Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 240202 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1002 PM EDT Thu Mar 23 2017 .SYNOPSIS... High pressure will slide off the coast tonight into Friday. A warmer southerly flow will develop Friday into the weekend ahead of a slow moving cold front that will approach the region Sunday. A series of upper-level low pressure areas will track across the central and southern U.S. through next week keeping an unsettled weather pattern in place. && .NEAR TERM /THROUGH FRIDAY/...
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As of 1002 PM EDT Thursday... Update to lower forecast low temps across the western valleys and out east given lingering very dry air per evening soundings and latest obs. This in conjunction with possible development of a weak bubble of high pressure over the east given ridging aloft, likely to allow good radiational cooling again tonight despite 850 mb warming as well as slowly rising dewpoints. Also band of broken mid/high clouds just west of the mountains likely to fade initially upon encountering the very dry air aloft so appears will stay clear longer espcly eastern half. Again expect some 20s in the western valleys and perhaps outlying areas across the east with overall low/mid 30s elsewhere, except around 40 across the higher ridges where better warm advection mixing will occur. Previous update as of 705 PM EDT Thursday... Forecast looks to be in pretty good shape through the next few hours, as clear skies for the first part of the evening allowing for temperatures to plummet quickly after sunset. I did make some changes for the late evening into the overnight period. Leading edge of warm front and a broken to at times overcast mid-level cloud shield extends roughly NNW- SSE from northern Illinois southeastward to the eastern Tennessee Valley. This cloud shield should advance eastward into our western counties around midnight and continue lifting in a northeastward fashion across the New River/Roanoke Valleys into the southern Shenandoah counties overnight, as reflected in past couple RAP model 700-300 mb RH profiles. Though Virginia Southside towns into the NC foothills and Piedmont probably stand to radiate fully the whole night...given that the clouds may be thick enough to impede or stop radiational cooling entirely elsewhere, I`ve utilized some of the warmer temperature guidance after midnight to reflect a slower cooling in cloudy areas. Dewpoints were also raised upward some overnight, accompanying the increase in clouds. In the Grayson Highlands and the NC High Country dewpoints are already on the rise from low afternoon values are now into the low to mid 20s. Given the trend in cloud cover, lows in the western counties probably reach lows in the mid 30s earlier with overnight lows occurring closer to sunrise in the Piedmont and Southside areas. Previous near-term discussion issued at 214 PM follows... Dome of high pressure along the east coast is going move offshore tonight into Friday allowing for the area to move into warm advection. Expect temperatures to drop again tonight to the upper 20s to lower 30s in the east and mountain valleys, except mid to upper 30s across the higher terrain in the west with southerly winds picking up more. Late tonight through Friday, models are showing increasing moisture in the mid and upper levels tracking from KY/TN into the mid- Atlantic with some light precip being generated north of our forecast area. Anticipate some increase in clouds late tonight into Friday mainly over the west and north, but still looking at more sun than clouds Friday as temperature warm into the 60s, except some 50s along the Blue Ridge.
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&& .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/... As of 345 PM EDT Thursday... A pattern transition will be underway this weekend as predominate northwest flow aloft comes to an end, replaced by unsettled split flow with series of southern stream storm systems of Pacific origin to parade across the CONUS. First in this series of storm systems will arrive Sunday. Until its arrival, the first half of the weekend will be dry, Saturday certainly a great day to be outdoors with temperatures in the 60s/70s. Late Saturday, moisture will be on the increase west of the Appalachians per the approach of an upper low to lifting out of the Southern Plains. Showers/thunderstorms associated with this system will be advancing east across the Tennessee Valley into far southwest VA or southern WV Saturday night. The upper low will then take a more northward track into the Ohio Valley and weaken as it encounters the upper ridge along the eastern seaboard. This will result in a weakening of the thunderstorm activity as it crosses the mountains, but still sufficient forcing, instability, to promote high probability of showers areawide for Sunday. Temperatures Sunday will be just a tad lower thanks to cloud cover and precipitation, but with increasing dewpoints, overnight lows will be warmer. With regard to QPF, models are in fairly good agreement, advertising 1/2 to 3/4 inch of rain along and west of the Blue Ridge Sunday, and 1/4 to 1/2 inch east of the Blue Ridge. Severe weather is not expected for our CWA for this first system. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 400 PM EDT Thursday... Next in a series of upper-level low pressure areas will move from the Southern Plains into the Tennessee Valley/Central Appalachians late Monday into Tuesday. While this system will again be weakening as it moves toward the western Atlantic upper ridge, it will have somewhat better dynamics and instability to work with than the Sunday system. Therefore, a chance of thunderstorms anticipated areawide for Tuesday afternoon. This still does not look like a widespread severe weather maker for our CWA, but slightly better potential for at least some stronger storms with small hail per warmer temperatures, higher surface dewpoints and slightly better instability compared to the Sunday system. Rainfall amounts again appear to be in the 1/4 to 3/4 inch range over all with this event. A quieter midweek period appears in order as another upper- level system deepens but slows as it moves into Texas and an upper ridge amplifies across the eastern U.S. A weak area of high pressure from the Great Lakes filters into the area for midweek. By Friday, this aforementioned system will move into the Mid-Atlantic region as yet another upper-level low pressure area moves from the southwest U.S. into Texas. Temperatures will remain mild through the upcoming week with no significant intrusions of Canadian air. A slight cooling will be noted midweek, but temperatures will favor the warm side of normal with highs in the 60s/70s and lows mainly in the 40s to lower 50s. && .AVIATION /02Z FRIDAY THROUGH TUESDAY/... As of 709 PM EDT Thursday... VFR through the period. Initial SKC conditions give way to a BKN mid-level altostratus deck after 06z and then lifts into northern Virginia by mid-morning. Should see VFR FEW-SCT cumulus in the warm sector the rest of the day. Winds light southeast tonight, then veer and increase to south 5-10 kts, strongest at Lynchburg and Danville. Extended Aviation Discussion... Good flying weather is expected to linger into Friday night before moisture starts to increase over the weekend ahead of an upper- level low pressure area moving northeast from the Southern Plains. Precipitation is not expected until Sunday when sub- VFR conditions become more of a possibility. Otherwise looking at overall VFR to start the weekend with most lower cigs remaining west of the area until later Sunday at this point. Periods of unsettled weather will continue into the first half of next week as a series of upper-level lows track from west to east across the U.S. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...KK/WP NEAR TERM...AL/JH/WP SHORT TERM...PM LONG TERM...PM/RAB AVIATION...AL/RAB/WP

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