Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 102308 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 708 PM EDT Thu Aug 10 2017 .SYNOPSIS...
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A weak warm front over the Carolinas will lift north into the area overnight before dissipating. Warm and more humid air will continue to flow north into the region Friday into Saturday ahead of a cold front approaching from the west. This will result in added rounds of showers and storms into the weekend before the front slides to the south of the area on Sunday.
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&& .NEAR TERM /THROUGH FRIDAY/... As of 245 PM EDT Thursday... Return flow around high pressure to the east is providing warmer and more humid conditions for the region. Current radar shows an area of showers pushing into the western portions of the forecast area however progress appears to be impeded by the terrain, therefore any precipitation for now should remain west of I-77. An isolated thunderstorm is not impossible this afternoon but does seem unlikely with rather poor indices and lack of solar insolation. Satellite also shows an area of mainly mid level clouds pushing into the region with only the far western counties seeing the sun right now. Friday, chances for showers and isolated thunderstorms become more widespread as a cold front pushes through the region. Limited daytime heating due to cloud cover should inhibit most thunderstorm development, however additional lift provided by the ridges make it more likely to occur in the higher elevations rather than areas east. Best chances for precip will occur during the afternoon into the evening. Temperatures look to be a bit warmer tonight than last night as clouds limit radiational cooling. Again with persistent cloud cover being the reason, daytime highs tomorrow will be very similar to today. Winds through the forecast period look to be light and from the south and east. && .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/... As of 245 PM EDT Thursday... Guidance offers a rather unsettled pattern for this period, from a stalled frontal boundary near or just south of the area and a complex upper-level pattern that looks to evolve across much of the northern tier of states. Broad troughing should exist from the Northeast to the northern Plains states, with a broadly cyclonic westerly zonal flow across the Appalachians and VA/NC Piedmont. This is a regime that will serve as a conduit for what most global-scale NWP solutions depict as weak/sheared-out spokes of mid-level energy from Northern tier states to move across the region through the weekend. Solutions show little consistency on specific location and timing of showers, due largely from large variability on timing the individual weak mid-level features in the zonal flow. Unfortunately this leads to a substantially reduced confidence scenario on timing when rain changes may be more likely. I do have several days in this period with Chance-level PoPs, with the only somewhat dry day being the first part of Sunday and mainly north of Route 460. Still, the weekend does not appear likely to be entirely a washout. A reasonable best estimate for the weekend is for a fair amount of cloud cover with periods of off-and-on showers and embedded isolated thunderstorms interspersed, especially across NC and far southwest VA given their expected proximity to the stalled front. In this period, I opted to side more closely toward the cooler end of the guidance envelope for high temperatures. This is mainly due to the generous degree of cloudiness that should be in place through the bulk of the period. Conversely for lows, I chose to weight more of the milder guidance. Highs should be generally in the upper 70s to middle 80s Saturday and Sunday with lows mainly in the 60s, though may see some mid/upper 50s readings Sunday evening along the western Appalachians/west of the Blue Ridge. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 245 PM EDT Thursday... Stalled frontal zone begins to return northward as a warm front from the Carolinas into the mid-Atlantic region Monday into Tuesday. Guidance hints at a stronger mid-level disturbance that appears to spark a weak surface wave low that could facilitate this front`s northward/eastward translation. Chances for rain showers and thunderstorms should be pretty high in this rather broad period. With several chances for rain from late this week into early next week, the cumulative effect of these multiple rain periods may lead to some potential hydrologic concerns to monitor but can only speak in generalities at this point. At this time, it appears that ridging and returning dry weather for the mid-week period. Still a rather high level of uncertainty in this period on the whole and as such, stayed more close to blended guidance. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/...
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As of 650 PM EDT Thursday... Widely scattered showers continue across the mountains this evening along a lobe of deeper moisture working in from the west. Appears most of the showers will likely fade early this evening given lack of support and instability per cloud cover. However expecting periods of MVFR cigs to linger espcly Blue Ridge west into the overnight with mainly VFR out east. Other issue with potential fog and low clouds overnight as guidance shows an axis of lower cloud bases moving north into eastern sections late, while any clearing west could lead to more stratus. As it stands now, low confidence for fog overnight due to cloud cover. However given trends off latest HREF will include some MVFR vsbys in spots late, and see how things unfold through the evening as models remain quite pessimistic in dropping vsbys to IFR in a few locations by dawn. Winds through the TAF period should be light while veering from a more easterly component tonight to a more southerly trajectory under 10 kts on Friday. Rather low confidence forecast continues into Friday with deeper moisture around while forcing mostly due to weak convergence and orographics at least early on. Appears any lower cigs will mix out by late morning but then quickly give way to developing VFR cumulus fields by early afternoon and at least scattered convection most spots through the end of the day. Since best potential appears over the western sections, will start with a VCSH mention most mountain locations early on as could even see showers near KBLF/KLWB during the morning, followed by prevailing sub- VFR vsbys including a VCTS mention near the Blue Ridge. Think can hold spots out east including KLYH/KDAN to mainly a vicinity shra mention for now and see how later trends evolve. Otherwise expecting a few hours of VFR cigs into Friday afternoon with more localized MVFR to IFR in convection by mid to late afternoon. Appears showers along with spotty MVFR conditions will persist into Friday night given deeper moisture around and weak disturbances passing across. This could also lead to more in the way of fog and stratus once showers taper off late. Extended Aviation Discussion... A cold front will approach from the west by early Saturday with more showers and storms possible espcly southern/east sections. However timing of shra/tsra on Saturday more uncertain pending coverage from Friday night, so areas of sub-VFR appear likely at times through the day Saturday. Region may slide into a lull behind a passing cold front on Sunday with mainly VFR conditions excluding the far southern sections where clouds and afternoon showers may persist. However unsettled conditions look to return to start the week, and likely continue into Tuesday with MVFR showers, as the frontal boundary stalls and lingers near or just south of the area.
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&& .EQUIPMENT... As of 200 PM EDT Friday Aug 4... KFCX doppler radar will be down for the rest of the month due to a failing bull gear. The radar will be down completely through Thursday regardless of weather conditions, then only operational for brief periods if an imminent significant widespread severe weather and/or hydrologic event occurs. Operating the system for any amount of time until the bull gear is replaced risks a catastrophic failure that would further extend system downtime. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH/JR NEAR TERM...JR SHORT TERM...AL LONG TERM...AL AVIATION...JH/JR/RAB EQUIPMENT...WERT

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