Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 101132 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 632 AM EST Sat Dec 10 2016 .SYNOPSIS... High pressure will build east across the Mid-Atlantic region today before sliding to the coast tonight and then offshore on Sunday. The associated cold airmass will remain over the area through early Sunday before moderating. A cold front will approach the region late Sunday night before working east through the area later Monday into Monday night. && .NEAR TERM /THROUGH TONIGHT/... As of 245 AM EST Saturday... Overall mainly a temperature forecast today into tonight as surface high pressure slides overhead this afternoon and to the coast overnight. Lingering upper trough along with passing weak shortwave energy may act to keep upslope low clouds/flurries across the far west this morning before drying and weakening westerly flow helps diminish clouds this afternoon. However 850 temperatures will be slow to warm in the wake of another impulse aloft, with most guidance now giving only 20s to lower 30s mountains, with somewhat warmer upper 30s/low 40s east per weak downslope. Some high clouds could also mix in and with the low sun angle suspect the colder side of guidance best. Thus lowered highs a little espcly west closer to the latest Euro Mos. Otherwise mainly sunny but still cold under diminishing winds. Warm advection aloft will develop behind the exiting ridge overnight with the main axis of lift taking shape to the northwest along a weak warm front aloft and within strong upper zonal flow. Appears most of this deep moisture will stay to the north with the upper jet helping to shear an axis of mid/high clouds eastward across mainly the northern half of the region through daybreak per most model humidity fields. However southward extent and thickness of the canopy to likely play into how low temps could go given residual very dry dewpoints in place. Think also likely to see some spots plummet early on before steadying out under the clouds and at elevation where return southwest flow will start to mix down late. Therefore running on the colder side of Mos valleys and southern sections per better radiational cooling while leaning a bit warmer north but still teens to low/mid 20s under intervals of clouds at this point. && .SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/... As of 433 AM EST Saturday... Broad surface anticyclone across the eastern seaboard, with ridging extending back westward to the Alleghany Mountains early Sunday, in a low-amplitude quasi-zonal mid-level flow regime. Ridging gradually shifts eastward into early Sunday evening. The daytime hours stand to be mostly sunny with veered/southerly return allowing for 850 mb temps to rise to -1 to +2C, supporting highs in the upper 30s to mid/upper 40s. Our weather then turns more active Sunday night and into a good part of Monday as a cold front moves across the region, associated with a developing winter storm affecting the northeast US. Strength of warm advection increases markedly Sunday night ahead of the cold front as low- level southwest flow increases to near 50 kts. Strongly non-diurnal temperature trend with a brief period of radiational cooling where lows in the 30s are more likely to occur. Surface temperatures then stand to steadily rise through most of the overnight hours. Most of the global models and the NAM bring in some light QPF overnight Sunday; further inspection of BUFKIT soundings off the GFS/NAM reveal an unsaturated cloud- ice layer with all the RH in the -3 or warmer isothermal level. Via the top-down methodology, feel that any precip into the overnight is largely drizzle. A brief period of patchy freezing drizzle and potential for slippery roads/sidewalks are possible where surface temperatures are initially near or below freezing, particularly in the Alleghany Highlands and in the elevated terrain in the southern New River Valley and the VA/NC border on I-77. But temperatures should warm above freezing rather quickly so the period of freezing drizzle is limited. As the column saturates we should see steady light to at times moderate rain associated with the front`s passage Monday with PoPs in the Categorical range before PoPs diminish down to slight chance behind the front Monday night. QPF amounts range from about a quarter to a half inch. Mondays highs should be well into the 40s to mid/upper 50s highest out in the Virginia piedmont and southside areas. For Tuesday, there`s some sizable differences apparent between the GFS and ECMWF as far as how far south the baroclinic zone associated with the cold front`s trailing edge makes it into North Carolina. The ECMWF pushes the front barely into the central NC piedmont and western mountains and would allow for some precip to overrun the frontal zone later Tuesday; while the GFS advances the front southward further enough to keep our area dry. Since the east-west front will essentially parallel the mid-level flow aloft, thinking closer to the slower ECMWF idea and maintained idea of Chance-level PoPs for mainly light rain Tuesday (mixing with wet snow in the Alleghany Highlands into Tuesday night). I also chose to keep highs cooler Tuesday than otherwise with more cloud cover - in the 40s with lows in the 30s. If the GFS proves correct, highs could be a few degrees warmer and lows cooler. && .LONG TERM /WEDNESDAY THROUGH FRIDAY/... As of 433 AM EST Saturday... Strong isentropic lift will develop over an in-situ wedge as a complex low approaches from the southwest. There may be some p-type issues at the higher elevations with the initial surge of warm air advection into the first part of Wednesday. However, a significant surge of cold air will start moving in during the day Wednesday behind the departing low and transition precipitation to snow, especially in upslope areas west of the Blue Ridge. There may also be some freezing issues as the cold air arrives on blustery winds and interacts with wet surfaces Wednesday night. Lingering snow showers west of the Ridge will dissipate as cold high pressure builds in through the end of the workweek. Temperatures will generally exhibit a cooling trend for most of next week with highs on Tuesday well above normal, falling to well below normal by Thursday. && .AVIATION /11Z SATURDAY THROUGH WEDNESDAY/...
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As of 1132 PM EST Friday... Upslope cloudiness should keep KBLF/KLWB and perhaps KBCB in MVFR to ocnl IFR at times through about mid morning before clouds diminish. Otherwise once the clouds fade, expecting widespread VFR through the period with high pressure building in from the west into this evening. Swath of mid/high clouds likely to skirt across central and northern sections overnight but still should see cigs remain above 8-10K feet into Sunday. Extended aviation discussion... Next weather system to follow will be a cold front, models suggesting a Sunday Night arrival which will likely produce sub- VFR conditions at times, and possibly wintry mix in the mountains. The cold front crosses the area Monday with continued threat of showers and sub-VFR at times, then somewhat of a break Monday night and maybe Tuesday, with another system arriving midweek with more precip, and more than likely sub-VFR at times.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH NEAR TERM...JH SHORT TERM...AL LONG TERM...AL AVIATION...KK/PM/WP

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