Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 211349 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 950 AM EDT THU JUL 21 2016 .SYNOPSIS...
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Surface high pressure will build across the mid-Atlantic states today, then move offshore tonight. A strong high pressure ridge will expand from the central U.S. acoss the Carolinas through the weekend, bringing hot and humid conditions.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As of 950 AM Thursday... Convection chances still appear quite low and confined to the SW CWA. Latest surface map shows the weak surface ridge nosing in from the NNE, poised to build overhead today as it weakens further. Humidity will remain elevated today as surface dewpoints drop minimally from their current readings in the upper 60s to lower 70s, and the lack of clouds currently overhead and upstream combined with dry air aloft as noted on the water vapor imagery (and likely to dry further with acceleration of the NNE-erly upper jetlet over the Delmarva/SE VA/NE NC today) should lead to no worse than partly cloudy skies today, boosting isolation and causing surface temps to peak in the upper 80s to lower 90s. Latest CAM runs including the HRRR/RAP and SPC`s SSEO favor a storm-free day for much of Central NC, with the exception of the far W and SW near the old boundary where low level mass convergence will take place, and perhaps just off the higher terrain which will be subject to differential heating. Convection over Central NC should be further smothered by slow steady warming aloft, with gentle but persistent mid level height rises continuing into tonight, leading to low CAPE values. Will limit pops to isolated thunder in the extreme west / SW. -GIH Previous discussion as of 355 AM Thursday... WV imagery and model analysis PV fields depict a couple of perturbations in NW flow aloft over the DelMarVA and Lower OH Valley. The models indicate the former will amplify off the VA/NC coast through 18Z, while the trailing one will dive across west-central NC, to NERN SC, through the same time. The tail end of the lead perturbation over the DelmarVA has already aided in the development of a few showers over the Shenandoah Valley, amidst an area of 6-9 thousand ft strato/alto- cumulus centered over central and SRN VA; and the HRRR suggests a few additional showers may develop over the NC Piedmont during the morning to midday hours, presumably as the strongest QG-forcing for ascent accompanying the trailing Lower OH valley wave moves SEWD. Otherwise, 1025 mb surface high pressure now over WV will build east across and offshore VA today, in the subsident wake of the aforementioned perturbations aloft. The surface ridge axis and associated NE low level flow around it, over the ERN half of NC, will result in temperatures AOB those of Wed, with generally upper 80s to around 90 degrees anticipated. To the west of the ridge axis, a light SLY return flow will develop across WRN NC, including the SRN and WRN Piedmont; and an associated 925-850 mb theta-e ridge there warrants a continued slight chance of an afternoon shower or storm. Light return flow will envelop all of central NC tonight, once the aforementioned surface ridge migrates offshore, with dry and mainly clear conditions. Lows in the upper 60s to lower 70s.
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&& .SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/... As of 410 AM Thursday... A strong sub-tropical ridge centered over OK at 500 MB and AR at 700 mb, will gradually expand EWD this period, and more so this weekend. Warmth beneath the ridge will likewise expand EWD, with highs in central NC mainly in the lower 90s. Lows 70 t0 75. Associated warm and dry mid levels will limit the chance of showers and storms to differential heating boundaries in the mountains and along the coast. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... As of 320 AM Thursday... Period of hot and humid and conditions with heat index values in excess of 100 expected for the weekend into Monday... Central NC will be located in along the eastern periphery of an eastward extending central Plains ridge at the beginning of the long term period resulting in a weak, diffluent northwest flow aloft. Over the weekend into early next week, the ridge will shift east with rising heights across the Carolinas. At the surface, a Piedmont trough will be present on Saturday and Sunday while a cold front across the Mid Atlantic washes out as it stalls near the Mason-Dixon line. A hot and humid air mass will be in place across the region with surface dewpoints in the lower 70s only modestly abated to the west of the Piedmont trough during day time mixing. PW values will average between 1.75 and 2.0 inches throughout the period. Deep mixing will likely generate some high-based afternoon cumulus most days but warming mid levels with 500 hPa temps warming to -5 to -4C on Sun and Monday in a generally subsident pattern should limit convective coverage, only warranting slight chance PoPs during the afternoon and evening. Morning thickness values in the 1420s will increase to 1435m on Sunday and Monday supporting highs in the mid to upper 90s during the period. The hottest days appear to be Sunday and Monday with heat index values climbing above 100 all three days and exceeding 105 on Sunday and Monday. The ridge relaxes a bit across the Carolinas on Tuesday into Wednesday allowing the westerlies to drop southward. A cold front will settle south across the Mid Atlantic on Tuesday, potentially moving into NC on Wednesday. Not real confident the front will be able to push that far south but its proximity, a more cyclonic flow aloft and increasing shear along with weak to moderate instability will result in an increase in the threat of convection. Increased cloud cover and the retreat of the ridge will result in high temperatures dropping back into the lower 90s with lows in the lower to mid 70s. -blaes && .AVIATION /12Z THURSDAY THROUGH MONDAY/... As of 745 AM Thursday... A disturbance in NNW flow aloft will dive SEWD across the Carolinas early today. The passage of this feature and associated lift combined with diurnal heating may cause a showers to develop and spread across the Piedmont, mainly over the SRN half (from KVUJ to KFAY), through midday. After early morning fog at KRWI and KFAY dissipates through 13Z, VFR conditions and a light and variable surface wind will follow, and continue through tonight. Outlook: Sub-tropical high pressure will expand across the SRN and Central Appalachians, and Carolinas, and result in mostly dry/VFR, and increasingly hot conditions, through the weekend. However, a small chance of early morning fog/stratus, and isolated to widely scattered afternoon and evening storms, will be possible each day, but the probability of occurrence at any given TAF site will be quite low. && .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/26 SHORT TERM...26 LONG TERM...BLAES AVIATION...26 CLIMATE...BLAES

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