Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 251511 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1111 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/...
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As of 1110 AM Friday... Latest surface analysis shows surface high pressure centered off the Mid-Alantic coast with a weakening stationary from extending across SOuth Carolina into Georgia. Further aloft, a ridge of high pressure extends from the subtropical Atlantic northwest across the Carolinas into the southern Appalachains. An embedded shortwave in the ridge across western South Carolina this morning will slowly lift north across western NC this afternoon and evening. As a southerly flow continues to become established, low level moisture and instability will increase especially across the southern and western Piedmont and the Sandhills, with a more stable air mass across the east and especially northeast. Widely scattered showers and a few thunderstorms will develop early this afternoon in an arc from the southern Coastal Plain northwest to the Triad with somewhat more numerous showers and thunderstorms lifting north across the western Piedmont later this afternoon and evening. Convection allowing models highlight the ongoing activity in South Carolina well this morning and support the evolution noted above. SPC has central NC outlined in generaly thunder for today and don`t expect much if anysevere weather given weak instability and light southeast to southwest flow with bulk shear values of around 10kts. Locally heavy rain resulting will be a limited threat. Highs today will range in the lower to mid 80s with lows in the upper 60s to around 70. -Blaes
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&& .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 /15Z FRIDAY THROUGH TUESDAY/... As of 615 AM Friday... MVFR to IFR cigs developed early this morning over the western forecast area including 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 today, likely not reaching VFR until close to 18z. Elsewhere, VFR conditions are expected as the offshore-centered high pressure stays in control. Patchy MVFR showers and an isolated storm or two are possible this afternoon (mainly 17z-22z) near INT/GSO and possibly approaching RDU, with other locations staying dry. VFR conditions are expected to rule at all locations from mid afternoon through 06z tonight. Sub-VFR conditions, mainly low cigs, are likely late tonight, after 08z, at all sites. Surface winds will be light, under 10 kts, mainly from the SSE or SE through tonight. Looking beyond 12z Sat, these sub-VFR cigs should lift to VFR by 16z 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...BLAES SHORT TERM...HARTFIELD LONG TERM...Ellis AVIATION...HARTFIELD

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