Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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093 FXUS62 KRAH 240429 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1229 AM EDT Sat Jun 24 2017 .SYNOPSIS... Low pressure will pass to our northwest, crossing the central Appalachians later tonight into Saturday morning, before moving off the Mid Atlantic coast. This will drag a trailing cold front through central NC late Saturday through Saturday night. High pressure will follow, bringing cooler and drier air into our region for next week. && .NEAR TERM /THROUGH TONIGHT/...
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As of 1225 AM EDT Friday... There would appear to be a risk of strong to severe storms during the next several hours over the Piedmont, as the current band of fast-moving, but generally weak convection crossing the Foothills encounters an instability axis of 1000-1500 J/KG MLCAPE centered over central NC. While the consensus of NWP guidance suggests this activity will further weaken with time and ewd extent, observational and objective analysis data would indicate otherwise. The height gradient and associated deep layer wind fields on the sern periphery of Cindy will remain strong for several more hours, before weakening by around 09Z, as the remnant Cindy circulation moves to the Mid-Atlantic coast. Resultant effective bulk shear and SRH values of 35-40 kts and 200-300 m2/s2, respectively, would support organized storm modes, including supercells/bows, with right- moving supercells favored owing to strongly-cyclonically-curved hodographs during the next several hours, before the height/wind field weakens. Damaging wind gusts and an isolated tornado or two may result, mainly west of U.S. Hwy 1. Radar trends indeed support an uptick in convective intensity and organization from Statesville to Gastonia, NC. As of 950 PM EDT Friday... Nothing on radar this evening except for a few sprinkles which is a nice change from previous days. This is not the case to our west however as the remnants of Cindy have combined with a frontal system that runs along much of the expanse of the Appalachians with the heaviest rainfall across the Ohio Valley. A relative minimum in the rainfall over eastern Tennessee will make its way eastward overnight but continuing to die out as it does so. It is possible to have some showers into the Triad between 6-9z but should die out by 12z. As far as stratus is concerned, some MVFR ceilings are possible in the triad but further east conditions should remain VFR. Part of the reason for this is that forecast soundings show good mixing down to the surface overnight and we have already seen some gusts to 15 kts start to make their way into the observations. This is expected to continue overnight and will likely increase in frequency and coverage. Temperatures across the area remain the the upper 70s to lower 80s with dewpoints in the upper 60s to mid 70s. Lows will only reach the mid 70s.
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&& .SHORT TERM /SATURDAY THROUGH SUNDAY/... As of 135 PM EDT Friday... A cold front will approach the central Appalachians from the NW late tonight. With the remnants of Tropical Cyclone Cindy progged to track a bit further N/NW of central NC than previously anticipated, the cold front is not expected to progress into central NC until Sat evening/night. With central NC on the eastern periphery of the pre- frontal trough, rich low-level moisture is likely to persist through the afternoon. Strong insolation and rich low-level moisture are expected to yield moderate instability by mid/late afternoon, ranging from ~1000 J/kg in the NW Piedmont to ~2000 J/kg in the SE Coastal Plain, in the presence of 30-40 knots of deep-layer shear. Convection allowing models suggest scattered convection will develop within the pre-frontal trough in vicinity of the I-77 corridor by mid/late afternoon (19-20Z), then quickly grow upscale into a SW-NE oriented line that progresses E/SE through central NC between 21-00Z (roughly). Though diurnal timing will be optimal, rich boundary layer moisture /relatively low T/Td spreads/ will yield marginal DCAPE (500-750 J/kg) and line-parallel (southwesterly) deep-layer shear will not favor new updraft development at the leading edge of the consolidated cold pool. As a result, the potential for damaging winds appears relatively marginal /isolated/. Expect highs ranging from the mid/upper 80s (NW) to lower 90s (SE). -Vincent Saturday night and Sunday, a sfc boundary trailing behind a low pressure system crossing the northern Mid-Atlantic, will cross central NC Saturday night and Sunday. This front interacting with a moisture rich air mass will support the development of scattered- numerous showers and thunderstorms Saturday evening. Bulk of convective will dissipate overnight Saturday night though isolated- scattered showers still probable due to the presence of the front and available moisture. By Sunday, the main focus for convective development should be primarily east and south of Raleigh as the front should lie in this vicinity. Nwly flow behind the front will advect a drier more stable air mass into the Piedmont Sunday, leading to drier conditions. -WSS && .LONG TERM /SUNDAY night THROUGH FRIDAY/... As of 305 PM EDT Friday... The drier air mass will overspread the remainder of central NC late Sunday and Sunday night. Monday shaping up to be warm and dry with wly flow aloft and a sfc high positioned over the TN Valley. A s/w in the northern stream projected to drop sewd across the lower OH Valley Monday night, and cross central NC Tuesday. 12Z ECMWF more adamant about the potential for lift and isolated/scattered showers compared to the drier GFS. Based on the favorable timing, potential will exists for isolated-scattered showers, primarily late morning through the afternoon. A modifying Canadian high pressure system will initiate a stretch of dry and relatively pleasant conditions (ie. less humid) across central NC Wednesday into Thursday. By Friday, return flow on the back side of the retreating high will signal a return to warm and humid conditions by the end of the week. No signals noted for extreme heat across our part of the country through the next 5-7 days. In fact, high temperatures Tuesday and Wednesday will likely average 3 to 8 degrees below normal. The modifying air mass Thursday and Friday will permit temperatures to return to seasonal norms. && .AVIATION /00Z Saturday through Wednesday/... As of 810 PM Friday... The most significant aviation hazard over the next 24 hours will be gusty winds from the SW, occurring over the next 12-15 hours, including a strong crosswind at INT. VFR conditions are expected to dominate central NC terminals through 00z Sun. Low pressure, the remnants of what was once Tropical Storm Cindy, will pass by to our NW and N tonight through Sat morning. While INT/GSO will likely see a period of MVFR cigs/vsbys in showers (with a lesser risk of thunder) between 04z and 09z tonight, this precipitation is expected to dissipate as it approaches RDU, leading to a much lower chance of MVFR conditions there, and the chance for sub-VFR conditions at RWI/FAY is even lower. Surface winds will increase from the SW through the evening, with sustained speeds reaching 15-22 kts and gusts as high as 25-35 kts, especially after midnight, lasting until just before or around daybreak Sat. Aviation interests should use extreme caution at INT, as this will present a significant crosswind at that site, and these winds may induce some low level turbulence at other locations. As the low shifts off the Mid Atlantic coast early Sat, it will drag a cold front slowly into the area, causing a shift of winds to be from the W or WSW with time Sat, but with lower sustained speeds and only sporadic gusts at most. VFR conditions will dominate Sat, although scattered thunderstorms producing brief sub-VFR conditions and enhanced gusts are expected near FAY Sat afternoon, with a lesser chance of storms near RDU/RWI. INT/GSO will remain dry. Looking beyond 00z Sun (Sat evening), mid and high clouds will continue to streak across the area, especially southern and eastern NC, through Sun. Confidence is high that VFR conditions will hold through at least Wed, with high pressure in control both at the surface and aloft. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MLM/GIH NEAR TERM...MWS/Ellis SHORT TERM...Vincent/WSS LONG TERM...WSS AVIATION...Hartfield

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