Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 260508 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 108 AM 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 region 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 TODAY/... AS of 1000 PM Monday... Heat Advisory in effect from noon to 8 pm EDT Tuesday for South Central Piedmont of Virginia. Widely scattered thunderstorms have been mainly confined to areas along and west of the Blue Ridge with forcing over the mountains providing just enough lift to trigger storm activity. Can`t rule out additional activity during the overnight, esp western slopes of the Appalachian Divide (Mt Rogers vicinity) where light westerly flow will continue to provide for weak low level convergence during the overnight. Overall intensity however, should wane per loss of daytime heating. Upper ridge will slowly weaken or flatten tonight into Tuesday as shortwave troughing passes to the north. Surface boundary sinks southward to just north of the area late tonight into Tuesday with the axis of higher pwats and weak lift strung out from the western slopes to across the north. This may result in convection linger especially across the north tonight. Otherwise, partly to mostly cloudy and very muggy expected tonight. Low temperatures tonight will range from the mid 60s in the mountains to the mid 70s in the Piedmont. The frontal boundary will drop south across our region on Tuesday. The combination of frontal ascent, orographic lift, and heating will result in scattered showers and thunderstorms especially during the afternoon. SPC in day two convection has portions of forecast area in marginal risk for damaging winds with convective clusters. High temperatures on Tuesday will range from the lower 80s in the mountains to the mid 90s in the Piedmont. Heat indices will climb as high as 105 degrees in the far east. && .SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/... As of 300 PM EDT Monday... The upper level ridge will continue to sink south across the southeastern US through Thursday. Lowering heights means temperatures will be a little bit cooler each day. However, temperatures will remain above normal until we can get a cold front to pass over the region. Unfortunately, there is no frontal passages expected this week. Afternoon temperatures will run around 5F warmer than normal with 80s across the mountains and low to mid 90s east. Dew points will also remain elevated ranging from the mid 60s to lower 70s. Heat indices values will run 5F-8F warmer than the actual temperature. Some heat relief will come in the form of showers and thunderstorms each afternoon. Even though these storms may knock temperatures down, they will increase dew points keeping conditions very uncomfortable. The coverage of storms will increase each day and start earlier and end later. With zonal flow aloft, storms will start across the mountains by noon, then drift east over the piedmont during the evening hours. Forcing both Wednesday and Thursday is not ideal for widespread strong storms, however with zonal flow aloft, any waves rounding the ridge could change that. For now, we will continue to see a typical summer pattern with scattered afternoon and evening pulse storms. && .LONG TERM /FRIDAY THROUGH MONDAY/... As of 215 PM EDT Monday... The ridge of high pressure will drift off the southeast coast Friday, allowing an upper level trough to move over the Ohio and Tennessee Valleys Friday. Models develop a surface reflection along a lee trough that will bring an increase chance for strong to severe storms into the region. Models currently are placing the stronger dynamics Friday north of DC, but with all the instabilities, heat and moisture in the region, the chance for widespread severe weather will increase for the area Friday and/or Saturday. If we do not see widespread significant weather Friday, then Saturday will be the day. The upper level trough over the Ohio Valley strengthens Saturday and will push bulk of the energy east to the coast on Sunday. The upper level trough remains to our west Sunday and Monday, which keeps the chance for showers and thunderstorms in the area. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... As of 1250 AM EDT Tuesday... Earlier convection has about faded out tonight resulting in widespread debris mid/high cloud canopy over some patchy strato-cu across the south. Given the current soupy conditions and lingering instability, cant totally rule out added isolated convection through daybreak but not enough to include mention attm. Otherwise mainly VFR expected aside from some river valley fog or shallow ground fog for areas which received rain Monday evening. Again appears that KLWB will drop down to a period of IFR/LIFR but less confidence than usual given degree of mid clouds around and more tropical nature conditions. Elsewhere could also see IFR at KBCB and MVFR at KDAN/KLYH right before daybreak. Any fog or stratus that does form will quickly disperse after sunrise. Given strong instability would expect greater coverage of storms Tuesday 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 upstream pre-frontal zone could lend to multiple clusters in spots Tuesday afternoon. For now will continue trend in including a VCTS mention most locations and attempt to refine spots Tuesday morning that have the best chance of seeing sub-VFR in convection in the afternoon. Otherwise mainly VFR with cu buildups expected Tuesday afternoon ahead of convection before again giving way to debris clouds and patchy fog Tuesday night. Extended aviation discussion... Little change in the overall scenario can be expected Wednesday through Saturday at this point with the upper ridge remaining just south of the area and a residual front nearby. This should allow for periodic daily convective coverage through much of the period. Appears more widespread sub-VFR possible in convection per a stronger wave along the front later Thursday 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... 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 && .RNK WATCHES/WARNINGS/ADVISORIES... VA...Heat Advisory from noon today to 8 PM EDT this evening for VAZ046-047-058-059. NC...None. WV...None. && $$ SYNOPSIS...JH/RCS NEAR TERM...KK/PM SHORT TERM...RCS LONG TERM...RCS AVIATION...JH/PM CLIMATE...PM

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