Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 281056 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 656 AM EDT Wed Sep 28 2016 .SYNOPSIS... A weak frontal boundary will continue to meander east of the Blue Ridge through late week. A strong upper level area of low pressure will also drop south into the Tennessee Valley Thursday into Friday before lifting back north by Saturday. The combination of these features will lead to rounds of showers and storms through the rest of the week before drier weather arrives this weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 250 AM EDT Wednesday... Bands of deep convection continue across southern sections early this morning to the east of the stalled surface front and under the tail of a passing jet max to the north. Latest short term guidance shifts this area of weak instability/convergence east by sunrise as a weak surface wave passes. This may bring a brief lull in coverage early this morning with low clouds likely to persist back to the Blue Ridge in the wake of this early shra/tsra per weak easterly flow. Strong upper low to the north should continue to dig south into the Ohio Valley later today causing sharpening of the backing southwest flow aloft across the region. This should act to spill moisture back westward by afternoon ahead of perhaps another weak surface wave sliding up the residual surface front to the south. Guidance suggests this will allow for a highly diffluent scenario to take shape aloft this afternoon with good shear including decent low/mid level flow of 30-40 kts espcly eastern third later on. In addition, arrival of cooling aloft should help overcome potential lack of good instability given low clouds lingering out east. Most solutions including the latest Cams tend to focus best coverage along/east of Highway 29 per high PWATS, then gradually fill in back into the Blue Ridge. Will also have a leading band of showers ahead of the upper low approaching the west late, but still appears will be a break between the two over the far west/southwest sections where drier air will remain nosed in. Therefore running with a gradient of likely/categorical pops east to likelys eastern slopes of the Blue Ridge to low/slight pops far west. Appears the east also has the best shot at isolated pulse/training storms given chilly temps aloft while QPF of 1-2 inches possible in spots but not widespread enough at this point for a watch today. Highs mostly in the 70s pending clouds/showers, but could get close to 80 southeast if convection is less or later to redevelop. Complex interaction of the residual front and bands of showers around the upper low will persist into the overnight with added potential for stronger storms north/east at least this evening per 00z ECMWF. Could eventually work into a dry slot aloft espcly western half later tonight as suggested by the latest HiRes-ARW but that remains iffy as features likely slower to exit than progged. Otherwise given expected good lift and continued deep moisture off models eastern half, will continue likely pops through around midnight and then slowly taper to mostly chance most sections late. With lots of clouds lingering and the front stuck across the region, expect lows to be warmer than earlier expected with mostly 50s mountains, while the east likely remains in the low/mid 60s overall. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... As of 400 AM EDT Wednesday... A closed upper low is expected to stall across the Ohio River Basin during the day Thursday, while a series of disturbances, including an encroaching cold front from the west, will begin to interact with the deep atlantic moisture and pulse along the mid Atlantic Seaboard through the period. As a result, ongoing showers and thunderstorms are expected to continue across the eastern Piedmont counties of Virginia and North Carolina during the morning hours Thursday. Showers and storms will likely increase in coverage and intensity by mid afternoon, continuing the spread with the flow of moisture around the low and along the boundary. Some of the thunderstorms could be strong with hail, gusty winds, and heavy downpours. Impressive low level lapse rates coupled with unseasonably low freezing levels could aid in ultimate hail potential. Thunderstorm activity is expected to diminish in large part due to the loss of daytime heating and the subsequent instability axis overnight Thursday. Continuing light to moderate shower coverage will maintain through much of the overnight hours, with uncertainty remaining in just how much precipitation will fall. The NAM/ECMWF models continue to indicate very wet conditions while the GFS continues to keep the heaviest precipitation a bit north of the forecast area. Have tended to split the difference between the two model camps when it comes to QPF/POPs. Temperatures during the period continue to trend cooler for highs and warmer for lows. Expect daytime highs struggling to breach 70 degrees THU/FRI thanks to cloudcover. Low temps will remain cool, but trending a bit warmer than guidance due to abundant cloudcover and continued Warm Air Advection East of the Blue Ridge prior to the low pulling back North. Sub 50s to the west will be remain possible Overnight Thursday and especially overnight Friday. && .LONG TERM /SATURDAY THROUGH TUESDAY/... As of 300 PM EDT Tuesday... Closed upper low continues to lift northward through the Ohio Valley into the weekend. The low center continues to push into the Great Lakes by Sunday evening and New England by Monday. The low will move into the Atlantic ocean on Tuesday. Meanwhile, the potential for tropical low development across the Caribbean may lead to a threat for the southeast early next week. This is being monitored by the NHC and WPC. Temperatures will start cooler for Saturday with continued improvement as precip/cloudcover comes to an end, then temperatures begin to moderate Sunday into Tuesday. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... As of 640 AM EDT Wednesday... Convection has continued to weaken and pass to the east of the TAF sites early this morning leaving a swath of low clouds across the east and patchy fog to the west. Expecting at least MVFR cigs with ocnl IFR to hang in along/east of the Blue Ridge this morning and perhaps into this afternoon. Things will also become more unstable east of the Blue Ridge with scattered showers, some thunderstorms and mainly sub-VFR cigs where any convection does develop. To the west, appears more in the way of VFR cigs likely once early fog/stratus erodes although isolated convection also possible across the west later in the day. Therefore keeping lower cigs longer across eastern locations while including more vicinity mention of shra/tsra in all except the KLWB/KBLF corridor, and prevailing lower conditions from KLYH-KDAN where storms are more likely. Showers and storms likely to linger into the overnight with best coverage again along/east of the Blue Ridge with periodic MVFR to IFR possible mainly KROA and points north/east. Some patchy fog also could occur to the west, mainly in the valleys but appears could be too much cloudiness to allow radiative processes to produce dense fog. Therefore only including mention for brief MVFR level vsbys in fog at KLWB/KBCB later tonight. Few showers also possible mountains with the upper low but too iffy to include mention. More widespread sub-VFR appears possible Thursday with the upper low just west of the mountains and deeper moisture in place along the residual surface front in the east. This may lead to periods of showers and storms Thursday into Thursday night including rounds of heavier rainfall espcly affecting sites along/east of the Blue Ridge. Extended aviation discussion... A deep upper low will remain over the Ohio and Tennessee Valleys through Friday night. This will keep variable clouds, MVFR cigs, and periods of -SHRA across the region through much of the period. Should finally see VFR return during Saturday and continue Sunday as the upper low lifts north and weak high pressure builds in. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...AMS/JH NEAR TERM...JH SHORT TERM...JM LONG TERM...JM/KK AVIATION...AMS/JH/RAB is the U.S. government's official web portal to all federal, state and local government web resources and services.