Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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308 FXUS62 KRAH 261958 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 300 PM EST Sun Feb 26 2017 .SYNOPSIS... High pressure over the area will move offshore late tonight and into the day on Monday. A warm front will approach from the south Monday night, then move north of the region Tuesday. Warm southwesterly flow will continue ahead of a cold front approaching from the west. && NEAR TERM /TONIGHT/... As of 250 PM SUNDAY... Flow aloft has become quasi-zonal in the wake of upper trough exiting the Mid-Atlantic region. While at the surface, modified cP parent high centered over the TN Valley this morning will shift east over the area through the afternoon and then slip offshore late tonight and into the day on Monday. Batch of broken high clouds in advance of the sheared shortwave energy ejecting eastward across the Lower MS Valley will bring an increase in high clouds late tonight/during the predawn hours Monday morning, which could temper low temps just a bit. Overnight lows in the 30s. && .SHORT TERM /MONDAY AND MONDAY NIGHT/... As of 250 PM SUNDAY... Surface ridge axis will extend west into the area from the parent high centered off the Mid-Atlantic coast. Resultant southerly- southeasterly low-level flow will allow for moderation of cP airmass with highs Monday a good 7 to 10 degrees warmer than Sunday. Highs ranging from lower 60s NW to upper 60s/near 70 SE. Strengthening southwesterly low-level WAA ahead of the sheared low- amplitude shortwave trough moving into region will result in increasing clouds by the late afternoon with isolated to scattered showers possible during the evening and into the overnight hours. The NAM is especially wet as it develops 500-750 J/Kg of elevated instability across the area, but believe this to be a bit overdone. Much warmer overnight lows in the upper 40s to lower/mid 50s. && .LONG TERM /Tuesday through Sunday/...
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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
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&& .AVIATION /18Z SUNDAY THROUGH FRIDAY/... As of 1227 PM Sunday... 24 Hour TAF Period: There is high confidence of VFR conditions through the 24 hour TAF period, as surface high pressure moves east across the region, becoming positioned off the NC coast Monday afternoon. Northwesterly winds in the 6 to 11 kt range will become light as variable late this afternoon and evening as the high shifts overhead, and will become south-southeasterly on Monday. Outlook: Warm moist air advection ahead of a upper level disturbance could produce the next chance for sub-VFR conditions Monday night with isolated to widely scattered showers possible. Scattered showers along with the threat of sub-VFR conditions could linger into Tuesday and Tuesday night. A cold front passage late Wed night or early Thu will bring a better chance for showers and possibly a few thunderstorms. Cool high pressure building into the area Thursday and Friday will bring a return to VFR conditions for late in the week and into the weekend. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...CBL NEAR TERM...CBL SHORT TERM...CBL LONG TERM...Hartfield AVIATION...CBL is the U.S. government's official web portal to all federal, state and local government web resources and services.