Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 140641 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 241 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 /MONDAY AND MONDAY NIGHT/... As of 335 PM Sunday... Monday, the low level return flow will aid to pivot the stalled sfc front into a sw-ne orientated fashion from the southern Piedmont into the northern coastal plain. The approach of the TN Valley shear axis interacting with the moist unstable air mass should trigger scattered-numerous showers and storms across a large part of central NC. Precipitable water values of 2-2.4 inches projected across the region will support torrential rainfall, and possible localized flooding concerns. Dependent upon what happens tonight, a flash flood watch may be needed for sections of the region Monday-Monday night. In addition, effective bulk shear will be of sufficient strength to support a strong/severe storm or two, if adequate low level instability exists. Convection will likely persist well into Monday night as the mid level shear axis lingers in our vicinity. Highs Monday tricky as overcast skies and scattered-numerous showers may limit insolation, resulting in cooler than forecast temps, especially in the Piedmont. For now will favor max temps upper 70s/around 80 northwest Piedmont to the upper 80s south. && .LONG TERM /WEDNESDAY THROUGH MONDAY/...
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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.
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&& .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...WSS LONG TERM...KC AVIATION...Hartfield

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