Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 271153 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 753 AM EDT Sat Aug 27 2016 .SYNOPSIS... A weak cold front will drop south across the area today and weaken. High pressure will be the dominant weather feature into Sunday, with just a chance for an afternoon shower or thunderstorm mainly along the Blue Ridge. Another weak cold front may slowly slide southward into the area by the middle of next week and continue the chance for a shower or thunderstorm from the Blue Ridge westward. && .NEAR TERM /THROUGH TONIGHT/... As of 300 AM EDT Saturday... Upper ridge will remain over our region today and tonight. A weak cold front across northern Virginia this morning will drop south today and weaken. Low level moisture and light winds will produce areas of low clouds and fog this morning especially along and west of the Blue Ridge. This fog will lift by mid morning. It will be another hot and humid afternoon with the chance for isolated cooling diurnal showers and thunderstorms mainly for the southern Blue Ridge heading into the northwest mountains of North Carolina. The day one convective outlook placed the threat for more organized thunderstorms with a marginal risk to the northwest across the Midwest. High temperatures this afternoon will range from the lower 80s in the mountains to the lower 90s in the Piedmont. Heat index values may be around 100 degrees in the Piedmont this afternoon. Any convection will fade quickly this evening, leaving partly cloudy conditions. Light winds and low level moisture will create pockets of fog and stratus tonight into Sunday morning. Low temperatures will vary from the lower 60s in the mountains to the lower 70s in the Piedmont. && .SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/... As of 430 AM EDT Saturday... High pressure aloft will continue to linger over the region, but weaken slowly through the period. This will allow a west-east oriented cold front to drift into the region from the north by late Monday, then drift very slowly toward the NC/VA border by Wednesday. The front combined with abundant low-level moisture and strong heating will result in widely scattered afternoon/evening showers/thunderstorms. Activity will tend to be most numerous near the front and across the mountains. Weak surface high across the northeast states will briefly attempt to push a drier air mass into the region Sunday. With the aforementioned front still well to the northwest, diurnal showers/thunderstorms should be confined mainly to the western areas, mainly along/west of I-77. The surface high will weaken for Monday and the front will drift into northern areas, which will result in increased coverage of diurnal convection across the I-64 corridor. By Tuesday, as the front continues it very slow southward push, expect a slightly better chance of afternoon/evening showers/thunderstorms into the southern and eastern parts of the CWA. It should be noted that all three of these days, given the very weak dynamics aloft, pops were kept at or below 30 percent. 850mb temperatures will hover near +20C throughout the period, which is only a degree or two cooler than what was observed across the CWA yesterday/Friday. This will continue to result in widespread mid 80s or higher western areas to lower 90s Piedmont. With high moisture content, minimum temperatures will be well above normal in the 65 west to 70 east range. Max and min temperatures will thus continue to average near 10 degrees above normal. && .LONG TERM /WEDNESDAY THROUGH FRIDAY/... As of 445 AM EDT Saturday... The upper ridge continues to weaken and shift to the southwest of the region through the period as troughing begins to take shape across the Great Lakes and northeast U.S. The weak frontal boundary will continue to gradually sink southward through the period and by Friday should be located across northern GA into SC, with drier northwest flow evident across the Mid- Atlantic/Central Appalachian region. Isolated to widely scattered diurnal showers/thunderstorms should continue near the front, thus mainly impacting areas east/south of the Blue Ridge Wednesday, then south of the NC/VA border during the remainder of the period. Regarding the potential for tropical systems to impact the area this period, this is beginning to appear increasingly unlikely as the upper trough digs into the region from the north resulting in northwest flow aloft and lowering heights. Most models, barring the Canadian, now depict a weak tropical wave or disturbance moving across Florida, then turning northeast and tracking just off the SC/NC coast toward the later part of the week. This would have little to no impact on the RNK CWA. The development of the trough and associated lowering heights aloft will lead to lower temperatures as 850mb temperatures fall back to +15C or lower. The ECMWF is not as sharp with the trough across the northeast U.S., so feel that cooling advertised by the GFS may be a tad overdone. At any rate, we should start to see temperatures drop back closer to seasonal normals through the period, namely max temperatures in the 70s west to 80s east and lows in the 50s west to 60s east. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/... As of 745 AM EDT Saturday... The upper ridge will remain across our region today into tonight. A shallow backdoor front will drop southward into our region and weaken with time. Patchy low clouds and patchy dense fog this morning will give way to bkn low end VFR cigs as easterly maritime upslope flow develops behind weak backdoor front. Convection should be confined to the western periphery of the wedge boundary this afternoon, generally west of most TAF sites. Not enough confidence or coverage to warrant including in the TAFs at this time. Any convection that does develop will dissipate quickly after 00Z. Stratocumulus deck will likely diminish after dark and easterly flow subsides. However, the combination of the clouds and easterly flow puts in question the amount of fog/low clouds that will develop early Sunday morning. For now, have not advertised anything worse than MVFR visibilities for Sun morning. Winds will be northeast to east 5-8 kts through much of the TAF valid period. Medium confidence in cigs and vsbys through the TAF valid period. Medium to high confidence in wind speed/direction through the TAF valid period. Extended aviation discussion... A weak west-east oriented front will drift south through the forecast area Sun-Mon. Isolated diurnally driven convection will be possible along the front, mainly north of I-64 Sun, toward the I-64 corridor Mon, then toward the NC/SC border by Tue. Coverage will be limited in duration and area on all days and have minimal impact on the TAF sites. Late night/early morning fog/low clouds are possible, but not a certainty. At this time, it does not appear that any tropical systems will impact the CWA. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...KK NEAR TERM...KK SHORT TERM...RAB LONG TERM...RAB/RCS AVIATION...JH/KK/RAB is the U.S. government's official web portal to all federal, state and local government web resources and services.