Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 210527 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1227 AM EST Tue Nov 21 2017 .SYNOPSIS... High pressure over the Carolinas will move east and off the southeast coast tonight. A cold front will move through the eastern United States Tuesday night, followed by high pressure on Wednesday and Thursday. Another cold front will cross the region this weekend bringing the next round of colder air. && .NEAR TERM /THROUGH TODAY/... As of 630 PM EST Monday... High pressure along the North Carolina coast tonight will move east into Tuesday. Made some minor adjustments to temperature this evening into tonight with latest surface obs, trends and GLAMP. Allowed for some thin cirrus clouds tonight with warm advection. With winds decoupling, expected a good radiational cooling night. Low temperatures tonight will range from the lower 20s in the mountains to the lower 30s in the piedmont. As of 200 PM EST Monday... Large high pressure area centered over the southern Appalachians is the main weather feature affecting weather across the Piedmont and into the Appalachians this afternoon. Temperatures have rebounded nicely back into the 40s to mid-50s under plentiful sunshine. A split flow regime was evolving aloft, with a southern stream trough over the southern Plains spreading an area of high clouds across the lower Mississippi Valley in a lower-tropospheric warm advection regime. Clear skies will initially predominate the region for the rest of the afternoon and into a good part of tonight. This should lead to rather strong radiational cooling areawide with a decoupled boundary layer leading to light surface winds. Radiational cooling should be enhanced in areas where light snowpack exists per satellite imagery across western Greenbrier County. Moderately strong surge of warm advection begins after midnight on a southwesterly 850 mb jet from 30-40 kts per 12z NAM-3km output, greatest south. Will also see an increase in high clouds across the southern third of the CWA. Given the low-level jet on the ridges and the aforementioned radiational effects, this should lead to low temperatures being the warmest at elevation with values in the mid 30s along the Blue Ridge and western side of the Appalachians, with lows in the lower valleys in the upper 20s to near freezing. For Tuesday, look for variable high cloudiness to exist early in the day. As the day progresses, weak shortwave energy rounding the base of the southern stream trough in diffluent flow should contribute to an increase in cloudiness mainly from the Blue Ridge foothills in NC and advancing into the Piedmont of NC and Southside VA. This appears to be more probable in the afternoon hours. Guidance has generally shifted the chances for (very) light rain into the Tuesday evening period, but left open the door for rain starting early as the afternoon with 15-20% probabilities along or south of Route 52. Rest of the region should be dry. Though temperatures should climb following typical diurnal trends pretty much everywhere, I`ve started to slow temperature climb by afternoon in areas under thickest cloud cover/chances for rain. A little less confident on temperature trends in these southern areas depending on timing thickest cloud cover. I may still not be low enough and the cooler 12z MET values (e.g. 51 at Winston-Salem, 54 at Mt Airy) may prove more correct if thicker clouds develop earlier in the day. Official forecast calls for highs in the 50s, in the lower 50s further south with warmer values in this range to the north and west. && .SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/... As of 200 PM EST Tuesday... High pressure slides offshore Tuesday night in advance of both northern/southern stream shortwaves within the lingering split flow regime. These features still remain out of phase with most solutions showing only a few light showers across the south/east with the surface low offshore, as well as isolated rain/snow showers far northwest with the cold front. Thus will keep in low end pops mainly Tuesday night and dry elsewhere for now. High pressure following these systems to bring drier weather including a period of weak cool advection into Wednesday night and Thursday, but with less wind than previously thought given a weaker post frontal jet aloft. Otherwise after more clouds Tuesday night through midday Wednesday, should see skies clear Wednesday into Thanksgiving before more clouds shift north ahead of the next southeast offshore wave Thursday night. Low temperatures mainly Tuesday evening before rising along the ridges overnight per warm advection/mixing and clouds. This supports a range from low/mid 30s valleys and east to 40s at elevation. Cool pool at 850 mb looks to only bleed into the west Wednesday and across the area on Thursday. Latest guidance even giving around 60 out east Wednesday afternoon ahead of the lagging cool advection with mainly 50s east so trended warmer with highs. Overall thickness in line with cooler highs mostly in the 40s on Thursday with lows 20s to around 30 overnight. && .LONG TERM /FRIDAY THROUGH MONDAY/... As of 130 PM EST Monday... Mean upper troffiness to prevail through the period with reinforcing energy arriving late in the weekend that looks to carve out an even deeper 500 mb cold pool into Monday. Otherwise should see mainly dry weather under weak high pressure and slightly below seasonal temps until a strong cold front arrives later Saturday. This front will again be followed by colder temperatures Sunday with cooler air lingering into early next week under chilly high pressure. Appears a few rain showers will be possible northwest ahead of the front Saturday afternoon, followed by western snow showers early Sunday, but little more than continued very low pops for now. Highs mostly 50s Friday/Saturday, cooling to mainly 40s Sunday-Monday, with perhaps 30s in spots across the mountains behind the front similar to this past Sunday. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/...
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As of 1220 am EST Tuesday... Broad surface high pressure will slide eastward tonight into Tuesday. Scattered cirrus, especially southern areas tonight, will support a decoupled boundary layer and light or calm surface winds. The air mass is too dry to support any fog overnight or early Tuesday morning. Expect more variable cloudiness into Tuesday, with the greatest cloudiness to the south and east from low-level warm advection. After 18z Tuesday, MVFR ceilings in the 020-030 range will likely begin to evolve from TNB northeast toward ROA, spreading across the remainder of the CWA west of the Blue Ridge after 00Z. Southwest winds increase Tuesday to around 6-8 kts and may gust up to 20 kts by late afternoon across southeast WV and southwest VA. Ceilings will continue to lower along Tuesday night in advance of a new cold front approaching from the west, with upslope clouds increasing in its wake west of the Blue Ridge. Medium to high confidence in ceilings through the TAF valid period. High confidence in VFR visibilities through the TAF valid period. Medium to high confidence in wind speed and direction through the TAF valid period. Extended Discussion... Another mainly dry cold front will move through Tuesday night into Wednesday morning. A few rain showers will be possible south and east of the Blue Ridge as a southern stream system tracks across the southeast states. High pressure then establishes itself for the Wednesday through Friday, including Thanksgiving, with an expectation of good flying conditions for Thanksgiving travel in the RNK airspace. Next chance for sub-VFR conditions is with a cold front on Saturday. Dry weather is anticipated for Sunday.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...AMS/JH NEAR TERM...AL/MBS SHORT TERM...JH LONG TERM...JH AVIATION...AL/KK/RAB

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