Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 270838 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 338 AM EST Mon Feb 27 2017 .SYNOPSIS... High pressure will move offshore today, followed by a warm front lifting through the area tonight. Meanwhile, warm southwesterly flow will continue ahead of a cold front approaching from the west through midweek. && .NEAR TERM /THROUGH TONIGHT/... As of 340 AM Monday... A 1028mb surface high is centered off the Delmarva this morning and will continue to shift east today, resulting in a light southerly flow that will increase 1000-850mb thickness by about 25m over Sunday. Thin high clouds will spread in from the southwest ahead of a shearing shortwave currently over MO/AR, but thicker mid clouds should hold off until this evening and the impacts on highs look negligible. The 25m increase in thicknesses supports guidance consensus of lower 60s northwest to 70 southeast. The aforementioned sheared shortwave will cross the region tonight, leading to increased cloud cover, initially mid/high level and then later in the form of stratus associated a warm front and strengthening warm advection. Most models continue to be essentially dry overnight, as upstream precip should dissipated with eastward extent this evening. However, the NAM still indicates some light showers breaking out with the warm front after midnight, due at least in part to some questionable elevated instability, and the 00Z ECMWF supports at least a slight chance POP after midnight. Mid and high clouds look like they`ll move east by midnight and may yield a period of brief clearing before stratus develops across the west. This should allow temps to fall into the mid 40s west to lower 50s east. && .SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/... As of 340 AM Monday... West-southwest flow will ensue on Tuesday as a surface warm front lifts north of the area. Morning stratus will likely hold longest across the west but full heating is expected for a large portion of the area as period of high clouds spread east in relatively unamplified flow. 1000-850mb thicknesses support highs in the lower 70s west to near 80 east. Dewpoints creeping into the upper 50s and modest 6.5-7 C/KM mid level lapse rates will lead to weak instability, but forcing is largely lacking outside of warm advection. Currently think showers and a few storms will be widely scattered across the Piedmont and coastal plain. Tuesday will be rather mild in the warm sector of a stronger low pressure system moving through the Midwest, with lows in the upper 50s and lower 60s. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... As of 255 PM Sunday... Tue/Tue night: The most likely scenario is that the warm front will be pushing NNW into the area early Tue, with the morning hours featuring low stratus in the west, where the stable pool should linger, and partly cloudy in the east, with isolated light precip in the west supported by moist isentropic upglide. Models show the entire area mixing and destabilizing during the afternoon, although climatology would suggest that the NW CWA could stay somewhat stable all day. Models depict marginal to moderate instability developing mainly along and east of Highway 1 in the mid-late afternoon, with good low level moisture streaming in, improving deep layer shear, and decent mid level lapse rates of 7.0-7.25 C/km. Dynamics are slim however, with a fairly flat mid level flow, and only weak upper divergence. Will have a slight chance of showers in the afternoon in the west, with a better chance of showers and thunderstorms in the east, lasting into the evening before the loss of heating prompts a trend down to small shower chances and the development of stratocumulus overnight. These clouds should mix out with heating Wed as we`ll be firmly in the warm sector, with a stout gusty breeze from the SW ahead of the cold front, which should push SE through the area Wed evening or Wed night (the GFS is several hours faster than the ECMWF and NAM). GFS instability is a bit higher Wed afternoon as compared to Tue, reasonable given the even greater influx of low level moisture, and if the slight cap noted around 800 mb on GFS forecast soundings comes to fruition, in conjunction with the GFS`s projected 7.5-8.0 C/km mid level lapse rates and strengthening deep layer bulk shear to 55-65 kts, we could get rapid development and intensification of convection during the afternoon, especially over the eastern CWA, with some late-day severe storms possible. This convection should remain supported by a pocket of strong upper divergence as it shifts over eastern NC through late evening, followed by frontal passage, although high clouds should persist over the area through Wed night as the positively tilted mid level trough will still be well off to our NW. With warm thicknesses, expect highs of 70-77 Tue except for mid-upper 60s NW. Morning thicknesses Wed around 1380 m, nearly 60 m above normal, will support highs from the mid 70s NW to lower 80s SE. Thu through Sun: A generally tranquil period with dry weather likely. The cold front will be pushing southeast ward off the coast Thu morning. Broad mid level troughing will persist over central/eastern Canada and the northeast CONUS into Sat, with the core of the polar low transferring from Hudson Bay to Newfoundland. An initial ridge of high pressure nosing in from the WSW Thu will bring thicknesses that are close to seasonal normals. Then, energy that swings through the trough base across the Mid Atlantic/Northeast on Friday will bring a reinforcing dry cold front southeastward through the area, followed by chilly high pressure that will build overhead by Sat morning. This should knock temps down to below normal for Fri night/Sat, with a good chance of orographically enhanced high clouds over the Piedmont early Sat within fast perturbed mid level flow. Temps should moderate for Sun as the highs drops to our SE with return flow and weak lee troughing for the latter half of the weekend. -GIH && .AVIATION /08Z MONDAY THROUGH FRIDAY/... As of 1245 AM Monday... High confidence in VFR today under influence of high pressure. A light south-southwest wind will develop today as the high moves east. Mid and high level clouds will increase this evening as a weakening upper level disturbance moves overhead and a warm front lifts north into the Carolinas. More substantial stratus, MVFR to IFR, will likely come after 06Z, but there is a small chance some MVFR ceilings, along with a few weakening showers, could develop at GSO and INT by 06Z Tuesday. Outlook: Stratus developing early Tuesday will burn off prior to midday, with scattered showers and storms possible during the afternoon and evening. A more substantial threat of sub-VFR is expected late Wednesday and early Thursday a cold front crosses the region. VFR will then return for the end of the week. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...SMITH NEAR TERM...SMITH SHORT TERM...SMITH LONG TERM...HARTFIELD AVIATION...SMITH

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