Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 200516 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 100 AM EDT Sun Aug 20 2017 .SYNOPSIS... A cold front across the eastern Carolinas will linger overnight, then dissipate on Sunday. A strong cold front will approach the area on Wednesday and reach the coast on Thursday. && .NEAR TERM /THROUGH TONIGHT/... As of 1010 PM Saturday... Little if any changes required to the near term forecast. At the surface, a stalled, weak sfc front was wavering across the eastern counties of central NC. With the setting sun, sfc dewpoints have recovered as dewpoints at or above 70 degrees were observed over all but the northwest Piedmont. In the mid levels of the atmosphere, a trough was exiting our region, leaving a drier air mass in its wake. Overnight, expect tranquil weather conditions under mostly clear skies. Could see a few pockets of fog or low clouds by daybreak in the Sandhills or coastal plain but most locations will have clear skies. Overnight, the stalled sfc front will gradually wash out as the mid/upper level trough lifts east-newd. This will allow a weak high pressure system to nose into our region by Sunday. Under mostly clear skies, overnight temperatures will generally be in the 70-75 degree range. && .SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/... As of 250 PM Saturday... A shearing short wave trough at 500 hPa shifts across the eastern Carolinas on Sunday morning with increasing heights on Sunday afternoon and Sunday night. The cold front that stalled near the coast will retreat inland and washout during the day. The light and variable low-level flow to start the day becomes southeasterly on Sunday afternoon and southerly on Sunday night. A drier atmosphere, ridging aloft, and limited forcing for ascent should keep central NC generally convection free on Sunday. It`s worth noting that the exception will be some isolated convection that develops across the higher elevations of NC that drifts east, weakens and likely dissipates as it approaches the NW Piedmont late in the afternoon/early evening. An isolated shower or storm is possible across the southern and southeastern tier in proximity to the cold front. Feel that warm mid-levels and ridging aloft will keep coverage very limited and will not include a PoP at this time. Low- level thickness values increase a few meters over Saturday and would support highs between 90 and 95. Dew points in the mid 60s to around 70 will result in heat index values less than 100 degrees. The southerly flow will allow nocturnal dew points to creep up and result in lows in the 69 to 75 range. -Blaes && .LONG TERM /MONDAY THROUGH SATURDAY/... As of 400 PM Saturday... Mon: The surface front over ern NC this afternoon will have stalled and begun to retreat nwwd, into srn and sern NC on Mon. The retreat of this by-then-diffuse boundary, marked by the leading edge of surface dewpoints in the lower-middle 70s, and which will be in the vicinity of a sea breeze that will likely make quick and deep inland progress owing to prevailing onshore low level flow, will favor a relative maximum in diurnal cumulus --some of which will grow into widely scattered showers and storms-- from the Sandhills to the Coastal Plain. In addition, a perturbation in wly flow aloft is forecast to amplify as it drifts east of the Appalachians early in the day; and this feature will also serve to stream a veil of cirrus newd across the ern Carolinas, including areas mostly east of I-95. As such, the relative best eclipse viewing will likely occur over the nwrn half of the RAH forecast area, from the Triangle to the Triad. Even where both the cirrus and diurnal cu noted above are likely to be maximized over the sern counties, the eclipse may still be visible, but more dimly so due to the high level moisture. Frankly, it will only take one cumulus cloud to obscure the view, so if you happen to be in an unlucky and untimely location even over the nwrn Piedmont, the eclipse could be obscured. It will otherwise be warm-hot, with high temperatures in the lower to middle 90s. Dry and seasonably mild Mon night, with lows 70-75. Tue-Sat: The pattern aloft will transition to a relatively amplified one, with a trough across ern NOAM by mid-late week. A slow sewd- moving surface cold front will mark the leading edge of the associated height falls aloft, and settle across central NC late Wed through Thu, with an associated high chance of convection during that time. Cooler and drier, post-frontal high pressure will follow for the end of the week into next weekend, with temperatures likely to peak in the lower to middle 80s in most locations Thu-Sat. && .LONG TERM /MONDAY THROUGH FRIDAY/... As of 244 PM Friday... Monday: As continental high pressure begins to merge with an offshore surface high the question for Monday will be how much moisture is in the weak southerly return flow and what will that result in as far as cloud cover for the eclipse viewing. Partly cloudy skies look likely but there should be enough breaks in the clouds to get a decent view of the moon passing between us and our closest star situated some 93,000,000 miles away. While temperatures are expected to rise into the lower 90s there will be a break in the heat from roughly 1:30 to 3:30 PM. A scattered shower or thunderstorm cant be ruled out, especially in the southern tier of the area. Rest of the week: Relative dry but warm weather continues through Tuesday before the next frontal system passes through the area on Wednesday in association with a low pressure system moving across southern Canada. High rain chances Wednesday will continue through Thursday in the east and possibly into Friday as the front begins to stall near the coast. Temperatures in the low 90s Tuesday and Wednesday will fall back into the mid 80s for Thursday and maybe into the low 80s by Friday. With that, some dewpoints in the lower 60s should make for some very comfortable weather heading into the weekend. && .AVIATION /05Z SUNDAY THROUGH THURSDAY/...
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As of 115 AM Sunday... 24 Hour TAF Period: Clear skies and calm winds will support the development of fog between 06 to 12z, mainly across eastern portions of the forecast where very moist low-level air remains pooled along the stalled frontal zone. The latest HRRR suggest visibility restrictions could fall as low as LIFR in dense fog at our eastern most TAF sites (KRWI and KFAY). Will introduce predominate IFR ceilings at KRWI and KFAY beginning at 08 to 09z, with a tempo group for LIFR conditions at these locations between 09 to 13z. Any fog that develops should lift and dissipate by 14z, with VFR conditions and dry weather are expected for Sunday afternoon. Outlook: The threat of mainly afternoon and evening showers or thunderstorms and late night/early morning fog/stratus is expected to increase a bit on Monday and Tuesday. A strong cold front is expected to approach the area on Wednesday and reach the coast on Thursdays bringing a greater chance of adverse aviation conditions in showers and thunderstorms.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...BLAES NEAR TERM...WSS SHORT TERM...BLAES LONG TERM...MWS AVIATION...CBL/BLAES

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