958 FXUS61 KRNK 041204 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 704 AM EST Fri Jan 4 2019 .SYNOPSIS... A vigorous low pressure system aloft will track from the south central U.S. into the southern part of the Mid-Atlantic region by tonight and Saturday. Widespread rain will accompany this system today and tonight. Cooler air will spread into the region behind this system Saturday as rain lingers across the mountains. Then, high pressure will build into the region for Sunday and Monday. Temperatures will continue above seasonal normals into the first half of next week. && .NEAR TERM /THROUGH TONIGHT/... As of 345 AM EST Friday... A distinct, compact and closed upper low in the southern stream will continue tracking east to east-northeast today through Saturday, moving from eastern OK this morning into the southern parts of the Mid-Atlantic region Saturday. Clouds have already overspread the region in advance of this system and rain is creeping northward through central and western NC this morning. Rain will overspread the region today. Periods of heavy rain are possible late this morning into the early evening, but most of the rain is expected to be light to moderate as deep Gulf moisture inflow is limited compared to systems in recent weeks. For most of the day, the main mechanism driving the rain will be isentropic lift over a shallow wedge of cooler air across the region. During the late afternoon/early evening, a dry slot will work its way north into the foothills and Piedmont of NC and possibly as far north as Southside Virginia. As the pocket of cold air aloft moves over this region, any brief pockets of sunshine will help to support isolated thunderstorms, mostly elevated, but still a possibility and in agreement with SPCs general thunder. The other area that may see an isolated thunderstorm is in the far western part of the CWA early this afternoon, west of I-77, which may move into the area with better instability from eastern TN. MOS thunderstorm pops are as high as 30% in that region of the state this afternoon, so added isold TSRA in the Marion/Richlands area for a couple of hours around 18Z. As noted above, widespread rainfall is expected, with intermittent periods of heavy rain possible during the late morning into mid-afternoon, mainly south of I-64, with lesser amounts further north where the air mass is somewhat drier. QPF totals are mostly 1 inch or less, with the 1+ inch amounts confined to the far southern areas, which is clipped by WPC marginal excessive rainfall area for Day1. SBNV2 is forecast to reach minor flood once again (at least the 3rd time in the past couple of weeks), and this seems very plausible given it is already at 16+ feet. Being a totally southern stream system with the northern stream near the Canadian border, all of the true Canadian/Arctic air remains mostly north of the Canadian border or across northern New England. All of the cold air with this system today/Saturday is aloft. It will have minimal impact on surface temperatures with no distinct CAA or change of air mass in its wake. Consequently, temperatures will remain above seasonal normals, limiting the threat of most all of the precipitation to liquid. A brief period of snow showers as the core of the cold air aloft drifts over the area early Saturday can be expected in the mountains, but surface/ground temperatures are well above freezing, so no threat of accumulations of winter precipitation with this event. Look for highs mainly in the 40s west to the 50s east with lows in the 30s west to the 40s east. /Confidence in Forecast Parameters/ Temperatures - Moderate to High, Precipitation Chances - High, Winds - Moderate to High Thunderstorm Chances - Low. && .SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/... As of 300 AM EST Friday... The stacked upper low will be pulling away from the Appalachians and central mid Atlantic region Saturday morning. This will bring an end to lingering upslope showers, mixed rain/snow showers at the higher elevations, west of the Blue Ridge Saturday morning. However, the low level wind field will continue to amplify and generate strong gusty winds Saturday into Saturday night. The strongest winds will be at the higher elevations along and west of the Blue Ridge, but diurnal mixing will allow for gusts east of the Blue Ridge Saturday afternoon as well. There may also be an opportunity for winds to funnel through Fancy Gap on I-77 Saturday night as winds back a bit and the inversion lowers. A large ridge will then build in from the west and, aside from some upslope clouds, the weather looks to remain quiet for Sunday. By Sunday night high pressure will be sliding off to our east and as winds become southeasterly clouds and moisture will be increasing through Monday. However our next chance of precipitation will hold off until Monday night when low pressure moving through the Great Lakes pushes another front into the region from the west. With little in the way of cold air behind the departing low, temperatures will remain well above normal through the period. && .LONG TERM /TUESDAY THROUGH THURSDAY/... As of 1105 AM EST Thursday... During this period, the synoptic models are in somewhat agreement Monday, but then shift to different camps Tuesday, with the 06z GFS more progressive with the front exiting the east early Tuesday, while the 00z ECM shows a deeper shortwave and slower timing with best overall chance of showers arriving Tuesday morning, exiting roughly in the afternoon/evening with lingering upslope showers across WV into Wed morning. Ensembles vary somewhat as well in their respective camps, so for now will trend a little faster in bring precip chances in Monday evening, and exiting by the end of the day Tuesday. Needless to say, this front is more of Pacific origin, and flow aloft is more west than south, so not as much Gulf of Mexico moisture in tapped, and pwats will not be as high. Will mainly be looking at high chance of showers in the mountains to low chance east for now, with temps around or above normal, with a low to nil threat of wintry wx. Beyond this system, enough agreement in models on drying things out thru Thursday, with both operational runs showing a trough off the east coast and ridging in the middle of the country into Thursday. This will also keep us above normal on temps. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/... As of 645 AM EST Friday... Poor aviation conditions expected through the TAF valid period with mostly IFR-LIFR ceilings and MVFR-IFR visibilities in rain, drizzle, and fog as a closed southern stream upper low tracks across the region from west to east through Saturday. Rain was spreading into the region from the south as of 12Z this morning and will continue to overspread the area throughout the day. The heaviest rain will generally remain south of I-64, but all areas are expected to see poor ceilings and visibilities developing and advecting into the region from the south by mid to late morning. While the heavier rainfall will shift east of the area by Saturday morning, conditions will remain poor until a wind shift evolves Saturday morning. Expect areas of fog and drizzle even when there is not rain, especially near and east of the Blue Ridge. Winds will be mostly northeast east of the Blue Ridge and east to southeast west of the Blue Ridge until early Saturday when they begin to shift to the west. Speeds through most of the TAF valid period will be 5-10kts, increasing from KBLF to KLWB 10-20kts very late in the TAF valid period. /Confidence in Forecast Parameters/ Ceilings - Moderate to High, Visibility - Moderate to High, Winds - Moderate. Extended Aviation Discussion... Saturday will be very windy, especially west of the Blue Ridge with west to northwest winds 15-25kts with some gusts 30-40kts, most notably west of the Blue Ridge. Ceilings and visibilities will improve to MVFR or better by late morning in the east as downslope west winds spread into the Piedmont. Western areas will have to endure a deformation zone that will be slow to move out of the area on the back side of the upper low. MVFR or worse ceilings and visibilities will likely prevail from KBLF to KLWB much of the day Saturday along with the gusty winds. VFR conditions are expected to return Sun-Mon. Another weaker weather system/front may bring MVFR in lower cigs and showers across the mountains later Monday night into early Tuesday, followed by improving conditions on gusty westerly winds Tuesday afternoon. VFR should prevail out east with lack of much moisture east of the mountains on Tuesday. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...RAB NEAR TERM...RAB SHORT TERM...MBS LONG TERM...WP AVIATION...RAB