Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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858 FXUS62 KRAH 221606 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1205 PM EDT FRI JUL 22 2016 .SYNOPSIS... A mid-level disturbance will drift across western North Carolina this afternoon and evening. A hot high pressure ridge will then expand from the central U.S. to the mid-Atlantic states over the weekend and into early next week. && .NEAR TERM /THROUGH TONIGHT/... As of 1010 AM Friday... Convection chances remain low for much of Central NC the rest of today into tonight, within a regime dominated by a warm cyclonic ridge aloft resulting in stable mid levels with weak steering flow, while low level thicknesses steadily climb. The MCV resulting from yesterday`s Great Lakes MCS will track southward over the southern Appalachians today as other disturbances emanating from upstream MCS activity over the Midwest follow a similar path, likely tracking just west of the CWA. Latest CAM runs -- as well as larger-scale models with parameterized convection -- show good continuity with yesterday`s model runs, suggesting that a few storms should form this afternoon over the far western CWA, closer to the MCV tracks, and perhaps over the far southern and SE CWA as well where low level mass convergence along an inland-moving sea breeze should take place. But coverage and upscale growth of any convection will be greatly suppressed over the remainder of the CWA given the weak mid level lapse rates (particularly during the peak heating period), lack of a convective focus, and little to no dynamic support. PW values are projected to rise a bit, but the 700-400 mb layer will remain quite dry. Will restrict low chance pops to the western and far southern CWA including the far SE this afternoon, tapering back down in the early evening as we lose heating. High-res guidance shows temps peaking in the 90-94 range, with dewpoints in the upper 60s and lower 70s helping to push the heat index values into the mid- upper 90s. -GIH Previous discussion as of 345 AM: Central NC will remain on the ERN periphery of a strong sub-tropical ridge centered over OK, while a surface trough will sharpen in the of the Appalachians. Within the associated N to NNW flow aloft around the ridge, a low amplitude, positive tilt mid-level trough, now extending from the Lower Great lakes to the OH Valley, will drift into NC this afternoon. An MCV evident in model analysis 700-500 mb vorticity fields and earlier satellite imagery is embedded within the broader mid-level trough, over ERN KY; and this feature is forecast to drift focus forcing for ascent as it drifts into the SRN Appalachians through the same time. While the relative highest chance of showers and storms will be along the track of the MCV and aided by differential heating -in the mountains- a shower or storm will also be possible in the vicinity of the lee trough, centered over the WRN Piedmont, despite rather dry mid levels. Return flow around high pressure centered near Bermuda will support slightly higher temperatures and dewpoints versus those of Thu, with highs generally 90 to 95 degrees. Light SSW stirring overnight should hold temperatures in the (lower) 70s, and also preclude the development of anything more than patchy fog, particularly given the presence of cirrus related to the MCS upstream/over IL. && .SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/... As of 400 AM Friday... Generally a persistence forecast, with a slight chance of an afternoon storm, and higher temperatures yet, owing to a slowly increasing influence of the sub-tropical ridge --and associated heat beneath it-- as it builds E. Highs 93 to 97 and lows in the middle 70s. Heat indices are expected to range from around 100 over the NW Piedmont to 105 over the ERN Sandhills and Coastal Plain. && .LONG TERM /SUNDAY THROUGH THURSDAY/... As of 335 AM Friday... ...Hot and humid and conditions with heat index values in excess of 100 expected to continue into Sunday and Monday... Central NC will be located along the eastern periphery of a west to east extending upper level ridge at the beginning of the long term period. A portion of the ridge strengthens across NC and VA late Sunday and then shift offshore on Monday into Tuesday as weak troughiness develops across the Great Lakes and OH Valley and a westward pushing upper low moves from the Bahamas on Sunday to the northern Gulf of Mexico on Tuesday. At the surface, a Piedmont trough present on Sunday will weaken on Monday and be replaced by the southerly flow associated with the circulation about a Bermuda high pressure system. A hot and humid air mass will be in place across the region with surface dewpoints in the lower to mid 70s contributing to a weak to moderately unstable air mass during the afternoon each day. Limited forcing for ascent in a generally subsident environment with some capping will keep convective chances limited on Sunday and Monday and increase slightly on Tuesday as a short wave trough approaches the region from the OH Valley. Guidance has cooled off a bit from previous runs with morning thickness values ranging in the 1420-1430m range during the period, perhaps as high as 1435m on Sunday which support highs in the mid to possibly upper 90s during the period. The hottest days will be Sunday and Monday with temperatures approaching 98 to 99 degrees in a few spots. The west-east oriented low and mid level ridge axis often support hot periods with higher boundary layer moisture and higher heat index values than north-south ridges which often result in hot and drier setups. Heat index values will climb above 100 and likely exceed 105 in most areas on Sunday and Monday. The ridge relaxes across the region On Wednesday and Thursday allowing the westerlies to drop southward and mean troughiness to develop across the Great Lakes and OH Valley. A cold front will settle south across the Mid Atlantic on Wednesday and potentially moving into NC on Thursday. The approaching trough aloft and the cold front 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 /18Z Friday through Wednesday/... As of 1205 PM Friday... High probabilities of VFR conditions persisting through the next 24 hours. Warm and dry air aloft will suppress most shower/storm activity over Central NC this afternoon through midday Sat, with clouds generally scattered and bases above 4 kft. Any isolated storms would be circumnavigable. The better chances of a stray storm would be near INT/GSO and FAY, although chances are too low to include as a prevailing condition. As always, erratic gusty winds and lightning can be expected in and near any storms. There is a small chance for patchy shallow MVFR fog in low-lying areas late tonight into early Sat morning at all TAF sites, but chances are too small to mention at this time. Surface winds will remain light through Sat, mainly from the southwest under 10 kts. Looking beyond 18Z Sat: A few storms are possible late Sat afternoon into Sat night, primarily at INT/GSO/FAY. Areas of MVFR fog may develop late Sat night into Sun morning. Shower/storm chances will start to improve late Sun into Sun night, with scattered daily storms possible through Wed as the air mass moistens more deeply over Central NC. Fog is possible early each morning Mon-Wed. -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 Mon Jul 25 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...Hartfield CLIMATE...BLAES is the U.S. government's official web portal to all federal, state and local government web resources and services.