Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 122335 AFDRAH AREA FORECAST DISCUSSION National Weather Service Raleigh NC 735 PM EDT Wed Aug 12 2020 .SYNOPSIS... Weak low pressure will linger over the Carolinas through the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 345 PM Wednesday... Convection thus far has held close to both expectations and the morning CAM solutions, confined largely to areas E and NW of the forecast area, with isolated showers/storms along and SE of the inland-moving sea breeze and more numerous storms just NW of the Triad, over the higher terrain of west-central and NW NC into VA and SW WV. Steering flow remains weak, thus storm propagation will be outflow-driven, making the attempts to forecast convection chances in central NC over the next several hours quite challenging. Can`t rule out a shower or storm anywhere through this evening, but the best chances appear to be over the Triad, where some very weak mid- upper level DPVA within very weak S/SW mid level flow will traverse, in conjunction with weak but focused low level SE upglide. Will retain the highest pops here until around midnight, with much lower pops elsewhere, ending earlier as heating winds down in the absence of any other mechanisms to force ascent. As has been advertised, isolated pockets of flooding are possible given the high PW near 2" and very slow storm motion favoring long-lasting heavy downpours and inflated rainfall totals. Expect fair skies tonight to give way to another round of fog and stratus, with model guidance and persistence suggesting equal chances areawide. Expect lows to be similar to last night, in the 70-74 range with some upper 60s in rural locations. -GIH && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... As of 355 PM Wednesday... More of the same expected, but with a bit better coverage than we`ve seen so far today. Steering flow from the SW will remain very weak, although we may see it pick up slightly as the weak upper trough over the Mid Miss Valley approaches. The weak low level low pressure area over the central/E Carolinas today is expected to drift to the NNE, leading to a band of more discernible confluence of low level flow through central and E NC as inverted troughing becomes more defined from NE NC SW through the CLT area. With the continued slow/meandering storm motion and PW that is likely to be 2-2.5", slow-moving heavy downpours remain possible, although the continued lack of large scale forcing for ascent may curtail coverage once again. But good chance to low-end likely pops still seem reasonable, and have largely held onto these, with minor tweaks. Temps should once again lean toward persistence, with highs in the upper 80s to around 90 followed by lows near 70 to the lower 70s. -GIH && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... As of 230 PM Wednesday... No major changes for the long term with the afternoon forecast package. Upper-level low pressure will remain over the southern Appalachians through the weekend, then slowly lifting east-northeast early next week across the area. At the surface, an inverted trough will remain over the Appalachians, extending from a low over northern MS/AL through the end of the week, shifting into central NC over the weekend as the low lifts through the Carolinas. This pattern, along with precipitable water values around 2 inches, will support scattered to numerous showers and thunderstorms across the region through the weekend. Most shower activity will be in the afternoons and evenings, with less coverage overnight. The upper-level trough will push east sometime Sunday/Monday, with slightly drier air behind the system. Showers and thunderstorms will be more isolated Monday and Tuesday. Lower dewpoint temperatures behind the system will make it feel less muggy early next week, with heat indices only in the upper 80s to low 90s by Wednesday. Another upper-level trough will develop just to our west by the middle of next week, and with an increase in moisture over the region, helping to increase shower and thunderstorm activity yet again across the region. Highs through the extended will be just below seasonal normals, with lows just above seasonal normals. && .AVIATION /23Z WEDNESDAY THROUGH MONDAY/... As of 730 PM Wednesday... Several factors are in play for tonight`s aviation forecast. First, in the near term it appears that a thunderstorm will clip RWI, and have added a VCTS to that TAF. In addition, over the next few hours, recent high-resolution models have shifted the timing of precipitation around the Triad, showing that now is likely the maximum for rainfall and that coverage will diminish through the evening, instead of increasing around midnight. Added rain to the INT TAF, but think that precipitation will stay west of GSO. Inherited IFR forecasts for all TAFs around sunrise, although a similar forecast last night only panned out at FAY/RWI, with INT/GSO/RDU all remaining VFR through the night. Nearly all guidance is once again indicating IFR conditions everywhere, and have decided to go ahead with a modified persistence forecast. Kept the lower visibilities at RWI/FAY, and actually decided to lower visibilities based on conditions 12 hours ago and good model agreement. However, a limiting factor to the development of fog/stratus overnight could be the high overcast moving into North Carolina from northwest to southeast. This could eventually temper low level impacts. Because of this increasing cloud shield and no rainfall at GSO/RDU, have decided to go with a VFR forecast overnight as the cloud shield should limit radiational cooling potential. Finally, INT has picked up over a quarter inch of rain in the last hour with a shower, and think that the influence of this rain should allow for some visibility reduction overnight, so kept the inherited MVFR visibilities there. Finally, for Thursday afternoon, inherited 50-60 percent chance of thunderstorms in the public forecast, so have gone with VCSH at all sites, as it seems too early to pick a particular site to mention either TS or prevailing rain. Looking beyond 00Z Fri, daily chances for showers and storms are expected each afternoon into the evening through Sun, as a weak upper low over the Mid Miss Valley drifts slowly eastward through the Mid Atlantic region. Early-morning sub-VFR fog and stratus are also expected across the area each morning through Sun. Some improvement is possible Mon as drier air moves in. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...Hartfield SHORT TERM...Hartfield LONG TERM...JJT AVIATION...Green/Hartfield is the U.S. government's official web portal to all federal, state and local government web resources and services.