Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 221848 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 248 PM EDT FRI JUL 22 2016 .SYNOPSIS... A mid-level disturbance will drift across western North Carolina this afternoon and evening. A hot high pressure ridge will then expand from the central U.S. to the mid-Atlantic states over the weekend and into early next week. && .NEAR TERM /THROUGH TONIGHT/... As of 1010 AM Friday... Convection chances remain low for much of Central NC the rest of today into tonight, within a regime dominated by a warm cyclonic ridge aloft resulting in stable mid levels with weak steering flow, while low level thicknesses steadily climb. The MCV resulting from yesterday`s Great Lakes MCS will track southward over the southern Appalachians today as other disturbances emanating from upstream MCS activity over the Midwest follow a similar path, likely tracking just west of the CWA. Latest CAM runs -- as well as larger-scale models with parameterized convection -- show good continuity with yesterday`s model runs, suggesting that a few storms should form this afternoon over the far western CWA, closer to the MCV tracks, and perhaps over the far southern and SE CWA as well where low level mass convergence along an inland-moving sea breeze should take place. But coverage and upscale growth of any convection will be greatly suppressed over the remainder of the CWA given the weak mid level lapse rates (particularly during the peak heating period), lack of a convective focus, and little to no dynamic support. PW values are projected to rise a bit, but the 700-400 mb layer will remain quite dry. Will restrict low chance pops to the western and far southern CWA including the far SE this afternoon, tapering back down in the early evening as we lose heating. High-res guidance shows temps peaking in the 90-94 range, with dewpoints in the upper 60s and lower 70s helping to push the heat index values into the mid- upper 90s. -GIH Previous discussion as of 345 AM: Central NC will remain on the ERN periphery of a strong sub-tropical ridge centered over OK, while a surface trough will sharpen in the of the Appalachians. Within the associated N to NNW flow aloft around the ridge, a low amplitude, positive tilt mid-level trough, now extending from the Lower Great lakes to the OH Valley, will drift into NC this afternoon. An MCV evident in model analysis 700-500 mb vorticity fields and earlier satellite imagery is embedded within the broader mid-level trough, over ERN KY; and this feature is forecast to drift focus forcing for ascent as it drifts into the SRN Appalachians through the same time. While the relative highest chance of showers and storms will be along the track of the MCV and aided by differential heating -in the mountains- a shower or storm will also be possible in the vicinity of the lee trough, centered over the WRN Piedmont, despite rather dry mid levels. Return flow around high pressure centered near Bermuda will support slightly higher temperatures and dewpoints versus those of Thu, with highs generally 90 to 95 degrees. Light SSW stirring overnight should hold temperatures in the (lower) 70s, and also preclude the development of anything more than patchy fog, particularly given the presence of cirrus related to the MCS upstream/over IL. && .SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/... As of 400 AM Friday... Generally a persistence forecast, with a slight chance of an afternoon storm, and higher temperatures yet, owing to a slowly increasing influence of the sub-tropical ridge --and associated heat beneath it-- as it builds E. Highs 93 to 97 and lows in the middle 70s. Heat indices are expected to range from around 100 over the NW Piedmont to 105 over the ERN Sandhills and Coastal Plain. && .LONG TERM /SUNDAY THROUGH FRIDAY/...
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As of 245 PM Friday... To begin the long term period, the strong upper ridge that provided multiple days of intense heat across the Central Plains will have dampened and became elongated in east-west fashion, extending into the region. As it does, heights will rise over central NC through the weekend. As such, max low level thickness values are progged to top out in the low to mid 1440s on Sunday (slightly lower than previous runs), with similar values on Monday. This combined with mostly dry conditions and temps not cooling off much as night, temps will be able to rise well into the mid 90s, maybe even the upper 90s (warmest on Sunday). This combined with a moist air mass may necessitate the issuance of a heat advisory, most likely across at least the eastern half of the forecast area, where heat index values will approach or exceed 105 degrees. With regards to precip chances, overall they will stay rather low through early next week, but will not be zero as there will be a persistent Piedmont trough that could be a focus for convective development, as well as the sea breeze and/or any weak disturbances that move through aloft. The aforementioned ridge will continue to dampen and shift more offshore through the middle of the week. Also, a shortwave trough is progged to cross southern Canada and the Great Lakes Monday into Tuesday. This will propel a cold front towards the region Tuesday into Wednesday, but as can be expected this time of the year, there is disagreement with just how far south it will make it and it will likely stall near or just north of the area and then meander for a few day. Another shortwave crossing the Ohio Valley will approach towards the end of the week. Therefore, with us gradually losing the influence of the upper ridge and with a cold front in the vicinity, precip chances will start to increase, at least back to the normal diurnal range, especially towards the middle to end of the week. The increased cloud cover and precip chances should allow temps to "cool" back to the low to mid 90s (however, still slightly above normal).
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&& .AVIATION /18Z Friday through Wednesday/... As of 1205 PM Friday... High probabilities of VFR conditions persisting through the next 24 hours. Warm and dry air aloft will suppress most shower/storm activity over Central NC this afternoon through midday Sat, with clouds generally scattered and bases above 4 kft. Any isolated storms would be circumnavigable. The better chances of a stray storm would be near INT/GSO and FAY, although chances are too low to include as a prevailing condition. As always, erratic gusty winds and lightning can be expected in and near any storms. There is a small chance for patchy shallow MVFR fog in low-lying areas late tonight into early Sat morning at all TAF sites, but chances are too small to mention at this time. Surface winds will remain light through Sat, mainly from the southwest under 10 kts. Looking beyond 18Z Sat: A few storms are possible late Sat afternoon into Sat night, primarily at INT/GSO/FAY. Areas of MVFR fog may develop late Sat night into Sun morning. Shower/storm chances will start to improve late Sun into Sun night, with scattered daily storms possible through Wed as the air mass moistens more deeply over Central NC. Fog is possible early each morning Mon-Wed. -GIH && .CLIMATE... Record high temperatures and the year in which the record was most recently set at Raleigh, Greensboro, and Fayetteville. Sat Jul 23 Sun Jul 24 Mon Jul 25 RDU 105/1952 101/2011 102/2010 GSO 99/1952 99/1914 101/1914 FAY 103/2011 105/1952 103/1914 && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...Hartfield/26 SHORT TERM...26 LONG TERM...KRD AVIATION...Hartfield CLIMATE...BLAES

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