftn and early evening, a temporary W to WNW wind trajectory occurs in the atm below 500mb. With little cloud cover and the expected tstorms mainly to fire later, early this evening and into tonight. This leaves plenty of insolation to occur along with some compressional heating from the slight downslope flow, both aiding an increase to the max temp fcst hier by 2 to possibly 4 degrees. However, could see a degree or 2 lower in the sfc dewpoints from possible drier air mixing down to the sfc. With fcst heat index readings already at the cusp of issuing a Heat Adv, applying the new changes results in Heat Indices reaching a solid 105 with some 106 degree readings possible. Previous.................................................... As of 1000 AM Saturday...Very little if any tweaking needed at this update. Widespread 90 degree readings expected all the way to the immediate coast prior to the sea breeze development and it`s inland progression. With winds slightly hier in the lower levels today than previous days, the inland progression of the sea breeze will be somewhat limited. Still however, looking at 101-104 degree heat indices this aftn and early evening. Could see a few short lived and sporadic 105 degree heat index readings but just not occurring long enough to warrant a Heat Advisory. Previous........................................................ As of 230 AM Saturday...The cold front located along the Ohio River is forecast to shift and stall just to the northwest of our area. The models are increasing the deep moisture over the area with precipitable water values reaching to just over 2 inches by late Saturday into the overnight. With afternoon temperatures reaching the mid 90s inland, instabilities will see surface based capes reach the 2200 J/kg level. This will increase the chances for thunderstorms that develop to produce a wet micro- burst. With the upper level trough the wet bulb zeros heights are seen to drop below 12000 ft late Saturday night so hail may be less of an issue until Sunday. With little shear the tornado threat will be low unless boundary collisions align correctly. The convection is not forecast to begin until after 18 UTC and continue into the overnight hours. With the dewpoints in the mid 70s on Saturday afternoon heat indices will max out in the 100-104 degree range which is just short of heat advisory criteria. Highs are expected to reach middle 90s inland and near 90 at the beached. Lows on Saturday night are expected to be in the middle 70s.
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&& .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... As of 230 AM Saturday...A favorable environment for convection will persist through the short term as a weak cold front and deeper moisture settle over the eastern Carolinas. Model consensus has the front stalled in our vicinity on Sunday and Monday as upper-level troughing deepens over eastern CONUS. Expect scattered to widespread convection to develop by Sunday afternoon and persisting with some lulls in the action into at least Monday afternoon. Model soundings show significant drying Monday night so expect the bulk of the event should be over by then. SPC has not highlighted the area in any sort of risk category for severe weather, but given P/W values elevated at around 2 inches and modest storm motions with the potential for training expect that localized flooding could become an issue. Temperatures will be more climatologically correct on Sunday and Monday as extensive cloudiness knocks a few degrees off our recently higher than average readings. && .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 3 PM Friday...A relatively narrow upper trough will sit along the U.S. East Coast early next week, sandwiched between the Bermuda ridge offshore and an upper ridge over the Central Plains states. A weak surface low near Washington DC will anchor a front separating our maritime tropical airmass from cooler Canadian air to the north. This boundary will probably make its closest approach Monday night before washing out in the NC mountains on Tuesday. A humid and moderately unstable airmass Monday will probably yield showers and thunderstorms with locally heavy rainfall possible. Clouds and precip should hold temps in the 80s Monday, a welcome reprieve from the heat of the past several days. Upper level heights should bottom out on Tuesday, however drier air wrapping through the mid and upper level trough may reduce our potential of thunderstorms from 50-60 percent Monday to 30-50 percent Tuesday. By Wednesday, the upper trough should lift out to the northeast as the Central Plains upper ridge begins to build east into the Carolinas. This should allow heat to build Thursday and Friday in advance of this ridge, with deep offshore winds and 850 mb temps approaching +20C by Friday allowing temperatures to climb back into the 90s even down at the beaches. Model guidance is closely clustered with temps next week. && .AVIATION /16Z SATURDAY THROUGH WEDNESDAY/... As of 12Z Saturday...Expect periodically lowered cigs and vsbys, mainly into the MVFR category, starting this afternoon and continuing overnight in scattered to widespread convection. Good confidence that the remainder of this morning will remain VFR. Extended Outlook...The threat for flight restrictions due to thunderstorms continues Sunday into early next week, as a frontal boundary drops southward and stalls across the forecast region. && .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 1015 AM Saturday...The sfc pg ahead of the approaching cold front will keep SW winds active to around 15 kt with gusts up to 20 kt especially nearshore during the height of the sea breeze circulation. Significant seas will run 2 to 4 ft. The persistent ESE ground swell at 8 to 9 second periods of the past few days, has now subsided back to around 1.5 ft. The 3 to 5 second period wind driven waves will become the dominant feature in the seas spectrum, especially once the sea breeze circulation sets up. Previous..................................................... As of 230 AM Saturday...A cold front currently over the Ohio River Valley moves into the central portion of North Carolina and stalls. This will keep the pressure gradient tight enough to allow for southwest winds of 15 knots this morning. As the pressure gradient slowly relaxes by this afternoon winds will weaken to 10 knots. Seas are expected to be around 3 feet with 4 footers north of Cape Fear early today and the seas will slowly settle out to 2 to 3 feet by Saturday night. SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... As of 230 AM Saturday...A weak pressure gradient will prevail through the short term as the western extension of the Bermuda high pushes south and east with the approach of a weak cold front. Winds will remain primarily from the S and SW at around 10 kts through the period as the front stalls over the central Carolinas. Seas will range from 2 to 3 ft through Monday night. The primary threat through this period will be in the form of convection, with increased chances for showers and thunderstorms for both days. LONG TERM /TUESDAY THROUGH WEDNESDAY/... As of 300 PM Friday...Weak low pressure along a cold front near Washington DC Tuesday will dissipate Wednesday. The Bermuda high will remain well offshore of the Carolinas and should have only a peripheral influence on our weather. South to southwest winds should dominate Monday through Wednesday, but with wind speeds generally remaining 10 knots or less outside of thunderstorms. The best potential of thunderstorms should exist Monday and Tuesday, diminishing substantially by Wednesday as high pressure aloft begins to build in from the west. && .ILM WATCHES/WARNINGS/ADVISORIES...
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SC...Heat Advisory until 7 PM EDT this evening for SCZ017-023-024- 032-033-039-053>056. NC...Heat Advisory until 7 PM EDT this evening for NCZ087-096-099- 105>110. MARINE...None.
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&& $$ SYNOPSIS...REK NEAR TERM...DCH/DRH SHORT TERM...REK LONG TERM...TRA AVIATION...REK

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