Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 231840 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 240 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 Sunday night/... As of 225 PM Saturday... This still looks like our hottest day, and convection chances appear to be very minimal. Models take the core of the upper ridge overhead Sun, with continued steady warming aloft evident on forecast soundings, cutting down considerably on the potential for destabilization despite surface temps peaking in the upper 90s. CAMs and models with parameterized convection favor virtually dry weather tomorrow, with only an isolated cell or two at most. Will keep an isolated thunder mention in the extreme west and extreme SE, with the potential for drifting terrain-induced cells and sea-breeze convection, respectively. Statistical guidance and model thicknesses support highs in the upper 90s, very close to earlier forecasts. With dewpoints remaining high but dipping a bit in the afternoon with mixing, heat index values are likely to reach 100-106, with the highest values along and east of the Highway 1 corridor. Will go forward with a heat advisory for these eastern sections. Even if some spots only reach close to 105 for an hour, given that we will have been atypically warm for a few days already, and with it being a Sunday and folks likely spending time outdoors, the risk for heat illnesses will be elevated. Any isolated convection is apt to dissipate quickly toward sunset, with fair and muggy conditions Sun night. Lows in the mid 70s. -GIH && .LONG TERM /Monday through Saturday/...
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As of 239 PM Saturday... With the upper ridge directly overhead and a surface high over the western Atlantic Monday is shaping up to be a very hot but mostly dry day to begin the long term. To the north, a low pressure system over Quebec will spin off to the northeast, dragging a weak cold front behind it that will approach the Appalachians by Monday night but get held up by the exiting high. On Tuesday the low pressure over Canada moves on, leaving the remnants of the cold front just north of the area. This could leave Tuesday fairly dry as well but an uptick in afternoon convection is possible with more moisture filtering into the area and the relaxation of the surface high replaced by a surface trough over central NC. The frontal zone slides further south on Wednesday bringing a much better chance for convection by Wednesday afternoon, particularly across northern portions of the forecast area. Story remains the same for Thursday with the added punch of a shortwave disturbance tracking out of the Mideast and arriving by 00z Friday. Several disturbances will continue to move through the area through Saturday as a low pressure system tries to become better organized over the mid-Atlantic states. No relief to very warm temperatures with mid-90s expected each day with lows in the mid 70s. Furthermore heat indices will run at least 100-105 most days with the potential for some >105 readings possible with Monday and Wednesday afternoons looking like the best chance for that.
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&& .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...Hartfield LONG TERM...Ellis AVIATION...Hartfield

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