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
-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KRNK 161740 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1240 PM EST Thu Feb 16 2017 .SYNOPSIS... Low pressure was along the New England Coast, with High pressure centered over the Lower Mississippi Valley. Pressure gradient between these two features will result in blustery cool conditions today. The area of high pressure will drift overhead tonight, winds diminishing. An area of low pressure will move across South Texas Friday, then across the Southeast and into the southern Appalachians this weekend with scattered rain showers. && .NEAR TERM /THROUGH FRIDAY/... As of 933 AM EST Thursday...Just small cosmetic changes to the grids, increasing sky cover slightly along and downwind of the Alleghany and Blue Ridge Mtns as morning visible depicts streets of mountain wave clouds. Additional areas of cloud cover associated with upslope flow in northern Bath, Alleghany VA into Greenbrier County, as well as in the OVC low-to-mid cloud layer associated with weak isentropic lift extending into Smyth and Tazewell County and into the eastern KY/TN/WV area. I also raised dewpoints a bit over the VA Southside into the NC piedmont over the next couple hrs. Should still be a relatively breezy day with falling dewpoints by the afternoon, though falling dewpoints especially to the south and west may be offset to some extent by warm front/isentropic lift which lifts northeast later in the day. No changes to highs at this point, which appear to be on track. Previous near-term discussion issued at 530 AM follows... Pressure gradient between the strong storm system off the New England Coast and High pressure over the Lower MS valley will result in a continuation of blustery northwest winds today. Strongest gusts will be across the the mountain ridges with occasional gusts of 30-40 kts. Lower elevations will also be entertained by a stiff breeze with wind gusts of 20-30 kts. Existing airmass is cold and dry with temperatures in the 20s/30s this morning and dewpoints in the lower teens and single digits. Cold air advection will continue through at least the first half of the day, so temperatures will be slow to respond with afternoon highs struggling to reach 40 in the mountains and 50 in the piedmont. Models are also forecasting SCT-BKN mid level cloudiness per increasing warm air advection and isentropic lift aloft. Some low level strato cu will also straddle the western slopes of the VA/WV highlands with scattered flurries. Combination of intermittent cloudiness, cold air advection in the boundary layer, will maintain cool apparent temperatures throughout the day. By tonight, surface high pressure will pass overhead resulting in diminishing winds. This should allow temperatures to slip into the 20s for lows, but this will depend on overall extent of the mid/upper level clouds. Models are hinting that at least a good portion of the CWA will have some mid/upper level cloudiness for a time during the overnight. As such temperatures may end up slightly warmer than guidance depending on coverage and thickness of this cloud cover. && .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/... As of 400 AM EST Thursday... The northern stream/northeastern U.S. upper trough will lift out of the area fairly quickly Friday. Mean upper ridging across central Canada will shift east through the period, keeping cold air increasingly blocked and locked up well to our north. In general, the northern stream, which has been the predominate flow for our region recently, will lift further north as well and remain generally north of 40-45 deg latitude through the period. Meanwhile, the southern stream will remain quite active yet suppressed fairly far south, generally near the southern U.S. border/Gulf Coast. A series of vigorous closed circulations will track through the southern stream as Pacific energy dives southeast toward the southern CA coast under the mean Canadian ridge, then tracks eastward near 25-30 deg. latitude finally beginning to lift northeast as it moves into the southeast states. As these systems move toward our region, they will be encountering confluent flow and mean upper ridging, in essence generally arriving in a much weakened state from the form they will take across the southwest and south central U.S. The first southern stream system to reach our area will arrive Saturday night and Sunday. Models in generally good agreement on the timing of this system, although differ on how much precipitation it will produce across the region. As noted above, this system will be in a weakening state moving into a mean ridge prevailing across the Mid-Atlantic/eastern U.S. It will also pass through the region fairly quickly as it is being booted out by a much stronger southern stream system moving into the far southwest/deep south Texas late in the weekend. The antecedent air mass across our region as this system arrives will be dry with dewpoints only in the 30s to lower 40s. Precipitation will generally fall from mid-level clouds and produce nominal amounts mostly less than 1/4 inch Saturday night into Sunday morning. The most likely area for meaningful precipitation with this system appears to be west of the Blue Ridge where isentropic lift will be somewhat better. There is no threat of winter precipitation with temperatures well above freezing and the air mass is entirely too stable for any thought of thunder. The short wave will exit the area Sunday evening as a high amplitude ridge evolves across the region in advance of the slow moving deep southwest/south central U.S. system mentioned above. 