Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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563 FXUS62 KRAH 290624 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 222 AM EDT Wed Mar 29 2017 .SYNOPSIS... Weak high pressure will move over central NC today and remain in control through Thursday before low pressure brings unsettled weather to the area for Friday and Friday night. && .NEAR TERM /THROUGH TONIGHT/... As of 915 PM Tuesday... Last bit of convection has exited the SE zones over the past hour, in concert with the exiting upper level trough and attendant deeper moisture moving off the Mid-Atlantic coast. At the surface, lead sfc front/trough has pushed east into the area, most distinguishable by the drier/lower sfc dewpoints that have advected into the NC Piedmont and Sandhills. However, it will be with a secondary NELY surge behind a back-door cold front late tonight between 06 to 12z that will bring the noticeably cooler air into the area. NAM fcst soundings and HRRR depict a layer of low-level moisture stratus advect into the area within the low-level NELY flow. Will increase cloud cover the north and northeast. Lows tonight in the lower to mid 50s. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY/... As of 335 PM Tuesday... Wed-Wed Night: With shortwave ridging aloft, expect mostly sunny to partly cloudy skies and above normal temps in the mid/upper 70s Wed afternoon. Subsidence in the wake of an upper level low moving offshore New England Wed evening will result in pressure rises along the eastern seaboard as an inverted sfc ridge extends southward through the Mid-Atlantic into the Carolinas, the leading edge of which will be marked by a backdoor cold frontal passage /wind shift to the NE at ~15 mph/. Lows Wed night will be determined by the precise timing of fropa. Based on the latest guidance, expect temps ranging from the mid 40s NE Coastal Plain to lower 50s in the SW Piedmont. Thu: In the wake of the backdoor cold front, NE low-level flow will veer to the E/ESE during the day, allowing temperatures to recover into the mid/upper 60s to lower 70s across the Sandhills and SE Coastal Plain Thu afternoon. A cold air damming wedge is expected to develop across portions of the Foothills and N/NW Piedmont as warm advection (via SW H85 flow) strengthens atop the shallow cooler airmass in place near the surface. As a result, broken/overcast cloud cover should largely offset diurnal heating across portions of the N/NW Piedmont where highs may struggle to exceed the mid 50s, esp in Forsyth county. -Vincent && .LONG TERM /Friday through Tuesday/...
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As of 220 AM Wednesday... Fri/Fri night: Stormy weather for central NC, as a mid level low will move over the Ohio Valley and central Appalachians to off the Mid Atlantic coast, a path which models agree fairly closely on, although the ECMWF is much weaker with this low than the GFS/NAM. A band of vorticity trailing this low down through the Mid South and Gulf early Fri will swing ENE with a negative tilt through the central Carolinas Fri morning, accompanying enhanced upper divergence and high PW nearing 1.5". Models including the SREF, NAM, GFS/GEFS, Canadian, and MPAS are unanimous with widespread showers/storms Fri morning into the afternoon, so will have categorical precip chances, trending down a bit from the SW late in the day and into Fri evening as the trough axis and DPVA pivot to our ENE, bringing partial drying in the mid/upper levels. While the mid and low level lapse rates are generally under 7 C/km and the strongest forcing for ascent is on track to move through the area prior to peak heating, the GFS spreads surface CAPE of 800-1200 J/kg through cntrl/E NC Fri afternoon, buoyed by a surge of high surface dewpoints of 55-60F, and kinematics are quite strong with 40-50 kts of deep layer shear and 150+ m2/s2 of 0-1 km helicity, so we may still see a few strong to severe storms Fri, generating both large hail and damaging winds, as well as a tornado risk, especially near the northward-retreating surface frontal zone possessing strongly curved low level hodographs. Precip chances should be ending over the NE CWA late Fri night as the mid level low/trough starts heading off the Delmarva coast, with a trailing front working eastward through the NW Piedmont of NC. Expect highs in the upper 60s/lower 70s followed by lows in the low-mid 50s. Sat through Sun night: Fairly quiet weather this weekend. The surface front is likely to settle near the NC/SC border, with no strong push in either direction, as initial weak NW mid level flow behind the exiting trough is slowly supplanted by a mid level ridge axis shifting eastward over the Southeast by late Sun. There`s no polar air behind this front, as a somewhat mild high crosses the Great Lakes region and Northeast. But models do suggest that the northeasterly low level flow into NC will draw in enough low level moisture within the low level stable layer to generate nighttime and morning stratus Sat night/Sun morning and again Sun night, with partial mixing-out during the daytime Sun for partly to mostly sunny skies. Model thicknesses are generally slightly above normal Sat and near normal Sun, suggesting highs in the low-mid 70s Sat, lows 47-52 Sat night, and highs Sun 67-73. Lows Sun night in the upper 40s to lower 50s, with fair skies NE and increasing clouds SW as the surface high moves off the Mid Atlantic coast, yielding gradually strengthening overrunning flow from the SE. Mon through Tue: More stormy weather as yet another potent wave tracks from the S Plains E then NE through the lower Miss Valley, dampening slightly as it traverses the Mid South and Central Appalachians. Model timing differences of as much as 12 hours make it impossible to pin down the details at this range, but it appears likely that we`ll see good coverage of showers and storms from Mon afternoon well into Tue, with the potential for some of these to be strong, provided there isn`t too much weakening as the shortwave trough approaches. The active southern-stream-dominant pattern favors temps continuing a category or two above normal. -GIH
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&& .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... As of 210 AM Wednesday... 24 Hour TAF Period: Some concern this morning over the development of some potential fog in the northeastern areas this morning. HRRR visibilities show fog skirting KRWI but not actually occurring at the airport. This may be in part due to earlier rainfall that occurred mainly north of the KRWI area. Closer to sunrise there is some hinting that at least scattered if not broken clouds in the MVFR range may move into the northeast as well and potentially affect KRWI and KRDU. These ceilings could persist through to almost 18Z before lifting later this afternoon. Otherwise expect VFR conditions and northeasterly winds. Long term: A low pressure system will cross the area on Friday through Friday night with the potential for showers and thunderstorms. High pressure with VFR conditions should return for the weekend. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Ellis NEAR TERM...CBL SHORT TERM...Vincent LONG TERM...Hartfield AVIATION...Ellis

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