Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 150030 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 730 PM EST Tue Feb 14 2017 .SYNOPSIS... An upper level low and attendant surface low pressure system over the Lower MS Valley will track east across the Deep South tonight, then gradually track off the Southeast coast on Wed. High pressure will follow for Wed night and Thu. && .NEAR TERM /THROUGH TONIGHT/... As of 345 PM Tuesday... Tonight: A band of light precipitation now stretching across TN/KY and the Central Appalachians is occurring in an axis of 500-850 mb frontogenesis along confluent low-mid level flow between an elongated srn stream low stretching across TX and the Lower MS Valley, and a pair of nrn stream ones in the vicinity of the Upper Great Lakes. This band of Fgen and associated mid level-generated light precipitation will spread E along the VA/NC border early tonight, at which time a sprinkle or brief light rain will be possible over the nrn Piedmont. Otherwise, most areas, and for most of the night, should be dry, as this axis of forcing lifts Nwd through VA. The better rain chances will hold off until very late tonight or early Wed, when a 1007 mb surface low over LA NEwd tracks closer /around the rim of the Srn Appalachians/ between 09-12Z Wed, and strengthens convergence and promotes rapid Fgen along a low level frontal zone now stretching from the aforementioned surface low NEwd into the Carolinas. This process will occur at the same time deeper saturation accompanying a mid level moist axis and lead impulse over the Lower MS Valley moves into the wrn Carolinas. The result will be a NEwd development/expansion of rain into the wrn Piedmont around daybreak Wed. Temperatures will be variable, with a period of decent radiational cooling possible over the srn third of the CWA amidst relatively clear skies this evening, whereas thickening and lowering ceilings (top-down moistening) should cause temperatures to be milder initially, then decrease with the onset of light rain and evaporational cooling late tonight. Lows should consequently average middle to upper 40s. && .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/... As of 410 PM Tuesday... Precipitation will continue to to expand Ewd across central NC early Wed as, as low pressure tracks NEwd through Sern NC and offshore by 18Z. Sloped ascent across an associated strong frontal zone will result in widespread rain area-wide early in the day, but with quick W to E clearing through the afternoon. A few elevated rumbles of thunder will be possible over SC, and perhaps as far N as a line from Wadesboro to Clinton, as up to a couple of hundred J/KG of MUCAPE accompany the passage of the low. A gusty NW wind will develop behind the clearing line as the mixed layer deepens and CAA behind the leading frontal zone follows the low offshore. Temperatures will indeed be a challenge, with the highest confidence 1) in the far SE, where early morning highs in the middle to upper 50s are likely, before temperatures fall into the lower 50s with the Ewd expansion of rain, and then likely will not have time to recover with brief afternoon clearing, and 2) in the far NW, where several hours of afternoon sunshine will favor moderating temperatures into the lower 50s. In between will be the biggest bust potential, where the duration of afternoon sunshine behind the clearing line is most in question and could result in either upper 40s if clouds linger, or lower to middle 50s if a few hours of afternoon sunshine materialize. Meanwhile, a nrn stream cold front now stretching across the Nrn Plains and Upper Midwest will approach from the NW and sweep E of the Appalachians Wed evening, with associated colder temperatures that will favor lows mostly in the lower to middle 30s, under a mainly clear sky that will fill with thin cirrus in NW flow late. && .LONG TERM /THURSDAY THROUGH TUESDAY/... As of 150 PM Tuesday... An active southern stream within a split flow pattern will will be a key player much of the long term period. First, in the wake of the departing and rapidly deepening low moving up the East Coast on Thursday, models suggest the pressure gradient will still be strong enough to yield some 20-25kt gusts, especially east, as deep mixing develops. Dry adiabatic technique supports highs on higher side of guidance in the 49-54 range. Thursday night should be mostly clear for much of the night, though some orographic cirrus may be possible late. With weak high pressure in control, lows should reach the upper 20s for most areas. From Friday onward, the longwave pattern is expected to feature above normal heights over the eastern US and below normal heights with a trough out west. This will lead to an overall warming trend through early next week. However, another upper low over the desert southwest (currently a shortwave dropping south through CA) is forecast to eject northeastward on Friday and then migrate east across the Southeast over the weekend. Models have trended a bit further south with the wave, and with the synoptic frontal zone suppressed to the GOMEX, there`s not much of a surface low reflection or moisture transport, so it`s still not clear how much precip this system will actually produce Sat night and early Sunday. Stronger ridging aloft will then develop Sunday through Tuesday, with continued uncertainty in yet another southern stream wave for the middle of the week. The forecast will be dry through Tuesday, with highs each day in the 70s and lows in the upper 40s. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
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As of 730 PM Tuesday... 24-Hour TAF period: Expect VFR conditions for the first several hours of the TAF period, with broken to overcast mid-clouds persisting through tonight. Winds overnight will be generally light and variable. Some light rain could develop over the KGSO/KINT/KRDU prior to 12Z, however expect the better chances and more widespread rain to move in from the west around 12Z and quickly cross Central NC by 18Z. With the rain, cigs could drop to around 1 kft, though visbys should remain MVFR/VFR. Winds could get strong and gusty out of the northwest, especially at KINT and KGSO, for a brief period during the afternoon/early evening. Expect a return to VFR conditions by the end of the TAF period at all terminals. -KC Looking ahead: VFR conditions will persist through the remainder of the week. Sub-VFR conditions will be possible by Saturday night/Sunday morning as a system over the southwest US lifts northeast toward our region. -Smith
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...MWS LONG TERM...SMITH AVIATION...KC/SMITH

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