Area Forecast Discussion
Issued by NWS Blacksburg, VA

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557 FXUS61 KRNK 261850 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 250 PM EDT Tue Jul 26 2016 .SYNOPSIS... Lingering strong high pressure aloft over the Carolinas will result in hot and humid weather into at least mid week. A weak frontal boundary just north of the area should also continue to oscillate across the Mid-Atlantic region through the end of the week. Weak impulses riding along the front will combine with deep moisture to produce periodic rounds of showers and thunderstorms each day. && .NEAR TERM /THROUGH WEDNESDAY/...
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As of 249 EDT Tuesday... Heat advisory remains in effect until 8 pm for South Central Piedmont of Virginia. The strong upper ridge is weakening and slide southeast tonight into Wednesday. A shortwave passing to the north this evening into tonight, will push the frontal boundary further south into higher pwat air around 2 inches including high surface based instability. This feature combine with differential heating, orographics, residual outflow and low level convergence will generate scattered showers and thunderstorms into tonight. On the Day One Convective Outlook, our forecast area remains in a marginal threat for severe storms with primary concern damaging winds. Given weak steering but some unidirectional westerly component aloft, looks like storms will be slow moving with locally heavy rains possible. The best severe chances will come from downbursts within a highly unstable water loaded type environment. Will mention isolated severe in HWO. Weak mid level wave along the front to the north should exit this evening into tonight allowing the boundary to sag south. How far south remains a question for debate. Outside of isolated convection, expect another very warm and muggy overnight with moisture and debris clouds. Low temperatures tonight will range from the mid 60s in the mountains to the mid 70s in the Piedmont. A weak surface front will stall across our region on Wednesday. Scattered showers and thunderstorms are expected Wednesday afternoon into Wednesday evening. SPC Day Two convection Outlook places eastern portions of forecast area in Marginal threat. The Shear is still not very impressive so the probability for widespread severe remains low. The main threat being pulse storms and any clusters that can organize due to outflow boundary interactions. High temperatures on Wednesday will range from around 80 degrees in the northwest mountains to the mid 90s in the Piedmont. Heat index may climb to near the century mark in eastern Piedmont, just short of heat advisory levels.
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&& .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
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As of 243 PM EDT Tuesday... Will start to see the strong upper ridge over the southeast break down this period as stronger upper wave moves across the Great Lakes. Models also overall in agreement in a stronger vort moving from the Mid Mississippi Valley Wednesday night into the eastern Ohio Valley by Thursday evening. This signal suggests an increased likelihood of storms with greatest coverage over the mountains Thursday. Therefore increase pops to likely along and west of the Blue Ridge for Thursday. There is good upper support with jet dynamics such that severe storms is possible if we get enough heating. However timing of complex may bring more clouds to the area Thursday morning limiting solar insolation. This wave shears to the mid Atlantic by Friday with 5h heights falling. Should maintain at least threat of storms Friday as frontal boundary starts to linger over the mid Atlantic. Question will be how far south this front makes it. We should start to see temperatures settle toward seasonal lat July norms by Friday but will remain sticky/humid. Highs Thursday will range from the lower to mid 80s west to lower 90s east. By Friday highs will be in the upper 70s to lower 80s west to around 90 east.
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&& .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... As of 130 PM EDT Tuesday... Overall pattern situation favors storminess every day but especially in the afternoon/evening. A frontal boundary situated from the Ohio Valley over to the Central Plains will slowly shift southeast into the Virginias and North Carolina over the weekend. Airmass will remain unstable and moist. Some issue with how far this front makes it as 5h ridge may be hard to break, but still looks like belt of westerlies will shift at least into our northern forecast area over the weekend. Highs will be seasonal with lows slightly above normal through most of the period. Highs will range from the lower to mid 80s mountains, to upper 80s to around 90 east. Lows will be in the lower to mid 60s mountains, to upper 60s to around 70 east. && .AVIATION /19Z TUESDAY THROUGH SUNDAY/... As of 138 PM EDT Tuesday... SCT to BKN VFR ceilings with pockets of MVFR/IFR convection expected this afternoon into tonight. Given strong instability would expect greater coverage of storms this afternoon compared to the widely scattered activity Monday. However, models continue to vary on expanse and locations of coverage as ridging aloft appears stronger than earlier forecast, while focus on residual outflow...southeast lee trough and the upstream pre-frontal zone could lend to multiple clusters in spots later this afternoon. Mention VCTS in most taf locations for this afternoon into this evening. Believe the taf site with the best chance of a thunderstorm is KROA. Widely scattered clusters of shra/tsra may linger into tonight before again fading to patchy fog/stratus overnight. KLWB is the taf site with the best chance for low clouds and fog late tonight into Wednesday morning. Scattered MVFR showers and thunderstorms are expected Wednesday especially during the afternoon and evening hours. Medium confidence on ceilings,visibilities and winds during the taf period. Extended aviation discussion... The upper ridge will remain just south of the area and a residual front nearby through Saturday. This should allow for periodic daily convective coverage through much of the period until the boundary either fades or sinks farther south. Appears more widespread sub- VFR possible in convection later Thursday per a stronger wave along the front with perhaps some decrease in coverage by the weekend as this feature passes. However given uncertainty appears at least diurnal MVFR/IFR possible each afternoon/evening through Saturday for now. Late night and early morning fog will likely occur at the usual valley locations, and those chances increase across the entire region if any rain occurs during the afternoon or evening at any site. && .CLIMATE...
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Record high temperatures for Tuesday (7/26) Roanoke.....101 in 1930 Lynchburg...104 in 1934 Danville.....99 in 2012 Blacksburg...94 in 1987 Bluefield....91 in 1993 Record high temperatures for Wednesday (7/27) Roanoke.....103 in 1936 Lynchburg...103 in 1936 Danville....102 in 1952 Blacksburg...94 in 1993 Bluefield....89 in 1966
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...Heat Advisory until 8 PM EDT this evening for VAZ046-047-058- 059. NC...None. WV...None. && $$ SYNOPSIS...JH NEAR TERM...KK SHORT TERM...WP LONG TERM...WP AVIATION...JH/KK CLIMATE...PM

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