Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 211717 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 117 PM EDT Wed Jun 21 2017 .SYNOPSIS... A front will stall from the Mid Atlantic states to the Mid Mississippi Valley today and tonight as Tropical Storm Cindy moves from the Gulf of Mexico to the Texas/Louisiana coast. By Friday a cold front will extend from the Great Lakes through the Central Plains will Cindy tracking between the front and high pressure off the Southeast Coast. The front will push through the Mid Atlantic region Sunday and Monday. && .NEAR TERM /THROUGH TONIGHT/... As of 1043 AM EDT Wednesday... This morning, deeper moisture remains south of the forecast area as evidenced on vis satellite, and mesoanalysis. 12z RNK sounding has pwat of 0.86 inches, which is actually drier than normal for late June. Radar showing isolated showers/sprinkles along the I-40 corridor in NC and points south. Still getting low clouds in southside VA into the NC piedmont/foothills, while a canopy of cirrostratus moves over this layer. The cirrus is thinner further north over VA. This afternoon, models are keeping threat of showers to a minimal, but could see a few break out in the NC foothills/piedmont after 2pm. Otherwise, more clouds than sunshine in the south, but expect some breaks this afternoon, while rest of the area stays partly to mostly sunny. Still warm but not too humid with highs generally in the lower to mid 80s, with cooler 70s in the mountains of NC/SW Va. Previous valid discussion... Upper ridge remains off the Southeast Coast and with little change in the overall synoptic pattern, so expect the cloud cover to persist tonight. Clouds will limit cooling tonight. Cold front from New York state to central Illinois will stall from the Ohio Valley into the Maryland panhandle by late today. Front becomes stationary far enough north that southwest Virginia, southeast West Virginia and northern North Carolina will be between the moisture and chance of precipitation along the front and the deep, tropical moisture surging through the Tennesse Valley late tonight. && .SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/... As of 415 AM EDT Wednesday... An interesting and complex forecast this period as T.S. Cindy moves initially northwest toward the TX/LA border, then north along the TX/LA border, then turns northeast late Fri, then ENE into Saturday, essentially following the I-40/I-81 corridor into southwest VA by Saturday afternoon. As we look at the current time, there is an ongoing interaction between the frontal boundary that moved through our area Monday and then stalled just to our southeast and the outer circulation of Cindy, with a deformation zone evident in the vicinity of these combined features over the SC/NC area. As we progress into Thursday, the core of Cindy and surface circulation from Cindy will separate from the baroclinic zone as upper-level ridging off the southeast coast splits apart the baroclinic zone/deformation zone and forces a weak upper-level short wave to track northeast away from the core of Cindy. All models are in good agreement on this scenario. So, our dry weather of yesterday and today will quickly come to an end Thursday as the deep tropical moisture, which originally tapped into Cindy and a Gulf moisture feed, translates northeast into eastern TN/southwest VA Thursday. Instability is fairly minimal at this point, so mainly looking for rain showers, arriving in southwest VA, southeast WV, and northwest NC during the morning, ramping up quickly to high chance/likely pops by evening, especially west of the Blue Ridge. Any pockets of instability will allow for isolated thunder, but nothing severe is expected Thursday as overall the air mass is fairly stable and dynamics are weak. The main concern will be for locally heavy rainfall. Given that recent rainfall has not been widespread, but rather heavy in localized pockets plus the fact that we have had a couple of days to dry out before the Thursday rain arrives, we do not anticipate any significant hydro problems yet Thursday. Friday, the situation becomes more interesting, especially during the afternoon. Upper heights begin to fall across the region as the broad persistent trough over the Great Lakes deepens once again. The core remnants of Cindy, as noted above, will essentially be tracking east to east-northeast along the I-40 corridor through western and central TN Friday, where there are indications of substantial rainfall in those areas. However, our CWA will remain in advance of this tropical core. Tropical moisture will already be in place across our CWA, having spread into the area from the pre-Cindy