Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 161613 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1113 AM EST Mon Jan 16 2017 .SYNOPSIS... A warm front across the Carolinas slowly lifts northeast today stalling across southwest Virginia. A cold front enters the area by Tuesday afternoon shifting off to our south Wednesday. This front edges northward again Thursday into Friday. && .NEAR TERM /THROUGH TONIGHT/...
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AS OF 1100 AM EST Monday... Fog finally lifting across the New River Valley. Satellite imagery still shows quite a bit of stratus, so not much hope for sun unless you are west of the Appalachian Divide. Confluent flow over the northeast at 500 mb will keep high pressure situated over the area, with a wedge of cool air down the east side of the Appalachians. Temperatures will struggle to get out of the 40s on the east side of the mountains this afternoon, but on the west side (west of a Boone NC to Bluefield WV line), it will be a much nicer afternoon with temperatures climbing into the U50s to near 60 along with some sunshine. Weather boils down to a tale of two weather regimes today with our far southwest CWA much warmer than the eastern three quarters. Wedge front will be aligned near I-77 and this will likely remain static for most of the day. Models try to erode this boundary from the west per increasing southwest winds aloft, but cold air is dense and heavy and does not like to move, so unless we can get some peaks of sun through this stratus to promote deeper mixing, then the thermometer is just not going to budge much this afternoon. Tonight, a decent shortwave pushes across the midwest. At the same time, surface high over the mid-Atlantic shifts offshore and well east of the NC coast. Will still see some cold air damming in the east tonight. Expect temperatures to drop a few degrees in the east with upper 30s to mid 40s, while the west drops a little more, though still mild for mid-January with mid 40s to lower 50s from Southern WV to the NC mountains. Upstream cold front stays far enough west that pops are expected to be less than previous forecast with limited forcing. With some low level convergence near the Blue Ridge, will see some low chance pops here overnight, with slight over little chance in the piedmont. Rain showers should get pretty close to southeast WV by dawn so have pops close to 50.
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&& .SHORT TERM /TUESDAY THROUGH THURSDAY NIGHT/... As of 415 AM EST Monday... While not overly significant, it continues to project to be a relatively active short-term forecast period with at least two and potentially three upper-level disturbances focusing rain chances with above-normal temperatures continuing through most of the period as we remain on the northern periphery of dominant, if rather flat southeast CONUS mid-level ridging. For Tuesday: 500 mb closed low roughly positioned over the mid- Mississippi Valley deamplifies as it moves northeast. It streams an weak warm front northeastward across the mid-Atlantic and Appalachian region during the day, the warm front associated with warming 850 mb temps and chances for rain. Given the best upper- level support for large-scale lift is confined to our northern counties (and frankly is better into northern WV and PA), I`ve showed something of a gradient in PoPs/QPF associated with the warm front with the highest respective values furthest north and lowest in the southside Virginia and the foothills and Piedmont region in North Carolina. PoPs then begin to decrease slightly into the Chance/low Likely range into the afternoon, in a narrow warm sector characterized by overcast conditions and weak to nil surface convergence in deep southwest flow, ahead of a cold front likely to be positioned over the Ohio/West Virginia border area. Rainfall amounts range from a few hundreths south to up to one-quarter inch furthest north. Tough forecast as it pertains to highs given the likelihood of overcast and early-day rain offsetting southwest flow and 850 mb temps warming to near +8 to +10C. I`ve sided toward some of the more pessimistic/cooler raw guidance into the mid and upper 50s. Should greater clearing be realized, these may be 2-4 degrees too cool. For Tuesday Night: Quasi-zonal confluent mid-level flow is replaced by 500 mb height falls as a positively tilted shortwave trough interacts with a southeastward-sagging cold front Tuesday night. Expect any break in afternoon showers to blossom back up along the boundary, with the highest PoPs across far southwestern Virginia, southeast West Virginia and building into northwestern North Carolina. Westerly boundary-parallel flow would argue for a slower southeastward advance of the front and potentially higher QPF values across the NC mountains into the Grayson Highlands/Mountain Empire region (forecast near 0.25") to a tenth of an inch or less elsewhere of additional rain. Cold advection should allow for low to dip into the mid/upper 40s, but areas east of the Blue Ridge into the Piedmont stand to only fall into the low 50s, a couple degrees cooler than daytime highs. For Wednesday: Baroclinic zone gradually builds southward into central North Carolina with any early-morning showers dissipating in southern sections. More variable cloud cover is anticipated with greatest coverage along and west of the Continental Divide into southeast West Virginia in weak ridging. 