Area Forecast Discussion
Issued by NWS Blacksburg, VA

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KRNK 171440 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 940 AM EST Sun Dec 17 2017 .SYNOPSIS... High pressure is centered along the Southeast U.S. Atlantic Coast. Low pressure over the Mid-Mississippi Valley was moving northeast toward the Ohio Valley. Clouds will be on the increase today with the potential for some light rain across the mountains west of the Blue Ridge during the late afternoon and evening. && .NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
As of 935 AM EST Sunday... Regional radar collective was starting to show some weak returns over the far western sections of the forecast area. However, believe this first attempt of the atmosphere to precipitate on our region will me met with plenty of dry air still in place for an initial round or two of virga. Our ongoing forecast doesn`t ramp chances of measurable precipitation into the slight chance category until around 100 PM EST in the far western sections. This timing still is looking like a good call, so will be making no changes to the probability of precipitation forecast for this afternoon. The only adjustments made currently will be minor ones to address tweaks to the hourly gridded forecasts for temperature, dew point, winds/gusts, and sky cover based upon the latest observations and expected trends into the early afternoon. As of 300 AM EST Sunday... High pressure was along the southeast Atlantic Coast. This feature will remain relatively stationary the next few days, blocking any significant weather systems from impacting the area. There is an impressive looking short wave coming out of the Arklatex with precip advancing northeast through the Mid/Lower MS valley, but this feature will encounter this high pressure road block. As such, anticipating bulk of the rain associated with the trough to get steered around the periphery of the Atlantic Ridge, any encroachment of precip drying up as it enters the dry air and subsidence associated with the anticyclone. Sensible weather today will reflect increasing cloudiness from the approaching short wave disturbance. Some light rain is possible west of the Blue Ridge during the late afternoon and evening, but not looking for anything measurable to make it east of the Blue Ridge, although can`t rule out some sprinkles. In spite of increasing cloud cover, temperatures will climb above freezing, although any significant rise of temperature will be dampened per increasing cloud thickness. Most areas should reach the 40s today, and around 50 Southside into the Piedmont of NC where clouds will be thinner...values close to the seasonal norm. Considerable cloudiness early tonight will give way to partial clearing as the system fractures. Westerly winds will permit continuation of upslope low level cloudiness along the western slopes, cloud depth shallow. With no dendritic growth forecast in the cloud, p-type would be limited to mainly drizzle. Temperatures tonight will be dependent on cloud cover, any clearing allowing readings to slip close to freezing, but if clouds persist then lows will be in the mid-upper 30s.
-- End Changed Discussion --
&& .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... As of 200 AM EST Sunday... The medium range models are in good agreement, especially early in the period that our region falls under a zonal flow with weak ribbons of elongated vorticity skirting to our north, especially Monday night and early Tuesday. Meanwhile, a progressive upper trof moving through the northeast U.S. Tuesday night/early Wednesday helps push a cold front through our area during this timeframe. The third feature of interest during the short term forecast is a cut off low currently near Baja California, which ejects northeast and weakens as it moves over our area Wednesday. The 00Z ECMWF is farther north with the track of a sfc low associated with this feature, and as a result, brings precip farther north into our southern zones (NC/southern VA) Tuesday night into Wednesday. For Monday, lingering moisture and upslope flow may generate some light precip in the mountains, and the GFS still hints at some light freezing drizzle/freezing rain in the Greenbrier Valley to Bath county early Monday morning. Most of the SREF members keep precip liquid or do not develop precip at all. Even if the worst case scenario unfolded with spotty freezing drizzle, amounts would be extremely light and no adverse impacts are expected. Continued to lean toward the warmer side of guidance for highs, especially in the east where more sun is expected under downsloping winds. An increasing low level jet Monday night, should keep ridges mixed resulting in warmer temps for lows Tuesday morning. Downsloping winds persist into Tuesday, which have the potential to bring very warm conditions to our region. This may be mitigated, however, by increasing high/mid level clouds. Therefore, made little adjustments to highs Tuesday which still fall on the warmer side of most guidance. Precipitation associated with the ejecting upper level storm system could arrive as early as Tuesday night, but GFS ensemble means indicate best chances for rain (south of Highway 460) would be Wednesday into Wednesday evening. Coldest air remains to the north, with just a glancing shot, so temps Wednesday will still be near to slight above normal. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... As of 210 PM EST Saturday... The second upper low also weakens as it moves northeast but takes a more southern track through the Tennessee Valley. This short wave crosses the Mid Atlantic region on Wednesday and Wednesday night. A third upper low reaches the Southwest United States late in the week with a larger spread in models solutions concerning location and intensity. The main track of the vorticity maximums will depend on the strength of the digging trof in the central United States and the upper ridging over the Southeast. Models were showing a spread of solutions for Thursday through Sunday. In-situ type wedge of high pressure may develop over the area on Thursday. Models keep the bulk of any precipitation south of Virgina. Will keep better probability of precipitation mainly on Friday night and Saturday. Decent plunge of much colder air advertised by the GFS and ECMWF on Friday and Saturday for the central and eastern United States. Air mass will be cold enough to support snow in the mountains on Saturday. && .AVIATION /15Z SUNDAY THROUGH THURSDAY/... As of 645 AM EST Sunday... Clouds will increase today,thickening and lowering with time, but remaining VFR. Light rain associated with a disturbance moving into the Ohio Valley may produce MVFR conditions later this afternoon and evening from the mountains into the Ohio Valley. Conditions east of the mountains are expected to remain dry with cloud bases remaining VFR. Extended Discussion... Little or no impact is expected to aviation for the central Mid-Atlantic through mid week as weather features remain well north and south of the geographic region. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...PM NEAR TERM...DS/PM/WP SHORT TERM...PH LONG TERM...AMS/PH AVIATION...PM is the U.S. government's official web portal to all federal, state and local government web resources and services.