Area Forecast Discussion
Issued by NWS Blacksburg, VA

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127 FXUS61 KRNK 220832 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 432 AM EDT Thu Mar 22 2018 .SYNOPSIS... Low pressure off New England will continue to lift northeast and away from the region today. Weak high pressure briefly returns to the area later today through Friday resulting in drier weather into Friday evening. Another potential winter storm will then affect the region over the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 300 AM EDT Thursday... Upper low continuing to pull out to the northeast with spokes of energy still rotating around making for lingering upslope clouds that are spilling east of the Blue Ridge early this morning. Latest short term models suggest that some of this cloudiness will linger into the afternoon as yet another mid level wave crosses the region this morning. However think enough drying and downslope to finally result in more sunshine this afternoon so leaning toward a gradual decrease in clouds today. Clouds have also limited mixing with winds overall below advisory levels attm. Does appear that another surge will come just before daybreak so leaving up the wind advisory a while longer for impact before perhaps removing around 12z pending obs. With cold northwest flow remaining in place, trimmed highs some over the west where may again stay in the 30s, while the east perhaps jumps closer to 50 with 40s in between. Weak surface high settles in tonight but likely not enough to deter mixing as the pressure gradient between low pressure to the northeast lingers a bit. May also see some jet high clouds work in overnight within the northwest flow aloft so will see overall partly cloudy west to mainly clear but cold east. Still expect enough decoupling under the 85h cold pool to support lows back in the 20s to lower 30s with possibly a few teens over snow cover in the deeper valleys. && .SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/... As of 300 AM EDT Thursday... Northwest flow lingers into Friday although not as cold with the 85h baroclinic zone lifting to the northeast a bit. This should allow some degree of warm advection despite lingering low level northwest trajectory which looks gusty at times. Cross sections also show some increase in at least high clouds by afternoon ahead of the next upstream system but overall mainly sunny and a tad warmer. Highs mainly 40s mountains to low/mid 50s east except colder over deeper snow cover in the Highlands and Greenbrier Valley. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... ...Yet Another Potentially Significant Snow Storm on the Way... A well established Alberta Clipper will track from south central Canada directly into the mid-Atlantic region within the back side of the northeast U.S. trough Friday night into Sunday. This system will gather enough Gulf Moisture on its track combined with strong dynamics to bring a well and long established swath of snow into the region. Dynamics are strong and the storm pivots somewhat through the Greenbrier and Southern Shenandoah Valleys as it translates into more of a Miller B setup by Sunday afternoon off the NC/SC coast. A very tight, compact, and vigorous system with ample moisture has the potential to bring significant amounts of snow to a relatively small area with a tight gradient. However, all of the synoptic mid to long range models have for several cycles, and even more so now, depict a significant swath of mostly snow through the CWA tracking from LWB toward ROA toward DAN late Friday night through Saturday evening. Models are all largely clustered around amounts of 6-8 inches with several models showing 10-12 inch amounts (GFS NAM for sure) clustered around LWB and the I-64 corridor over to Alleghany. WPC has followed suit with warning criteria snow in this same area. Clearly the bullseye for snow with all models is centered near BCB and the north central part of our CWA for this event. Given the consideration that some of these same areas just received 8-15 inches of snow yesterday, another 8-12 inches would be quite an event that soon. For this reason, the tight clustering of the models, and strong support from WPC for greater than 50% confidence of warning criteria snow in these areas, have hoisted a Winter Storm Watch for snow across Greenbrier, Monroe, Alleghany VA, Bath, Craig, and Botetourt. With time additional counties to the south, west, and east may need to be added to this and more likely for a large area even out into the Piedmont will eventually see an advisory. Look for more changes in the hours/days ahead! As with the last event, the areas most likely to escape accumulating or at least much accumulating snow will be west of I-77 and across western NC. There is actually the potential, given the track of this system, for Piedmont areas to receive more snow than was observed yesterday. Temperatures will remain well below normal through the period as the upper trough across the eastern U.S. keeps a pocket of cold air across the region. 850mb temperatures will largely remain at or below 0C through the period, especially north of the NC/VA border, with around -6C in the mountains. This will further support this being an all snow event, with little to no threat of freezing rain and only a brief period of sleet at the onset. && .AVIATION /08Z THURSDAY THROUGH MONDAY/... As of 115 AM EDT Thursday... Snow showers/flurries should continue to fade overnight as drier air works in from the north behind the departing upper low along the coast. However KBLF and KLWB will continue to see MVFR to IFR ceilings under northwest flow, with VFR ceilings lingering east of the mountains until Thursday morning. Should finally see ceilings rise to VFR Thursday morning over the west as well allowing for widespread VFR across all sites this afternoon. Gusty northwest winds are expected during the TAF period as the pressure gradient between the approaching upstream high and the strengthening Noreaster becomes stronger overnight into early Thursday. Wind gusts to 35-40 kts could occur mainly along the ridges and including KROA into Thursday. The weather pattern will change somewhat as we move beyond the weekend snow storm with a high amplitude progressive upper ridge drifting eastward across the region. Temperatures should finally trend to near and slightly above normal levels by midweek. The next system, a rain system, will arrive late in the week after this period. Extended Aviation Discussion... Mainly VFR conditions are expected by Thursday night through Friday night under weak high pressure. Saturday into Sunday, a return to sub-VFR conditions is expected as our next potential winter weather system crosses the area. VFR to return on Monday with high pressure to the north wedged south along the mountains. && .EQUIPMENT... As of 1021 AM EDT Wednesday... The Mount Jefferson NWR remains off the air. The radio unit needed to repair the system is expected to arrive tomorrow (Thursday). The earliest this system will again be operational will be Thursday afternoon. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...Wind Advisory until noon EDT today for VAZ007-009>020-022>024- 035. Winter Storm Watch from Saturday morning through Sunday morning for VAZ018>020-023. NC...Wind Advisory until noon EDT today for NCZ001-002-018. WV...Wind Advisory until noon EDT today for WVZ042>044-507-508. Winter Storm Watch from Saturday morning through Sunday morning for WVZ044-507-508. && $$ SYNOPSIS...JH NEAR TERM...JH SHORT TERM...JH/RAB LONG TERM...RAB AVIATION...AL/JH/JR EQUIPMENT...AL/AMS is the U.S. government's official web portal to all federal, state and local government web resources and services.