Area Forecast Discussion
Issued by NWS Blacksburg, VA

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
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
-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KRNK 201433 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1033 AM EDT Tue Mar 20 2018 .SYNOPSIS... Low pressure over the lower Ohio and Tennessee Valleys will cross over the central Appalachians today, sparking the development of a coastal storm tonight and Wednesday that will turn into a Nor`easter as it moves northeast along the Mid Atlantic and New England Coast. High pressure will build across the region Thursday into Friday. && .NEAR TERM /THROUGH WEDNESDAY/...
-- Changed Discussion --
As of 1015 AM EDT Tuesday... Making notable adjustments to the forecast for today. The biggest adjustment will be a break in the likely precipitation between the departing activity to the northeast, and what is expected to arrive mid-afternoon across the southwest portion of the area. In between these two systems, most areas will experience more of a patchy drizzle for most of the middle portion of the day. The precipitation will be a little more concentrated across southeast West Virginia. However, by the late afternoon, precipitation make a generous push eastward across the area. It make take until the evening hours for measurable precipitation to return to the far eastern sections. Latest precipitation-type forecast suggest that the onset of wintry precipitation may have a brief period of a rain/sleet mix before the onset of snow across western and northern sections. As of 530 AM EDT Tuesday... Confidence increasing for heavy snow for parts of the Mid- Atlantic into southern New England tonight and Wednesday, with lingering effects Wednesday night. A complex evolution of fronts and surface lows will evolve through the near term, as moisture moves northeastward from the Gulf Coast region interacting with colder air moving south from New England. This clash of the airmasses will result in a strengthening baroclinic zone which will be the focus for rapid development and deepening of low pressure over the mid-Atlantic tonight. Several pieces of upper level energy, short waves, will consolidate over the OH/TN valleys today, this energy sparking the development of a coastal storm tonight that will rapidly deepen along the existing baroclinic zone. Models suggest this feature will develop into yet another Nor`easter with the surface pressure dipping under 985 mb by late Wednesday. During the evolution of this system, both dynamic cooling aloft and cold air advection from the north into our region will result in steadily falling temperatures...precipitation across our region changing from rain to snow. The forecast challenge will be to identify where the rain will change to snow first vs. last and and to assess snow yield potential. The ground is warm, so it will have to snow pretty intensely to get it to stick to the pavement. Greatest intensity and lift from this system is forecast along the spine of the Appalachians,and this is where we have the highest confidence of significant accumulating snow. For most of the daylight hours today, forecast is pretty simple...lingering clouds, occasional rain and steady or falling temperatures through the 40s and into the upper 30s. The rain may actually come to an end for a while this afternoon before redeveloping this evening. Onset of snow tonight will occur between sunset and midnight for areas along and west of the Blue Ridge, then after midnight for the foothills and piedmont. The greater potential for heavier snowfall accumulations will be across the higher elevations of the Appalachians near the WV/VA border with amounts of 3 to 6 inches in the valleys and as much as 8-12 inches for elevations above 3000 feet. East of the Blue ridge, amounts will drop off quickly as this area will experience a change over much later in time. The exception will be for areas along and north of 460 including Lynchburg and Appomattox, where colder air arriving from northern VA will permit more accumulation there (up to 3 inches). From the city of Danville and areas to the south into the Piedmont of NC, the expectation is for an inch or less. IF enough cold air can get drawn south behind the developing coastal storm Wednesday, it is conceivable for a bit more across the piedmont, but even then it will be a challenge to get it to stick to anything other than the grass and elevated objects per the warmer ground temperatures in the piedmont. Low temperatures tonight are expected to range the upper 20s in the mountains, along and west of the Blue Ridge, to the mid 30s in the NC Piedmont. For Wednesday went cooler than guidance with respect to the high temperature, most areas remaining in the 30s due to snow cover and continuation of cold air advection from the north. As the storm takes shape and moves northeast, expect increasing northwest winds Wednesday afternoon, gusts 30 to 40 mph across the higher ridges.
