Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 171508 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1105 AM EDT Thu Aug 17 2017 .SYNOPSIS... A surface low pressure trough will extend from western North Carolina through South Carolina today through tonight. This trough will shift northeastward late tonight, hold over the Piedmont of North Carolina Friday, then shift east to the I-95 corridor on Saturday. && .NEAR TERM /Today through tonight/...
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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
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&& .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 /12Z THURSDAY THROUGH MONDAY/... As of 640 AM Thursday... IFR/LIFR conditions will persist for another couple of hours over the northeast portions of the forecast area, including RWI, where cigs and vsbys will slowly lift to VFR through 15z. Elsewhere, isolated pockets of MVFR fog will linger until around 13z. After late morning, VFR conditions will then dominate through the day, although scattered showers and storms generating a period of sub-VFR conditions and erratic winds will be possible at each site, mainly 18z-00z. VFR conditions should prevail this evening into tonight, although MVFR fog may develop starting around 05z. Winds will be light and variable this morning, becoming mostly from the south by midday, at 6-10 kts this afternoon diminishing to 3-6 kts starting this evening. There is a good chance of MVFR fog at all sites 06z- 12z. Looking beyond 12z Fri, after the light fog lifts, VFR conditions are expected after 13z. But scattered showers and storms are expected, mainly mid afternoon through mid evening Fri, with the greatest coverage impacting RDU/RWI/FAY. Additional isolated storms remain possible through Fri night, with a chance for sub-VFR fog/stratus. Best shower/storm chances shift to our SE for Sat into Mon, with VFR conditions prevailing, although FAY may continue to see a storm threat. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...Blaes SHORT TERM...Hartfield LONG TERM...Ellis AVIATION...Hartfield

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