850mb temperatures will warm dramatically during this period as mean ridging evolves over the area and the source of any Canadian air lifts well north of the region. Most models are in agreement that 850mb temperatures will level off in the +12C to +14C level over the weekend and generally remain in place at such levels into the new week. Although Friday morning will start cold as the Canadian air mass rapidly retreats, afternoon temperatures will reach the upper 50s to lower 60s, some 10-15 degrees above normal despite mid-level warm advection cloud cover streaming from northwest to southeast across the CWA. This cloud cover will be associated with the northward lifting northern stream. On Saturday, mid/high cloud cover will be on the increase from the south as the weakening southern stream system approaches the area. This will leave Saturday`s temperatures only a few degrees above those observed Friday, yet still a good 15 degrees above normal across the CWA. After Friday morning, below freezing temperatures are generally not expected. Sunday will see temperatures on par with Saturday with clouds and light rain in the morning, becoming partly cloudy during the afternoon. && .LONG TERM /MONDAY THROUGH WEDNESDAY/... As of 430 AM EST Thursday... Extended period of unseasonably warm temperatures to continue. Mean ridging across central Canada will gradually shift eastward into eastern Canada. This will keep the northern stream and any source of Canadian/Arctic air mostly north of the U.S. Canadian border through the period. The result will be well above normal temperatures throughout the entire period and beyond. The warm air mass will be locked in place across the eastern U.S. with the cold air blocked to our north and high amplitude mean ridging across the eastern U.S. drifting only slowly east through the period in advance of a strong, closed low circulation across deep south Texas into the Gulf through the period. 500mb heights are expected to hover near 580dm through the period with 850mb temps averaging in the +12C to +14C range. There remain some significant differences on how the aforementioned southern stream system will eventually impact our region. The ECMWF keeps this system on a very far southern track taking it slowly across the Gulf and into Florida late in the week. Meanwhile, the GFS paints a much dirtier picture, keeping the main low track far to the south, but allowing associated pieces of weak energy to lift north into the TN Valley and Mid- Atlantic region. The Canadian is very bullish with the southern stream system lifting it further north into GA and developing a strong wedge across our area with overrunning precipitation. At any rate, given this is a closed, vertically stacked, essentially barotropic system, it will be very slow to move east and the main effects do indeed appear to remain well to our south. We should begin to see an increase in clouds as we head into Wednesday, but timing and amounts of precipitation remain questionable, but certainly none before Wednesday at the earliest. ECMWF MOS creeps pops into the slight chance category by Wed, while the GFS gets into the high chance range. For now, have confined mentionable pops mainly to west/southwest areas Wed, with Mon-Tue dry. As noted above, with 850mb temps stuck in the +10C to +14C range much of the period, surface temperatures will continue to be well above normal, with max temps in the 60s west to lower 70s east with lows only in the 40s. These readings are a good 15-20 degrees above normal. Certainly no signs of any winter weather next week! && .AVIATION /18Z THURSDAY THROUGH TUESDAY/...
-- Changed Discussion --
As of 1240 PM EST Thursday... VFR through the TAF period. Main effect on aviation interests this TAF period will be continued gusty northwest winds up to 30 kts at ROA, as well as potential for turbulence due to potential mountain wave activity in/around the Blue Ridge. These should primarily last through 00z with a decrease in speeds and gusts to light/variable conditions overnight. While FEW- SCT fair wx cu persist across the TAFs, will see an increase in mainly mid- level cloud cover from SW to NE as a dry warm front advances northeastward. Gradual thinning/decrease in mid-level cloud cover anticipated by Friday afternoon. Extended Aviation Discussion... VFR conditions remain the rule through Saturday. Next potential for sub- VFR conditions is late Saturday into Sunday as a disturbance moves into the area from the Deep South. Warmer temperatures will accompany this system, so any precipitation should be in the form of rain showers. Lower ceilings associated with these showers may linger into Sunday before clearing and return to VFR Sunday night through Monday. Dry weather will prevail Monday night into Tuesday.
-- End Changed Discussion --
&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...PM NEAR TERM...AL/PM SHORT TERM...RAB LONG TERM...MBS/RAB AVIATION...AL/PM is the U.S. government's official web portal to all federal, state and local government web resources and services.