Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 192003 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 400 PM EDT Sat Aug 19 2017 .SYNOPSIS... A cold front across the eastern Carolinas will linger tonight and then dissipate on Sunday as it retreats northwest. A strong cold front will approach the area on Wednesday and reach the coast on Thursday. && .NEAR TERM /THROUGH TONIGHT/... As of 225 PM Saturday... The latest surface analysis shows the cold front extending from near Kitty Hawk southwest to near Lumberton. Surface dew points have fallen into the mid to upper 60s across the Piedmont and western Sandhills. Dew points have even fallen into the upper 60s to lower 70s just behind the front across the Coastal Plain. The dew points at 17Z was 71 at KFAY and 70 at KGSB! Further aloft, the 925 hPa trough was located across the coastal region while the 850/700 hPa trough axis lagged across western Piedmont. A prominent short wave trough at 500 hPa was analyzed across the eastern OH and TN valleys early this afternoon. Deep layer moisture across the region continues to decrease with precipitable water values ranging from 1.1 inches across the western Piedmont to 1.7 inches across the Coastal Plain. The latest GOES 16 visible imagery shows a developing cumulus field across the southern Piedmont, Sandhills and southern Coastal Plain with a broken line of convection extending from coastal SC northeast into coastal NC. This convection is developing in a region of local convergence near and ahead of the cold front in a region of moderate to strong instability with MLCAPE values ranging from 1500-3000 J/Kg. While the primary axis of the thunderstorms is about 5 to 20 miles inland from the coast and generally southeast of Cumberland, Sampson and Wayne counties, the convection may work its way further north and inland. This warrants maintaining the 20-30% PoPs in the far southeast. While the wind field is notably stronger than previous days, winds are generally unidirectional from the southwest with the strongest flow confined to heights well above the mixed layer. Thus, the threat of any severe weather is limited and should be confined to locations near and east of the front and outside the RAH CWA. With storm orientation lined up with the mean flow, localized heavy rain could be an issue, but again that should be confined to locations just outside the RAH CWA. Any deep convection should largely dissipate by around sunset with just a shower or too possible into the evening hours. Otherwise, dry weather with partly to mostly clear skies are expected this evening and overnight. Some patchy, mainly high clouds associated with the upper trough. Drier air tonight, especially across the Piedmont with dew points in the mid to upper 60s will result in a much less muggy night. Overnight lows will range from the upper 60s in the northwest Piedmont to the lower 70s in the Coastal Plain. -Blaes && .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 /18Z SATURDAY THROUGH THURSDAY/... As of 105 PM Saturday... Other than widely scattered showers across the southern Coastal Plain and Sandhills potentially impacting the KFAY terminal, widespread VFR conditions are expected through the 24 hour TAF period. The greatest threat of a local restriction of cigs or vsbys near the KFAY terminal will be from 18 to 22Z with greater coverage to the south and east. Otherwise...skies will be mostly clear through the period with scattered cumulus at around 5kft this afternoon with a mix of scattered fair weather cumulus and cirrus clouds expected on Sunday. Light mainly northwest to northerly winds at less than 7kts are expected this afternoon with light and variable winds expected tonight. Mainly northeast winds less than 6kts on Sunday will veer to east and southeasterly during the afternoon. Looking beyond the 24 hour TAF period... Generally fair weather with VFR conditions are expected on Sunday. The threat of mainly afternoon and evening showers or thunderstorms and late night/early morning fog/stratus increases a bit on Monday and Tuesday. A strong cold front approaches on Wednesday and reaches the coast on Thursdays bringing a greater chance of adverse aviation conditions in showers and thunderstorms. -Blaes && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...BLAES NEAR TERM...BLAES SHORT TERM...BLAES LONG TERM...MWS AVIATION...BLAES is the U.S. government's official web portal to all federal, state and local government web resources and services.