Area Forecast Discussion
Issued by NWS Blacksburg, VA

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KRNK 112022 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 322 PM EST Mon Dec 11 2017 .SYNOPSIS...
-- Changed Discussion --
High pressure remains in control through tonight. An Alberta Clipper system will pass over the region on Tuesday, ushering in periods of snow and blowing snow, cold temperatures and gusty northwest winds through Tuesday night. Chilly but dry conditions return for Wednesday before temperatures begin to slowly moderate on Thursday.
-- End Changed Discussion --
&& .NEAR TERM /THROUGH TUESDAY/...
-- Changed Discussion --
As of 319 PM EST Monday...Modest warm advection regime underway across the Appalachians into the central mid-Atlantic region, ahead of a potent Alberta Clipper system and lead parent mid- level trough. Another shortwave is evident in water vapor imagery north of the Great Lakes associated with a strong shot of Arctic air. Each of these features will go to produce a period of wintry weather, cold temperatures and gusty northwest winds, especially along and west of the Blue Ridge Tuesday. Several hazard headlines have been issued with this package. Winter Weather Advisories have been hoisted for western Greenbrier County in West Virginia, and in Ashe and Watauga County in western North Carolina for accumulating snow and low wind chills (low wind chills primarily for Tuesday night). A Wind Advisory has also been hoisted along the southern Blue Ridge from Roanoke down to Boone. Each of these products run until 12z Wednesday. Quiet weather anticipated for the first part of the evening. Will start to build clouds in progressively with time from the east as clipper system approaches from the west. Should see increasing chances for snow showers into the pre-dawn hours of Tuesday from the mountains of NC northward into the central Appalachians and into western Greenbrier County. Low temperatures tonight should be in the mid 20s to near freezing. Guidance generally agrees on Arctic frontal passage tied to the clipper system from 12-16z Tuesday. By most indications, it should be a well defined and strong cold frontal passage as indicated in simulated reflectivity progs. Noticed on the NAM-12km that steep low- level lapse rates, CAPEs of 50-100 J/kg and Snow Squall Parameter values > 1 unit support an environment conducive to short-duration snow squalls with the Arctic frontal passage, especially along the I- 81 and I-77 corridors during the morning commute. As the air mass behind the front is cold, snow in western counties should be powdery in nature with snow-to-liquid ratios likely greater than 16:1. Pattern then transitions to one of typical northwest flow snow setups, with a Great Lakes moisture connection to Lake Michigan indicated in the higher-resolution NWP. I`ve left open the possibility for light accumulating snow to make it into the New River and Roanoke Valley, but the most persistent snows will be confined to the NC Mountains and in southeast West Virginia (particularly in western Greenbrier County). Including continuing snows for tomorrow night, forecast accumulations run from 3-5" in western Greenbrier County, 1-4" across the rest of southeast West Virginia, 1-3" in Ashe and Watauga Counties in NC, and a coating to an inch in more intermittent snow showers roughly along the I-81 corridor. Specific to winds, these will tend to peak immediately behind the frontal passage. While breezy conditions will exist in most locations west of the Blue Ridge, the strongest winds capable of causing minor damage appears more likely along the southern Blue Ridge with gusts up to 55 mph possible. With the powdery nature of the snowfall and breezy conditions, this will lead to periods of blowing/drifting snow. For temperatures Tuesday, opted for a non- diurnal temperature trend with early high temperatures in the 30s to mid 40s before sharply falling to the mid 20s to upper 30s by late afternoon under strong cold advection.
-- End Changed Discussion --
&& .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
-- Changed Discussion --
As of 319 PM EST Monday... Strong cold advection will persist Tuesday night as the center of the cold pocket aloft passes to the north. This should continue to provide a favorable fetch of upslope driven moisture to result in bands of snow showers overnight espcly western slopes but also with some possible spillover out to the Blue Ridge per strength of the jet. Expect coverage to slowly fade later Tuesday night as soundings show moisture depth decreasing but still likely another 1-3 inches far northwest slopes to an inch elsewhere with only light accumulations farther east. Strong northwest winds will also still be an issue with another round of subsidence overnight when the coldest 850 mb air should be helping lower the inversion. Therefore will need to keep or expand going wind headlines into early Wednesday morning at this point. This combined with lows in the teens to around 20 likely to spell wind chill issues from the foothills west so keeping mention in the HWO for now. Otherwise should see clearing take shape out east Tuesday night and elsewhere by Wednesday with this lingering into Wednesday night. Next weak clipper will then arrive from the west late Wednesday night and moreso Thursday as this impulse shears east and offshore Thursday afternoon. System appears lacking moisture per lack of digging so only including more clouds and slight pops northwest late Wednesday night and mainly low chance pops Thursday before lift gives way to weak upslope. Otherwise more clouds north and less south with highs 30s north to 40s south.
-- End Changed Discussion --
&& .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
-- Changed Discussion --
As of 319 PM EST Monday... Upper flow will again undergo a quick transition from zonal flow to start Thursday night back to a deeper eastern trough regime on Friday before again flattening over the weekend into early next week. This in response to development of split flow ahead of the last in a series of digging clipper systems that will attempt to phase with energy dropping out of the Rockies. However latest models show quite a spread with this system, from basically dry with a split between the clipper passing farther north and low pressure offshore, to somewhat better linkage with low pressure closer to the Carolinas and thus at least some light precip per the GFS. Boundary layer appears rather marginal for snow outside of the mountains but could arrive early Friday so something to watch. Otherwise will include some low rain/snow pops on Friday most sections for now. Lingering upslope snow showers again likely Friday night before heights build allowing for some temperature moderation on Saturday under warmer westerly flow which should push most into the 40s. This in advance of yet another system swinging northeast out of the southern plains that will link with the next upstream cold front and bring rain showers into the area late Sunday into Monday before coldere drier air follows later on Day 7. Appears most precip will be liquid given warming aloft ahead of the system Sunday night with only perhaps some snow showers at the end far west Monday morning.
-- End Changed Discussion --
&& .AVIATION /20Z MONDAY THROUGH SATURDAY/...
-- Changed Discussion --
As of 1256 PM EST Monday... VFR through at least 06z, though ceilings will steadily lower from west to east, especially into the evening/overnight hrs. Winds southwest 4-8 kts. We`ll then expect deterioration in flight categories as approaching Alberta Clipper and shot of modified Arctic air introduces periods of MVFR to LIFR snow showers, along with gusty northwest winds. These conditions are more likely west of Roanoke along the southern Blue Ridge in NC up into southeastern West Virginia. May see a period of short-duration snow squalls associated with the Arctic frontal passage between 11-14z at Bluefield, Lewisburg and perhaps Blacksburg. Ceilings expected to drop to sub-VFR levels by early morning along and west of the Blue Ridge. VFR conditions expected away from the mountains, with gusty post-frontal northwest winds developing. Sustained winds between 10-15 kts with gusts up to 30 kts, highest at Roanoke. Extended Discussion... A continuation of MVFR to IFR snow showers are expected west of the Blue Ridge through Tuesday night. Weak high pressure builds in Wednesday followed by another weaker clipper Thursday that passes to our north. Into Friday, potential for a stronger clipper system to re- energize off the Atlantic coast, inducing a period of sub-VFR with light to moderate snow. Conditions then trend VFR for Saturday.
-- End Changed Discussion --
&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...AL NEAR TERM...AL SHORT TERM...JH LONG TERM...JH AVIATION...AL/WP

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.