Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 131203 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 703 AM EST Fri Jan 13 2017 .SYNOPSIS... A cold front will sag southward across the region today, then stall across northern North Carolina Saturday before returning north as a warm front late Saturday night. This front will then oscillate north and south across the region into early next week keeping an unsettled and wet weather pattern in place. By the middle of next week, a stronger frontal system will finally approach from the west and move the pesky front out of the area. && .NEAR TERM /THROUGH TONIGHT/... As of 430 AM EST Friday... Tricky forecast this period as a 1045mb surface high moves east from the Great Lakes into New England pushing a backdoor front southward into our region before stalling across northern NC as a strong upper ridge holds across the southeast states and prevents further southward movement. The front was drifting southward through the region this morning and at 4 AM was near a KBLF to KDCA line. Light rain was noted across western parts of the CWA. This precipitation will tend to refocus further southwest into eastern TN through the daylight hours. Temperatures were very mild this morning ahead of the front with many areas still in the lower to mid 60s. With the exception of the Piedmont, high temperatures today will generally be this morning. Potential for temperature forecast busts today are fairly high as it was a struggle to forecast max temps only a few degrees higher than current temperatures. However, with persistent cold advection, feel temperatures will remain steady to slowly fall as the day progresses. Greater amounts of sunshine than currently expected could throw that off, but given a persistent stream of mid/high clouds from the west, sunshine should be limited. Again, the exception will be areas south of the front, NC and the VA Piedmont, where cooling will hold off until afternoon. Given the synoptic setup, the cold air will be very shallow, confined mainly to the surface to 925mb layer, with temps at 850mb remaining above freezing. Meanwhile, a series of disturbances emanating from an upper low in the southwest U.S. will track along the baroclinic zone parked over our area. This will generate periods of light precipitation that will spread back into the region overnight. Temperatures across the I-64 corridor area and as far south as Craig and Monroe will dip just below freezing after 4 AM and hold near there until Saturday afternoon as a result of wet bulbing and evaporative cooling. Given the very shallow nature of the cold air, precipitation will primarily fall as freezing rain in these areas. There may be a brief period of sleet early Saturday as the depth of the cold air mass approaches 2000 ft. thick but the predominate p-type will be freezing rain. Given the well above normal temperatures the past couple of days, current thinking is that accumulations will be confined mainly to elevated objects such as trees and power lines. QPF with the overnight/Saturday event should only be around 1/10 inch or less, yielding 1/10 inch or less ice accumulation. In consideration of all of this, have issued a Freezing Rain Advisory for areas generally along and north of a Union-New Castle-Pleasant View line from 4 am to 4 pm Saturday. For now, have left western Greenbrier out of the advisory given the difficulty the cold air wedge should have pushing west of the Alleghany front. Included Botetourt and Amherst counties mainly for scattered higher elevations in the northern and western parts of those counties. Later shifts may need to evaluate the need to included Western Greenbrier county as well as any other further southward areas. Have leaned heavily toward the NAM guidance for temperatures this period. The GFS is quite warm and would suggest no ice keeping most temperatures above freezing. The ECMWF is a good compromise between the two confining freezing temperatures early Saturday mainly to Rockbridge, Bath, and eastern Greenbrier counties. