Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 201747 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 147 PM EDT Sat Aug 20 2016 .SYNOPSIS... Weak high pressure will slide across the region today into tonight keeping warm and humid conditions in place. A strong cold front will approach from the west late tonight before crossing the area Sunday. Somewhat cooler and drier air follows the front for much of next week. && .NEAR TERM /THROUGH TONIGHT/... As of 1007 AM EDT Saturday... Pockets of low clouds and fog are slowly mixing out this morning. The low clouds and fog will burn off or lift by late morning, returning sunshine for this afternoon. The combination of low level moisture and instability will generate scattered showers and thunderstorms this afternoon into this evening. The best chances of convection will occur across the southwest mountains. With pwats around 1.4 inch, any slow moving thunderstorms could produce locally heavy rains. Adjusted temperatures with latest obs and trend, then shaped early afternoon with lav guidance. Blended in the HRRR for pops this morning into this afternoon.More changes later today. As of 240 AM EDT Saturday... Overall rather diffuse weather scenario to continue today with dry air aloft per vapor loop sliding in behind the departing wave from Friday and over returning low level moisture from the southwest later on. This in conjunction with broad zonal flow aloft but with lack of much upper forcing given weak high pressure in place. However models agree that low level convergence should take shape initially over the west this afternoon along the leading edge of the higher pwats and where the flow turns more southwest similar to a warm front aloft. This also aided by a more southeast trajectory along/east of the Blue Ridge as the residual low level surface trough to the south starts to lift back northeast under weak return flow. Latest short term solutions support this convergence maximizing near the southern Blue Ridge initially before the axis shifts east later in the day. Progged instability not overly impressive given possible early mid deck although decent return of 850 mb theta-e ridging mountains likely enough to pop a few clusters/bands of slow moving convection given weak flow aloft. Therefore going with a small window of low likely pops southwest sections this afternoon with chance pops gradually spreading in from the southwest as the belt of deeper moisture lifts east/northeast. Could easily see northeast sections again go basically dry where the weak residual wedge may hang on so lowest pops there as expect guidance again overdone. Exodus of mid clouds this morning along with warming aloft should push high temps back into the upper 70s/low 80s west and mid/upper 80s east. Expect any evening convection to basically fade by midnight given lack of support and loss of heating before lift associated with the upstream pre-frontal band of convection approaches late. Rapid movement of this weakening convective band well ahead of the actual cold front likely to be near the far western counties by daybreak if it holds together. Thus after cutting pops back after this evening, ramping back up to high chance/likelys western slopes late per latest GFS/EC, with little east of the Blue Ridge. Otherwise partly cloudy early with more clouds west by dawn including patchy fog again valleys and out east. Expect a little more mixing west ahead of the front to hold lows up in the 65-70 range with mainly low 70s east. && .SHORT TERM /SUNDAY THROUGH TUESDAY/... As of 300 AM EDT Saturday... A strong cold front will move over the region Sunday. This front will remove dewpoints in the upper 60s to lower 70s and replace them with 50s. Even though this is an impressive front, convection activity will be some what lacking, mainly due to weak dynamics and showers coming across the area during the morning and early afternoon. Showers are expected to be along the western slopes of SW VA/SE WV by sunrise, then to the Blue Ridge by noon. There should be a wide area of rain as the front moves over the mountains. Winds quickly become westerly following the front which could limit areal coverage east of the Blue Ridge. A rain shadow may occur over the foothills with a secondary line forming across Southside during the afternoon (NAM solution). However, the front slows its eastward progress as it approaches the Blue Ridge. Winds will be able to back long enough to carry and maintain showers across the foothills and piedmont counties during the afternoon. Instabilities not overly impressive, therefore will have scattered thunderstorms instead of thunderstorms likely. Can not rule out a strong thunderstorm or two towards Southside, especially if clear skies are maintained through much of the morning. Models, particularly the NAM, displaying strong convection developing east of Route 15 (Kerr Reservoir-Occoneechee State Park). Showers will end quickly from west to east through the afternoon, exiting the piedmont by sunset. Temperatures and dewpoints will dramatically fall as the rain and front moves east. Monday and Tuesday afternoon highs will be below normal, ranging from the mid 70s to lower 80s. Relative humidity each afternoon will be at or below 50 percent. The coolest air arrives Monday night with lows dipping into the low to mid 50s. && .LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/... As of 245 PM EDT Friday... High pressure will remain over our region through at least Wednesday of the upcoming week. By Thursday, the center of the high will be far enough east for western portions of the area to see a return of isolated to scattered showers and a few thunderstorms. By Friday, guidance currently offers a solution of a cold front moving into the Ohio and Tennessee Valleys. Anticipate an increase in showers and storms across most of the forecast area. Only the far eastern part of the area may miss out on the activity. Temperatures during the early part of this portion of the forecast will be at or slightly below normal. Thursday into Friday temperatures will be increasing again so that they will be around normal. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/...
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As of 147 PM EDT Saturday... Deeper moisture will return to our area ahead of a strong upstream cold front approaching from the west this afternoon into tonight. Isolated to scattered showers and thunderstorms with periods of MVFR/ocnl IFR will continue this afternoon into tonight. The best chances of convection this afternoon into this evening will be from the Blue Ridge west, then scattered storms will travel eastward into the Piedmont this evening into tonight. A second round of showers and thunderstorms including possible MVFR/IFR may take place late tonight with the pre- frontal band of convection ahead of an approaching strong cold front. This could tend to limit fog formation given cloud cover and mixing. Otherwise VFR outside of any added showers until late tonight when will include some sub-VFR in most locations due to fog and/or showers. Another round of showers and thunderstorms including MVFR/IFR will take place Sunday along a strong cold front that will pass through the region by Sunday night. Medium confidence in ceilings,visibilities and winds during the taf period. Extended aviation discussion... Much drier air is anticipated after Sundays frontal passage with a dry forecast for Monday through Wednesday promoting VFR for much of the Mid- Atlantic. By Thursday, the center of the high will be far enough east for western portions of the area to see a return of isolated to scattered MVFR showers and a few thunderstorms.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH/KK NEAR TERM...JH/KK SHORT TERM...RCS LONG TERM...DS AVIATION...JH/KK is the U.S. government's official web portal to all federal, state and local government web resources and services.