Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 230558 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 155 AM EDT Sun Apr 23 2017 .SYNOPSIS...
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A cold front will push southward through North Carolina overnight, reaching the South Carolina border by daybreak. A strong low pressure system will slowly cross the region through Tuesday.
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&& .NEAR TERM /THROUGH TONIGHT/... As of 950 PM Saturday... Colder air has begun to overspread central NC from the north. Temperatures at mid-evening ranged from the lower 50s far north to the mid-upper 70s far south. The cold front, which marked the leading edge of the change in air mass, stretched west-to-east from Albemarle to Ft Bragg to south of GSB at 01Z. This boundary should exit our southern counties prior to midnight. Area of showers will overspread most of central NC behind this boundary overnight as an upper level disturbance exits the TN Valley and crosses our region. Could see a few isolated elevated storms though severe parameters are much weaker than compared to earlier in the day. Still expect the bulk of the showers overnight to occur across the Piedmont counties and the northern coastal plain where better forcing will exists. Rainfall amounts expected tonight will total a half inch or less, so not expect anything to set off any flooding. The rain tonight into early Sunday will prime the soils for the heavier, more prolonged rain expected later Sunday into early Monday. Main adjustment to the near term forecast was to bring the colder air in faster than previous forecast as temperatures at mid evening were running some 2-4 degrees colder across the north than expected. This required a downward tweak in the minimum temperatures, primarily across the south. && .SHORT TERM /SUNDAY THROUGH TUESDAY/... As of 355 PM Saturday... ...Flood Watch from midnight tonight through 800 AM Tuesday... The beginning of a long duration rain event will be underway over the western and central Piedmont by 12z/Sunday. The mid/upper trough is forecast to become negatively tilted during this period as it drifts ESE from the Tennesse Valley region across the southern Mid- Atlantic states. At the surface, a backdoor cold front will also begin Sunday either over far southern NC or near the NC/SC border region. This will place nearly all, if not all of central NC in the cooler stable air. Models suggest that a surface low pressure will be located over NW Georgia around 12z/Sunday, then move east across eastern GA and SC Sunday PM. As the low pressure slowly strengthens as it moves east across SC Sunday night and Monday, the low level boundary should back NW and just inland of the coast Monday. This still leaves central NC on the cool, wet side of the boundary with copious amounts of very moist warm air advection from off the Gulf Stream and western Atlantic expected to ride up and over the frontal zone. This occurs as the mid/upper system becomes more negatively tilted as it essentially crawls eastward, just to our south Sunday night and Monday. The heaviest rain is expected to fall along and north of the frontal zone through the period as the strong dynamic forcing slowly advances east across the area. This will place the Piedmont and Sandhills in the heaviest rain Sunday. The heaviest rain is forecast to spread east with time, covering much of our region Sunday night into Monday. Models are not as robust with the elevated instability Sunday night and Monday as they are on Sunday. However, the influx of very high precipitable waters off the Gulf Stream and western Atlantic should will aid in heavy rainfall at that time. The threat of flooding will be the main hazard with this system since our region will be in the more stable area north of the main frontal zone. QPF storm total for the entire event is on the order of 3-5 inches, with potentially 6 inches locally. The main time frame for the heaviest rain should be from midnight tonight through midnight Monday night. Flash Flood Guidance numbers will lower with time, which are currently running high. 6 hour FFG is on the order of 2.5 to 3 inches, and this will lower to around 1.5 inches by Sunday afternoon. Urban areas have much lower thresholds, and they will become an issue well before the rural locations. The soils, which have recently been dry will become wet and saturated with the showers/storms this evening into Sunday. This will lead to runoff issues with the widespread heavy rain Sunday afternoon through Monday evening. Gusty NE winds will be felt in all zones with sustained winds of 15-25 mph, gusts to 30-35 Sunday into Monday. Less important forecast parameters include the temperature forecast which will be much cooler with the heavy rain and breezy NE winds. Highs Sunday should only be in the 50s/60s NW/SE both Sunday and Monday. Lows will be only about 5-7 degrees lower than daily maxes, if that. The heaviest rain should move offshore on Tuesday or Tuesday evening, with the threat of moderate river flooding on the main stem rivers expected into late week. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... As of 345 PM EDT Saturday... Much warmer air associated with a building subtropical mid level ridge can be expected late week into the weekend when highs should solidly get into the 80s. && .AVIATION /06Z Sunday through Friday/...
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As of 155 AM Sunday... High confidence in poor aviation conditions over the next 24 hours, With IFR conditions common in all locations except mostly MVFR at FAY. A cold front dropped southward into and through NC this past evening, and is now settling near the NC/SC state line. This front will remain stretched across northern SC and southeast NC through the next 24 hours, while surface low pressure drifts slowly from northern AL toward southwest NC, and strong mid level low pressure passes over the Mid South. This will all keep unsettled weather over central NC, with deep moisture leading to low cigs, lowest at INT/GSO, through Sunday night, with periods of MVFR to IFR rain, most widespread at INT/GSO but likely everywhere. Surface winds will be mainly from the NE at 10-15 kts gusting to 15-20 kts infrequently through Sunday night. While winds aloft (4000-5000 ft AGL) will be strengthening from the SE late Sunday through Sunday night to 25-35 kts, however the shift of winds in the vertical from NE to SE through the low levels will not meet low level wind shear criteria, although it may make handling of small aircraft difficult. Looking beyond 06z Mon: Poor aviation conditions will continue to dominate through Monday night as the deep low pressure system slowly crosses the region, with periods of rain through Mon, tapering down from south to north Mon night, and persistent low MVFR/IFR cigs and vsbys. Cigs should rise gradually to MVFR areawide Tue as the mid level low slowly departs the area, then trend to VFR Tue night lasting through Fri with a drier air mass and deep SW flow, although a few afternoon showers are possible Thu/Fri. -GIH
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&& .RAH WATCHES/WARNINGS/ADVISORIES... Flood Watch through Tuesday morning for NCZ007>011-021>028-038>043- 073>078-083>086-088-089. && $$ SYNOPSIS...Hartfield NEAR TERM...WSS SHORT TERM...Badgett LONG TERM...Badgett AVIATION...Hartfield

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