Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 171942 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 341 PM EDT Thu Aug 17 2017 .SYNOPSIS... A trough of low pressure at the surface will extend across the Piedmont of Virginia south into the Carolinas through Friday. A cold front will move across the area from the west late Friday into Saturday and then stall along the Carolina coast on Sunday. && .NEAR TERM /through tonight/... As of 325 PM Thursday... Early afternoon surface analysis shows a weak surface trough extending north to south across the western Piedmont of the Carolina`s into central Georgia. A low-level southerly flow has strengthened across the area allowing both surface and deep layer moisture to increase. Dew points remain very high with many locations in the Sandhills and southern Coastal Plain reporting dew points in the upper 70s and even an 80 at KMEB at 19Z. Analyzed precipitable water values have increased to 2.0 to 2.3 inches this morning. Scattered showers and storms ongoing across the Piedmont and Coastal Plain at mid afternoon will slowly move east and southeast into the early evening. Additional convection across the higher terrain of western NC associated with an approaching short wave trough will move east into the western Piedmont during the evening. Convective coverage and intensity should wane during the overnight but unlike the past couple of nights, the potential for a few showers or an isolated storm will persist overnight and will carry slight chance PoPs into the pre-dawn hours. The atmosphere is moderately unstable with MLCAPE values of around 1500 J/Kg but modest mid level lapse rates and weak shear should limit severe weather potential. Tall, wet storms with damging downburst winds and excessive lightning appear to be the main threat. Given the very wet airmass, storms will be efficient rain producers and could produced localized flooding. Temperatures this afternoon climbed into the upper 80s to lower 90s with dewpoints reaching the upper 70s to lower 80s in spots result in heat index values of 105 to 110 in many locations and even a heat index of 116 at 1pm at KMEB. With a good deal of cloud cover and moisture, don`t expect temperatures to fall too much tonight. Soupy lows will range in the 73 to 78 range. -Blaes && .SHORT TERM /Friday through Friday night/... As of 345 AM Thursday... Weak mid level height falls will continue into Fri as a shortwave trough pivots from Michigan/SE Ontario through the St Lawrence Valley, with a weaker/broad reflection down through the southern Appalachians. The Piedmont trough will strengthen and shift slightly eastward through Fri night, with plentiful low level moisture remaining in place over central NC (especially along and east of the surface trough), PW over 2.0", and passage of weak perturbations within the gently cyclonic southwesterly mid level flow. Under these conditions, convection should start early, in the morning (as soon as the surface-based inversion mixes out), over the Coastal Plain and eastern Piedmont/Sandhills. Additional convection is likely by afternoon just to our W and NW, over the Appalachians, and this should slide eastward later in the day, bringing a second peak in shower and storm coverage over central NC during the evening and early overnight hours. Expect plenty of clouds near and soon after daybreak, perhaps briefly breaking up with mixing, mainly over the southwest, before broken to overcast skies redevelop quickly with heating. Highs 89-95 with partly to mostly cloudy skies. Expect a good chance of showers/storms in the evening, decreasing and shifting southeast overnight as the surface trough kicks east toward the coast with a weak surface high building into W NC from the west. Lows from 70 NW to 76 SE. -GIH && .LONG TERM /SATURDAY THROUGH THURSDAY/... As of 341 PM Thursday... A short wave trough axis will cross the area during the day and evening Saturday, thus a few scattered showers may reform along the stalled front near the coast...so best chance for rain on Saturday and Saturday evening will be east of I-95. Any showers over our area should end shortly after sunset with dry conditions Saturday night. Sunday looks mostly dry as ridging aloft to our south begins to build northward over our area. Then for Monday, the forecast has been trending better the past few model runs, regarding cloud coverage and rain chances, although we`re keeping an eye on the weak short wave in the westerly flow aloft, which both the GFS and ECMWF suggest will pass by mostly to our north, but heights over us do trend down during the day. For now will hold cloud coverage around 50% with PoPs slightly below climo...20-30% during the afternoon Monday. The pattern for the rest of the long term period will feature a deepening through over the East, so look for mostly diurnal chance PoPs each day Tue-Thu. Temps Sat-Mon will run a couple degrees above normal with a building ridge, then falling back to or below normal mid-late next week with the deepening trough. && .AVIATION /18Z THURSDAY THROUGH MONDAY/... As of 310 PM Thursday... Scattered showers and thunderstorms across the Piedmont and Coastal Plain early this afternoon will drift slowly east resulting in areas of adverse aviation conditions. Local MVFR to possible IFR restrictions with reduced vsbys and cigs are expected through the early evening impacting the KRDU terminal and especially the KFAY and KRWI terminals. Additional showers and storms are likely to move east from the mountains this afternoon into the western Piedmont this evening resulting in possible restrictions at the KINT and KGSO terminals. Convective coverage and intensity should wane during the overnight but the potential for a few showers or isolated storm will persist. Another round of MVFR fog and stratus is possible again overnight although guidance is less bullish on this than previous days. Light south to southwest winds at 3 to 6kts are expected tonight with southwesterly winds at 5 to 10kts are expected on Friday. Low level flow will increase tonight atop the surface inversion with a southwest wind at 25kts will approach LLWS criteria across the Sandhills with a weaker flow and shear to the north and west. Looking beyond 18Z Friday...Scattered showers and storms are expected on Friday afternoon and evening, ahead of an approaching cold front. The front will shift southeast on Saturday and Sunday with the scattered mainly afternoon and evening showers and storms focused near KFAY. -Blaes && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Blaes NEAR TERM...Blaes SHORT TERM...Hartfield LONG TERM...np AVIATION...Blaes

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