Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 200231 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 931 PM EST Fri Jan 19 2018 .SYNOPSIS... High pressure will provide for mainly dry and mild weather through the weekend. A cold front and its associated precipitation will cross the region Monday into early Tuesday. High pressure quickly returns to the area by Wednesday, along with a return to drier weather. && .NEAR TERM /THROUGH SATURDAY/...
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As of 915 PM EST Friday... Main concern again with forecast low temps given ongoing wide range between ridgetops and valleys with some spots still in the 40s and others in the 20s. Since winds aloft look to increase again late tonight, appears this trend to persist, so bumped up lows a little more at elevation and reduced in the valleys including outlying spots out east. Evening soundings show a very arid airmass still over the region which should cause the low deck now approaching from the TN valley to initially fade before perhaps things moisten enough for some clouds to make it into the far west around daybreak. Thus kept late night clouds in along the western perimeter similar to the previous update. Models again show the westerly 85h jet increasing to around 40 kts espcly over the north/west after midnight but appears much of this only to clip the higher ridges until better mixing develops on Saturday. Previous update as of 654 PM EST Friday... Current satellite imagery depicts clear skies across the Blacksburg forecast area with high pressure still in control. RH profile resembling desert-like conditions. Even as of 600 PM, RH values were still ranging from the 15 to 35 percent range. Dewpoints will only be slow to recover, with a more substantial increase expected Saturday. Expect gradual recovery in RH as temperatures plummet in good radiational cooling conditions as boundary layer decouples. Less decoupling anticipated along the Blue Ridge Mountains, and in a strong radiational regime at night these areas are often notably warmer than lower-lying valleys. More noticeable changes to the forecast were then made to sky cover west of the Blue Ridge into the central Appalachians and extreme eastern Tennessee Valley for late overnight into Saturday. METARs and GOES East satellite RGBs confirm a well defined stratus deck near or just west of Nashville, TN in regime of west- southwest warm advection. 18z/19 NAM and RAP- based BUFKIT profiles depict saturated RH below 875 mb for the areas where sky cover was increased, so they may be better depicting this stratus layer perhaps better than the GFS is. Extrapolation of the western TN stratus layer brings it into Smyth and Tazewell County around 09z, which is about when I start to increase clouds. Opted toward partly/mostly cloudy conditions after 09z in these areas, while maintaining clear skies for the foothills/Piedmont. Previous discussion issued at 200 PM follows... High pressure was centered over southern Alabama. Its associated ridge axis extended north into the Upper Ohio Valley. Plenty of sunshine has helped to melt snow today, with some areas in the west having little or no snow remaining on grassy surfaces. After coordination with GSP/RAH, there will be no Winter Weather Advisory for black ice tonight across our North Carolina Counties due to limited expected coverage. In its place will be a Special Weather Statement that will highlight isolated coverage from roughly Wilkes County and points eastward. This statement will also include most of our Virginia counties east of the crest of the Blue Ridge. High pressure at the surface will continue to build into the region. Concurrently, zonal flow aloft will increase with 850 mb winds expected to be around 45 kts by daybreak Saturday. The result will be decouple valleys and the Piedmont overnight with ridge tops staying mixed, thus milder. On Saturday, these stronger winds aloft will start mixing the surface, and provide for a gusty day. Temperatures will trend milder through tomorrow as heights build and 850mb temps increase. Anticipate lows tonight in the the mid 20s for much of the region. The exception will be the higher ridge tops where lows closer to 30 degrees are forecast. Also, the area of Southside Virginia and neighboring sections of north central North Carolina will be closer to 20 degrees thanks to the greater snow pack there. On Saturday, anticipate high temperatures milder than those realized today. The upper 40s to the lower 50s are expected across the mountains with mid 50s to around 60 forecast across the Piedmont.
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&& .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/... As of 315 PM EST Friday... Keeping close to previous forecast and it appears warm frontal precip with weak isentropic lift may move across the mountains of WV/far SW VA Sat night-early Sunday mainly as light rain/possibly drizzle. Cannot rule out some ice pellets north of Lewisburg WV Sat night. As warm front heads further north we will see southwest flow increase but with a dry period Sunday night-early Monday before cold frontal showers move in from the west, with a consensus on most of this occurring Monday night. Appears to be a good rain with one quarter to one half inch expected. Winds along and ahead of this front will be strong in the low levels but instability appear weak. Still could see some gusty showers, especially in the mountains Monday afternoon/evening. Temps modifying with lows in the lower to mid 30s Sat night, then upper 30s Sunday night to upper 30s to lower 40s Monday night. Highs Sunday will be mild with 50s west, to lower 60s east, similar again Monday. && .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 200 PM EDT Friday... Timing of front per models showing it moving east of the mountains Tuesday morning and into the piedmont by midday. Will see falling temperatures mainly in the mountains with any rain showers turning to snow showers in the higher elevations. However, overall airmass behind this front is not that cold as its Pacific in origin, so not arctic blasts. Beyond this temperature start to rebound as we dry out with surface high building in from the TN Valley midweek, and off the VA coast by Friday. && .AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
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As of 654 PM EST Friday... VFR SKC conditions projected for most of the TAFs through 09z, as high pressure continues to govern the region. Only significant aviation operational weather impact in this period will be from low-level wind shear w/ westerly low-level jet of 35-40 kts as winds decouple. This could lead to areas of turbulence especially along or west of the western mountains/Blue Ridge. After 09z, ceiling forecast becomes less certain along or west of the Blue Ridge. Current stratus layer near Nashville is making steady progress into the western Cumberland Plateau in TN. Combination of extrapolation and recent 18z forecast profile of RH depicts this stratus layer into at least the eastern Tennessee Valley by 09z, perhaps advancing toward Bluefield and Blacksburg by 12z. Will show ceilings lowering to at least a SCT deck between 09-12z for these two TAFs, then trend closer to BKN/OVC VFR/MVFR (025-040 bases). Confidence in ceilings lower than VFR is low to medium for these two TAFs, but given recent trends expect there to be at least VFR stratus around. Would expect VFR SKC conditions elsewhere. Though west winds should increase to 10-12 kts tomorrow, there may still be pockets of low-level wind shear at Bluefield and Blacksburg with low-level jet increasing to 40-45 kts. Extended Discussion... Generally VFR for the TAFs through Sunday, with exception being lingering SCT-BKN MVFR stratus Saturday night west of the Blue Ridge. Sub-VFR conditions will start to return to the area Sunday night into and through Tuesday night as a cold front and its associated precipitation moves through the region. Very gusty northwest winds return to the area Tuesday night into Wednesday on the backside of the departing system. Lingering sub-VFR conditions possible across SE WV thanks to strong upslope flow and residual low level moisture.
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&& .EQUIPMENT... As of 325 PM EST Friday... NOAA Weather Radio, WXL60 (Roanoke Transmitter) which broadcasts at 162.475 MHz remains off the air. The phone company reported that the circuit line had been cut and will take until Monday January 22nd to fix it. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...DS NEAR TERM...AL/DS/JH SHORT TERM...WP LONG TERM...DS/WP AVIATION...DS EQUIPMENT...WP

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