Area Forecast Discussion
Issued by NWS Blacksburg, VA

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730 FXUS61 KRNK 040527 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1227 AM EST Sun Dec 4 2016 .SYNOPSIS... High pressure will shift east into the area tonight before sliding offshore on Sunday. An upper low across the southwest states will slide east into the lower Mississippi Valley into early next week. Several disturbances ahead of this feature will bring periodic chances of mainly rain Sunday through Tuesday. && .NEAR TERM /THROUGH TODAY/... As OF 1000 PM EST Saturday... No precipitation has reached the CWA yet even though some light returns are showing on radar in North Carolina. It is most likely virga due to drier air near the surface with dewpoints still in the mid 20s to the lower 30s. Small adjustments were made to the low temperatures, but the overall forecast appears on track at this time. As of 300 PM EST Saturday... 12Z sounding from Blacksburg this morning showed dry air below 500 MB. Bufkit forecast showed mid and high level clouds remaining in the area this evening then the column saturating from top down and becoming moist enough for precipitation in northwest North Carolina between 09Z/4AM and 12Z/7AM with the precipitation spreading northwest across northwest North Carolin and southwest Virginia through the day Sunday,reaching Lynchburg and Lexington by mid to late afternoon. Models have been consistent with the timing and amounts of precipitation for the past several runs. Clouds had limited temperature rise today. Expecting a small drop in temperatures after sunset then plume and meteogram forecasts forecast a nearly steady temperatures for the rest of the night. However, may get some evaporative cooling since starting with dry air near the surface as the precipitation develops. Most guidance only showed a limited coverage of any freezing temperatures late tonight and on Sunday...mainly at the highest elevations of far southwest Virginia and northwest North Carolina and along the spine of the southern Blue Ridge. So have brief periods of snow and sleet mixing in where there are colder surface and near surface temperatures. Have followed a non-diurnal trend for temperatures tonight and lowered maximum temperatures for Sunday. && .SHORT TERM /TONIGHT THROUGH TUESDAY/... As of 300 PM EST Saturday... Dual corridors of rainfall will continue to cross the region Sunday night as split northern/southern stream waves ride through weak shortwave ridging across the region. Appears best coverage will reside more with the southern stream impulse over the southern and southwest sections early on, then perhaps across the southeast into the overnight where guidance has weak diffluence along the edge of the theta-e gradient. Farther north quite iffy in seeing little more than spotty light rain where will still be deeper into the initial dry air. Could see spots across the higher elevations of Bath/Greenbrier wetbulb back close to freezing and with isothermal forecast soundings that are near freezing at the surface, added in some patchy light snow/fzra mention but quite iffy. Otherwise likely to chance pops overall with some split possible central sections. Lows mainly in the 30s with some slow rises late. Deeper moisture exits with the passing mid level trough Monday leaving the area under weak high pressure that will shift in from the west early and orient into wedge formation by the end of the day. This influx of drier air aloft likely to slow down the next round of rainfall that will be heading northeast toward the area from the main upper low ejecting out of the southwest states. Some models remain rather fast but blended trend of the GFS/EC would suggest going slower into the wedge with little pop except chance far south/west by late Monday which may be generous. With rather warm temps aloft and more of a northwest trajectory under perhaps some sun before the wedge digs in, expect a little bump in highs with 50-55 east and 45-50 west. Surface low progged to track just west of the mountains later Monday night into Tuesday with lots of lift/deeper moisture over the deepening wedge. This will make for a chilly and increasingly wet Monday night and a very cool Tuesday before things dry slot from southwest to northeast late in the day. Guidance showing quite a warm nose aloft as well that should keep most precip liquid except perhaps again in the highest elevations across Bath county where may mix in some wet snow at the onset along with spotty icing ridges if surface temps get caught around freezing early Tuesday. Other concern could be some cutoff in the degree of QPF per convection to the south/southeast and a subsequent secondary surface wave off the Carolinas on Tuesday which may act to funnel drier air into the wedge. Otherwise looking at categorical pops for a soaking rain event including QPF of an inch or two espcly south and along the southern Blue Ridge where upslope aided at the onset. Southeast winds will also increase over the far west around BLF but appears not strong enough per less mixing for headlines at this point. Kept highs quite cool on Tuesday, mostly 40s although may struggle to get out of the 30s north, while a few 50s possible on the western edge of the wedge. