Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 191751 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 151 PM EDT Fri Aug 19 2016 .SYNOPSIS... A weak residual boundary just south of the area will continue to dissipate today as weak high pressure slides in from the west overnight into Saturday. A strong cold front over the central United States 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/... AS of 957 AM EDT Friday... Made some minor adjustments to temperatures and dew points leaning towards the latest surface obs and trends and shaped towards lav guidance this afternoon. Adjusted this morning pops and weather towards radar images and their progression in time. Modified pops for late morning and early afternoon blending towards the HRRR solution. No severe thunderstorms expected this afternoon with our area in general thunderstorms on Day One Convective Outlook. With pwats relatively high, locally heavy rain may be possible with a slow moving storm this afternoon. More changes later.... As of 240 AM EDT Friday... Rather uncertain forecast continues today with impulses within the deep westerly flow aloft riding over lingering moisture but without much surface support. Current embedded shortwave responsible for mid deck and associated patchy showers should move across southern sections near the lingering surface trough early taking residual showers to the east after sunrise. This may allow for a brief break in clouds outside of far southern/western sections this morning, before yet another wave aloft arrives from the west this afternoon and shears across this evening. Models tend to develop some instability between these features espcly mountains this afternoon while keeping some weak low level wedging out east within weak easterly flow. Appears guidance again likely overdone with lift espcly the Nam in showing a swath of stronger UVV`s over western/southern zones this afternoon with deeper convection spreading over to the Blue Ridge. However most solutions do suggest better coverage along the I-77 corridor into northwest NC and less north/northeast sections where more sunshine possible. Convective potential still looks iffy unless more heating takes shape as winds aloft remain weak with better pwats just to the south. Thus will include some higher pops over the south-west later this afternoon per short term model consensus, and continued chance elsewhere although this may be generous across northeast sections. High temps quite tricky with clouds to start and then possibly some breaks before filling in again. Given cooler trends of late, will lean toward the EC mos a little more. However given such a warm start will only take brief heating to send readings up more than expected espcly Blue Ridge west. Otherwise going with mostly mid/upper 70s mountains to the mid 80s out east for now. Deeper moisture slides to the south/east later this evening leaving only weak upslope far west late. Best coverage again early on likely southern sections closer to the residual surface trough axis and just south of the weak wedge to the north. Forecast soundings also show some decrease in deep moisture over the leftover low level eastern wedge, so mainly decent chance pops espcly south/east early, decreasing to isolated or less overnight. Lows mostly 60s west to lower 70s east. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... As of 300 AM EDT Friday... Heights increase Saturday following the passing of a mid level disturbance tracking across North Carolina Friday night. A weak bubble high will also develop over the area for Saturday. With these two layers of ridging, the chance for rain are less for Saturday than previously forecasted. However, models are showing convergence in the low levels across the mountains and along with orographical lift in a semi-tropical environment, scattered thunderstorms are possible during the afternoon and evening hours. A strong cold front will move across the region Sunday, bringing a big change in airmass for much of next week. This front will move from the Mississippi Valley Saturday afternoon, over the Ohio and Tennessee Valleys Saturday night, then to the Mid Atlantic Coast late Sunday afternoon. The stronger dynamics with this system will be north of DC and into New England. Another area with weaker dynamics will track across the Tennessee Valley south into the Gulf States. With no really good support for organized storms and showers entering the area in the morning, we are not expecting any widespread outbreak of severe weather with this frontal passage. This front will be clearing out the tropical-like air, therefore heavy rain is possible Sunday. Light easterly flow should produce cooler than guidance temperatures in the east Saturday. However, with less rain expected, high sun angle will help warm temperatures to near normal levels. With rain coming across the mountains during the morning Sunday, high temperatures will range below normal. If the front is slow to move east of the mountains in the afternoon, temperatures across the piedmont may peak near normal in the upper 80s. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 310 PM EDT Thursday... Our biggest air mass change in some time is expected for next week. A broad area of dry, and cooler high pressure will become situated over the region by Tuesday. Its influence will continue across the area through at least Wednesday. By Thursday, the center of the high may shift far enough east for moisture to start wrapping north along its western flank. With greater low level moisture and a weaker cap, isolated showers will be possible across the mountains during the afternoon hours. Temperatures will trend cooler through Tuesday before inching higher through Thursday. Readings will be within roughly two to three degrees of normal. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
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As of 151 PM EDT Friday... Axis of deeper moisture will remain in place under westerly flow aloft this afternoon into tonight. Another mid level shortwave riding through the moisture plume will travel east across our region this afternoon into tonight. This will result in scattered MVFR showers and thunderstorms this afternoon into tonight. The taf site with the best chance of a thunderstorm is KBLF. With scattered showers expected across the west, will continue VCSH from KLWB to KBCB/KROA, while leaving out in the east. Any diurnal MVFR convection will diminish this evening into tonight. The combination of low level moisture and light winds will result in areas of fog late tonight into Saturday morning. The taf site with the best chance of IFR/LIFR is KLWB. Morning low clouds and fog will burn off or lift by mid morning Saturday returning most taf locations to VFR. A weak high pressure will build into our area Saturday morning with deeper moisture mainly south/west of the region ahead of a strong upstream cold front. This may only result in isolated to scattered MVFR shra/tsra Saturday with better coverage holding off until Saturday evening into Saturday night with the pre-frontal showers and thunderstorms. Medium confidence in ceilings, visibilities and winds during the taf period. Extended aviation discussion... Best likelihood of more widespread showers and thunderstorms including MVFR/IFR will take place Saturday night into Sunday ahead of a strong cold front that will pass through the region by Sunday night. Much drier air is anticipated after Sundays frontal passage with a dry forecast for Monday into midweek promoting VFR for much of the Mid-Atlantic.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH/KK NEAR TERM...JH/KK SHORT TERM...RCS LONG TERM...DS AVIATION...JH/KK

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