feature noted above, although not quite sure it qualifies as a PRE (predecessor rain event). Any pockets of heating, which seem quite feasible, will result in ample instability combined with the deep moisture in place to result in some fairly robust thunderstorms producing torrential downpours, heavy wet precipitation loading, hence localized damaging wind gusts, and likely frequent lightning. SPC has consequently placed the area in a marginal risk, which agrees with my assessment of the situation as well. As SPC notes, the severe threat is highly conditional on expected heating, but a scenario similar to what we saw last Thursday would not be out of the question. It is not unusual for the day preceding the main system (in this case Cindy) to end up being the more active weather day of the two. Of course another concern with any thunderstorms Friday would be localized flooding or flash flooding as with PWATS approaching 2 inches and tropical moisture to boot, thunderstorms will be very efficient rainfall producers and this could really end up being the major concern. At this point, it looks like it would be localized enough to preclude the need for a Flood or Flash Flood Watch, but such headlines are certainly possible with later forecast packages. Saturday, the core remnants of Cindy are progged by all models to track right over the CWA, enter southwest VA early in the day, exiting the coast near Virginia Beach by evening. Widespread cloud cover and a saturated atmosphere will limit the thunderstorm threat Saturday, but persistent heavy rainfall in areas that receive excessive rain Friday will certainly be primed for flooding and/or flash flooding. However, the thunderstorm threat seems less of an issue due an increased stable, saturated atmosphere. Look for well above normal minimum temperatures thanks to the tropical atmosphere in place this period, with slightly below normal maximum temperatures owing to the extensive cloud cover, tropical air mass, and precipitation. && .LONG TERM /SUNDAY THROUGH TUESDAY/... As of 430 AM EDT Wednesday... The remnants of Cindy will quickly move out of the picture late Saturday and no longer be a factor in our forecast. Over the past several days, the models had been advertising a transition to a much drier pattern across the region evolving into next week as Cindy left the region, but that is not quite as clear this morning. Broad upper troughing will remain in place across the Great Lakes, keeping a somewhat unstable, albeit, weak west- northwest flow aloft across our region. A baroclinic zone will unfortunately linger across the southern part of our CWA or perhaps just to the south. The upper trough is not deep enough to shunt the baroclinic zone and deeper moisture far enough south of us for it not to be a potential factor in our forecast. With these features in place as listed and the potential for upper-level disturbances to impact northern areas, we cannot advertise a dry forecast, unfortunately. As the weak progresses and the upper trough deepens through midweek, cooler, drier air attempts to spread south and this should push the baroclinic zone further south away from the CWA with a better potential for minimal convection at that point. For now, have use the Superblend pops in the extended as there is really no clear consensus on any dry or not dry weather among the models. Most suggest southern sections, at least, will likely see diurnal convection. Temperatures look to average a tad below normal, especially in northern areas through the period with lows in the 50s and highs in the 70s, trending more toward lows in the 60s and highs in the lower 80s south. && .AVIATION /17Z WEDNESDAY THROUGH SUNDAY/...
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As of 115 PM EDT Wednesday... Gain a cu field this afternoon over much of the area which is expected to stay VFR and scattered. Should stay VFR through 18z Thursday at the taf sites, with increasing mid/high clouds overnight/Thursday ahead of a front, and moisture from remnants of Cindy. A possibility for fog at LWB/BCB but given extra day of drying, not putting any in the tafs. Extended Aviation Discussion... Ceilings lower to MVFR Thursday evening into Friday with first surge of showers advancing SW to NE. More sub-VFR conditions through at least early Saturday with periods of moderate to heavy rain. Less threat of showers Saturday evening into Sunday so mainly VFR after Saturday morning, but fog Sunday morning is possible.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...AMS NEAR TERM...AMS/WP SHORT TERM...RAB LONG TERM...RAB/WP AVIATION...AMS/KK/WP

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