Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 220016 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 716 PM EST Tue Feb 21 2017 .SYNOPSIS... An upper level low to our south along with a weakening surface cold front will serve as a focus for clouds and showers tonight into Wednesday. A warm front returns northward from the Carolinas across the region on Thursday, focusing additional opportunities for rain showers. Weak high pressure then builds in for Friday, with a strong cold front expected to move across the forecast area early in the weekend. Temperatures through the rest of the workweek remain above normal. && .NEAR TERM /THROUGH WEDNESDAY/...
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As of 321 PM EST Tuesday...Much of the central Appalachians and VA/NC Piedmont region remain under the influence of ridging from a broad surface anticyclone centered over coastal New England. Residual cold-air damming/easterly flow is also holding tough in northern and central VA Piedmont areas. A light southeast moisture return is in place across the southern Blue Ridge/NC mountains and foothills areas. Sunshine has been filtered from high clouds spiraling north- northeastward in advance of an upper low centered over western TN; moisture from which streams northeastward into the Ohio Valley. For Tonight: Expect clouds to lower and thicken through midnight from west to east as deeper plume of moisture shifts east- northeastward. Chances for precipitation also increase in kind as well, though it will be fighting lingering lower-tropospheric dryness as well. That being said, recent indication from most of the global and higher-resolution output suggests that as the mid-level low builds southeastward into the Gulf later tonight, precipitation becomes focused along a mid-level deformation axis that slowly pivots southeastward from southeast WV/southern Shenandoah Vly into our central CWA after midnight and into the early morning hrs. With a shallow inversion developing later tonight and an increase in low- level moisture along with light to calm winds, periods of patchy fog would be possible especially in the eastern Piedmont. Rainfall amounts tonight range from a couple hundreths east to up to two- tenths north and west. Best chance of rainfall looks to be after midnight. I sided toward the warmer guidance tonight for temperatures, which are generally in the mid to upper 40s areawide. For Wednesday: Cold front more or less washes out overnight, with aforementioned rain band building southeastward into NC during the day on Wednesday. However, as in-situ CAD signature is maintained along with the shallow inversion that appears to be very tough to mix out per forecast BUFKIT soundings, I`m not hopeful for much improvement. Since mid-level moisture profiles dry out due to increasing/zonal flow aloft, periods of drizzle or mist/fog and low clouds appear likely to hang tough into the afternoon. Thus, with a wetter/cloudier outlook for Wednesday, I`ve biased temperatures toward a colder end of guidance (actually, a few degrees colder than 12z MAV/MET MOS). These highs are actually pretty uniform, mainly in the upper 50s to low 60s, a couple degrees cooler than today despite milder 850 mb temperatures. Any locations that were to mix out would stand to be several degrees warmer than indicated here; but I`m not optimistic that outcome will happen. Winds Wednesday are light and variable.
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&& .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/... As of 321 PM EST Tuesday... During the Wednesday night into Thursday time period, the axis of surface high pressure will shift east to off the Atlantic coast. The general prevailing flow across much of the region will be south to southwest on the west side of this ridge axis. Low level moisture will progress into the area, and help maintain clouds and patchy light rain in areas primarily along the crest of the Blue Ridge. Also, a weak upper level disturbance will progress eastward along the Ohio Valley, and allow for precipitation more in the form of isolated to scattered showers across the far northwestern portion of the region. The coverage of these showers will shift eastward to near the crest of the Blue Ridge by thursday afternoon, all while the extent of the stratiform precipitation decreases and becomes confined to the far eastern part of the forecast area. Also on Thursday afternoon, guidance is suggesting surface based instability may be large enough to support some isolated thunderstorms across parts of southeast West Virginia, south into the Northern Mountains of North Carolina Late Thursday afternoon through Thursday night, a warm front is expected to develop across the area and head north. Expect some patchy precipitation associated with the front early in the evening. By early Friday morning, we expect only some limited light rain near the crest of the Blue Ridge as southerly flow yield some light upslope precipitation in this area. Friday night, a strong cold front will approach the area from the west. Very strong southerly winds are progged to increase in advance of this cold front, helping to maintain very mild conditions across the area. Showers will be on the increase through the night, especially across western sections of the region. Instability may increase enough for some isolated thunderstorms across the far southwest section of the forecast area. Temperatures during this portion of the forecast will average around twenty degrees above normal. && .LONG TERM /SATURDAY THROUGH TUESDAY/... As of 321 PM EST Tuesday... A strong cold front will cross the area on Saturday. Anticipate a distinct line or area of showers to cross the region during the course of the day, with coverage greatest across the northern third of the region. Surface based instability may be great enough in the afternoon for some isolated thunderstorms generally along and east of a line from Danbury, NC to Bedford, VA. Colder air will move into the area Saturday night. Gusty northwest flow behind the cold front will help maintain isolated showers across parts of southeast West Virginia that will transition to isolated snow showers by late Saturday night. For Sunday, our pattern transition to zonal flow aloft with surface high pressure providing dry weather to the region. Sunday night into Monday, a weak disturbance within this flow is expected to bring isolated to scattered showers to the far western parts of the area. Monday night into Tuesday, southwest flow increases across the area in advance of a developing upper level trough. Look for a warm front to develop over the region and move northward. Anticipate cloud cover and patchy light rain to develop across the region, and be concentrated the greatest across the northern sections of the area, nearest the warm front. Temperatures will still be some ten to twenty degrees above normal on Saturday, but trend to near normal by Sunday behind the cold front. Temperatures will slowly moderate Monday into Tuesday to reading about ten degrees above normal. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
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As of 715 PM EST Tuesday... High confidence in TAFs trending to IFR through the first part of the valid period and remaining as such through the remainder of the period. A wedge of high pressure will linger over the region through tomorrow with weak isentropic lift and some short wave energy running over the top of the wedge. This will lead to lowering of clouds with showers gradually spreading across TAF sites from west to east after Midnight. Lowest IFR cigs will set in by daybreak but may trend upward by the end of the period. Best chances for precipitation will be through mid morning but low visibilities in drizzle and fog will linger into the afternoon. Winds will be light through the period. Extended Aviation Discussion... Significant improvement does not appear likely until Wednesday evening. As a warm front returns northward on Thursday, an eventual redevelopment of light showers is possible with likely MVFR conditions Thursday evening through Friday. Area will slide in between weak low pressure off the southeast coast Friday and the next stronger upstream cold front that looks to arrive by midday Saturday. This should allow for some improvement in cigs/vsbys within the warm sector Friday as the low level jet increases. Expect a mix of MVFR and low end VFR ceilings and mainly VFR visibilities during the day with surface wind gusts of 20 to 30 kts possible across the higher terrain. Band of showers including a period of sub-VFR to arrive late Friday night into early Saturday with the front, followed by drier weather and increasing northwest winds by afternoon behind the boundary.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...AL NEAR TERM...AL SHORT TERM...DS LONG TERM...DS AVIATION...MBS/AL

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