Area Forecast Discussion
Issued by NWS Blacksburg, VA

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234 FXUS61 KRNK 230452 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1252 AM EDT Tue May 23 2017 .SYNOPSIS... A weak stalled front over northern North Carolina will remain in place today as ripples of low pressure slide northeast along the boundary resulting in added rainfall into tonight. Yet another area of low pressure will arrive midweek with added showers likely for Wednesday and Thursday. Weak high pressure will follow this system for Friday. && .NEAR TERM /THROUGH TODAY/... As of 1132 PM EDT Monday... Watching slow moving moderate to heavy showers in the NC foothills/piedmont, along a weak convergence zone leftover by the front. Models indicate that isolated to scattered coverage will be the way to go over the next few hours per moisture convergence off the high-res models. Appears best rainfall will say just south of our CWA but looking for some increase northward overnight as low level flow turns to the southeast. The latest RAP indicates better deep moisture convergence pooling toward the NC foothills after 06z, but only briefly. Looks like rain showers will spread northeast along the Blue Ridge through morning, while other are surges northeast to the southside of VA. At the moment QPF seems low enough to not have any watches at this time. Better threat arrives more toward dawn. Will be watching slow moving cells for any local advisories. Previous discussion from early evening... Enough of an instability gradient over the NC foothills/piedmont to keep isolated to scattered convection around this evening. The high-res (HRRR/RAP) favor showers/a few thunderstorms from the NC/VA border in the foothills through southside VA through this evening, then should be weakening somewhat, transitioning to a more rain. Previous discussion from this afternoon... Water vapor loop showed a well defined short wave over Arkansas early this afternoon. Models track this feature into southern Virginia overnight. Surface and 850MB front cross the area this afternoon, but with little change in air mass behind it. 850MB winds back to the southeast by midnight brining the deep moisture north along the Blue Ridge and foothills. Best convergence will be from 12-18Z/8AM-2PM Tuesday. GFS may have some convective feedback and may be moving the wave too fast and too far northeast compared to other guidance. Some decent isentropic lift on the 3km NAM Tuesday morning. Leaned toward NAM and WPC for QPF .WIll have to monitor amounts since some locations have had lots of rain in the past 72 hours and have saturated soils as a result. Surface front reaches central North Carolina as high pressure moves from West Virginia into Pennsylvania. By Tuesday morning the in-situ wedge will be in place down the Appalachians aided by precipitation on the cool side of the front. Clouds and precipitation will keep temperatures down on Tuesday. Trending toward cooler guidance for maximum temperatures. && .SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/... As of 330 PM EDT Monday... Large upper trof will be traversing the eastern US, keeping us in a wet pattern through the period. Multiple waves along the front to our east will be pulling away from the region Tuesday night. However, a low over the Ohio valley will be captured by the upper trof as it closes off and the stacked system will wrap up a cold front a push it into our area from the west Wednesday morning. There will be a bit of an in-situ wedge ahead of the front to limit instability and convective development, but good isentropic lift and dynamic support will make for widespread rainfall and some possibly some embedded thunder from lift over the stable layer. Also, there may be a very narrow window just ahead of the front where the wedge has weakened that may allow for deeper instability to support elevated convection in a highly sheared environment. While the overall probability of severe weather is low, the situation bears watching until fropa occurs early Wednesday night. Expect some lessening of showers overnight Wednesday night in muddy dry slot of stacked low spinning over the Ohio valley. Diurnal heating will pop showers and thunderstorms with steepening mid/upper lapse rates under the cold pool aloft as the upper trof swings through. Small hail/graupel in low topped convection look possible mainly west of the Blue Ridge. Showers/storms taper quickly with loss of heating in the evening, leaving some lingering upslope precipitation west of the Ridge into Friday morning. && .LONG TERM /FRIDAY THROUGH MONDAY/... As of 330 PM EDT Monday... Our unsettled pattern will continue through the weekend as a progressive upper ridge moves across the eastern US, followed by the development of another closed low moving through the upper midwest. This will allow a frontal boundary to sink into the region from the north and stall on Saturday, with a series of waves shearing off to our north dragging along weak, occluded fronts. While not likely a complete washout, we look to keep a good chance of showers and thunderstorms in the forecast through the weekend and into the first part of next week. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... As of 1250 AM EDT Tuesday... Will see a gradual deterioration in flying conditions overnight as scattered convection to the south combines with added moisture heading north to bring a quick lowering of cigs through daybreak. Rain should start spreading northward overnight and cigs will start to sink to MVFR or lower, especially along/east of the Blue Ridge. The rain will become steadier and possibly heavier late tonight into Tuesday from KBCB/KROA and points east. Should also see areas of fog with mountain obscurations likely as well into Tuesday. This pattern will stick around through the end of the taf period, but rain will be lighter over KBLF/KLWB. Extended Aviation Discussion... The chance of precipitation continues Wednesday and Thursday with sub-VFR conditions associated with any of the precipitation. Friday will be drier with a better chance of VFR ceilings and visibilities. Another front reaches the area for Saturday with more precipitation and sub-VFR conditions. && .HYDROLOGY... As of 345 PM EDT Monday... An inch to inch and a half of rain is expected tonight and Tuesday. Amounts will have to be monitored as some locations along the Virginia/North Carolina border, especially Carrol, Patrick and Henry Counties in Virginia and Stokes, Rockingham, and Caswell Counties in North Carolina. FFG along parts of the southern Blue Ridge was in the 1.5 to 2.5 inch range. More rainfall is expected Wednesday and Thursday, which could lead to small stream and river flooding. Models continue to favor areas along/east of the Blue Ridge, possibly resulting in another 1 to 3 inches of rain. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...AMS/JH NEAR TERM...AMS/WP SHORT TERM...MBS LONG TERM...MBS AVIATION...AMS/JH/WP HYDROLOGY...AMS

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