Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 210000 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 800 PM EDT Sat Jul 20 2019 .SYNOPSIS... High pressure will continue to build across the region into Sunday resulting in a third day of the summer heat wave with temperatures about 10 degrees above normal. A cold front should cross the area later Monday bringing cooler and less humid weather by the middle of next week. && .NEAR TERM /THROUGH SUNDAY/... As of 800 PM EDT Saturday...Heat indices have currently fallen below heat advisory/excessive heat thresholds, but are expected to reach those levels again tomorrow in the standing areas under an advisory/excessive heat warning. To clear up any confusion (e.g. why a heat product is in effect when heat indices are at their lowest point in the diurnal cycle), I tweaked some of the phrasing in the NPW text product for the heat advisory/excessive heat warning. The text changes are somewhat nuanced, but tries to convey that the highest heat indices will be for Sunday afternoon with little relief expected tonight. Hopefully, that helps to clarify things. Still a very warm and muggy early evening across the area, with current temperatures having cooled into the mid-upper 80s. Did add some isolated thunderstorms across Monroe, Summers and southern Greenbrier County through late evening based on current radar trends. These will likely be short-lived and unlikely to reach even strong levels as daytime instability wanes with loss of strong insolational heating. Strongest convective activity currently is over southeast KY and northeast TN, buoyed by weak vorticity maxima in southeast low/mid-level flow which is helping to induce a weakness in the heat ridge. 18Z GFS brings some of these showers or storms into Tazewell and Smyth counties after midnight - confidence is pretty low if this does occur given lack of other guidance agreement. Will continue to monitor and if trends and/or forthcoming guidance indicate better chances, I`d then look to increase PoPs in this area but too uncertain to go any higher than 20% PoPs. Previous discussion from 250 PM Saturday... Dangerous heat wave ongoing from the central CONUS to the East Coast. Excessive Heat Warnings and Heat Advisories extend from parts of the Kansas to the Middle Mississippi/Ohio Valleys and parts of the Great Lakes as well as parts of the Northeast southward to the Southern Mid-Atlantic as upper-level ridging extends from parts of the Southwest eastward to the Northeast/Mid-Atlantic. Hot air is being funneled from the desert Southwest all the way across the country, and combining with high levels of moisture off both the Gulf of Mexico and western Atlantic (dewpoints in the mid-upper 70s) to produce high heat indices. Afternoon temperatures in the mid to upper 90s combined with high dewpoints will result in heat indices of between 105 to 115 for a big chunk of the country. Temperatures across the foothills and piedmont have warmed into the mid to upper 90s with heat indices into the triple digits this afternoon. With less of a chance for a cooling shower or thunderstorm across the piedmont tomorrow, a repeat of Heat Advisories and Warning criteria are again expected during the afternoon. Mountain temperatures have also been very warm today with readings in the upper 80s to lower 90s. Temperatures may be a little cooler across the mountains Sunday with a better chance for afternoon and evening showers. Temperatures will still remain warmer than normal with highs in the mid to upper 80s. For most of the day today, showers and thunderstorms have been confided to a boundary draped along a line from Raleigh to Boone NC. This convection may wobble slightly to the north and south before fade this evening. Once west wind mixing decreases this evening, scattered showers and thunderstorms may form and linger into the early morning hours across the area. The upper level ridge will slowly move east and weakening on Sunday well ahead of height falls aloft in advance of a developing upstream trough. The moisture and energy aloft associated with an upper wave along the Gulf coast will try to lift northeast and split the heat dome in two. This may be enough to create some scattered showers and thunderstorms along and west of the Blue Ridge given the flow turning more southwest ahead of the cold front to the northwest. && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/... As of 230 PM EDT Saturday... Diurnal convection likely to linger at least over the mountains Sunday evening with perhaps some of this coverage persisting across the north into the overnight as a weak wave aloft unfolds to the northeast. However with loss of heating not expecting much more than chance coverage despite progged lingering instability through the night. Otherwise partly to mostly cloudy and muggy with only isolated pops over the southeast in the evening and then dry overnight outside of the northwest. Lows mainly in the 70s with a few 60s mountains. Pattern change will take shape heading into early next week as a sharp mid level trough dips southeast