Area Forecast Discussion
Issued by NWS Blacksburg, VA

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745 FXUS61 KRNK 210941 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 441 AM EST Sun Jan 21 2018 .SYNOPSIS...
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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.
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&& .NEAR TERM /THROUGH TONIGHT/...
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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.
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&& .SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/...
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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.
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&& .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 /09Z SUNDAY THROUGH THURSDAY/... As of 1120 PM EST Saturday... Scattered to broken MVFR clouds in the western mountains will continue to spread east to the Blue Ridge at times and perhaps east of the mountains to near KLYH overnight. This should result in periods of VFR to MVFR cigs from KBLF/KLWB east to KBCB, including scattered to broken at KROA, and perhaps KLYH. As moisture increases, may also see cigs lower further around KBLF overnight with IFR cigs possible late tonight into Sunday morning. However this quite iffy given dry air so raised cigs more to MVFR levels overnight from previous. Visibilities are expected to be mostly VFR through the TAF valid period. Westerly winds at 7-15 kts mountains, and around 10 kts out east will continue to diminish overnight, becoming mainly light and variable across eastern sections late. However a few gusts may linger over the higher ridges as the jet aloft remains strong until late tonight. This may also result in areas of LLWS especially At KROA/KBCB and KLYH overnight as surface winds decrease. Best axis of low level moisture will reside over the western sections on Sunday as decent westerly flow continues. Some of this may keep sub-VFR cigs going into mid or late morning west of the Blue Ridge with at least scattered low clouds out east into the afternoon. However moisture pinned in against the mountains may keep KBLF/KLWB MVFR at times well into the afternoon. Isolated showers may also track in from the west across far northwest sections on Sunday, but since iffy and mainly west of KLWB wont include mention. West winds should be much lighter on Sunday with speeds of 5-15 kts before backing southwest during the afternoon. Low confidence in ceilings, with medium confidence in visibilities and winds through the TAF valid period. Extended Discussion... Sub-VFR conditions will likely redevelop at least across the mountain locations Sunday night and across the entire area Monday afternoon into Monday night as a cold front and its associated precipitation approaches/arrives. Strong convective showers are expected with this front, including a potential QLCS and isolated thunderstorms. Should see a return to VFR east of the mountains by Tuesday afternoon with lingering upslope driven MVFR cigs across the western mountains into Tuesday night. Very gusty northwest winds return to the area as well Tuesday night into Wednesday on the backside of the departing system. Snow showers could also bring periods of sub-VFR vsbys Tuesday afternoon and night across the SE West Virginia sites thanks to strong upslope flow and residual low level moisture. High pressure should build in resulting in drier weather and diminishing winds on Thursday. && .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...RAB SHORT TERM...MBS LONG TERM...MBS/WP AVIATION...JH/KK/RAB EQUIPMENT...WP

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