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... As of 200 PM EST Saturday... Remnant upper low responsible for the early week rainfall will depart Tuesday evening followed by a weak cold front of Pacific origin early Wednesday. Lingering moisture trailing this system likely enough for a few added showers east early on Tuesday night, then across the far west overnight. Otherwise clouds early then decreasing in all except the mountains overnight with lows mostly in the 30s. Will be in between systems midweek as brief zonal flow gradually evolves into a deepening upper trough regime with a large dome of arctic air heading south through the Midwest by early Thursday. This may allow more sunny periods Wednesday with temps rebounding into the 40s and 50s which will be the warmest for a good while to come. Very strong cold front associated with the 500 mb trough will cross the region Thursday with some timing differences in models as slightly faster trends continue. Lobe of deeper moisture right along the front may bring a band of showers west, with a quick change to snow showers far west as seen with similar arctic fronts in the past. Some of this coverage may even spill east of the mountains in liquid form so running with decent to high chance pops west and slight coverage east. Pending timing, temps to fall from west to east by afternoon with the core of the cold air arriving Friday into Friday night under strong northwest winds, and lingering snow showers despite very dry air by weeks end. Gradient given depth of the cold advection perhaps enough to warrant advisory level winds in spots over the mountains otherwise very cold. Appears highs wont get out of the 20s to around 30 mountains Friday and 30s east with lows teens most spots Friday night and even single digits in the deeper valleys. This should also push wind chills to around zero if not colder in spots by early Saturday. Thermal trough including the coldest air aloft will lift out by Saturday but still highs only 30s to low 40s despite sunshine. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/...
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As of 1150 PM EST Saturday... Generally VFR conditions expected to prevail until the later portion of the TAF valid period. Extensive mid/high clouds will overspread the region in association with a southern stream system moving across the Gulf Coastal states. Light precipitation from this system will spread into areas south of the NC/VA border during the morning hours, then northward into the bulk of the TAF sites toward the end of the TAF valid period. Ceilings should remain VFR until the rain arrives, thus at least through 18Z, possibly as long as 20-21Z Sunday, and may remain VFR for KLYH and KROA until closer to 00Z Monday. However, cigs will progressively lower from the current 180-250 into the 040-080 range by 18Z Sun. After 00Z Mon, ceilings will quickly lower through the MVFR range and most likely IFR at KBLF, KLWB, and KBCB around 00Z. Visibility is expected TO remain VFR through the TAF valid period with no fog development given lower-level dry air and extensive mid/high clouds cover. Winds will be light and variable overnight as weak high pressure drifts across the region, trending more toward the ENE-ESE through the day Sunday with speeds mostly 5kts or less all areas. Medium to high confidence in cigs/vsbys through the TAF valid period. High confidence in vsbys through the TAF valid period. Medium to high confidence in wind speed/direction through the TAF valid period. Extended aviation discussion... Rain, mostly light, will spread northeast Sunday evening and will continue Sunday night. A break in the rain into Monday may allow for some VFR with sub- VFR returning late Monday night ahead of low pressure moving into the Tennessee Valley with widespread rain expected into Tuesday. Expect a bit of improvement after Tuesday as front moves offshore with another front entering from the west, with mainly VFR expected then though some MVFR cigs BLF/LWB lingering with good upslope flow behind an Arctic cold front.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH/WP NEAR TERM...AMS/PW/RAB SHORT TERM...JH LONG TERM...JH AVIATION...AMS/RAB/WP is the U.S. government's official web portal to all federal, state and local government web resources and services.