Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 181351 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 951 AM EDT Thu Aug 18 2016 .SYNOPSIS... A weak residual boundary across the region will continue to dissipate today allowing weak high pressure to slide in from the west overnight into Friday. A strong cold front over the central United States on Friday will cross through the region late Sunday into Sunday night. Somewhat cooler and drier air follows the front for early next week. && .NEAR TERM /THROUGH TONIGHT/...
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As of 952 AM EDT Thursday... Made some minor adjustments in pops shaping towards WSR-88d images and trends for this morning, then leaned towards HRRR for late morning into this afternoon. Overall, it still looks like the best chance of for best convective for this afternoon will be in southwest portions of CWA especially along and west of I-77. More changes later... As of 230 AM EDT Thursday... Overall zonal flow aloft to remain in place through the next 24 hours with subtle lowering of upper heights slowly flattening the offshore ridge to the south into tonight. However water vapor shows the plume of deeper moisture now across the area from the southwest with the residual surface boundary having basically washed out just to the north. This will make for more uncertainty with pops into this evening given added shortwave energy sliding into the southwest zones while pwats slowly decrease from north to south in the wake of the shortwave from late yesterday. Latest short term guidance also showing weak west/northwest flow across much of the region today following this feature with the remnant axis of the boundary/outflow now over southern/southwest sections. This looks to be the area for best convective chances, espcly along/west of I-77, as well as into northwest NC, where the flow may turn southwest ahead of the impulse and forecast instability is a bit more. Otherwise like most chance pops south of highway 460 today with perhaps mostly dry far north after any early morning shra fade. Weak but unidirectional flow aloft suggests some potential for more banded convection espcly south but parameters less for much more than isolated pulse severe at this point. High temps not quite as hot out east given slight cooling aloft and mid clouds that could limit rises over the west where some spots may stay in the 70s/low 80s. However with weak downslope appears will still be around 90 Piedmont sections with overall 80s elsewhere pending exodus of the mid deck. Latest ensembles suggest that isolated convection could linger south/west into this evening with continued westerly flow perhaps keeping some shra threat over the far west overnight. Since guidance showing a gradual return of moisture southwest late, while having added shortwave energy shear in from the west, leaving in some low chance pops I-77 corridor overnight, but mainly dry elsewhere with fog around. Lows likely a little cooler with dewpoints slightly lower allowing most to drop back into the 60s outside of the far southeast.
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&& .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... As of 300 AM EDT Thursday... A lee trough will shift east over the coastal piedmont on Friday with a washed-out boundary in the vicinity of the TN/VA-VA/NC border. A mid level short wave is expected to track over the southern Ohio Valley Friday morning, then move over the south- central Appalachains Friday evening. This wave and lingering boundaries in the area will bring another chance for showers across the mountains Friday morning, then a chance for thunderstorms for the entire area during the afternoon and evening. The strongest of the storms should reside along and south of the VA/NC border. The overall threat for widespread severe storms Friday will be low. The short wave will pass to the east during the evening with the flow becoming zonal going into Saturday. This zonal flow will limit showers and thunderstorms across the area Saturday afternoon, however a few pulse storms could become severe. It is worth noting that the GFS wants to bring a wave across the Tennessee Valley which could bring more areal coverage of storms Saturday, but appears to be the outlier. Most models are holding the more widespread showers and thunderstorms with a strong cold front on Sunday. Temperatures will continue to remain above normal each afternoon through Sunday. Temperatures will range from the low to mid 80s west and near 90F over the piedmont. Overnight lows will remain muggy and in the mid 60s to low 70s. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 235 PM EDT Wednesday... A strong cold front will approach the region Sunday morning, and cross the area either Sunday night or early Monday morning. Guidance is still flip-flopping on this detail. In advance of the front, look for a significant increase in the coverage of showers and storms. In the wake of the front, either Monday morning or Monday afternoon, the area is expected to experience its first notable change in airmass that has occurred in some time. A cooler air mass with lower dew points will be in place across the area by Tuesday and Wednesday. Both of these days, expect highs across the mountains in the mid 70s to near 80 with the low to mid 80s across the Piedmont. Low temperatures will range from the mid to upper 50s across the mountains to the low to mid 60s across the Piedmont. && .AVIATION /14Z THURSDAY THROUGH MONDAY/... As of 700 AM EDT Thursday... Lower IFR to MVFR cigs persist in spots across the far west early this morning with mid deck VFR canopy elsewhere where seeing some lighter showers still ongoing. Expect only slow improvement around KBLF with weak upslope and added upstream light showers likely holding sub-VFR in place until early afternoon. May also see lower MVFR cigs fill in over the next couple of hours at KLWB/KBCB/KROA before slowly mixing out by late morning into early afternoon with heating. However mid deck canopy may be slow to exit with strato- cu also possibly lingering before the next wave over the TN valley arrives. In addition once heating takes shape expect to see more cumulus buildups in the afternoon but to a lesser extent than previous days given less instability and lingering mid clouds. Convective coverage also iffy with main focus likely over southern/southwest sections where somewhat drier air aloft wont work into before the impulse arrives from the west. Think other than KDAN/KBLF, too uncertain to include any vicinity mention of shra/tsra with most sites likely to stay dry after early sprinkles/showers under more clouds south and less across the north later in the day. Showers may again linger across the south this evening before fading to patchy MVFR/IFR fog prior to clouds returning north late tonight. Extended aviation discussion... Deeper moisture to the south will start to return north Friday with coverage of showers and storms spreading back across the region by late in the day. This should bring a return of periodic sub-VFR in shra/tsra into Friday evening, with added at least scattered coverage again Saturday afternoon given deeper moisture in place. Best likelihood of more widespread showers and storms including MVFR/IFR will take place Sunday ahead of a strong cold front that will arrive Sunday night. Much drier air then looks to return VFR to the region behind the front on Monday. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH NEAR TERM...JH/KK SHORT TERM...RCS LONG TERM...DS AVIATION...AMS/JH/WP

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