Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 070517 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1217 AM EST Wed Dec 7 2016 .SYNOPSIS... A weak cold front trailing the departing area of low pressure will move across the area late tonight into early Wednesday. High pressure builds east in the wake of this front by Wednesday afternoon followed by a stronger cold front that should cross the region on Thursday. && .NEAR TERM /THROUGH WEDNESDAY/... As of 950 PM EST Tuesday... Surface low responsible for the rain today centered off the VA coast late this evening with all the rain well east of the CWA. Most stations continue to report low overcast and some fog although these conditions will slowly improve overnight. Still expect gradual clearing toward morning as winds become northerly behind the departing storm system. Low temperatures tonight will range from around 30 degrees in northwest Greenbrier county to the upper 30s in the Piedmont. Any very light wintry mix of lingering precipitation across western slopes of Greenbrier County Wednesday morning will taper off by afternoon. High temperatures will vary from around 40 degrees in the northwest mountains of Southeast West Virginia to the mid and upper 50s in the Piedmont. && .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/... As of 245 PM EST Tuesday... Brief quiet period under zonal flow aloft Wednesday night will quickly transition to one of eastern troughiness with a subsequent Arctic front crossing the region from northwest to southeast on Thursday. Models remain rather inconsistent in the degree of return moisture ahead of the boundary starting later Wednesday night and with the actual 850 mb front Thursday. Not seeing a lot of support to include much precip but given some slight backing as well as possible slowing of the front, think prudent to keep in some low pop mention espcly southwest sections under the tail of a passing jet streak. This would consist of mainly a rain/snow shower mix to just spotty rain showers south/east pending timing of the cold advection, followed by a switch to mainly post frontal upslope snow showers later in the day. Kept temps mostly in the 30s Wednesday night as clouds/mixing increase with a range of highs from steady mid 30s northwest, to 40-45 Blue Ridge, to low 50s southeast Thursday pending timing of the actual frontal passage. Cold advection will dominate the remainder of the period as strong northwest flow continues ahead of high pressure building slowly east from the central U.S. Guidance remains in line in showing winds just below advisory levels most spots Thursday night into Friday while dropping 850 mb temps down to as low as -15C mountains. However with the core of the Arctic air sliding by to the north, should be warmer out east of the ridges given less pronounced digging of the trough off latest runs. This would support blustery lows in the mid/upper teens mountains to low/mid 20s east with western wind chills zero to 10 above. Appears to be just enough low level moisture coinciding with the coldest air aloft and stronger upslope flow to result in periods of snow showers mainly far northwest. However since coverage iffy given such mixed/dry air, only including a low pop northwest slopes into Friday for now. Otherwise expecting a mainly sunny but cold and continued blustery day Friday outside of the upslope western zones where more clouds may persist. Appears highs will stay below freezing for much of the mountains Friday, while rebounding into the 30s to around 40 piedmont where cold advection offset by downsloping flow will occur. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... As of 130 PM EST Tuesday... Upper trough lifts out Friday night allowing cold surface high pressure to build overhead by Saturday morning. This should bring diminishing winds overnight but also good radiational cooling within the residual piece of Arctic air in place. Still some potential to see warm advection high clouds invade late Friday night into Saturday morning which could keep readings from bottoming out. Thus running with mostly clear and lows teens mountains to upper teens/low 20s east for now. Surface high should cross the region Saturday with a fast zonal flow regime developing that will continue into early next week. Exodus of the cold pool aloft should allow for gradual moderation in temps into the 30s to lower 40s Saturday before much stronger warm advection on southwest flow develops Sunday into Monday ahead of an approaching upstream cold front. Latest models have slowed down the eastward progression of deeper moisture with this initial front similar to the earlier ECMWF with most pops holding off until Sunday night or Monday. This should be after warming aloft has won out with mostly chance rain/showers with perhaps some snow mixed in far west/northwest. Lots of uncertainty moving ahead toward midweek in whether or not a punch of dry air follows this boundary before the next northern stream wave approaches Tuesday, or does it stall with moisture returning back north. For now will dry things out on day7 per WPC and latest 12Z ECMWF with overall temps 40s west to 50s north Monday/Tuesday. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
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As of 1217 AM EST Wednesday... Degraded aviation conditions expected to continue at least through 12-14z with sub-VFR conditions the rule. These will predominantly be MVFR to IFR mainly from ceilings, but with brief intervals LIFR. Region is under weak surface ridge with winds being light/variable and areas of fog/mist at times given highly saturated conditions. Nearly all guidance indicates improvement in ceilings in the first few hours, but feel this is overdone based on upstream MVFR ceiling obs across KY/TN. While trend should be for slow improvement in ceilings, confidence in ceiling trends is low. Ceilings/visibilities should improve further toward VFR through the afternoon hours Wednesday. Winds initially light/variable but will trend northwest around 6-10 kts across the airspace after 08z before trending light northwest through the rest of the TAF period. Low to medium confidence in ceilings, visibilities and winds during the taf period. Extended aviation discussion... Clouds and possibly a few showers may return Wednesday night in advance of an approaching Arctic front that is expected to move through the region Thursday. Limited moisture may result in a few rain or western snow showers in advance of the boundary Thursday morning. However upslope conditions should support snow showers across the mountains behind the front Thursday afternoon into Friday along with a significant surge of cold air. This will lead to VFR conditions east of the Blue Ridge through much of the period beyond Thursday, but MVFR conditions may linger into Friday across the West Va sites. West to northwest winds behind the front will be strong into Friday with gusts likely topping 25-30 kts at times. Winds and any residual low level cloud cover should quickly fade by Saturday as high pressure builds overhead making for overall VFR conditions this weekend ahead of the next cold front that wont arrive until early next week.
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&& .CLIMATE... Blacksburg set a record daily precipitation for December 6th with 1.26 inches today. Record event report /WBCRERRNK/ will be sent when it becomes official at midnight. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...KK NEAR TERM...KK/PC SHORT TERM...JH LONG TERM...JH AVIATION...AL CLIMATE...

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