Area Forecast Discussion
Issued by NWS Blacksburg, VA

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922 FXUS61 KRNK 240819 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 419 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 TONIGHT/...
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As of 350 AM EDT Sunday... Mid Atlantic region will be firmly beneath the upper ridge today and tonight. Cirrus was filling over Virginia and North Carolina early this morning. This cloud cover and the temperature/dew point spread will result in less extensive fog than on Saturday morning. Typical valleys from Greenbrier into the NRV will still have patchy dense fog around sunrise. Day to day persistence has been verifying well for maximum temperatures. Highs today will be similar to Saturday. Used bias corrected MAV/MET guidance as a base for low temperatures tonight.
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&& .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
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As of 350 AM EDT Sunday... Deep-layer ridge broadly centered over the Southern Tier of NY will continue to provide subsidence and dry conditions to the region Monday into part of Tuesday. 00z deterministic and ensemble NWP shows the ridge beginning to break down and weaken later Tuesday as Maria makes an approach to coastal NC. Weak ridging should prevail Wednesday across the western third of the forecast area, with the 00z GFS and ECMWF solutions do show an increased pressure gradient for locales east of the Blue Ridge and into the VA/NC Piedmont as Maria makes her closest approach to the Carolina coast Wednesday. Latest forecast calls for Maria`s center to likely remain off the coast with the only effect on our forecast area being a modest increase in northeasterly to north wind speeds midweek. For more details specific to Maria, consult the latest forecast and advisories from the National Hurricane Center. The chief guidance differences in this period is the extent of cloud cover Monday and Tuesday with an influence on temperatures. The 00z NAM generally advects much more RH in northeast flow back westward than either the GFS or the ECMWF show. Should see partly to mostly sunny skies each dry conditions Monday. On Tuesday afternoon, the NAM also shows some light QPF along the eastern slopes of the Appalachians and the Blue Ridge associated with slightly better moisture convergence. Both the NAM and the GFS show some low-level convective instability - being capped above 700 mb. Did include 15- 20% PoPs Tuesday on the eastern lee side of the terrain for showers. Shallow convective depth should preclude any thunder so kept as light showers. For Wednesday, expecting more variable cloudiness greatest with eastern extent - particularly east of a rough line from Appomattox to Rockingham Counties where cloudiness associated with Maria`s far northwestern circulation could overspread. Partly to mostly sunny skies should exist further west. What should be a noticeable trend through each day in the period is a gradual increase in northeast winds, greatest on Wednesday. With that said, gusts are no higher than 25 mph. As for temperatures...warmest day still appears to be Monday with highs in the upper 70s to mid/upper 80s. Kept high temperatures in the mid 80s Tuesday and Wednesday given at least some partial cloudiness. Lows Monday night are in the mid 50s to mid 60s, but are about 3 degrees warmer with some clouds around and increased wind speeds than experienced recently.
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&& .LONG TERM /WEDNESDAY THROUGH SATURDAY/...
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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 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.
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&& .AVIATION /08Z 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...AMS SHORT TERM...AL LONG TERM...WP AVIATION...AL/JH

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