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... As OF 430 AM EST Friday... Quasi-stationary front will be over the area this weekend promoting abundant cloud cover and threat for some light precipitation. Focus early Saturday will be the low level cold wedge which will drive boundary layer temperature into the 30s on the east side of the Appalachians, with near freezing temperatures as far south as the higher ridges surrounding the Roanoke Valley. For a 6 to 8 hour period Saturday morning, expecting the Blue Ridge Parkway northeast of Roanoke and the Highlands along the VA/WV border (Craig and Monroe counties and points NE) to drop below freezing. This will promote a period of freezing rain or freezing drizzle with impacts mainly to elevated surfaces. Elsewhere expecting just a cold rain and/or drizzle, although amounts are forecast to be light (less than a tenth of an inch). Greatest isentropic lift is forecast to occur north of Interstate 64, so rain amounts of a tenth to a quarter inch are possible across the far northern CWA and areas to the north, but lift for precipitation production wanes quickly as you approach the NC/VA border with little or no rain expected across the Carolinas and southern Appalachians. Temperatures will be the warmest across the far western CWA (west of the Appalachian Divide) Saturday where readings may test 50 degrees. Within the wedge, temperatures will struggle to get much above 40. Wavy surface front will be over the area Saturday night through Sunday night, with cooler temperatures prevailing on the east side of the Appalachian Divide vs. warmer air over the Tennessee Valley again Sunday. Sunday morning is forecast to be a few degrees warmer overall compared to Saturday, so no freezing rain issues expected Sunday. Some of the models are hinting that slightly cooler air will drift back into the area Sunday night as the front gets a little nudge to the south. If this turns out to be the case, then some of the higher elevations along and north of I-64 could see some freezing rain/drizzle Sunday night. Again it would be low QPF and mainly on elevated surfaces. && .LONG TERM /MONDAY THROUGH THURSDAY/... As OF 220 PM EST Thursday... Wavy front across the area Monday morning lifts north into New York Tuesday as strong upper low moving across the central U.S. amplifies ridge downstream. Will see less threat of showers Monday but still looks cloudier, though some sunshine should peek out. Warm air will stick around into midweek with models slowing the front moving into the CWA until late Thursday into Friday. Decided to keep pops low Tuesday with mainly dry in the foothills/piedmont then chance pops start Wednesday with better threat Thursday. Highs running about 10- 20 degrees above normal Tue-Thu. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/...
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As of 645 AM EST Friday... Generally deterioriating to poor aviation conditions expected through the TAF valid period as a backdoor front sags southward through the region, then stalls just south of the NC/VA border, returning northward slowly Sat-Sun. The first wave of light rain and associated MVFR-IFR cigs traversing southeast WV at this hour. This precipitation will sag southwest into eastern TN/far southwest VA by afternoon. The next upper disturbance and stalled front will return rain to the region later this evening and overnight. Cigs will remain/trend toward IFR-LIFR in the west and become generally MVFR in the east as this area of rain spreads east overnight. As cold air spreads southward from the northeast overnight, a brief period of freezing rain will be possible at KLWB late tonight/Saturday morning. Visibilities will be mostly MVFR in areas of rain this morning and again overnight, but VFR otherwise. Winds generally WNW-NW 5-7kts west of the Blue Ridge, becoming NE-ENE east of the Blue Ridge with speeds increasing to 9-10kts by afternoon. Later this afternoon/evening, winds will also become ENE-ESE at 5-7 kts west of the Blue Ridge as the wedge air mass builds westward. Medium to high confidence in ceilings through the TAF valid period. Medium to high confidence in visibilities through the TAF valid period. Medium to high confidence in wind speed/direction through the TAF valid period. Extended Aviation Discussion... A baroclinic zone will remain anchored across the region sandwiched between a strong upper ridge over the southeast states and an active jet stream from the southwest U.S. into the northeast U.S. Thus, an unsettled, wet weather pattern is expected to remain in place through the extended periods. The frontal boundary may lift north enough by Monday for a brief period of mainly VFR, but a stronger front will arrive By Tuesday with more showers. Generally looking at MVFR much of the period, although periods of VFR as well as IFR-LIFR can be expected at times through the period. Overall, not the best weather for aviation.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...Freezing Rain Advisory from 4 AM to 4 PM EST Saturday for VAZ018>020-023-024-035. NC...None. WV...Freezing Rain Advisory from 4 AM to 4 PM EST Saturday for WVZ044-507. && $$ SYNOPSIS...RAB NEAR TERM...RAB SHORT TERM...PM LONG TERM...WP AVIATION...JH/RAB/RCS

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