Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 260802 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 400 AM EDT Sun Mar 26 2017 .SYNOPSIS... A backdoor front will settle into and stall over central VA today, while a weakening upper level disturbance pivots northeast across our region. Bermuda high pressure will otherwise extend west into the southeastern U.S. through Mon. && .NEAR TERM /THROUGH TONIGHT/... As of 345 AM Sunday... On the sern periphery of an upper low that will become an open wave as it lifts from the Middle MS Valley NEwd across the Great Lakes through tonight, a lead mid level trough axis now extending across the TN Valley will edge Ewd into the wrn NC Piedmont this afternoon. An associated axis of moisture aloft, and weak forcing for ascent, will likely result in the slow NEwd maintenance of a band of showers now moving through W-central GA. While these showers will likely weaken with Ewd extent into the W-central Carolinas, as they near the wrn periphery of a sub-tropical ridge and associated dry and capping influence centered near Bermuda, a few may drift into the wrn Piedmont by mid-late afternoon. While CAM`s also indicate the potential for much shallower showers to the east, ones capped above by the aforementioned subsidence inversion sampled by proximity RAOBS around 5-6 k ft last evening, it`s unlikely that barely positive CAPE would support deep enough cumulus to indeed support any showers elsewhere. Otherwise, like Sat, diurnal heating of a seasonably moist BL characterized by surface dewpoints generally in the lower 50s should again support a scattered to broken cumulus field by midday-early afternoon, but with enough breaks of sun to allow temperatures to again reach the middle to upper 70s. While shortwave ridging aloft behind the departing mid level trough will likely yield dry conditions tonight, the mid level moist axis accompanying the trough will be left behind; and this may support a lingering shower or two over the wrn Piedmont tonight. Low temperatures centered in the middle 50s. && .SHORT TERM /SUNDAY AND SUNDAY NIGHT/... As of 255 PM Saturday... A lead s/w rotating around the mid MS Valley upper low will lift newd from eastern TN into the central Appalachians Sunday, brushing our nw sector. This system projected to weaken with time and while atmosphere continues to moisten, model rh cross sections still depict a decent layer of dry air in the mid levels of the atmosphere. Accordingly, models have been trending drier, so will follow a similar trend. Plan to confine chance PoPs to the NW Piedmont, with slight chance PoPs elsewhere across the Piedmont. Over the east and far south sections, will advertise PoPs less than 15 percent. Expect quite a bit of cloudiness, limiting insolation. Still, warm sly flow along with partial sun should be able to boost temperatures back into the low-mid 70s. Continued mild Sunday night under variably cloudy skies. Weak confluence and a series of weak perturbations aloft will continue a minor threat for a few showers over the NW Piedmont. Elsewhere, probability of a shower appear too remote to mention at this time. Overnight temperatures in the mid-upper 50s. && .LONG TERM /Tuesday through Saturday/...
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As of 355 AM Sunday... Tue/Tue night: The mid level shortwave trough and its accompanying surface trough is expected to cross the area during the first half of the day, during which time there should be enough low level heating in combination with the thermal trough aloft to prompt marginal to moderate instability. Forecast soundings show subsequent warming and drying aloft during the latter half of the day as the shortwave trough shifts to our east and 850 mb SW flow slowly decreases. With above normal PW decreasing in the west in the afternoon, expect a good chance of showers and storms in the morning, tapering down west to east through the afternoon. The lagging weak cold front will drop SE through the area Tue night with low and mid level winds becoming northwesterly and westerly respectively, and with heights rising aloft behind the wave, expect a trend to mostly clear skies overnight west to east. Much above normal thicknesses in the warm sector support highs of 77-82. Lows 52-58 with marked cooling not arriving until late. Wed-Thu: Skies should be partly to mostly sunny Wed with generally dry air in place, although a weak inverted surface trough extending up through central NC -- ahead of an approaching backdoor front -- along with a col area at 850 mb and a rebounding of PW values across southern NC may yield broken clouds in the afternoon. The backdoor front is expected to drop NNE to SSW through central NC Wed night with cooling low levels and increasing moisture in the 900-800 mb depth, which is likely to bring a trend to mostly cloudy skies overnight. These clouds will disperse somewhat with heating and mixing across the Coastal Plain Thu, but the Piedmont will see strengthening moisture influx with an increasing 850 mb SW flow atop the intruding cool wedge nosing in from the NNE, and this overrunning should lock in clouds especially in the western CWA through the day, with some light drizzle possible in the far western Piedmont. High uncertainty with temps in this period given the lingering mild air Wed ahead of the backdoor front and the incoming wedge air mass for Wed night/Thu. Prefer the milder ECMWF/Canadian thicknesses Wed, indicating highs in the mid 70s to near 80. Will have lows of 46-53 Wed night and highs Thu 60 N to 70 S. Thu night-Sat: A deep low over the Four Corners late Tue will track eastward and gradually fill late in the week, in response to yet another powerful storm system crashing onto the West Coast and crossing the Rockies, but the degree of weakening of the lead system and the tilt of its trough differs between the ECMWF/GFS. A deepening polar low just SE of the Canadian Maritimes will help drive the cool surface ridge southward into the NC Piedmont, and as the mid level low/trough approaches late week, moist isentropic upglide atop the cool air mass should lead to increased rain chances, considerable cloud cover, and cooler temps. The open wave will then shift eastward through the region with ample deep moisture in place and an occluded frontal system, so have kept in a good chance of rain Thu into Fri, and we may see a few thunderstorms Fri especially across the SE CWA, which could get into the warm sector. The trailing cold front is expected to push through and SE of the area sometime Sat, so will show a trend toward lower pops. Expect temps to be below normal Fri and near normal Sat, but uncertainty in these details is high, given the strength of this frontal system and model timing differences. -GIH
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&& .AVIATION /06Z SUNDAY THROUGH THURSDAY/... As of 155 AM Sunday... Mainly VFR. Morning to midday heating of a seasonably moist air mass around Bermuda high pressure will favor the development of a field of stratocumulus that will initially develop around 2500-3000 ft, and may be briefly broken in that range this morning in the few hours surrounding 15Z, before lifting into the 3500-5000 ft range this afternoon. The passage of an upper level disturbance and associated moistening aloft may allow a few showers to move into and affect INT and GSO this afternoon and evening. Otherwise, SSWly surface winds will increase into the 8-13 kt range after 14-15Z, with occasional gusts up to 20 kts, then lessen after sunset. Outlook: Late night-early morning fog and/or stratus, then MVFR range cloudiness as that moist layer is heated through midday, will be possible each day through the middle of next week. Otherwise, a chance of showers and associated sub-VFR conditions will exist late Mon through Tue. The probability of any such shower at any given TAF site will be relatively low, however, given limited overall coverage. Lastly, a backdoor cold front will settle into SC Wed night; and "overrunning" flow atop the boundary will result in the development of MVFR-IFR conditions and associated cold air damming as early as late Thu, but more likely just beyond the outlook TAF period - Thu night-Fri. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...WSS LONG TERM...Hartfield AVIATION...MWS is the U.S. government's official web portal to all federal, state and local government web resources and services.