Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 171914 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 310 PM EDT Thu Aug 17 2017 .SYNOPSIS...
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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.
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&& .NEAR TERM /Today through tonight/... As of 1105 AM Thursday... The latest surface analysis shows a weak surface trough extending north to south across the western Piedmont of the Carolina`s into central Georgia with a weak low center on the trough near the NC/SC border. The backdoor cold front across the Mid Atlantic marking the leading edge of an air mass with dew points in the the 50s across parts of PA and NY has begun lifting north as a warm front. A low- level southerly flow has developed across the area allowing both surface and deeper layer moisture to surge north. Dew points at 10 range from 82 at KMEB, 81 at KGSB, and 80 at CTZ to 77 at KRDU and KRWI, and 76 at KGSO. Analyzed precipitable water values have rebounded into 1.9 to 2.2 range this morning. Expect today to be more convectively active than yesterday with a couple of potential bouts and clusters of storms. Once area of showers moving across southern VA and far northern NC near the lakes appears to be driven in a region of isentropic lift/moisture advection atop the 500 hPa short wave ridge across the area. More importantly, additional scattered showers and storms will develop early this afternoon across the eastern Piedmont and Sandhills in a region instability is expected to be maximized and coincident with moisture convection. Additional convection may move into central NC from the west late this afternoon and early this evening as mid-level troughing approaches from the west. Low level thickness values today are a handful of meters greater than yesterday which would support highs of 89-95 this afternoon. Crazy high dew points will push heat index values into the 97 to 103 range today with values of 100-103 over the Sandhills. Warm and continued very muggy lows tonight of 71-77 under partly cloudy skies with patchy fog. -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 /FRIDAY THROUGH TUESDAY/... As of 335 AM Thursday... A strong low pressure system moving north of the Great Lakes will move eastward and drag a cold front across the Carolinas on Friday and Friday night before stalling out near the Carolina Coast. This will keep precip chances in the forecast for Friday and but should confine things to the extreme southeastern portions of the area by Friday night. With the leftovers hanging around for much of the weekend expect eastern areas to maintain higher precip chances through much of the weekend. As the weekend comes to a close, continental high pressure will move in from the northwest which could help to lower precip chances by Sunday afternoon/evening. Interesting forecast for the eclipse on Monday with models starting to come into agreement with zonal flow aloft and surface high pressure sitting right off of the Carolina Coast. The positioning of the high pressure will most likely yield moist return flow around the back side of the high which unfortunately would most likely lead to at least partial cloud cover for Monday afternoon. That being said, the GFS solution is interesting that it lags the continental high back to the west a little bit and if that happens it could potentially suppress cloud cover to the south. Still way too early tell but at least a partly cloudy forecast looks likely. For midweek return flow around the high will continue, bringing daily precip chances with another surface low well to the north that may bring another front through the area by later on Wednesday. && .AVIATION /18Z THURSDAY THROUGH MONDAY/...
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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
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Blaes NEAR TERM...Blaes SHORT TERM...Hartfield LONG TERM...Ellis AVIATION...Blaes

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