Area Forecast Discussion
Issued by NWS Blacksburg, VA

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817 FXUS61 KRNK 240531 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 131 AM EDT Sun Sep 24 2017 .SYNOPSIS... High pressure over the eastern United States will continue to bring mainly warm and dry weather to the region through the first part of next week, while Hurricane Maria stays just off the east coast. A cold front is forecast to cross through the area on Thursday. && .NEAR TERM /THROUGH TODAY/... As of 131 AM EDT Sunday... No significant changes needed to the forecast for the rest of the overnight. Did lower temperatures a little quicker than prior indications in the western river valleys over the next 3 hours as good radiational cooling and very dry airmass in place (PWAT of 0.63" per 00z RNK RAOB) has allowed for temps to plummet as low as the mid 50s in the deeper valleys. As for fog potential tonight, other than in Wilkes and Watauga County which saw rain earlier today am less confident on fog starting any sooner than 08z, if it forms at all. Crossover temperatures this afternoon were as low as the upper 40s and while dewpoints have recovered some, recent guidance shows mixed signals on such development. It may be until an hour or two before sunrise before fog starts developing in the climo favored river valleys but lowest visibilities may be a bit greater than prior nights. Previous discussion as of 255 PM EDT Saturday... No change in the general synoptic pattern as a large ridge of high pressure dominates the eastern US while tropical systems over the Atlantic remain far enough removed from the region influence our weather this weekend. Combination of diurnal instability, orographic effects, and some weak short wave energy will keep a chance/slight chance for a shower/thunderstorm in the forecast from the southern Blue Ridge into the mountains of NC. Any precipitation will fade quickly by early this evening with dry conditions for the overnight period. Expect another round of patchy fog/stratus development primarily west of the Blue Ridge. Any fog/low clouds will burn off early Sunday, followed by pleasant weather for to close out the weekend. Temperatures will be similar to previous days. Expect lows tonight in the lower 60s east of the Blue Ridge with mid 50s/around 60 to the west and some cooler readings in the valleys. Highs Sunday will be in the mid 80s/near 90 east to low/mid 80s west. && .SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/... As of 257 PM EDT Saturday... Dome of high pressure surface and aloft will reside over the mid- Atlantic Sunday night into Monday night keeping the region dry, though some east-northeast flow allows for some cloudiness to move in from time to time. Temperatures staying above normal. Tuesday, Hurricane Maria shift further north allowing a weakness in the ridge and smaller band of high moisture to head west into the piedmont during the afternoon. However, small threat of showers at this point with subsidence in place. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... As of 147 PM EDT Saturday... Just minor changes to the previous forecast this period as we watch Hurricane Maria track northward off the east coast. An upper ridge over the northeast will slow Maria down some, and as it lifts northeast a slight heading to the northwest toward the Outer Banks looks likely before the stronger upstream 5h trough shifts Maria back east and out to the sea into Friday/Saturday. For our weather still looking fairly dry with warmer than normal temperatures Wed-Thu, then some cooling trend Friday-Saturday as front and upper trough shift across. However, the front lacks moisture so shower chances are very low, as we continue a drier than normal trend. Model trends beyond 7 days continues to paint us mainly dry, but temperatures should be a little closer to or below normal. && .AVIATION /05Z SUNDAY THROUGH THURSDAY/... As of 131 AM EDT Sunday... Question for the overnight into early morning is areal coverage and how low visibilities drop in radiation fog. Air mass is significantly drier in the western climo favored river valleys (e.g. Lewisburg and Blacksburg TAFs) compared to prior nights. Confidence only medium on visibilities in fog, of which I`ve shown a general MVFR to IFR visibility with tempo LIFR starting at these two TAF sites no sooner than 08z/4 am. Slightly higher dewpoints in the southern VA/northern NC Piedmont may be offset by high clouds, but did show an MVFR mist at Danville as well toward sunrise. Otherwise VFR SKC conditions for the rest of the TAFs for overnight hrs. Under high pressure, winds tonight into early morning should stay calm. Fog should have fully burned off by 14z/10 am to VFR conditions. May only see a few fair weather cumulus at best along with some SCT cirrus. Clearing anticipated with sunset with good radiational cooling potentially supporting fog in the favored river valleys, though best onset time after the 06z TAF issuance. Initially calm winds Sunday trend generally light northeasterly for the daylight hours, then trend light/variable for the first part of the overnight. Extended Aviation Discussion... Overall persistence forecast into early next week as strong high pressure aloft builds in from the northwest keeping tropical moisture offshore. VFR conditions should prevail in the daylight hours, along with late night/early morning IFR/LIFR radiation fog through Wednesday morning. An overall dry cold front crosses the region later Wednesday night into Thursday as Maria passes off the Outer Banks. These features likely to cause increasing northerly winds Wednesday into Thursday as the combination of the pressure gradient with Maria kicks in Wednesday, followed by cool advection behind the front on Thursday. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...MBS NEAR TERM...AL/MBS SHORT TERM...JH/WP LONG TERM...WP AVIATION...AL/JH is the U.S. government's official web portal to all federal, state and local government web resources and services.