-- End Changed Discussion --
&& .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/... As of 500 AM EDT Tuesday... The slow moving vertically stacked upper low and associated deformation zone will linger across the southern half of the forecast area before shifting east-northeast off the Mid-Atlantic coast by Thursday morning. Expect snow to linger in the shrinking deformation zone, which most models agree will be located in the southeast KY, east TN, southwest VA, northwest NC vicinity. Northwest winds may aid in upslope snow, especially across the Alleghanys. Thus, in concert with neighboring offices, will continue the Winter Storm Warning/Winter Weather Advisory through Thursday morning 12Z, keeping in mind that the bulk of any additional hazard level snow will likely occur prior to 04Z Thu. Temperatures will remain well below normal through Thursday with lows in the 20s and 30s and highs in the 30s and 40s. Gusty northwest winds during the day Wednesday will begin to diminish overnight into Thursday morning as high pressure starts to move south from the Great Lakes. For Friday, weather will become a bit quieter as the upper low moves northeast of the area and out to sea and a high amplitude yet progressive upper ridge drifts from the central U.S. into the eastern U.S. Surface high pressure will build southward into the area from the Great Lakes leaving temperatures yet again well below normal with highs mostly in the 40s west to 50s Piedmont and lows in the 20s to lower 30s. && .LONG TERM /SATURDAY THROUGH MONDAY/... As of 430 AM EDT Tuesday... Progressive pattern will continue with a series of vigorous short waves tracking across the U.S. from west to east. A vigorous highly kinematic system that will bring heavy rain to southern CA in the next couple of days will reach our region by the weekend. Thus, after a brief break from the active weather on Friday, a warm front extending from low pressure in the midwest will begin to push precipitation back into the region Saturday. Models are a bit slower than in previous runs in bringing this precipitation into the region, generally in the afternoon. Temperature profiles would suggest some potential for wintry precipitation again, more so though if the precipitation arrived earlier in the day. A cold front then pushes southeastward through the region Sunday into Monday with additional rounds of precipitation, some which could be heavy. Mainly a rain event, but temperatures will be close to levels, especially during the morning hours, to be at least slightly concerned about winter precipitation. Temperatures are expected to remain well below normal through the entire period. && .AVIATION /15Z TUESDAY THROUGH SATURDAY/... As of 800 AM EDT Tuesday... Rain will end by mid morning...then redevelop this evening and change to snow after midnight tonight. This is the result of an upper level low pressure area over the lower OH/TN valleys that will approach the mountains from the west today, then redevelop as a coastal storm tonight. The break in the precipitation today will allow visibilities to improve, but think cigs will continue to teeter with the IFR/MVFR category threshold. Change of p-type will occur around midnight tonight as colder air arrives from the north associated with the northeast wind and cold air advection on the back side of the developing coastal low. Heavy wet snow is likely later tonight from the Roanoke valley north and west into the mountains bordering WV/VA. Flight conditions will deteriorate rapidly tonight once the rain changes to snow with potential for LIFR after midnight and through the morning push Wednesday. Confidence is medium through the forecast period. Greatest uncertainty will be with forecast snow amounts tonight... the warm ground aiding in the melting process. Extended Aviation Discussion... As a low pressure system heads offshore later Wednesday winds will increase from the northwest and the snow will taper to flurries. Drier air should finally result in improving conditions Thursday as high pressure builds from the northwest. Another low pressure system will bring rain and the associated MVFR or lower conditions for Friday and Saturday. && .EQUIPMENT... As of 335 PM EDT Monday... The Mount Jefferson NWR remains off the air. The radio unit needed to repair the system is expected to arrive on Wednesday. The earliest this system will again be operational will be Wednesday afternoon. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...Winter Storm Warning from midnight tonight to 8 AM EDT Thursday for VAZ007-009>020-022>024. Winter Weather Advisory from midnight tonight to 8 AM EDT Thursday for VAZ032>035-045>047. NC...Winter Storm Warning from midnight tonight to 8 AM EDT Thursday for NCZ001-002-018. WV...Winter Storm Warning from midnight tonight to 8 AM EDT Thursday for WVZ042>044-507-508. && $$ SYNOPSIS...PM NEAR TERM...DS/PM SHORT TERM...RAB LONG TERM...RAB AVIATION...PM EQUIPMENT...AMS is the U.S. government's official web portal to all federal, state and local government web resources and services.