Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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841 FXUS62 KRAH 140650 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 250 AM EDT Mon Aug 14 2017 .SYNOPSIS... A frontal zone stalled out across eastern and southern North Carolina this morning will very slowly weaken and lift northward as a warm front through Tuesday. This weak front will hold over North Carolina through mid week. && .NEAR TERM /TODAY THROUGH TONIGHT/... As of 228 AM Monday... Moisture will continue to increase and deepen across central NC through tonight, resulting in mostly cloudy, humid, and unsettled weather. The surface frontal zone extends roughly along the NC/SC border then northeast over eastern NC early this morning. This front will continue to weaken today, resulting in little more than a diffuse band of mass convergence across the state tonight as dewpoints climb areawide. Models depict a band of positive vorticity stretching SW to NE across western and far northern NC through tonight, although the weak wind field over the region through the column will allow for little in the way of DPVA. But with higher PW values surging into the area (including a daily record high value at MHX last evening), even the smallest of dynamic forcing for ascent will support convection, particularly after some heating this afternoon (although considerable thick cloudiness will limit insolation). Expect no more than isolated showers this morning, ramping up to high chance to low likely pops, highest in the southeast CWA (near the frontal zone) and in the NW/Triad (where isentropic upglide, albeit weak, will be focused). While MUCAPE is projected to be moderate in the southeast this afternoon (a likely function of higher dewpoints there), deep layer shear will be small, under 20 kts. Shear will be better across the NW, however MUCAPE will be smaller there, NW of the frontal zone. That said, any cell, particularly those that develop in or on the edge of areas that see some sunshine, will need to be watched for potential strong or severe wind gusts. Perhaps the larger concern will be the risk of locally heavy rainfall with slow-moving centroids through this evening, although this threat should be isolated. Expect highs today from the lower 80s across the north and NW, ranging to mid-upper 80s elsewhere, highest in the far south. Showers and storms should decrease in coverage and become confined to the north and west CWA late evening through the overnight hours, with nocturnal low level stabilization and lack of dynamic forcing features outside of the aforementioned vorticity axis. Lows 70-75 with areas of fog. -GIH && .SHORT TERM /Tuesday through Tuesday night/...
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As of 250 AM Monday... Continued damp with a volatile air mass. Moisture will steadily deepen with increasing surface dewpoints, resulting in slightly higher MUCAPE by Tue afternoon. Mid level flow remains weak from the W or WSW, with little agreement among the models as to where minor perturbations might track. The NAM, which did the best in detecting the convective complex over the OK/TX border early this morning, is the only large scale model that retains its resultant MCV and has it approaching NW NC late Tue into Tue night. But even then, it`s hard to have confidence in tracking a feature in flow this weak. And with the column becoming so damp, it won`t take much to prompt precip. As the models develop areas of showers and storms aligned with subtle boundaries and outflows with little spatial agreement among them, forecast uncertainty rises, with convective details difficult to pinpoint with confidence. Will start out with low chance pops in the morning, increasing to likely areawide (with PW projected to reach well above 2.0") from midday through the mid evening before trending pops downward NW to SE, as models show a weak surface trough tracking ESE through central and eastern NC overnight. Highs 83-90 and lows 69-75. -GIH
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&& .LONG TERM /WEDNESDAY THROUGH MONDAY/... As of 240 AM Monday... There is still quite a bit of uncertainty with respect to where and when the best chances for convection will be during this part of the forecast, resulting in below average confidence. Wednesday through Thursday Night: Expect the climatological diurnal convection through the period (higher chances during the aft/eve, general lull overnight into the early morning hours. Medium range models also suggest the highest chances will be along the sea breeze and in the lee of the Appalachians. The upper level pattern will be characterized by high pressure over the deep south and weak cyclonic flow over and north of Central NC. The surface pattern will consist of a weak low/trough over the eastern half of the region with weak high pressure ridging into the northwest. Temperatures will be on the increase, with highs increasing from the mid 80s North to near 90 degrees South on Wednesday to upper 80s to low 90s on Thursday. Lows generally in the 69-75 degree range, highest southeast. Saturday through Monday: A cold front is expected to approach the Carolinas on Friday and impinge on Central NC Friday night into Saturday. It is unclear at this time if, and how far, the front will progress into the area since the medium-range models really diverge at that point. Meanwhile aloft, an upper level shortwave disturbance will swing through the Great Lakes and Ohio Valley. As stated above, details regarding timing, coverage and location of the convection during this part of the forecast are highly uncertain. As for Temperatures, highs will top out in the low to mid 90s on Friday, gradually decreasing thereafter. Lows will generally range from upper 60s to mid 70s through the rest of the extended period. Although it is at the tail end of the extended period, the partial solar eclipse expected over the region on Monday will result in a period of lower temperatures Monday afternoon. && .AVIATION /06Z MONDAY THROUGH FRIDAY/... As of 1230 AM Monday... Confidence is fairly high that all central NC TAF sites will see MVFR to briefly IFR conditions early this morning. As a frontal zone holds across the southern and eastern edges of the forecast area, considerable low level moisture will continue to pool over central NC, resulting in lowering cigs to 800-2000 ft AGL at all sites by 09z (RDU and RWI are already predominantly MVFR). Vsbys may drop to MVFR for a couple of hours in the 08z-13z window. Cigs will be slow to lift through the MVFR category through the morning, with TAF sites likely reaching VFR 16z-18z. Scattered showers and storms are expected in the afternoon, lasting through the evening. These are slightly more likely to occur at INT/GSO/RWI/FAY, but can`t be ruled out at RDU as well. Showers will decrease in coverage after 03z this evening but are still possible areawide, especially at INT/GSO, through the end of the TAF valid period. Winds will be light, under 8 kts, through the next 24 hours, but may be stronger in/near storms. Looking beyond 06z Tue, a very moist, humid, and unsettled pattern will hold in place through much of this week, as the weak frontal zone meanders across NC. There will be a good chance of showers and storms each day, most likely from mid afternoon through the evening, as well as a good chance of early morning sub-VFR stratus and fog at all sites. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...Hartfield SHORT TERM...Hartfield LONG TERM...KC AVIATION...Hartfield

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