Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 241235 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 735 AM EST Sat Feb 24 2018 .SYNOPSIS... A strong cold front will slowly approach the Appalachians and central mid Atlantic region from the west resulting in an increased threat for showers this weekend. Until the front crosses the area Sunday, temperatures will remain well above normal. && .NEAR TERM /THROUGH TONIGHT/... As of 500 AM EST Saturday... Areas of fog mainly east of the Blue Ridge this morning, with lowest visibilities east of Highway 29 with many observing stations AOB 1/2sm. This fog is part of the remnant cool wedge from yesterday, all of which will erode later this morning as the sun comes up and mixing begins. A cold front over the Ohio and Tennessee Valleys stretches from NE-SW along a PIT-LEX-MRM-LIT line. This front will begin to move east later today as an upper level trough over the Rockies begins to move east. Meanwhile, the subtropical ridge of high pressure near the southeast Atlantic Coast will begin to weaken, but not before we go through another 24 to 36 hours of above seasonal warmth. The entire CWA will be under the influence of a warm moist southwesterly winds today with temperatures returning to the 70s areawide, and near record warmth. Shower threat will be the greatest across far western VA and into WV, closer to the front. The HRRR model seems to capture the moisture over the TN valley the best, so went with a high likelihood threat for showers later this morning as this area of rain moves NE toward Bluefield and Lewisburg. Not sure how much of this activity will survive the trip over the mountains, but think areas near I-64 will have the better chance of showers crossing the Highlands into the Shenandoah Valley and areas north of Roanoke-Lynchburg. Farther south, do not think much wetting will occur today. If anything, fewer clouds and greater potential for afternoon sun and deeper mixing will help elevate the temperatures. Can`t totally rule out a rumble of thunder for areas west of I-81 this afternoon per CAPE values increasing into the 500-1000 j/kg range in the upper TN valley ahead of the front. For tonight, forecast area remains on the warm side of the advancing front, temperatures remaining above 50. Shower threat will again be mainly confined to the western and northern CWA closer to the approaching frontal boundary. && .SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/... As of 400 AM EST Saturday... For a while now, our forecast has been reflecting the passage of a cold front during the course of the day Sunday. This is still the case. Guidance across the board is demonstrating good consensus of the front arriving across the mountains during the morning to mid- day, and then crossing the Piedmont during the afternoon. What has worked its way into the guidance solutions is the potential for a bit of breaking up of the activity once it is east of the mountains. This is not an uncommon event with cold frontal passages as the associated precipitation begins to experience the affects of northwest flow subsidence off the crest of the Blue Ridge. Reformation of a more substantial line of convection is possible just as the activity has exited, or is exiting the forecast area to the east out of the direct influence of this downslope component. Our forecast will reflect categorical coverage of showers across the mountains, but with only likely coverage in the east. Timing of the front in the east will coincide with peak heating of the day. Weak surface based instability is forecast, and SPC Day 2 Convective Outlook has general forecast for the area. These two elements will continue to allow for the mention of a slight chance of storms east of the mountains during the afternoon and early evening. Temperatures will continue to be on the very mild side for this time of year. Anticipate highs of the mid to upper 60s across the mountains with readings around 70 to the lower 70s across the Piedmont. Breezy conditions are expected on Sunday with a 35kt low level jet ahead of the front with some gusts at the higher ridge tops in the 30 to 40 mph range. Gusts of 15 to 25 mph will be more common with the mountain valleys and across the Piedmont. Sunday night into Monday, guidance has trended to be in better agreement as compared to 24 hours ago. Previously, the GFS had been on its own with a definite exiting of the cold front, with no impact across the region in assocation with a Gulf Coast wave that was progged to ride northeast along the exiting front. Its foreign counterparts to our north and across the Pond along with its NAM cousin were leaning more on this Gulf wave stalling the front, and allowing a return of precipitation across at least the southern half of the forecast area. Granted, each of these other models differed on timing and qpf, but nonetheless, did not have a dry forecast rapidly entering the forecast picture. Fast forward 24 hours and the GFS is now onboard with a similar scenario. Our forecast had been reflecting the wetter solutions of the consensus of guidance. That strategy is looking more promising. Look for showers across mainly areas south of Route 460 Sunday night and Monday, with the bulk of the activity across portions of Southside Virginia and neighboring sections of north central North Carolina. While temperatures will trend cooler, they will still average 10 to 15 degrees above normal, rather than the 20 to 25 degrees above normal prior to the cold frontal passage. Monday night into Tuesday, there is good model consensus for a surface high around 1030 mb to build overhead. This will provide for a push for drier and cooler air to work its way into the area. Still readings will be slightly on the mild side for this time of year with values 5 to 10 degrees above normal. Tuesday night will be characterized by increasing cloud cover from southwest to northeast thanks to an approaching area of low pressure through the Lower Mississippi Valley. Temperatures as a result will be slightly milder than those realized Monday night. Precipitation is expected to work its way northeast as close as the Smokies, but not reach the southwest sections of the area until Wednesday morning. && .LONG TERM /WEDNESDAY THROUGH FRIDAY/... As of 100 PM EST Friday... The run of quiet weather looks to be brief as the flow again backs/amplifies by midweek ahead of a strong upper low that will eject out of the southwest states into the Great Lakes and Mid- Atlantic region by Friday. Pieces of mid level energy ahead of the main upper system will give rise to overrunning across a warm front to the southwest by later Wednesday with this boundary crossing the region Wednesday night/Thursday as the main surface low tracks into the upper Midwest. Quick return of deeper moisture per model Pwats suggests an increasing threat for showers/rain from southwest to northeast later Wednesday and across the region Wednesday night into Thursday ahead of the trailing cold front. Upper trough looks to deepen across the region with a switch to colder northwest flow by Friday in the wake of the cold front. This likely to produce some upslope rain/snow showers with breezy/windy conditions elsewhere with more sunshine returning out east. Temperatures mainly 50s/60s for highs early on with warmest Thursday under strong southwest flow ahead of the front and then much cooler Friday under cold advection resulting in highs 40s mountains to low/mid 50s east. && .AVIATION /13Z SATURDAY THROUGH WEDNESDAY/...
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As of 730 AM EST Saturday... Widespread IFR was found mainly east of the Blue Ridge. This fog and stratus is expected to erode through the morning, with transition to MVFR, then VFR for the afternoon. Front west of the mountains will be the focus for showers, with some of this activity crossing the mountains of WV and into NoVA today. Any sun today will result in deeper mixing which will tap stronger winds aloft. If/when this occurs expect surface gusts of 15-20 kts. Primary direction from the southwest. Medium Confidence for both cigs/vsbys through the valid taf pd. Extended: During the day Sunday, showers become more widespread as a cold front crosses the region from the west. Sub-VFR conditions may extend through Monday as the front stalls to the south allowing for showers to linger in the region throughout the day. High pressure builds over the region Monday night into Tuesday which should bring drier conditions and VFR, at least temporarily.
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&& .CLIMATE... Records For... Saturday 2/24/2018 Site MaxT/Year HiMin/Year BLF 71/2017 53/2017 DAN 79/2012 51/1996 LYH 79/2012 53/1985 ROA 80/1985 52/1943 RNK 73/1975 49/1975 && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...PM NEAR TERM...PM SHORT TERM...DS LONG TERM...JH AVIATION...PM CLIMATE...PM

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