Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 221647 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1247 PM EDT Tue May 22 2018 .SYNOPSIS... A warm front lifts north into the mid-Atlantic this afternoon, followed by a cold front shifting southeast across our area late tonight into Wednesday. High pressure noses down from the Ohio Valley and Mid Atlantic Wednesday night into Thursday, then off the coast by Friday. && .NEAR TERM /THROUGH TONIGHT/... As of 1030 AM EDT Tuesday... Warm front has basically lifted northeast of the area this morning with the region in a lull within the moist warm sector well ahead of the cold front northwest of the Ohio Valley. Morning soundings show a bit stronger steering aloft today with more of a west/southwest trajectory ahead of the upstream front that should allow cells/bands to move a bit faster. Latest short term solutions show some development near and just west of the Blue Ridge before perhaps a more organized broken band of convection slides into the region by this evening as seen via the latest HRRR. This may allow for stronger storms to work farther south as depicted with the new SWODY1 so bumped up pops central sections a bit sooner while increasing coverage heading east later in the day. Otherwise some small adjusts to remove fog and reduce clouds some as expect a decent amount of heating given breaks off latest visible satellite pics to support going highs of 70s west to 80s east before convection becomes more widespread. Previous discussion as of 250 AM EDT Tuesday... Showers still lingering along warm frontal boundary from central WV to the Alleghanys and into the area north of Lynchburg, with even isolated coverage per some moisture convergence and weak wave aloft in central NC. Fog has developed given higher moisture at the sfc and in the low levels. However, extensive cloud cover at least over the northeast 3/4ths of the forecast area is limiting coverage of dense fog. Meanwhile, clearing taking place in the southwest CWA may act to enhance the fog here through the morning. May have to issue an dense fog advisory if coverage increases for low vsbys. Otherwise, a special wx statement will cover it. Today, models in reasonable agreement on keeping our area in the warm sector as the warm front lifts north into the mid-Atlantic. Expect storm motion this afternoon to be more from the west to east ahead of the front and a little faster, around 15 to 20kts. Still high pwats around 1.25 to 1.5 inches will lead to localized flash flood threat, especially if storms line up in a wsw to ene orientation and train over the same area. Coverage is not enough to warrant a flash flood watch but folks should be alert to torrential downpours and be prepared to act if flooding is observed. As for severe threat, we have a marginal risk roughly north of U.S. 60 from Lewisburg WV to Buckingham VA. High-res models suggest enough clearing to allow for destabilization, with better low and mid lapse rates further north over Northern VA, west northwest to the Ohio Valley. Looking at SBCAPEs of 1000-1500 J/KG in this area, so cannot rule out some damaging winds from wet microbursts. The models diverge this evening in terms of coverage of storms, with high-res and 00z ECM drying things out east of the mountains while the GFS and to an extent the NAM hang onto the convection a little longer in the east. With a west-northwest flow aloft expect some drying but will not completely erode pops out east until late, with all models keeping a secondary surge of showers over the mountains of WV/far SW VA by 12z ahead of the front. As far as temperatures go, not much change with highs in the mid 70s to around 80 west, to mid 80s east, possibly upper 80s if enough sunshine occurs. Tonight, still sticky with lows in the 60s. && .SHORT TERM /WEDNESDAY THROUGH FRIDAY/... As of 225 AM EST Tuesday... As center of large ridge shifts westward toward the mid-Mississippi Valley Wednesday, northwest flow aloft will become carved out across the mid-Atlantic and Northeast. At the surface, a slow-moving cold front should extend central and eastern Virginia. Convergence along the front looks pretty good and daytime heating should help to develop showers and thunderstorms. There is some level of uncertainty on the exact position of the front, as 12z NWP guidance has sped up the front`s southeastward push a little sooner. Its position also will likely depend on convective developments from the today/tonight period. MUCAPE values approach 2000 J/kg with effective shear values around 30 kts supporting some potential loosely organized multicells or short line segments given along- front forcing. Given the damp ground from recent rains, potential would exist for localized flooding in thunderstorms with the best chance east of the Blue Ridge. However I could see at least a small corridor of potential strong storms along/south of the front (best chance from Farmville to Wilkesboro southeast). Where the front is positioned early Wednesday would significantly influence the forecast in a big way; if the front is slower to advance southeast, it would put more of the area in a greater chance at seeing stronger storms than presently envisioned; likewise, frontal position closer to the VA/NC border would keep any convective threat rather limited spatially. So still some important details to iron out, but Wednesday offers some potential for an active day. In the Day-2 convective outlook, SPC maintains a 5%/Marginal Risk for mainly Southside. This seems reasonable given aforementioned uncertainties in frontal position. Southward push of the front with more northwest surface winds should stabilize things quickly around late afternoon/early evening. Behind the front, a sprawling high pressure area centered over New England then wedges into the region overnight Wednesday through Friday. This will force a drier northerly flow into the region, with cooler 850 mb temperatures (around +11 to +13C) and shifts the axis of higher precipitable water air further south into central North Carolina. This appears to be our best chance at at least a day or two of much needed dry days after nearly daily rains. Best chance for any rain is in the southern Blue Ridge, and it is pretty limited. Given the very wet soils, there may be a greater potential for fog if winds stay light/calm enough but not much confidence to place in the grids attm. Wednesday projects to be the warmest and most humid of the period with highs mid 70s to mid 80s. Highs Thursday and Friday should be a couple degrees cooler but about 5-7 degree lower dewpoints leading to more comfortable conditions. Lows Wednesday and Thursday nights in the 50s to lower 60s. && .LONG TERM /FRIDAY NIGHT THROUGH MONDAY/... As of 300 PM EST Tuesday... Coverage of showers and thunderstorms will increase during the weekend as a warm front lifts northward through the mid Atlantic, bringing a return of deeper moisture from the Gulf coast region. Afternoon temperatures will range from the mid 70s to the mid 80s each day, while overnight lows will generally be in the 60s areawide. && .AVIATION /16Z TUESDAY THROUGH SATURDAY/...
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As of 1245 PM EDT Tuesday... Clusters of showers and storms developing across the western mountains will shift slowly east reaching the Blue Ridge by 19-20Z/3-4PM, and eastern locations between 20-23Z/4-7PM. Will likely see more of a scattered coverage west to start with most Taf sites having at least thunder in the vicinity but will likely include a Tempo period of thunder from northwest to southeast into this evening. Potential to see at least a broken line along and east of the Blue Ridge later this afternoon so boosting thunder mention east later on. Looks like activity wanes in the evening with some clearing taking place to allow for fog, dense at times to form. Should see at least MVFR fog to IFR stratus at most sites, with dense fog at KLWB/KBCB late. Appears any low clouds/fog will fade by mid morning Wednesday leading to more in the way of VFR across the region through early afternoon. Added sub-VFR conditions will be possible mainly southeast of a line from KLYH- KDAN with most activity likely south of the region later in the afternoon. .Extended Aviation Discussion... Conditions are will be drier and are expected to be VFR Thursday and Friday. Tropical like moisture streams back north as a warm front moves through Saturday with a return to showers/storms and potential sub-VFR conditions and heavy rain by Saturday afternoon/evening.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...WP NEAR TERM...JH/WP SHORT TERM...AL LONG TERM...NF AVIATION...AMS/JH/RCS/WP

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