Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 170555 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 155 AM EDT Thu May 17 2018 .SYNOPSIS... A weak front across the region will remain about stationary through the end of the week. Low pressure lifting north into the Tennessee Valley will combine with the stalled boundary to bring periodic rounds of showers and storms into the weekend. && .NEAR TERM /THROUGH TODAY/... As of 905 PM EDT Wednesday... Bands/clusters of heavy rain producing convection continue to lift north across parts of the region this evening within a very tropical environment aided by deep south/southwest flow. Latest analysis also showing enough leftover instability combined with the moisture to likely result in lingering showers espcly south/east where old outflow resides. Short term models finally show things diminishing after midnight as an initial wave passes to the north and in advance of the next feature well to the south. However given the degree of moisture around per GSO PWAT of better than 1.5 inches, would expect some showers to linger, so leaving in likely pops although may become quite scattered/isolated late as suggested by the HRRR and several other solutions. Therefore will hold off on any watches at this point since expecting some decrease in bands overnight with loss of heating and uncertainty with where localized heavier rain may occur. Otherwise just some adjusts to short term pops/QPF with muggy lows in the 60s on track overnight. Previous discussion as of 400 PM EDT Wednesday... The main focus through Thursday will be quasi-stationary front to our north and subtropical low lifting north into the southern Appalachians from the eastern Gulf of Mexico. Airmass south of the front and covering the entire southeast CONUS is more indicative of August as opposed to May with PWATs 2 standard deviations above normal. As such, showers and thunderstorms which occur within this environment will be very rain efficient. For our forecast area, anticipate numerous to widespread showers. CAPE has been limited to generally 1000 j/kg or less, so nothing severe, but lack of a cap has allowed for showers to bubble up all over the CWA... more of a shotgun pattern but nothing organized. Since the front is well north of the area, not much to focus the heavy rain, so no need for a flood watch attm, but may need to consider possibility of headline pending track of subtropical low as it lifts north into the southern Appalachians Thursday. Until then will entertain occasional showers with embedded thunderstorms with brief heavy downpours. Temperatures/dewpoints will remain summerlike with overnight lows above 60 coinciding with the August-like dewpoints. && .SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/... As of 340 AM EDT Wednesday... The portion of the forecast is continuing to offer wet conditions across the region. From Thursday night through Saturday, an upper level area of low pressure will make gradual progress from western TN to Wisconsin. Saturday night, the low will open into a wave and start to be transported eastward as it reaches the northern jet. Its associated trough axis will still be extending south into eastern KY. This trough axis will cross our region Saturday night. On the east side of this low/trough, southerly, moisture-rich flow of air will be streaming across our area with its origins off the eastern Gulf of Mexico. It will be this moisture that will allow for a very generous coverage of moderate to heavy rain showers to cross our region during this time period, along with some isolated to scattered thunderstorms, especially during the late afternoon and evening hours. We will be monitoring precipitation patterns and amounts as we progress into this time period. This will help us gauge where and/or if any flood watches may need to be posted. The first time period of increased focus will be Thursday into Thursday night. WPC currently has posted a slight chance for excessive rainfall during this time period. Temperatures during this portion of the forecast are expected to average about five degrees above normal. Low will range from the low to mid 60s across the mountains with mid 60s to near 70 across the Piedmont. High temperatures are forecast in the the mid to upper 70s across the mountains with upper 70s to around 80 across the Piedmont. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... By Sunday, the upper low/trough that has been impacting our weather pattern the past several days, will be far enough north to be caught up by the northern jet, and heading eastward towards New England. This will return our region to a flow that initially will be predominately westerly, all while another baroclinic zone establishes itself along or near the Ohio River Valley by Monday evening. Concurrently, an upper high in the western Atlantic, east of GA/FA will hold fast, and anti-cyclonic flow around this feature will keep a decent fetch of moisture into our region at the lower levels. By Wednesday, the front to our north is expected to have trended farther south to over, or just north of our region. The result of the above scenario will be a weather pattern that will still have daily chances of showers and some thunderstorms. On average, chances will be greatest during the afternoon hours during the peak heating of the day. Chances will also on average increase by mid-week as the frontal boundary gets closer to, or overhead of, the area. Temperatures across the region will begin this portion of the forecast averaging five to ten degrees above normal. While a slight cooling trend is expected, by Wednesday, temperatures will still be averaging five degrees above normal. && .AVIATION /06Z THURSDAY THROUGH MONDAY/...
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As of 145 AM EDT Thursday... Generally marginal to poor aviation conditions will continue through the TAF valid period as a pseudo-tropical area of low pressure tracks north through the southeast states and into the southern Appalachians and the eastern TN valley. The low pressure area will combine with a stationary front across the northern part of the area keeping widespread low clouds, areas of fog, rain showers, and a few thunderstorms in the forecast for the next several days. As the core of the remnant low pressure area tracks north through the region tonight and early Friday, that is when the best coverage of rainfall, lowest ceilings, and lowest visibilities are expected overall. This applied pretty much to the entire forecast area, however ceilings and visibilities will tend to be lower across areas west of the Blue Ridge and especially through the higher terrain where ceilings and visibilities could be LIFR through much of the TAF valid period. Periods of MVFR to low end VFR will be most likely across the Piedmont during the late morning into the early evening before deterioriating to MVFR or worse there as well. Winds are expected to be light southeast 3-5 mph through most of the day veering more to light southwest overnight into early Friday. Speeds remaining 5kts or less through most of the TAF valid period. Medium confidence in ceilings and visibilities through the TAF valid period. High confidence in wind speed, medium to high confidence in wind direction through the TAF valid period. Low to medium confidence on thunderstorm potential through the period. .Extended Aviation Discussion... The pseudo-tropical low and the lingering frontal boundary will begin to drift north of the CWA Friday and especially into the weekend. This should bring about a slight decrease in rain coverage Friday with activity trending more scattered and diurnal in nature as we go into the weekend and high pressure ridging is noted across the southeast states. However, still feel that chances for showers/thunderstorms and associated aviation issues will be greater than normal for this time of the year, at least through Saturday with periods of sub-VFR possible. Fog and low clouds will be common during the late night and early morning hours as well. After more isolated storms on Sunday, appears another weak cold front may bring increasing coverage of showers and thunderstorms again on Monday.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH NEAR TERM...JH/PM SHORT TERM...DS LONG TERM...DS AVIATION...JH/PM/RAB

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