Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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078 FXUS62 KRAH 231702 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 100 PM EDT SAT JUL 23 2016 .Synopsis... A ridge of warm high pressure aloft will extend across the region through early next week, bringing a period of hot and humid conditions to our area. && .Near Term /through tonight/... As of 1045 AM Saturday... See no reason to depart significantly from the earlier forecast. The current surface analysis shows a diffuse MSL pressure pattern with weak lee troughing holding in place and a soggy air mass with dewpoints in the 70s areawide. We should see some dip in dewpoints with mixing this afternoon, down into the upper 60s to lower 70s, however given that observed thicknesses this morning are nearly 10 m higher than yesterday, heat index values are still expected to reach the upper 90s to around 100. The weak shear/moisture axis aloft along which last night`s convection developed is slowly pushing through southern NC, and the latest CAM runs suggest this feature serving as a focus for deeper moisture resulting in organized convection formation this afternoon. Will retain the greater rain chances across the southern CWA, in line with the RAP/HRRR/SSEO output, although we`ll need to monitor development trends as a bump- up to scattered coverage may be warranted. We should see highs in the mid 90s, factoring in high-res temp guidance, current trends, and expectations of more diurnal cloudiness in the south this afternoon. -GIH Previous discussion as of 315 AM: An expansive area of high pressure aloft centered over the central/southern plains will shunt the main band of westerlies near or north of the Canadian border. This pattern will result in a weak flow aloft over central NC. Thus, any convection that develops later today will be focused on outflow boundaries from Friday`s convection, or move into our region from the higher terrain to our west-nw. Expect the highest chance for isolated convection south of highway 64 where better low level moisture expected to reside. if later meso analysis depicts sufficient low level convergence, a bump up in PoPs to chance may be warranted. Strong low level lapse rates suggest strong gusty winds probable in vicinity of any convection. Afternoon low level thicknesses projected to be 7-10m warmer than Friday. This is supportive of max temps solidly in the mid 90s. Heat indices will be in the upper 90s northwest to 100-104 degrees elsewhere. Tonight, any isolated convection will quickly dissipate with loss of heating. Overnight temps will lower into the mid 70s. -WSS && .SHORT TERM /Sunday THROUGH MONDAY NIGHT/... As of 310 AM Saturday... Sprawling area of high pressure will build more so into the Carolinas, bringing hot and dry conditions to our region. The warming aloft will cap the atmosphere, limiting convective development to just a stray thunderstorm or two. Thicknesses Sunday afternoon approach 1450m in the Piedmont, supportive of temps well into the 90s, and heat indices in the heat advisory criteria. Comparable conditions expected Monday, though bulk of short term models drag a westward moving s/w across northern FL/coastal GA, the tail end of which may brush our southern counties. This feature interacting with available moisture and instability may trigger a concentrated area of convection. Overnight conditions will remain muggy. Most places will likely see temperatures remain above 80 until well after midnight. Any convection that develops Monday afternoon should dissipate within an hour or two after sunset. && .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 245 AM Saturday... Additional s/w energy is expected to track across Southern/Southeastern Canada and the Great Lakes and Northeast U.S. next week, which will allow a weak cold front to approach the region (likely stalling to the north of the area though). This will allow the mid level ridge to dampen across our region early next week and relocated to the south and southeast of central NC. This should place central NC on the southern fridge off potential disturbances tracking atop/around the ridge, which should lead to a better chance of mostly diurnal scattered showers and storms each afternoon/evening. Given the predictability of such hard to time features this far out in the forecast, will go with around 30-35 percent chance for showers and storms each day (generally climo). This additional associated cloud cover is expected to lead to temps a bit cooler, though highs are still expected to at least be in the lower to mid 90s. && .Aviation /18Z Saturday through Thursday/... As of 100 PM Saturday... High confidence in VFR conditions prevailing through mid afternoon Sunday. A weak disturbance aloft will reside over southern NC today into early tonight, and with a moist and hot air mass in place at the surface, a few showers and storms are expected this afternoon into tonight, with the best coverage (still just scattered) across the south (including FAY) and only isolated cells elsewhere (including INT/GSO/RDU/RWI). The chance that a storm will impact any particular TAF site is quite low, so will not include thunder as a prevailing or tempo condition at this time, but will monitor. As always, lightning along with erratic/gusty winds are possible in and near any storms. Otherwise, clouds today will follow a typical diurnal cycle with maximum cloud coverage in the late afternoon, decreasing slowly this evening/tonight. Any clouds will be based above 3 kft. Later tonight, isolated patches of MVFR fog are possible, but chances are too low of this affecting a TAF site to include in the forecast. High pressure in the mid and upper levels of the atmosphere will continue to build atop the region through Sun, resulting in drying and warming aloft and a reduced chance of showers and storms Sunday. Looking beyond 18z Sunday: VFR conditions will be dominant through this period, with no significant, large-scale sub-VFR conditions on the horizon, although shower/storm chances will start to rise during the mid week (Tue night into Thu). There will, however, be improving chances for late night / early morning sub-VFR fog as we head into next week. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...Hartfield/WSS SHORT TERM...WSS LONG TERM...BSD AVIATION...Hartfield

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