Area Forecast Discussion
Issued by NWS Blacksburg, VA

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145 FXUS61 KRNK 281109 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 709 AM EDT Fri Jul 28 2017 .SYNOPSIS... Low pressure along a front across the Midwest will track east crossing the Mid-Atlantic region later today into this evening. A trailing cold front from this system should pass east into the area later this afternoon before exiting to the east of the region overnight. High pressure follows behind the front bringing drier and cooler weather from later Saturday into early next week. && .NEAR TERM /THROUGH TONIGHT/... As of 300 AM EDT Friday... Rather complicated forecast continues today with strong shortwave energy seen in water vapor across the western Great Lakes set to dig southeast while deepening a surface wave that looks to track just north of the area into tonight. However before this feature consolidates by this evening, forecast remains uncertain due to pieces of fragmented upper waves that will scoot east ahead of the trailing cold front and subsequent closing off upper system aloft. Models remain quite overdone with showers early this morning since the region remains basically in between a mid level wave to the southeast from Tuesday, and pockets of better defined lift south of the front across KY/TN attm. This seems handled best by the GFS which holds better coverage to the west through midday before enhancing lift along the front over the west this afternoon, and out east late into early evening perhaps along a lead pre-frontal type outflow band. Thus trimmed pops back a bit this morning, although expect some increase by daybreak, at least with coverage of more mid deck showers. Questions remain with severe/flooding potential this afternoon as most guidance less impressive with severe parameters per projected weaker instability given degree of early clouds/showers around. Does appear best severe threat across the west if can get more multicell clusters early on, and then possibly with a more organized band by this evening east pending the degree of any heating as shear aloft still decent. Overall flooding threat mainly from southeast WVA across the far north where coverage may be more widespread closer to the front/surface low. However given uncertainty with just how far south the more organized belt of deeper convection will be, and overall dry antecedent conditions expect flooding more of the isolated nature, so holding off on any watch for now. Otherwise kept pops similar to previous with values ramping up to likely/categorical from west to east this afternoon including a heavy rain mention given moist PWATS. Highs tricky per early clouds and timing of more widespread convection which supports staying with a cooler Mos consensus for now. Upper low closes off just to the north overnight with the trailing surface cold front swinging through mainly after midnight. Expect best convective coverage over the east/north during the evening before dry slotting aloft from the southwest overnight. However potential wrap around/upslope flow likely to keep bands of showers going most sections overnight as cool advection increases late. Therefore trend of diminishing pops looks good after this evening with winds turning blustery along the ridges by daybreak. Appears this mixing and clouds to limit temp falls despite strong cool advection so kept most in the 60s overnight. && .SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/... As of 315 AM EDT Friday... The combination of the closed upper low dropping south through the Appalachians and the surface low pulling off toward the coast will keep some lingering showers across the region Saturday with our chances for precipitation decreasing throughout the day. The closed upper low will then then take up residence over the mid Atlantic coast through the weekend and nudge the surface low a bit further offshore with the last of the lingering showers tapering off Saturday night. A large area of high pressure will then build in from the upper midwest with fair weather expected into the first part of next week. With a cool north to northeast wind this weekend, expect temperatures to be 5 to 10 degrees below normal on Saturday and Sunday with highs generally in the low to mid 70s west of the Blue Ridge and upper 70s/around 80 to the east. Nights will be notably cooler as well with lows by Monday morning in the lower 50s west to upper 50s east. Expect a gradual warming trend through the first part of next week with highs Monday in the middle 80s east to middle 70s/near 80 west. && .LONG TERM /TUESDAY THROUGH THURSDAY/... As of 1245 PM EDT Thursday... Upper low opens up and lifts northeast back into the northern jet stream through Tuesday with 500MB heights rising Tuesday and Wednesday over the Mid Atlantic region. Still under long wave troughing over the eastern United States through the end of the week with models showing some signs of through amplifying by Friday. 850MB temperatures gradually warm Monday through Wednesday back close to +18 to +20 for Wednesday and Thursday. Will maintain dry forecast through Thursday. Once surface high moves offshore on Friday a slight chance of precipitation will return to the mountains. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/...
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As of 705 AM EDT Friday... Looking at mainly VFR to MVFR conditions to prevail this morning with pockets of LIFR/IFR in fog/stratus gradually improving while bands of shra/tsra result in possible local IFR espcly over the mountains through mid morning. Otherwise low confidence TAF forecast continues today with showers spreading across the west early followed by redevelopment this afternoon as showers/storms increase ahead of a cold front to the west. However timing, strength and extent of stronger more widespread thunderstorms highly contingent on sufficient cloud breaks. For now will continue with a VCTS mention at most locations from west to east this afternoon, and TEMPO in a period of sub-VFR as perhaps a more organized area shifts east from the western terminals early this afternoon and into eastern sections by late afternoon/early evening. Any thunderstorm may be capable of torrential downpours and associated IFR to LIFR visibility and lightning. Expect coverage to gradually exit the east after sunset but lingering wrap around likely to produce low cigs and lingering shower bands across most of the region until around midnight. Appears most rainfall will be along and north of a KLWB-KLYH line by daybreak Saturday with patchy fog possible despite increasing northerly flow late. Appears Saturday will start out mainly dry under low cigs. However given upslope northwest flow across the KBLF/KLWB vicinity, and the upper low dropping south across eastern sections, expect a return of periodic return of showers until late in the day. Should see cigs rise some as drying aloft gradually works in but still appears will stay sub-VFR for much of the day espcly western mountains and east of the Blue Ridge. Aviation Extended Discussion... Expect widespread VFR to return Sunday-Tuesday under high pressure following the front/upper low.
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&& .HYDROLOGY... As of 322 AM EDT Friday... More in the way of widespread showers and storms can be expected ahead of a strong cold front this afternoon into tonight. Locally heavy rainfall could accompany any of the stronger showers and storms with rainfall rates of better than 2-3 inches per hour possible. This heavy rainfall could lead to at least isolated flooding or flash flooding especially if rainfall tends to train across the same locations. However lingering antecedent conditions remain quite dry with only the far northwest sections having seen more widespread heavier rainfall from Thursday. This combined with very high flash flood guidance and low stream flow supports less in the way of widespread flooding issues, especially given the uncertainty in projected rainfall through this evening. Thus will hold off on any watches with this package and handle with short fuse products if needed later today for now. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH/RCS NEAR TERM...JH SHORT TERM...MBS LONG TERM...MBS AVIATION...AL/JH/RCS HYDROLOGY...JH

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