Area Forecast Discussion
Issued by NWS Blacksburg, VA

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895 FXUS61 KRNK 190807 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 307 AM EST Thu Jan 19 2017 .SYNOPSIS... High pressure overhead this morning shifts east to the coast tonight as a warm front lifts north from the Gulf Coast states into the southern Appalachians. The warm will swing north across Virginia and into the mid-Atlantic Friday, before stalling. Another storm system moving across the southern U.S. will impact our region Sunday into Monday. .NEAR TERM /THROUGH TONIGHT/... As oF 230 AM EST Thursday... Amplified 5h ridge over us today will give way to upper low/trough moving across the midwest tonight. Will see a period of warm advection high clouds today with increasing mid clouds starting to roll into the southwest by dusk. We will be staying warmer than normal again today with highs mainly in the mid to upper 50s. Sunshine will be in and out, and expect to see more sunshine east of the mountains. Isentropic lift increases after sunset across the mountains of NC and shift to the rest of the forecast area overnight. Models advertise more rain in the mountains with lower threat in the piedmont. Clouds will overspread the area. Will see the warm front stay southwest of us into early Friday morning. Rainfall amounts overall will be under a quarter inch with locally higher in the mountains of NC to Southeast WV. Lower dewpoints in the evening combined with increasing moisture allows for temperature drop once the rain starts to fall, but since more clouds and some steady rains, lows should stay mild for this time of year with upper 30s in the Alleghanys/Greenbrier Valley to upper 40s Mountain Empire. && .SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/... As of 230 AM EST Thursday... During the day Friday a broad area of isentropic lift progresses northeast through the region on the eastern side of a Upper Mississippi Valley low, and on the west side of an upper level shortwave ridge that will be positioned over the mid-Atlantic region. By sunrise Friday, the bulk of the precipitation will be oriented northwest to southeast across the central portions of the region, heading northeast. Anticipate most of the precipitation to have moved northeast of the region by the early to mid afternoon. Friday night into early Saturday, another 500mb shortwave ridge briefly takes up residency across the area, all while the 850mb flow remains southwest, tapping Gulf of Mexico moisture. We expect a break in the precipitation Friday evening into part of the overnight hours Friday nights. Models differ on just how quickly the next wave of precipitation enters the southern half of the region. A consensus forecast allow for a slight chance by day break Saturday across our North Carolina counties, and perhaps one tier north of Virginia counties. As Saturday progresses, a shortwave trough within the prevailing southwest flow is progged to move toward the region and cross late Saturday night and Sunday. Surface based lifted index values vary from model to model during the Saturday through Sunday period. Some have readings right around zero through the region, others are slightly negative. Given this will favor showers as compared to stratiform rain for Saturday. Will introduce isolated thunderstorms across the far southern and southeastern sections of the area Sunday afternoon. This corresponds the good agreement of guidance for slightly negative LI values in this area along with some small amount of surface based CAPE. There is also good spacial agreement with neighboring offices to the south for its inclusion into the forecast. This wave moves north of the area by early Sunday evening. While there may be a small break in the activity, it will be short lived. Precipitation on the eastern and northern flank of the parent closed upper low is expected to traverse the region Sunday night. Temperatures will continue to be very mild during this portion of the forecast, averaging some fifteen to twenty degrees above normal. && .LONG TERM /MONDAY THROUGH WEDNESDAY/... As of 315 PM EST Wednesday... Guidance remains generally consistent with the big picture details into the first part of next week with some variation in the finer details. A large vertically stacked closed low will move across the deep south and bring a strong and very moist flow of air to the region. Several spokes of energy rotating around the low will bring several surges of precipitation to the region Monday before the system starts to pull away from the area by Monday night. So while the main baroclinic zone is now expected to be much closer to the coast, the overall scenario still favors widespread precipitation with significant orographic enhancement along the Blue Ridge. Will continue to keep a close eye on how this situation evolves as the indicated QPF amounts generally in the 1 to 3 inch range by Monday night may result in some flooding. Instability to drive thunder will likely reside closer to the baroclinic zone, though with enough forcing under the cold core upper low some thunder is possible but confidence not high enough at this point to include in the forecast. Will keep ptype as all liquid though dynamic cooling under the deep upper low may generate thickness values favorable for some wintry mix, but confidence in this is low. Some wrap around precipitation will linger west of the Blue Ridge through Tuesday before we can get a brief break ahead of the next system approaching later Wednesday night. Temperatures will trend down through Tuesday as the cold core low moves over the region, though readings will still remain above normal through the first part of next week. && .AVIATION /08Z THURSDAY THROUGH MONDAY/... As of 1200 AM EST Thursday... The first of several negatively tilted upper systems will approach the forecast area from the south Thursday night. High clouds will overspread the area in advance of this system, and are already doing so. Low clouds linger across eastern WV, but the lack of a significant west wind field has resulted in scattering out of the low clouds at KBLF, while they hold in at KLWB. All indications are that these clouds will gradually dissipate from the south through the night leaving both sites KBLF. Otherwise, expect BKN-OVC high clouds throughout much of the TAF valid period at all sites. Any further sub-VFR ceilings and precipitation will be beyond the end of the TAF valid period. No issues expected with visibility through the TAF valid period. Winds diminishing and becoming light and variable throughout the CWA. The winds will veer to the southeast through the day Thursday, but speeds are expected to remain mostly 5kts or less through the TAF valid period. Medium to high confidence in ceilings throughout the TAF valid period. High confidence in visibilities throughout the TAF valid period. Medium confidence in wind direction, high confidence in wind speed throughout the TAF valid period. Extended Aviation Discussion... Conditions will begin to deteriorate Thursday night from southwest to the northeast as a wave of low pressure track across the Tennessee Valley. Expect periods of rain Thursday night through Friday afternoon, then again Sunday into Monday. During this time expect sub-VFR cigs and at times vsbys. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...WP NEAR TERM...WP SHORT TERM...DS LONG TERM...MBS AVIATION...RAB/RCS

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