850 mb temperatures fall in cold advection to values a couple degrees either side of 0C, and Wednesday may be the only time our low-level thermal structure is this cool for the foreseeable future. While post-frontal downslope flow should push temperatures east of the Blue Ridge into the mid 60s, highs in the lower/mid 50s are more likely west of the Blue Ridge into the Alleghany Highlands. For Wednesday Night: Mid-level heights then begin to rise Wednesday night in response to digging upstream trough over the central Plains. Surface high pressure the rule in an otherwise uneventful forecast, with some high clouds advancing in toward early Thursday morning. Temps look to fall back into the upper 30s under better radiational cooling conditions than the past couple nights. For Thursday/Thursday Night: Ridging should generally prevail through most of Thursday, but is gradually replaced by neutral to negative height falls in mid-levels by Thursday night as highly- amplified mid-level closed low over the central Plains moves into the Mississippi Valley. Deep southerly flow across most of the South yields a large shield of precipitation, some potentially convective well to our southwest over the Tennessee Valley. It`s not likely we see rain into our western zones until overnight Thursday/early Friday morning. Think in reality the QPF shield may look similar to that depicted in the 00z ECMWF, so I`ve weighted PoPs more heavily in that direction. Highs Thursday in the 50s to near 60 in northwest NC, with lows in the upper 30s/low 40s. && .LONG TERM /FRIDAY THROUGH SUNDAY/... As of 330 PM EST Sunday... The upper pattern will become highly amplified as we head into the weekend with a sharp ridge along the east coast and a southern stream closed low moving across the deep south. This pattern will eventually bring abundant moisture to the region as we head into the start of next week. Focus for steadiest widespread rain remains on Friday. High pressure over New England will then form a wedge down the east side of the Appalachians for the weekend. Isentropic lift will be steadily increasing as low pressure develops over the lower Mississippi valley and low level southerly winds ride up over the wedge. This will steadily increase our chances for precipitation, especially for Sunday into Sunday night. && .AVIATION /16Z MONDAY THROUGH FRIDAY/... As of 615 AM EST Monday... Have low confidence that the majority of the area will rise above MVFR today. Wedge in place will keep cigs down around 2kft or lower especially in the mountains and foothills. A bit of LIFR to VLIFR fog this morning at BCB. A few model try to bring some breaks in the clouds this afternoon in the BCB/BLF corridor but will keep it under VFR. BLF has the best chance if any to clear the wedge enough to see VFR but will not forecast that yet. Any fog should lift and/or increase to 5-6sm by midday. Patchy drizzle/light rain may impact LWB early, most locations damp but limited in precip today into this evening. Approach of a front expected late tonight may bring showers to the BLF/LWB corridor, otherwise, think wedge bucks back toward the mountains overnight as the surface high moves offshore. Could see sub 1kft cigs at BCB/ROA again and possibly LYH/DAN/LWB. Will go more pessimistic as both GFS/NAM keep cigs very low. Extended Aviation Discussion... A stronger front will arrive By Tuesday with more showers including widespread sub-VFR. Generally looking at MVFR much of the period, although periods of VFR as well as IFR-LIFR can be expected at times. Models remain uncertain with timing of another wave along a passing cold front during midweek. Some guidance showing another round of showers with sub-VFR on Wednesday with improving conditions Thursday. This while others slower with a break on Wednesday before moisture returns from the southwest Thursday afternoon into Thursday night, lasting into Friday as front stays south of us allowing moisture to spread north into the mid-Atlantic. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...PM/WP NEAR TERM...PM/WP SHORT TERM...AL LONG TERM...MBS AVIATION...RCS/WP

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