Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 181742 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1242 PM EST Sat Feb 18 2017 .SYNOPSIS... High pressure across the region this morning will gradually give way to increasing moisture ahead of a weakening upper level area of low pressure this afternoon into tonight. This system exits the area early Sunday followed by high pressure that should remain over the region into early next week. && .NEAR TERM /THROUGH TONIGHT/... As of 942 AM EST Saturday...Variable mid-level cloud cover (I suppose I`d call it more intervals of mid-clouds) continue to periodically pinwheel across the Central Appalachians/Piedmont Region this morning, associated with moisture advecting northward acround a mid-level low centered over the Deep South. As we remain on the northeastern periphery of greater/deeper moisture feed implied on morning visible imagery to our southwest, I opted to adjust sky cover a bit for a more optimistic cloud cover forecast for the first part of the day, changes most notable particularly in the Piedmont/Southside VA area. Expect at least filtered sun through the morning/early afternoon across the forecast area. Expect a greater areal increase/lowering in cloud shield beginning around early/mid afternoon. As far as rain chances go, with the predominantly northward motion of the main rain band over AL/TN, I`m becoming less and less convinced at the prospect of seeing much of any precipitation before sunset. In fact, a consensus from recent higher-resolution convection- allowing guidance doesn`t bring in light precip around/after 01z. So I started to trend back precipitation chances especially southern areas. Best chance of seeing some light showers would be late this afternoon in western Smyth and Tazewell counties. No other changes made to highs at this point. Previous near-term discussion issued at 215 AM follows... Upper ridging in place to start today will gradually get undercut by an opening upper low to the south that should fan quite a bit of high/mid clouds into the region early on, followed by thickening canopy this afternoon. However latest forecast soundings show quite a bit of residual dry air stuck beneath the increasing moisture aloft, which looks to delay moistening of the low levels until late in the day or this evening. Latest guidance also keeping any measurable precip mainly confined to far western/southwestern sections toward late afternoon when diffluence aloft in advance of the upper wave is progged to be best. This supports mainly low chance pops generally along and west of the I-77 corridor with mainly increasing clouds elsewhere per latest HRRR output. Despite cloud cover appears just enough mixing under very warm 850 mb temps to push highs into the 60s mountains, with some low 70s possible east pending just how fast clouds thicken. This could produce a shot at record highs in spots mainly west per the climate section below. Remnant upper low will cross the region tonight with models differing on just how much precip works east given best shortwave energy passing around the system to our south, while deeper moisture tends to split to the southwest. Forcing looks rather weak until perhaps the trailing deformation axis enhances a little along the northwest edge of the passing core of the upper system where lapses will be better overnight. This suggested mostly by the wetter NAM with most other solutions quite dry per latest ECMWF, and the GFS which keeps most of this trailing shower coverage over the far west. However with the low level flow already turning more northwest, NAM appears overdone, while the potential to get much precip to shift east of the Blue Ridge also quite iffy within increasing downslope flow late. Therefore kept pops chance over the west with less coverage heading east overnight. Even possible for spots over the far southeast to stay dry as best lift passes south early on, and northwest trajectory helps clip off deeper moisture heading east late. Lows mostly in the 40s under developing weak cool advection on the back of the passing low, although may stay around 50 or warmer east if rainfall is less and the cloud canopy remains in place through daybreak. && .SHORT TERM /SUNDAY THROUGH TUESDAY/... As of 245 AM EST Saturday... A weak upper level trough will track over the south-central Appalachains Sunday morning, generating a low off the southeast coast. This low will become the dominate feature, pulling moisture away from the deformation zone moving over the area Sunday morning. Both the 00Z NAM/GFS keep a fairly large area of light showers over the mountains Sunday morning. However, the 00Z ECM is mostly dry expect near dawn with a few rain showers in Western Greenbrier. We believe the NAM/GFS has a better handle with the deformation zone, even though rainfall will remain light. Through the afternoon, both the trough and surface low move off the southeast coast with high pressure building from the west. Before this high moves over the region during the evening, a pressure gradient will bring breezy and gusty conditions to area along and west of the Blue Ridge. Nothing near advisory level. Some cooler air will filter into the region Sunday afternoon, but not enough to drop temperatures any where close to normal. Highs Sunday will range from the low to mid 60s west to the upper 60s to lower 70s east. A northern stream surface ridge will merge with the ridge over the area Sunday night. These two surface features place a shallow weak wedge east of the Blue Ridge. Some clouds will accompany the wedge Monday afternoon into Tuesday morning, but no precipitation is expected to fall until Tuesday night as the next system enter the region. This wedge will place uniform temperatures over the area with highs in the mid to upper 60s Monday. Increasing cloudiness is expected Tuesday as rain shield approaches the area. These clouds and a light easterly flow will help keep Tuesday cooler with highs in the low to mid 60s. Normal highs for this time of year are mid 40s across the mountains to near 50F east. && .LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/... As of 308 PM EST Friday... During this portion of the forecast, the upper ridge over the region will shift east in response to a shortwave trough heading eastward through the Great Lakes region. Southerly flow in advance of this trough, and in the wake of the ridge, will tap Gulf of Mexico moisture, and advect it northward into our region by Tuesday night. Look for increasing chances of showers during this time period with a cold frontal passage late Tuesday night into early Wednesday. Showers will linger during the day Wednesday. Wednesday night into Thursday, solutions between the GFS and ECWMF are consistent with a quick return to a southerly wind flow pattern across the region. What differs is the degree to which moisture impacts the area with some light rain across the area Wednesday night into Thursday. Thursday night into Friday, the guidance is in fairly decent agreement of amplifying or closing off an upper trough/low across the Upper Mississippi River Valley. Very strong southerly low level flow is progged to develop in advance of this system`s associated cold front that will be near the Mississippi River by Friday afternoon. This flow will tap the Gulf of Mexico, once again sending moisture into our region in the form of scattered rain showers and cloud cover. While there are indications from the GFS that surface based instability may be sufficient for some thunderstorm activity on Friday, will leave it out of the forecast at this time given it is alone on this solution for our area, and it is the Day 7 time period. Temperatures during this portion of the forecast will cool slightly on Tuesday, but still average some ten degrees above normal. Temperatures will start to rebound again Wednesday through Friday and be in the neighborhood of fifteen to twenty degrees above normal. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... As of 1240 PM EST Saturday... VFR with gradually lowering/thickening mid-level cloudiness through the rest of the afternoon. A continued lowering in VFR cloudiness expected from southwest to northeast tonight with a period of likely unrestricted rain showers advancing northward through midnight. Rain band then pivots back to the northwest after 06z, affecting BLF and perhaps LWB with MVFR to IFR ceilings and MVFR vis in potential areas of mist/light showers through 12z. Improvement anticipated by mid morning for these two western TAFs. Elsewhere, expect more breaks in OVC VFR 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 22 kts at ROA. Medium to high confidence in cigs/vis through 00z, then medium to low confidence in cigs/vis 00-12z, medium confidence in cigs/vis 12-18z. Medium to high confidence in winds. 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. && .CLIMATE... As of 302 PM EST Friday... Record High Temperatures and Year of Occurrence Feb 18 Blacksburg, VA..65 in 2011 Bluefield, WV...64 in 1997 Danville, VA....77 in 1976 Lynchburg, VA...75 in 2011 Roanoke, VA.....72 in 2011 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...JH NEAR TERM...AL/JH SHORT TERM...RCS LONG TERM...DS AVIATION...AL/JH CLIMATE...AL is the U.S. government's official web portal to all federal, state and local government web resources and services.