Area Forecast Discussion
Issued by NWS Blacksburg, VA

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881 FXUS61 KRNK 150908 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 408 AM EST Sun Dec 15 2019 .SYNOPSIS... High pressure will briefly build into the area today. A low pressure system will impact the area Monday through Tuesday. High pressure returns Wednesday and Thursday. The high center will slide off into the Atlantic ocean Friday, as low pressure approaches from the Mid- Mississippi Valley. && .NEAR TERM /THROUGH TONIGHT/... As of 619 PM EST Saturday... Upslope precipitation and clouds will wither away this morning as moisture moves north of I-64. Winds may also be a bit breezy this morning before a surface high pressure builds into the region under zonal flow aloft this afternoon. Temperatures this afternoon will warm into the 40s across the mountains to the 50s east of the Blue Ridge. Today`s temperatures will be 3F-6F warmer than normal. A warm front will stall across the southern Ohio Valley tonight. Short waves tracking along this boundary may bring a brief period of snow to southeastern West Virginia around midnight, changing to rain through the morning hours Monday. There is a small chance that surface temperatures will dip below freezing while warm air enters aloft across Greenbrier county and the Alleghany Highlands tonight. This may produce a period of light freezing rain between midnight and sunrise. Snow (around an inch) and ice (glazing) accumulations will remain light to not warrant any headlines. For areas south to HWY 460 a cold rain is likely. South of 460 into northwest North Carolina should remain dry until Monday. Low temperatures (in the 30s) across the mountains should occur by midnight, then remain steady or slowly rise overnight. With more time under clear skies and light winds tonight east of the Blue Ridge, lows will occur at their normal time, just before sunrise. && .SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/... As of 315 AM EST Sunday... Whatever wintry precipitation occurs across the Interstate 64 corridor from early Monday morning should transition over to rain before noon as temperatures increase above freezing. The entire region should be under the influence of the warm sector from the low pressure system by Monday afternoon and Monday night. The bulk of the moisture should push eastward during Monday night into Tuesday morning ahead of an approaching cold front. The increased confidence of rain occurring during this time period has been denoted in the higher probabilities toward categorical status. Although model guidance appears good in agreement with one another through Monday night, that agreement begins to waver by Tuesday as the latest GFS pushes the cold front toward the coast several hours faster than the ECMWF and Canadian models. A middle of the road approach was utilized for Tuesday by delaying the departure of the precipitation a little from the previous forecast. Temperatures will follow a non-diurnal curve as they fall for most of the day behind the frontal passage west of the Blue Ridge, while the Piedmont may remain mild until the afternoon when the cold front arrives. As temperatures fall below freezing in the mountains courtesy of cold air advection from increasing northwest winds, expect the rain to transition to snow showers. Only minor snowfall accumulations are anticipated for western Greenbrier County for Tuesday afternoon into Tuesday night. Wind gusts were also bumped upward during the same timeframe for the entire region, and it may be possible for the higher ridgetops to approach advisory criteria. The snow showers, cold air advection, and gusty northwest winds should begin to subside by early Wednesday morning as high pressure begins to build eastward from the Plains. 850 mb temperatures should dip toward -10 C along the Interstate 64 corridor as the upper level trough passes to the north during Wednesday. The cooler side of guidance was favored for high temperatures on Wednesday to accommodate for the passing upper level trough and the lingering cold air advection from northwest flow. The center of high pressure should reach the Appalachian Mountains by Wednesday night, which will lend to good radiational cooling. && .LONG TERM /THURSDAY THROUGH SATURDAY/... As of 350 PM EST Saturday... By Wednesday, enough drier air is expected to have arrived to both end the light snow showers and also clear out the remaining cloud cover, though winds will remain very gusty into Wednesday evening. A Wind Advisory for some western counties will likely need to be considered with later forecast packages for this time frame. High pressure will head eastward through the southeast U.S. into Thursday, with our region experiencing no precipitation and little to no cloud cover. Temperatures will drop to well below normal levels with widespread lows in the teens and 20s during the later half of the week. Once the center of the high reaches the GA/SC coast on Friday and low pressure moves east into the mid- Mississippi Valley, look for a return of southwest winds and both increasing temperature and moisture advection. At this time, no precipitation is forecast for Friday. However, cloud cover is expected to be on the increase. The weekend is very questionable weatherwise and no specifics can be addressed yet at this point in time. The GFS advertises potential for a snow storm by the weekend while the ECMWF insists that such a weather system will remain far to the south with little to no precipitation this far north. Have left the weekend with 15% pops for now and just a rain/snow mix. Wednesday through Friday, temperatures are expected to average five degrees below normal. Confidence in this portion of the forecast is moderate to high. && .AVIATION /09Z SUNDAY THROUGH THURSDAY/... As of 1155 PM EST Saturday... VFR conditions will prevail in the east of the Blue Ridge with downsloping winds through Sunday. MVFR conditions will continue overnight and into Sunday morning associated with snow showers. Isolated sub-VFR vsbys will be possible across the highest terrain. Winds will continue to be gusty across the mountains through Sunday early afternoon before diminishing. Gusts of 30kts will be possible at the higher elevation with 15 to 25kt gusts more probably in the mountain valleys. Piedmont regions will have limited gusts with most under 15 to 20kts Confidence in the above aviation forecast is moderate. Extended Aviation Discussion... VFR conditions and decreasing winds are expected Sunday night. Monday through Tuesday our next weather system will cross the area bringing a return to sub-VFR and gusty conditions. A return to VFR is expected Wednesday and Thursday but with winds remaining gusty. Confidence in the above aviation forecast is moderate to high. The biggest question is the timing, and for some locations precipitation type, with Monday/Tuesday system. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...RCS NEAR TERM...RCS SHORT TERM...PW LONG TERM...RAB AVIATION...PM

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