Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 182332 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 632 PM EST Sat Feb 18 2017 .SYNOPSIS... An upper level disturbance will increase cloud cover tonight and bring a period of rain showers, mainly concentrated in western locations. The upper low moves east of the region early on Sunday, leading to a couple days of mild and dry weather. Temperatures are expected to remain above normal for the next 5 to 7 days. After tonight, the next chance for rain is not until Tuesday night. && .NEAR TERM /THROUGH SUNDAY/... As of 307 PM EST Saturday...Visible satellite reveals mid- level cloud cover has begun to overspread the central Appalachians and Blue Ridge, while skies in the Piedmont remain generally clear. Filtered sunshine through much of today has resulted in temperatures well into the 60s to the low 70s for many locations this afternoon, though is also accompanied by dry low-levels (mid 20s to low 30s dewpoints common along with large dry layer below 700 mb sampled well by 12z GSO/RNK RAOBs). Increasing cloud shield is associated with pronounced moisture plume seen on water vapor imagery on the eastern end of an upper low centered over western TN. Regional composite radar mosaic and upstream METARs show a south-to-north band of light to occasionally moderate rain extending from near central KY southward through GA into FL. For Tonight: Clouds will continue to lower and thicken with time. Band of rain should also advance northeastward, but it will be running into aforementioned dry layer of air that will only slowly saturate up. High-res guidance pivots this band northeastward through midnight across the forecast area, though given how dry the preceding air mass is, I`m not sure many areas east of the Mountain Empire and southeast West Virginia will see much of any measurable precip as the initial band pivots north. As the upper low pivots into eastern KY/TN after midnight, nearly all higher res and coarser- res global model guidance depict an enhancement in QPF/simulated reflectivity along a roughly east-west 700-500 mb deformation axis as the primary band of rain pivots back northwestward across southeast WV, the Mountain Empire in VA and perhaps into the NC mountains. As the rainband rotates NW, a dry slot should produce at least partly to mostly cloudy skies for the Piedmont and perhaps as far west as the foothills of the Blue Ridge. Thus, the best chance for rain in far western sections where the highest PoPs are tonight where QPF amounts are around one-tenth of a inch. Temperature advection aloft is pretty much near neutral, but transitions back to cold advection especially toward morning west of the Blue Ridge. Think we`ll be looking at lows only falling into the 40s tonight. For Sunday: Upper low opens up into an open wave and exits off the Atlantic coast Sunday morning. While many areas will likely start off mostly clear to partly cloudy, the leftover showers and overcast in far western areas begins to improve as shortwave ridging aloft builds back over top of the forecast area later in the day. Due to "cold" advection (850 mb temps only falling to around +4 to +6C) and steepening low-level lapse rates, northwesterly winds should turn breezy. I`ve also lowered dewpoints somewhat a bit more than raw and statistical guidance would indicate during the afternoon hours given some dry air mixing potential. Highs may be only a degree or two lower for the Piedmont, foothills into the Roanoke Valley compared to today - upper 60s to low 70s, but closer to the upper 50s to low 60s due to some cloud cover for areas along/west of the Blue Ridge. While well above normal, projected forecast highs are just below record highs for our long-term climate sites. See the climate section for more details on these high temperature records. && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/... As of 307 PM EST Saturday... Surface high pressure over the Tennessee Valley will move east Sunday night and Monday and will be offshore on Tuesday. Some return flow around the high off the Atlantic but low pressure over the northern Gulf of Mexico will limit return of Gulf Moisture. 500MB ridge over the eastern United States until Tuesday then a weak short wave in the northern stream will bring a weak front through at the surface. GFS has this feature moving east faster than some of the other guidance. Not out of the question to have the probability of precipitation arrive in the mountains late in the day Tuesday. Maximum temperatures on Monday will be above normal. Based on enough sunshine and a dry air mass have gone slightly above guidance. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... As of 307 PM EST Saturday... Best probability of precipitation from the northern stream short wave will be on Tuesday night. 500 mb pattern becomes more amplified on Friday and Saturday with a deepening trof moving across the central United States and more spread showing up in the modest by that time frame. Increasing southwest winds on Friday will increase moisture and keep temperatures above normal ahead of the front. Timing of the frontal passage across the Appalachians looks to be on Saturday morning with precipitation along and ahead of the boundary. Much colder air comes in behind the front for the end of the weekend. The combination of a modest low level jet and strong cold air advection will result in strong gusty winds behind the front, possibly through Sunday morning. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/...
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As of 632 PM EST Saturday... An upper level system will increased clouds and create a few showers across the Appalachians tonight into Sunday. VFR conditions will prevail, but MVFR ceilings are possible in the west with rain showers. The main rain band pivots back to the northwest after 06z, affecting KBLF and perhaps KLWB with MVFR to IFR ceilings and MVFR visibility in potential areas of mist/light showers through 12z. Improvement anticipated by mid morning Sunday for these two western TAFs. Elsewhere, expect VFR conditions from southwest to northeast. West to southwest winds trend light westerly overnight (variable at times at BLF). As upper low shifts to the southeast tomorrow, northwesterly winds pick up to around 6-10 kts with gusts to 23 kts at ROA. Medium confidence in ceilings, visibilities and winds during the taf period.. Extended Aviation Discussion... High pressure should bring VFR Sunday night through Tuesday. MVFR rain showers are possible Tuesday night into Wednesday with the next weak cool front crossing the region midweek. A stronger cold front arrives for the end of the week with better chance for MVFR/IFR showers.
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&& .CLIMATE... As of 307 PM EST Saturday... Record High Temperatures and Year of Occurrence Feb 19 Blacksburg, VA..65 in 1994 Bluefield, WV...66 in 1994 Danville, VA....73 in 1981 Lynchburg, VA...76 in 1939 Roanoke, VA.....77 in 1939 Feb 20 Blacksburg, VA..68 in 1984 Bluefield, WV...67 in 1986 Danville, VA....74 in 1971 Lynchburg, VA...76 in 1930 Roanoke, VA.....75 in 1939 && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...AL NEAR TERM...AL SHORT TERM...AMS LONG TERM...AMS AVIATION...AL/KK CLIMATE...AL

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