Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 201738 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 138 PM EDT Tue Jun 20 2017 .SYNOPSIS... A front stalls from North Carolina to Texas today and tonight. A potential tropical system moves through the lower Mississippi Valley and into the Tennessee Valley on Thursday through Saturday. This feature will interact with a front crossing into the Mid Atlantic region on Saturday and Sunday. && .NEAR TERM /THROUGH TONIGHT/...
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As of 137 PM EDT Tuesday...No major changes needed, though did tweak dewpoints to get them better in line with present observations and expected afternoon trends. Mild and more comfortable early afternoon for the northwestern two-thirds of the forecast area. As one advances further southeast, humidity levels do start to creep up with mid/upper 60s still common on the far northern periphery of a stalled front. All told, a nice late June afternoon. Highs upper-70s to mid-80s look on track. Previous near-term discussion issued at 300 AM Tuesday follows... Surface front from southeast Pennsylvania to central Georgia will drift south then stall this morning. This will push deeper moisture out of extreme southern Virginia and northern North Carolina along with the probability of any precipitation. Hi-Res models and RAP guidance take northern edge of the light showers south of Yanceyville by 13Z/9AM. Stratus and northern edge of cloud shield will erode this morning then more sun this afternoon. Enough heating to lean toward warmer side of guidance for maximum temperatures. Little change in the position of the upper trof and the light west surface and low level winds tonight. Lows clouds fill back in across North Carolina and into far southern Virginia. Only minor adjustments to overnight low temperatures.
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&& .SHORT TERM /WEDNESDAY THROUGH FRIDAY NIGHT/... As of 400 AM EDT Tuesday... We will start this period with what appears to be an increasingly short respite from the high humidity and daily rounds of showers and thunderstorms. The first complication in bringing any lengthier period of less humid/drier air to the region results from a persistent upper trough across the Great Lakes region. In general, this large scale synoptic feature will remain in place. Just to our southeast, roughly from ATL to RDU lies the old baroclinic zone delineating the very warm/humid air to our southeast from the slightly drier air over our region. As a short wave tracks through the upper trough anchored over the Great Lakes tonight into Wednesday, this will attempt to pull the baroclinic zone and associated moisture back to the northwest somewhat. At this time, it appears this northwest return of moisture should be maximized right at the beginning of this period, then begin to retreat back to the south as a short wave ridge is evident with the passage of the upper trough. Will continue to advertise slight chance pops across the far southeast corner of the CWA at 12Z Wed, then retreat this back southeast out of the CWA during the later morning hours. The period from 18Z Wed to 12Z Thu will likely prove to be the only period with below mentionable pops for the remainder of the forecast package. The remainder of the period will be heavily influenced by the potential tropical system developing in the central Gulf, slated to move northwest toward the TX/LA border late in the week. As this system moves northwest Thu, deep tropical moisture will be drawn north from the southeast and Midsouth states, especially into the TN Valley as well as adjacent areas of VA/WV/NC. The weakening of the upper flow to our north will also encourage this scenario. Most of the models indicate a potential tropical-like feeder band tracking from GA into eastern TN and southwest VA by Thu afternoon. While this is initially tied to the potential tropical system, it breaks off from the tropical low, at this point in the Arklatex region, and tracks eastward across our CWA on the northwest side of a building Bermuda subtropical high. This moisture then appears to remain stuck across the CWA until the weekend, when a frontal system approaches along with the remnant moisture from the tropical system. Bottom line, is any dry period will be very brief, likely confined mainly to Wed/early Thu, before we see several days of scattered to numerous showers and thunderstorms with locally heavy tropical downpours. The main concern Thursday through the weekend will be localized flooding from the expected torrential tropical-like thunderstorms. This threat will generally be confined to areas west of I-77 Thursday, then spread eastward along the developing baroclinic zone over the area and the north side of the subtropical ridge Friday. Will continue to highlight the threat for flooding in the HWO and eHWO during these periods. With increasingly humid conditions once again, look for minimum temperatures to be well above normal through much of the period, coolest Wednesday morning, then just plain muggy Thu-Fri. On the other hand, the cloud cover and precipitation will hold down the maximum temperatures to near or even slightly below normal levels. && .LONG TERM /SATURDAY THROUGH MONDAY/... As of 415 AM EDT Tuesday... A very wet weekend, with any luck trending drier toward Monday. As noted above, the combination of residual tropical moisture, the remnants of whatever the ongoing potential tropical system evolves into during the next couple of days, and increasing troughing within the persistent broad upper trough anchored over the Great Lakes, will bring widespread showers and thunderstorms to the entire CWA over the weekend. Localized flooding will remain the main concern, although a few strong to severe thunderstorms also cannot be ruled out especially as dynamics increase with the strengthening upper trough and associated frontal boundary, this is clearly not the main concern with this event. Most indications are that the heaviest rainfall associated with the tropical system will remain across the OH and TN valleys until an upper trough and associated frontal system track this moisture through our CWA Sun-Mon, after which there is some promise for drier conditions. Temperatures will remain well above normal at night, and near to slightly below normal during the daytime as a result of the persistent very humid air mass present over the region. && .AVIATION /17Z TUESDAY THROUGH SATURDAY/...
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As of 137 PM EDT Tuesday... VFR all terminals through the afternoon and early evening hours, with southwest to west winds 4-8 kts. Generally FEW-SCT fair weather cu, though with some high level clouds spilling in with southeastern extent. Toward mid-evening, stalled frontal boundary`s northeast advance may brush a BKN020/MVFR ceiling at Danville through overnight with relatively high confidence of occurrence. May even be an isolated unrestricted shower but am less confident of that. Later in the evening will be watching for radiation fog with higher confidence of MVFR/temporary IFR visibilities at Lewisburg and Blacksburg. Potential is there at Lynchburg as well but a little less confident there as it will depend on extent of cloudiness, so opted for a 6SM BR after 09z for Lynchburg. Winds should trend light and variable again tonight. Should trend VFR again tomorrow, though like today, greater low to mid-level cloud cover further southeast. Winds again become west to southwest 4-8 kts. Extended Aviation Discussion... Generally VFR Wednesday late afternoon through Thursday afternoon. Low-confidence prospect for radiation fog Wednesday evening. More active aviation forecast period Thursday evening into the weekend. Lowering, sub-VFR conditions anticipated Thursday evening into Friday with first surge of showers advancing SW to NE. Potential for low-level wind shear western terminals. Continuation of sub-VFR conditions Friday evening into Saturday with moderate to at-times heavy rain. Confidence is low on timing of rain.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...AMS NEAR TERM...AL SHORT TERM...RAB LONG TERM...DS/RAB AVIATION...AL/AMS is the U.S. government's official web portal to all federal, state and local government web resources and services.