Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 231925 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 325 PM EDT SAT JUL 23 2016 .SYNOPSIS... A ridge of high pressure will expand across the Carolinas bringing increasingly hot and humid conditions through the weekend and much of next week. Isolated showers and thunderstorms are possible each afternoon, and heat advisories will likely be needed each day beginning Sunday. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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As of 330 PM Saturday...Hot and humid day continues as broad upper ridging begins to expand to the east. The combination of Bermuda high pressure and this expanding upper ridge has produced temps into the 90s away from the coast, which combined with low 70s dewpoints has pushed heat index values up over 100 degrees most areas. While this is hot, it is likely the coolest of the next several days... This heat and humidity is also leading to a highly unstable airmass. Latest analysis from SPC shows 1000-2000 J/kg of MLCAPE with LI`s to -6 and steep low level lapse rates. There is minimal mid level forcing however, but diffluence remains at jet-level in a somewhat weakened state from this morning as the RRQ of a southward sinking jet moves off the GA/FL coast. This in addition to residual outflow from this morning`s tstms has allowed convection to develop across SC, and should expand at least somewhat west this evening, with new development also possible in southern NC. No severe is expected, but very slow storm motion thanks to anti-parallel winds from the surface to the mid-levels could produce an isolated flooding threat through this evening. Convection will wane after dark with no mid- level energy expected to tap residual elevated instability. Once tstms wane, expect a clear to partly cloudy night with some stratocu possible late near the coast. Guidance was far too cool with mins last night, but the LLJ is forecast to be 15-20 kts weaker than last night, so a blend of the guidance is preferred, and lows are forecast to be a bit cooler than last night, 74 well inland to 78 near the coast. While fog is not forecast to be widespread or significant, some patchy fog is possible where rain has been heaviest. Local UPS Fog procedure develops just some spotty fog, so have left any mention out of the Wx grids as most areas will keep unrestricted visibility.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/...
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AS OF 330 PM SATURDAY...Hot and dry will be the rule beginning Sunday as a massive ridge of high pressure envelops much of the southern tier of the CONUS. Although the ridge itself does not have tremendous latitudinal amplitude, it is quite strong and 1000-500mb thicknesses rise towards 580dm Sunday and Monday, with heights climbing towards 595dm directly overhead the Carolinas by Monday aftn. At the same time, 1000-850mb thicknesses approach 1435m, fueling 850mb temps around 20C. This ridge suppresses a weak mid-level low to the SW, moving overhead Florida late Sunday, with easterly flow developing through all but the lowest 100-150mb of the column. Typically this is a moistening flow direction, but in this case trajectories originate from a dry air mass offshore, and PWATs drop towards the bottom quartile for late July by Monday. At the surface, return flow prevails however, so ample sunshine combined with warm/moist flow and bulging thicknesses aloft will create hot and humid conditions but with very few tstms. Highs Sunday will rise well into the 90s, with mid 90s expected inland and around 90 at the beaches. On Monday, temps will be just a bit cooler thanks to the aforementioned upper low causing slightly reduced thicknesses, but will still rise into the low 90s. These hot temps combined with dewpoints climbing back into the low/mid 70s, will necessitate a heat advisory for Sunday, and one has been issued, valid from 11am to 8pm, for all zones. Slightly cooler temps and and lower dewpoints Monday will keep heat index values just below advisory thresholds. Mins both nights will be well above climo, mid and upr 70s. While the airmass will be very unstable this period, convection will be isolated at best, thanks to increasingly dry air aloft and warming mid-level temps. Although 500mb and 850mb temps drop a bit on Monday, the airmass dries even further, so will cap POP at SCHC Sunday and Monday, with the highest values along the sea breeze in SC.
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&& .LONG TERM /TUESDAY THROUGH SATURDAY/...
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AS OF 330 PM SATURDAY...Overall medium range guidance is pointing to strong mid level ridging, on the order of 594DM Tuesday into Wednesday. Heights slowly fall from that point onward through the remainder of the period. Other than the Piedmont trough, still not much in the way of forcing for convection. Certainly subtle mid level features will help to kick off activity but all but impossible to pinpoint at this time. The forecst of slowly increasing pops still looks good with the best chance Thursday when PWs jump to just over two inches. No changes to the temperature forecast.
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&& .AVIATION /19Z SATURDAY THROUGH THURSDAY/... As of 18Z...Potential for MVFR in afternoon thunderstorms at KLBT and KFLO. Otherwise, expect VFR through the valid TAF period at all the terminals. Scattered showers and thunderstorms are expected to develop along the seabreeze and Piedmont trough as well as along residual outflow boundaries left over from morning convection. The high resolution models are showing the convection developing W of the coastal terminals with only slight movement to the S. Thus, will only include tempo for MVFR ceilings and visibilities at the inland terminals 18-21z. Winds may briefly gust to 25 kt or higher in slow moving thunderstorms, otherwise south winds will be 10 kt or less and up to 11 kt at KMYR and KCRE into early eve. EXTENDED OUTLOOK...Isolated to scattered afternoon convection Tuesday through Thursday may create periods of MVFR/IFR. Otherwise expect VFR. && .MARINE...
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NEAR TERM /THROUGH TONIGHT/... As of 330 PM Saturday...SW winds of 5-10 kts this aftn will slowly increase tonight to 10 to as much as 15 kts around offshore Bermuda high pressure. Near shore, a sea breeze has backed winds to the south with a subtle increase in speed, but this will gradually return to the synoptic SW flow this evening. Seas will remain 2-3 ft, with an 8 sec SE swell and 4 sec SW wind wave comprising the spectrum. SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... AS OF 330 PM SATURDAY...Bermuda ridging will remain the most influential feature through the short term, creating consistent wind and wave conditions. SW winds will prevail both days, with speeds increasing from around 10 kts Sunday, to 10-15 kts on Monday. A persistent but weak 2ft/8sec SE swell will exist in the spectrum, but avg wave periods will gradually shorten as a SW 4-5 sec wave amplifies. Wave heights will be 2-3 ft through Monday, becoming more uniformly 3 ft late. LONG TERM /TUESDAY THROUGH THURSDAY/... AS OF 330 PM SATURDAY...Expect south to southwest winds of 10-15 knots through the period as the Bermuda Azores high pressure system and the Piedmont trough are the main drivers of winds. Significant seas will be 1-3 feet with wave periods mostly confined to shorter period wind waves.
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&& .ILM WATCHES/WARNINGS/ADVISORIES...
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SC...Heat Advisory from 11 AM to 8 PM EDT Sunday for SCZ017-023-024- 032-033-039-053>056. NC...Heat Advisory from 11 AM to 8 PM EDT Sunday for NCZ087-096-099- 105>110. MARINE...None.
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&& $$ SYNOPSIS...SHK NEAR TERM...JDW SHORT TERM...JDW LONG TERM...SHK AVIATION...RJD

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