Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 211933 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 330 PM EDT THU JUL 21 2016 .SYNOPSIS... Surface high pressure will over the mid-Atlantic states will move offshore tonight. A strong high pressure ridge will expand from the central U.S. across the Carolinas over the weekend, bringing hot and humid conditions. && .NEAR TERM /THROUGH TONIGHT/...
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As of 300 PM Thursday... A weakening surface ridge remains over the region, with relatively warm and dry air aloft. Isolated cells have tried to get going over the northern Piedmont but are facing marginal mid level lapse rates, poor deep layer shear, and insufficient moisture through the column (PW < 1.5"), conditions that are likely to persist at least into the evening when the loss of heating will foster stabilization. Latest CAM runs including the HRRR/HRRRX show very little to no convective activity in Central NC for the rest of the day, focusing instead on areas to our south and west near the old boundary, in areas with steeper low level lapse rates and better MLCAPE and moisture, and at the coast with weak DPVA and sea breeze contributions to lift. Will retain an isolated storm mention across the far west and SW CWA for the next few hours, followed by no pops overnight. A little light fog or shallow ground fog is possible late tonight, but should not be widespread or dense based on the dry air just off the surface and minor stirring near the ground overnight. High-res guidance supports lows in the upper 60s to lower 70s. -GIH
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&& .SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/... As of 330 PM Thursday... Another fairly quiet day is expected, but with gradually building heat, and uncertainty regarding the fate of the MCV leftover from the complex now dropping through the Great Lakes. Models are not doing well handling the timing/movement of this MCS (too slow), thus their reliability is questionable. But using the timing of the SREF mean and steering flow would suggest that this could venture into the southern Appalachians by tomorrow, likely working with differential heating in the higher terrain and weak mass convergence along a lee trough to spawn scattered afternoon convection mostly to our west, although some of this could certainly spill into our far western Piedmont. But overall, the gradually rising warmth and dry air in the mid levels will limit the CAPE potential with continued poor mid level lapse rates. And the PW, while improving, should mean greatly reduce coverage. Will have isolated showers and storms over the NW Piedmont in the afternoon, trailing back off in the early evening as we lose any instability. Rising thicknesses will equate to highs in the lower 90s, even given the potential for some convective debris cloudiness early in the day, and this combined with dewpoints in the lower 70s and minimal reduction with mixing will generate heat index values in the mid to upper 90s -- a prelude to the more intense heat over the weekend. Lows in the lower to mid 70s Fri night with light fog possible. -GIH && .LONG TERM /SATURDAY THROUGH THURSDAY/... As of 240 PM Thursday... To begin the long term period, the strong upper ridge that provided multiple days of intense heat across the Central Plains will dampen some and start to spread east. 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 Saturday (slightly lower than previous runs) and the mid to upper 1440s on Sunday. 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 and even the upper 90s by 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 the weekend, but will not be zero as there will be a persistent Piedmont trough that could be a focus for convective development, as well as any weak disturbances that move through aloft. The aforementioned ridge will dampen and shift even more over our region into early next week and eventually offshore, after another rather warm day on Monday. Also, a shortwave trough is progged to cross 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. Regardless, 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. The increased cloud cover and precip chances should allow temps to "cool" back to the lower 90s, especially Tuesday through Thursday. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... As of 1210 PM Thursday... High probabilities of VFR conditions persisting through the next 24 hours. Weak high pressure over the region combined with warm and dry air aloft will suppress most shower/storm activity over Central NC this afternoon through much of Friday, with clouds generally scattered at most with bases above 4 kft. Any isolated storms would be circumnavigable and be very unlikely to affect a TAF site. There is a small chance for patchy shallow IFR fog in low-lying areas late tonight into early Fri morning, and if it occurs, it would be most likely to affect RWI. Surface winds will remain light/variable through daybreak Fri, then be from the southwest under 10 kts. Looking beyond 18Z Fri: Chances for storms Fri afternoon/evening will remain low. VFR conditions are expected to dominate through at least Sat, as the warm/dry air aloft persists. A few storms are possible late Sat into Sat night, but coverage will not be widespread. Areas of sub-VFR fog may develop late Sat night into Sun morning. Shower/storm chances will start to improve late Sun into Sun night, growing through Tue as the air mass moistens more deeply over Central NC. Fog is possible early Mon and Tue mornings. -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 Sat Jul 23 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 SHORT TERM...Hartfield LONG TERM...KRD AVIATION...Hartfield CLIMATE...BLAES

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