toward the area Monday before passing overhead Tuesday/Tuesday night. Models suggest either a lead pre- frontal trough or residual outflow will enter the region Monday afternoon ahead of the actual surface cold front that wont push through until Monday night or early Tuesday. Decent instability given lingering moist dewpoints and increasing southwest flow aloft ahead of the upstream shortwave trough should act to generate clusters/bands of convection over the higher terrain Monday afternoon before progressing into the eastern lee trough later in the day. Since still appears a bit slower, cut back on pops early Monday followed by likelys to low end categorical across the west Monday afternoon and high chances out east. With forecast soundings showing an inverted V under dry air aloft appears some pulse severe potential into late Monday. Highs still quite warm outside of the far west with readings likely topping back into the low/mid 90s east, and low/mid 80s for most of the mountains, but below heat advisory headlines at this point in the piedmont. Surface front pushing into eastern sections by early Tuesday will be followed by the 850 mb boundary along the leading edge of the trough aloft into Tuesday afternoon. Still some uncertainty as to how things may evolve between features as guidance shows added showers over the west with the dewpoint type boundary later Monday night and then enhancing these showers upon heading southeast during the day under cooling aloft. This may be more post frontal nature type rainfall with limited thunder except over the southeast in the afternoon per instability. However given consensus of solutions indicating a decent band of lift and subsequent rainfall, went ahead with higher pops Tuesday that should decrease from northwest to southeast by late in the day. Will be cooler with lows mostly 60s Monday night and only in the 70s to low 80s Tuesday under the clouds and influx of cool advection. Axis of deep moisture will finally slide to the southeast Tuesday evening resulting in clearing skies and lower dewpoints. May see a few showers linger southeast into the evening espcly if a wave forms along the boundary, otherwise decreasing pops/clouds with skies clearing from northwest to southeast by morning. Will be much more comfortable with lows in the 50s and 60s with even a few upper 40s in the valleys. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... As of 100 PM EDT Saturday... Mean upper trough regime will dominate starting midweek with a brief return to more zonal flow by the weekend. This combined with cooler surface high pressure building into and northeast of the region should lead to mainly dry as well as much more comfortable conditions through much of the period. However moisture may slowly return into far southwest sections by late in the week and across the mountains next Saturday. Thus will include some isolated pops along portions of the southwest mountains given heating/orographics but iffy since still looks quite dry aloft. Otherwise plan to leave out pops with mainly sunny days and clear overnights for most of the area at least into late week. Highs mostly 70s mountains to low/mid 80s east given rather cool 850 mb temps for late July except a bit warmer by Day7 as weak return flow develops. Lows quite pleasant with 50s west, including perhaps a few 40s valleys Thursday/Friday pending fog, and mostly 60s east of the Blue Ridge. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/... As of 800 PM EDT Saturday... VFR conditions should predominate until overnight when we`ll see opportunity for sub-VFR mist/fog in the western mountains (mainly affecting Lewisburg and Blacksburg). Didn`t hit visbys as hard with afternoon temperature-dewpoint spreads being rather sizable. Kept visbys no worse than prevailing MVFR, with a tempo IFR at Lewisburg. Winds light southwesterly. Any mist/light fog should erode quickly with heating by early Sunday morning. Will likely see greater thunderstorm coverage by as soon as early afternoon, but overall coverage likely no better than scattered and mainly in the mountains. Will indicate VCSH after 17z at Roanoke, Lynchburg, Bluefield and Blacksburg. Winds mainly light southwest under 6 kts. .Extended Aviation Discussion... Sunday afternoon, a bit better coverage of showers/storms is expected late Sunday and even better chances Monday as a cold front approaches slowly from the west. The front is expected to stall in or near the area thereafter leaving good chances for showers and storms just about every day next week, especially along and east of the Blue Ridge. Temperatures will be cooler, however. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...Heat Advisory until 11 PM EDT Sunday for VAZ034-035-044-045. Excessive Heat Warning until 11 PM EDT Sunday for VAZ046-047- 058-059. NC...Heat Advisory until 11 PM EDT Sunday for NCZ005-006. WV...None. && $$ SYNOPSIS...RCS NEAR TERM...AL/RCS SHORT TERM...JH LONG TERM...JH AVIATION...AL/RCS is the U.S. government's official web portal to all federal, state and local government web resources and services.