Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 211432 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 932 AM EST Sun Jan 21 2018 .SYNOPSIS... High pressure will drift southeast of the area through Monday while building northward aloft from the Southeast U.S. into the Mid-Atlantic. A warm front across the northern portion of the area will drift north into Ohio and Pennsylvania. By Monday, a strong cold front will move into our region from the west accompanied by heavy rain showers and gusty winds. Relatively mild temperatures through Tuesday will give way to colder conditions again behind the cold front Wednesday, but nothing like the bitter we saw the first half of the month. && .NEAR TERM /THROUGH TONIGHT/... As of 932 AM EST Sunday... Adjusted cloud cover to account for large area of stratus to our west noted on the morning Satellite images. Increased clouds for late morning into this afternoon in the west. Modified temperatures with the latest surface obs, their trends and shaped towards GLAMP which captured the slightly cooler morning temperatures followed by the mild afternoon. High temperatures this afternoon will range from the lower 50s in the mountains to the lower 60s in the piedmont. As of 420 AM EST Sunday... Moderating temperatures will continue across the region today and Monday as the remnant former Arctic high to our south drifts east into the western Atlantic. The clockwise flow around the large high is pulling warm and gradually more moist air northward first into the Tennessee and Ohio Valley behind a weak warm front that is near the I-64 corridor and which will drift further north into PA/OH today as high pressure aloft amplifies across the southeast states. The moisture is spreading more slowly east across the Appalachians. This pattern will continue through Monday as a strong southern stream storm system moves eastward from the Southern Plains. Warm advection cloud cover will be located primarily to the west of the region as it was yesterday, but would expect the eastern edge of this to continue to creep further eastward with time, just as it did yesterday. By afternoon it should as far east as the I-81 corridor and the Shenandoah Valley, while also eroding some across the south where the upper ridge will strengthen. Temperatures were quite mild this morning compared to the many recent bitterly cold nights in the single digits to even below zero that we have endured frequently since Christmas. 850mb temperatures will remain above freezing for the next couple of days, hovering in the +8C to +10C range. For the next couple of days low temperatures, except for a few colder valleys in the east where there are less clouds, will remain above freezing with lows in the mid 30s to mid 40s. The warmest readings will be across the higher ridges where winds are stronger and hence better mixing. Daytime temperatures will be quite mild and among some of the warmest we have seen this entire month with 50s west to 60s east. Temperatures will average about 15 degrees above normal today and Monday. && .SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/... As of 330 AM EST Sunday... The Appalachians and central mid Atlantic region will start next week with fair but breezy conditions through the first part of Monday with temperatures well above normal. However, this fair weather will be short lived as the chance for showers will be increasing by Monday afternoon west of the Blue Ridge as a strong cold front approaches from the west. The front has good dynamic support, being driven by low pressure moving through the Great Lakes. The front is expected to be accompanied by widespread rainfall and mid/upper level lapse rates have steepened a bit with some hints of surface based instability. Believe the kinematic and thermodynamic environment now appears sufficient to support a slight chance for embedded thunder with convective elements along and just ahead of the front Monday night mainly east of the Blue Ridge. Additionally, the low level wind field amplifies considerably and there is a good amount of shear along the front so embedded convective elements may be able to mix down strong wind gusts even without thunder. Guidance has been relatively consistent in handling the evolution of this system for the past several model runs so while the likelihood of severe weather is not great due to the lack of instability, the possibility can not be dismissed due to the energetic nature of the system. Timing of the frontal passage has slowed a bit so expect precipitation to be lingering in the east early Tuesday morning with a gradual transition to some upslope snow showers west of the Blue Ridge. Winds behind the front will become quite strong with gusts to 50 MPH possible into Wednesday morning, and additional short wave energy will combine with upslope flow and low level moisture to keep some snow showers/flurries going at the higher elevations west of the Blue Ridge into Wednesday as well. Any accumulation looks to be confined to the higher elevations with amounts generally half an inch or less. && .LONG TERM /THURSDAY THROUGH SATURDAY/... As of 130 PM EST Saturday... Overall pattern stays progressive with shortwave moving across midweek with limited moist, with brief cool down, but still close to normal temps for late January. 5h heights build late in the week while, strong trough shifts into the western U.S. As this strong trough moves into the middle of the country Saturday, southwest flow increases over us with moisture shifting toward our area. Surface high should be off the mid- Atlantic coast, but in-situ type wedge seems to set up allowing for potential of wintry mix during Saturday although at the moment will carry mainly rain, mixed at times with snow, and overall looks like Sat night-Sunday are wetter with wedge breaking. && .AVIATION /15Z SUNDAY THROUGH THURSDAY/... As of 650 AM EST Sunday... Scattered to broken mainly low end VFR clouds, but potentially high end MVFR clouds across the western mountains/Alleghanys will continue to spread slowly east through the day as surface high pressure moves off the NC coast. The clouds should spread toward the eastern CWA border before daybreak Monday, including KLYH and KDAN. Right now there is no clear indication of anything worse than MVFR through the TAF valid period, and mostly VFR. Any threat of precipitation has generally shift to the north and northwest of the CWA. Visibilities are expected to be mostly VFR through the TAF valid period, although there is some potential for patchy MVFR BR early Monday. Winds today will be mostly W to SW and much lighter than what was evidenced Saturday. Look for speeds mostly in the 4-8kt range, with little if any gustiness today. With this TAF set, the mention of all LLWS has been removed. Medium to high confidence in ceilings today, dropping to medium confidence after 00z. High confidence in visibilities through 08Z, then medium to high confidence in visibilities. Medium to high confidence in wind direction and speed through the TAF valid period. Extended Discussion... Sub-VFR conditions are expected to expand from west to east ahead of a strong cold front during the day Monday. While there may be scattered light to moderate rain showers out ahead of the front, of greater concern is a line of convective showers, possibly a QLCS with isolated embedded thunderstorms, that will accompany the front and a strong 60kt associated LLJ. Consequently, the greatest concern with these showers will be strong wind gusts, potentially of 45-50 mph or possibly even greater for a short duration in the Monday evening/early Tuesday morning time frame. Strong gusty northwest winds are expected behind the front Tuesday into Wednesday. VFR ceilings should return to the Piedmont by Tuesday afternoon, but MVFR ceilings with low clouds and potentially -SHSN can be expected further west across the Alleghanys, and possibly as far east at times as BCB. High pressure and VFR conditions along with diminishing winds should return to the entire area by Wednesday. && .EQUIPMENT... As of 325 PM EST Friday... NOAA Weather Radio, WXL60 (Roanoke Transmitter) which broadcasts at 162.475 MHz remains off the air. The phone company reported that the circuit line had been cut and will take until Monday January 22nd to fix it. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...RAB NEAR TERM...KK/RAB SHORT TERM...MBS LONG TERM...MBS/WP AVIATION...RAB EQUIPMENT...WP

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