Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 281657 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1257 PM EDT Tue Mar 28 2017 .SYNOPSIS... A cold front will slide east across the region from the west this afternoon before exiting the piedmont early this evening. High pressure works in from the north later tonight into Thursday. Another storm system moves in from the southwest with showers and storms by the end of the week. && .NEAR TERM /THROUGH TONIGHT/... As of 950 AM EDT Tuesday... Still seeing bands of showers pushing slowly east through the area this morning ahead of the weak pre-frontal type trough axis seen over western Va. This also along the back edge of the complex of deeper moisture per water vapor that should be exiting to the east this afternoon. However upper low currently crossing West Va will shift east across the region by mid to late afternoon before exiting early this evening. This combined with a trailing weak cold front likely to provide enough weak lift/convergence to spark added shra/tsra provided can get enough breaks/heating as colder air aloft arrives. Latest guidance shows much of this added coverage over the east where seeing some instability along the leading edge of the cold pool aloft. Latest CAM solutions have more showers along the actual front back toward the Blue Ridge while the HRRR/RAP show more of a cold pool shotgun pattern once current coverage fades. Since this looks a bit more likely given exodus of deep moisture and developing westerly flow, bumped up pops west through midday, and then out east this afternoon where storms could produce some hail given developing steep lapses. Otherwise becoming partly sunny most spots with highs perhaps not quite as warm northwest per early clouds/showers, while pushing inTO the 70s out east. Previous update as of 710 AM EDT Tuesday... Made adjustments to morning forecast based on radar trends, and shifting higher pops more over the piedmont of VA into the Alleghanys with less in the NC foothills. Deeper moisture evidenced on IR and WV satellite has shifted to the piedmont. Upper low/trough over WV works eastward through early afternoon. Where it is during peak heating to determine best coverage. At the moment should be along and east of the Blue Ridge, but even that should be mainly scattered. Previous discussion from early morning... Area of thunderstorms over the NC foothills/piedmont shifting northeast toward southside VA picked up somewhat by high-res models but as usual, the high-res models are too slow by an hour or 2. Still should see higher pops in the piedmont this morning with this batch, with another concentrated area ahead of the front over WV into the Alleghanys. Most support for convection in the east this morning, subsides west, then as we head toward early afternoon, with the front, another band of convection forms from Amherst to South Boston, per RAP, with isolated/scattered showers lingering post frontal in the west. SPC showing marginal risk in the piedmonts today, mainly for this morning into early afternoon. Stabilization per rainfall/clouds will inhibit a good chance of strong to severe storms, but a little bit of sunshine per some of the models this afternoon could enhance the updraft enough to produce a strong/severe cell or two. Appears will see this threat mainly east of a line from Lynchburg to Danbury NC. Expect decreasing trend in pops by dusk with lingering upslope rain showers over WV til midnight. High today will be dependent on sky cover/areal coverage of showers, but leaned a little cooler than MOS. Still expect highs from the mid to upper 60s west, to mid 70s east. Tonight, should be cooler than this morning, but still about 10-15 degrees above normal, with lows in the mid to upper 40s mountains, to lower to mid 50s elsewhere. && .SHORT TERM /WEDNESDAY THROUGH FRIDAY NIGHT/... As of 350 AM EDT Tuesday... High pressure will move out of the upper midwest and wedge down the east side of the Appalachians for the latter portion of the workweek. By Friday, an upper level trof will drive an area of low pressure into the region to do battle with the wedge. Abundant moisture coupled with good dynamic forcing and isentropic lift will make for an increasing chance of precipitation Thursday night and Friday looks to be quite wet. There are indications in the latest guidance that the wedge will hold firm until the cold front passes and this will be a substantial limiting factor in severe weather potential. However, if the wedge retreats and allows warmer unstable air to move in from the south and west there will be strong dynamics in play to support severe weather. It is still a bit too far out to resolve the many details of this nuanced forecast and possible severe threat so later model runs will be watched closely. Will be above normal on Wednesday, but once the wedge becomes established readings on Thursday will be quite cool with most locations in the 50s. Temperatures on Friday will be largely dependent on the ability of the wedge to remain entrenched and look to remain below normal. && .LONG TERM /SATURDAY THROUGH MONDAY/... As of 350 AM EDT Tuesday... An upper level ridge will build over the region behind the departing low pressure system. This will allow high pressure to build at the surface and once again wedge down east of the Appalachians this weekend. Overall precipitation chances will be low with some lingering upslope showers west of the Blue Ridge early in the period, followed by a few sprinkles with the building wedge. Temperatures will continue to be well above normal into the first part of next week. && .AVIATION /16Z TUESDAY THROUGH SATURDAY/... As of 1245 PM EDT Tuesday... Bands/pockets of showers continue to develop and push east across the mountains under the upper cold pool aloft seen passing across the region early this afternoon. Lower cigs and vsbys within the vicinity of this rainfall will continue to bring periods of sub-VFR mainly across the mountain locations through at least mid afternoon, with perhaps some deeper convection over the east prior to early this evening. Thus thinking best thunder threat mainly from KROA east to KLYH/KDAN so keeping in VCTS mention at these spots given isolated nature. Will also see upslope lower cigs redevelop around KBLF late which could keep them MVFR to IFR even as the shower threat fades. Cold front associated with the upper low will finally work through the region this evening allowing clearing to develop as deeper northwest flow develops. However MVFR bkn cigs seem likely at KBLF this evening into the overnight, and perhaps at KLWB/KBCB with northwest flow taking shape, and some spillover of low clouds late. High pressure slowly builds in from the north on Wednesday with a low level wedge of cooler air developing east of the mountains. Should see some drying under the increasing subsidence but also some uncertainty with the degree of residual cloud cover given heating and flow turning light northerly. This suggests that KBLF may stay sub-VFR into Wednesday morning with perhaps low end VFR cigs possible elsewhere by the end of the valid TAF period. Extended Aviation Discussion... High pressure continues to build in from the north Wednesday night into Thursday with the next storm system moving in the Mississippi Valley Thursday night into Friday. A threat for sub- VFR cigs appears likely as the high wedges southwest Wed night into Thursday for most sites bringing widespread low cigs and possible light precip. The highest probability of rain will be on Friday along with sub- VFR cigs/vsbys with the showers. Post-frontal northwest flow sub- VFR into Saturday mountains with gusty northwest winds possible. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH/KK/WP NEAR TERM...JH/WP SHORT TERM...MBS LONG TERM...MBS/RCS AVIATION...AMS/JH/WP is the U.S. government's official web portal to all federal, state and local government web resources and services.