Area Forecast Discussion
Issued by NWS Blacksburg, VA

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933 FXUS61 KRNK 201831 CCA AFDRNK Area Forecast Discussion...CORRECTED National Weather Service Blacksburg VA 231 PM EDT Fri Sep 20 2019 .SYNOPSIS... High pressure will reside across our area through the weekend, the shift offshore Sunday night. A weak cold front will drift into the area from the northwest early next week. && .NEAR TERM /THROUGH SATURDAY/... As of 142 PM EDT Friday... West to northwest flow into the mountains along a weak theta-e boundary will keep scattered to at times overcast skies along the mountains this afternoon, with skies clearing this evening. A few sprinkles not out of the question, but deeper moisture appears to stay west of the divide. Expect another surge of clouds Saturday morning as a weak impulse moves across the Ohio Valley/Central Appalachians. A few models showing shower potential increasing with this feature but overall system will be weak, so mainly going isolated/widely scattered coverage across the mountains. Anticipate a mix of clouds and sun in the mountains, with more sunshine in the piedmont, a little more cloud cover along the ridges. With high pressure moved east some, boundary layer will be slightly more moist, so lows tonight will be in the 50s, with some 40s in deeper valleys. Saturday will mild/warm with upper 70s to lower 80s mountains, though some lower 70s in the higher ridges. Should be reaching the mid to upper 80s across the piedmont and Roanoke area. Confidence in this forecast is medium to high. && .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/... As of 130 PM EDT Friday... High pressure will be centered off the North Carolina coast during Saturday night and Sunday. A large upper level ridge will also be situated over the Mid Atlantic. Although the GFS tries to show a couple pop-up showers west of the Blue Ridge during Sunday, the NAM and ECMWF models do not show anything developing over the CWA. The consensus of the NAM and ECMWF was preferred here as it should stay dry throughout the day with the vertically stacked ridging in place. High temperatures were bumped upward on Sunday by a few degrees to accommodate the expected plentiful sunshine and light southwest flow providing warm air advection. By Sunday night, high pressure should head further out to sea, and a weak cold front will arrive over the Appalachian Mountains during Monday. The models continue to advertise a moisture-starved boundary that will be lucky to provide any meaningful amounts of rain. Sprinkles at the most may reach the I-81 corridor, and there is high confidence that the Piedmont will remain dry throughout the frontal passage. Thus, the unseasonably warm and dry trend from late summer should continue into the first day of autumn. Any moisture will dissipate during Monday night as high pressure returns from the west. && .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 153 PM EDT Friday... Very few changes in this period since the last update. An upper level trough that moves over the Great Lakes region Monday and Tuesday will begin to shift into New England and exit off the coast of Nova Scotia by Wednesday. Some leftover showers may stick around in the mountains of West Virginia Tuesday morning from the weak NW flow behind the front. A broad ridge then begins to build into the southeast United States for Wednesday and especially Thursday. There are still some model differences in regards to rainfall. The GFS is finally advertising some rainfall due to a weak frontal boundary draped west to east across the region and a generally flatter flow at 500mb. However, the ECMWF is much faster in building in the 500mb ridge and leaves our area with little to no precip through this entire forecast period. Other than these differences, the models tend to agree temperatures will likely be above normal with 850mb temps reaching anywhere from +16 to +20. Will likely side with the persistence of a dry pattern and go with a blend of the ECMWF and NBM for this period. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... As of 120 PM EDT Friday... High pressure in control although working east and allowing some clouds to move into the mountains as flow turns west-southwest. Cu/Stratocu will be bkn/ovc around BLF, possibly LWB/BCB this afternoon but should stay above 3kft. Cannot rule out a sprinkle or very light shower, but no impact to terminals. Winds remain light, and mainly variable or southwest. Will see clouds wane this evening but another increase in cloud cover will nudge into WV Saturday and possibly into the BCB area by end of the period. MVFR seems possible around 09-12z at LWB. Will have to watch for fog in the valleys, but given dry ground, should be limited to near rivers, so backed off the dense fog at LWB due to increased clouds. Confidence is high for most of the period, but lower Sat morning in the mountains for the cloud cover/vsbys. .Extended Aviation Discussion... High pressure to our northeast will continue to build southwest over the region promoting mainly VFR into Sat afternoon into Sunday. Only exceptions may be late night and early morning fog in the mountain valleys which would impact the usual terminals (e.g., KLWB and KBCB). A weak cold front may bring scattered MVFR showers on Monday, mainly in he mountains. Otherwise VFR. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...RAB/WP NEAR TERM...WP SHORT TERM...PW LONG TERM...BMG AVIATION...RAB/WP is the U.S. government's official web portal to all federal, state and local government web resources and services.