Area Forecast Discussion
Issued by NWS Blacksburg, VA

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374 FXUS61 KRNK 210848 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 448 AM EDT Sat Sep 21 2019 .SYNOPSIS...
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High pressure at the surface and aloft will remain over the area into the first half of next week. A weak upper disturbance will move across the area today, while a weak cold front approaches the area late Monday. Warmer and more humid conditions will return to the area through the first half of next week. Precipitation chances will remain minimal to none.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As of 430 AM EDT Saturday... A weak impulse aloft was moving through the region this morning from the northwest. This has triggered a few showers mainly west of the Alleghany Front where moisture levels are higher. Otherwise, low to mid clouds linger across the southern Blue Ridge, mainly far southwest VA and northwest NC, with mostly clear skies elsewhere. Patches of fog had developed primarily in the river valleys west of the Blue Ridge. Fog was a bit more widespread today than yesterday morning thanks to the slowly increasing dewpoints and return of southerly flow around the slowly southeastward moving surface high. Temperatures averaged about 8 degrees warmer this morning than at this time yesterday ranging from the mid 40s at Burkes Garden to the mid 60s at Roanoke and across much of the Piedmont. Isolated showers may pop up through the afternoon west of the Blue Ridge as the weak impales drifts east and dissipates. No meaningful rain is expected. Will confine pops to areas west of the Blue Ridge and keep no higher than 25% at this point. Clouds will linger again to some extent west of the Blue Ridge, but it should be mostly clear to the east. Tonight will bring more of the same with partly cloudy skies, patchy fog, again a bit more widespread and of longer duration than the previous days, and a continued slow warming trend. Temperatures today will reach above normal levels again with near 80 west to mid and upper 80s east, with 70s in the western mountains. Lows tonight will be in the 50s west to the 60s east. /Confidence in Forecast Parameters/ Temperatures - Moderate to High, Precipitation Probabilities - Low to Moderate, Winds - Moderate, Thunderstorm Threat - Little to None.
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&& .SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/...
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As of 330 AM EDT Saturday... On Sunday, the upper ridge rebuilds across the region after today`s passage of a weak shortwave trough. No precipitation and temperatures around ten degrees above normal are expected Sunday into Sunday night. On Monday, a cold front is still progged to make progress toward the western extent of the forecast area. However, it will be encountering the persistent upper level ridge and relatively dry air across the region as it arrives. With the Gulf of Mexico cut off as a moisture source, any moisture associated with the front it will have to bring along with it from the Great Lakes/Ohio Valley region. Showers will be isolated to scattered in distribution with little if any activity east of the crest of the Blue Ridge. Other than slightly cooler temperatures in the west, although still above normal for this time of year, no notable change in our temperature pattern is expected in Monday with the front still to our west. Monday night, the front is expected to cross the area with some isolated to scattered showers across the west. Lows temperatures will be slightly cooler than those expected Sunday night. On Tuesday, drier and cooler air will work its way into the region. High temperatures will still be a few degrees above normal, but cooler than the previous day`s readings. Confidence in the above forecast scenario is high.
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&& .LONG TERM /WEDNESDAY THROUGH FRIDAY/...
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As of 153 PM EDT Friday... A broad ridge then begins to build into the southeast United States for Wednesday and especially Thursday. There are still some model differences in regards to rainfall. The GFS is finally advertising some rainfall due to a weak frontal boundary draped west to east across the region and a generally flatter flow at 500mb. However, the ECMWF is much faster in building in the 500mb ridge and leaves our area with little to no precip through this entire forecast period. Other than these differences, the models tend to agree temperatures will likely be above normal with 850mb temps reaching anywhere from +16 to +20. Will likely side with the persistence of a dry pattern and go with a blend of the ECMWF and NBM for this period.
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&& .AVIATION /09Z SATURDAY THROUGH WEDNESDAY/...
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As of 145 AM EDT Saturday... Surface high pressure, which has been northeast of the region, now located over the forecast area. This high was moving slowly east off the North Carolina coast which will allow low level winds to become west to southwest Saturday morning while remaining mostly calm overnight tonight. Concerned with good radiational cooling and few clouds noted upstream, that some patchy dense fog could develop in the mountain valleys and near rivers later tonight, so have increased/added fog potential at KLWB and KBCB as a result, as well as a brief period of MVFR at KLYH. The remainder of the TAF valid period will feature VFR conditions with a persistent inversion in the lower atmosphere and trapped marine moisture from several days of easterly flow across the region yielding once again a fair amount of cloud cover during daytime heating, especially in the west. A weak upper-level disturbance will help in this regard as well. There could even be a few sprinkles in the western mountains, but overall feel atmosphere is try dry for much if anything, so am not advertising it in any TAFs at this time. Winds becoming WSW-W 5-8kts after 13Z, with low end gusts possible around KBLF. /Confidence in Forecast Parameters/ Ceilings - Moderate to High, Visibility - Moderate through 13Z, then High, Winds - Moderate, Thunderstorm Threat - None. .Extended Aviation Discussion... High pressure will keep conditions VFR into Sunday. Only exceptions may be late night and early morning fog in the mountain valleys which would impact the usual terminals (e.g., KLWB and KBCB). A weak cold front may bring scattered MVFR showers on Monday, mainly in the mountains. Otherwise VFR Tuesday and Wednesday.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...RAB NEAR TERM...RAB SHORT TERM...DS LONG TERM...DS AVIATION...AMS/RAB/WP

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