Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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691 FXUS62 KRAH 250744 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 344 AM EDT Fri May 25 2018 .SYNOPSIS... High pressure centered over the western Atlantic will extend westward across the Carolinas today. The resulting wind flow from the south, along with an upper trough approaching from the west, will lead to increased cloud cover and unsettled weather over the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 240 AM Friday... A fairly quiet day expected, particularly over the NE. Surface high pressure has drifted off the Mid Atlantic coast, and will continue to extend back across NC today/tonight, as the narrowing and weakening mid level ridge noses in from the SE. The resulting low level flow from the SE and S is quite light but projected to increase a bit through the day, causing sufficient low level mass convergence over the W CWA for low clouds early this morning. These should be slow to lift with tempered heating today, leading to slow partial clearing by afternoon, as the NE CWA stays partly to mostly sunny within the greater influence of the ridge. GOES water vapor channels show well the deep dry air over the northern two-thirds of the forecast area, with deeper moisture across far southern NC, north of the dissipating surface front that dropped through the area Thu. This moisture is expected to pivot clockwise with an increasing low level upslope component, and PW rising to over 1.75" over our far S and W sections. Forcing mechanisms are restricted to weak DPVA riding northward into W NC around the edge of the ridge tonight, and this may be just enough to spur a few showers and isolated afternoon storms (with marginal CAPE expected) through tonight. Will maintain low chance pops in the far SW, spreading to cover the W half of the CWA tonight as 700 mb steering flow veers to southwesterly and strengthens overnight. Highs in the low-mid 80s W and mid-upper 80s E. Lows in the upper 60s to around 70. -GIH && .SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/... As of 255 AM Friday... Moisture will continue to deepen across W NC, as the influence of both the surface and upper ridge axes across the area decrease. Deep layer wind flow strengthens considerably from the SW, evident from 925 mb up through 700 mb and strongest over W NC, as broad troughing aloft crosses the Great Lakes region and becomes loosely linked to low pressure over the Gulf. Shower and afternoon storm chances will increase Sat morning across the NW half of the forecast area, and while pops will be non-zero elsewhere (the SE half), the Gulf low may serve to build the ridge extending through NC Sat/Sat night, resulting in a greater chance of neutral to sinking air through the column. Highs from the lower 80s NW to the upper 80s over much of the SE half of the forecast area, under partly (SE) to mostly (NW) cloudy skies. Shower/storm chances will hold through the evening mainly NW but will drop overnight as models indicate a band of lower PW spreading northward through NC late. Expect considerable mid and high clouds to persist, but will trend down to no pops late Sat night. Lows within a degree or two of 70 everywhere. -GIH && .LONG TERM /SUNDAY THROUGH THURSDAY/... As of 345 AM Friday... Sunday will start out fairly dry for central NC as the area will be between a frontal zone to the north and what could be the first tropical system of the year to the south. That frontal zone to the north will become more active with the heating of the day and possibly impinge upon our northern and western counties by late afternoon. Overnight Sunday night into Monday morning the first wave of tropical moisture will arrive from the south with some upper level support and this could linger in the area through early Tuesday morning. Periods of heavy rain can be expected during this time, particularly across southern and eastern areas. This wave will move out to sea on Tuesday and thus Tuesday could be fairly dry with attention turning to the next wave of tropical moisture which will enter the southwest Piedmont by late Tuesday evening and progress northeastward across our area on Wednesday. All of this depends upon the actual track of the low which is still very much in doubt at this point but the more consistent EC solution keeps it west of the Appalachians as it moves northward. The system is then expect to take a turn to the east on Thursday, keeping rain chances in the forecast through the end of the forecast period. Rain and potential flooding will be the main point of emphasis as far as impacts are concerned for central NC. Wind will not be an issue with this system in this area. Urban and small stream flooding risk will be the greatest risk early on with river flooding possibly becoming a problem later in the period depending on actual rainfall totals and observed locations. Temperatures through the period in the 80s for highs with lows in the upper 60s to low 70s. && .AVIATION /06Z FRIDAY THROUGH TUESDAY/... As of 220 AM Friday... Chances are good of MVFR to IFR cigs developing early this morning (by 08z) at INT/GSO, a result of low level moisture pooling within a light SE flow. These low cigs will be slow to rise with heating through the MVFR category, likely not reaching VFR until close to 18z. Elsewhere, VFR conditions are expected as the offshore-centered high pressure stays in control. Patchy showers and perhaps an isolated storms are possible this afternoon (mainly 16z-21z) near INT/GSO, with other locations staying dry. VFR conditions are expected to rule at all locations from mid afternoon through 06z tonight. Surface winds will be light, under 10 kts, mainly from the SSE or SE through tonight. Looking beyond 06z Sat, sub-VFR conditions, mainly low cigs, are likely late tonight, 08z-13z, at all sites. These should lift to VFR by 15z Sat with an increasing surface wind from the SW, along with increasing shower/storm chances, especially at INT/GSO Sat afternoon and evening. This scenario is expected to repeat on Sun, with sub- VFR daybreak conditions and a risk of afternoon storms, mainly in the NW CWA. Rain chances may rise further Sun night into Mon as tropical moisture lifts into the area from the SSE, bringing a good chance of sub-VFR conditions into early Mon. Mon/Tue are likely to remain unsettled, with considerable clouds, better-than-usual rain chances, and a high probability of sub-VFR conditions. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...Hartfield SHORT TERM...Hartfield LONG TERM...Ellis AVIATION...Hartfield is the U.S. government's official web portal to all federal, state and local government web resources and services.