Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 250540 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 140 AM EDT Sun Sep 25 2016 .SYNOPSIS...
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A backdoor front slide south into the Carolinas today, before stalling. High pressure following the front will wedge south along the eastern slopes of the mountains Sunday into early Monday. Another cold front will shift in from the west Monday night into Tuesday bringing better chances of showers and isolated thunderstorms for early next week.
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&& .NEAR TERM /THROUGH TODAY/...
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As of 125 AM EDT Sunday... Backdoor front located near the VA/NC border will continue southward this morning. Still a few showers skirting the piedmont and will see transition to patchy light rain/drizzle with low clouds along/near the Blue Ridge mainly north of Roanoke then shifting toward Southside by dawn. Expecting some patchy fog along the river valleys outside the wedge where its clear. Previous valid discussion... Low level flow remains northeasterly which should limit chances for measurable precipitation for the next 24 hours. However, moisture is shallow (under 4 kft), but will remain thick and overcast through the day Sunday. With some weak warm air advection, isentropic lift and flow turning more easterly on Sunday, light rain/drizzle is possible along eastern slopes of the Blue Ridge. As the front moves to the south, cloudy conditions will keep temperatures on the cool side for the next 24 hours or so. Considering the depth of the wedge is around 3000 to 4000 feet, just about everyone will see cooler than normal temperatures Sunday. Temperatures will only warm into the 70s with eastern slopes likely to stay in the 60s. The Bluefield-Richlands area will be on the western flank of the wedge and could see some erosion in the afternoon. A warm upper level ridge over the southern Mississippi Valley could stretch east into area, allowing southwest Virginia to warm to near 80F.
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&& .SHORT TERM /TONIGHT THROUGH TUESDAY/... As of 245 PM EDT Saturday... Low level wedge looks to be at its strongest Sunday night into early Monday with the axis of the surface high just east of the mountains aided by continued light rain/drizzle across the west and shortwave ridging aloft. Guidance even suggests that some drier air from the northeast could work into eastern sections during the evening given the strength of the high, allowing for brief clearing before the flow aloft starts to turn more southwest overnight. This should once again propel the shield of low clouds back east by early Monday with lingering low pops for light rain/drizzle espcly Blue Ridge and points west into midday Monday. Lows mostly 50s to lower 60s Sunday night with coolest air over the north/northeast. Wedge should begin to scour out Monday afternoon as ridging aloft flattens in advance of the strong upstream upper trof that will push an associated cold front toward the mountains by late in the day. Models also show quite an increase in moisture depth ahead of the front with PWATS near 2 inches under decent southwest flow aloft. This deepening flow looks to gradually weaken the wedge from west to east by Monday evening although far northeast sections may not see the cool pool exit until overnight when the pre-frontal showers arrive. However does appear to be enough instability and added focus as the warm front lifts north and the pre-frontal lobe enters, to support some low chance thunder mainly south/west late Monday, with more widespread shower coverage progressing east during the overnight. Latest ensembles as well as a mix of the GFS/EC also support a swath of around one half to as much as one inch of qpf espcly central/eastern sections. Therefore running with a period of high chance to low likelys from west to east starting late Monday mountains and out east into early Tuesday. Boundary may slow enough during Tuesday given the stalling nature of the strong upper low to the north, to linger some shower pops eastern sections, with more clearing developing mountains by afternoon. Stayed with cooler highs Monday, 70-75, except perhaps near 80 far west where will exit the wedge sooner. Appears enough cool advection to hold much of the mountains in the 60s to around 70 Tuesday espcly if clouds persist longer, with the east mainly mid 70s pending how soon the showers end. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... As of 145 PM EDT Saturday... Upper low/trof should push east across the mid-Atlantic during midweek with its associated cold front exiting the region to start the period. However latest model trends suggest a somewhat slower scenario with lots of uncertainty in just how fast this will happen given the slow evolution of this complex upper system to the north. Based on current and still rather progressive model solutions, could still be looking at a few evening showers southeast Tuesday night as the front perhaps slows per added low pressure rippling northeast. Also passing of the center of the 500 mb trof axis/cold pool may also generate a few showers mainly northern/western sections late Wednesday into early Thursday but iffy. Otherwise should see much drier air invade the area as ridging both surface and aloft take control from later Thursday into next weekend. Expect mostly seasonal temps with highs 60s west to 70s east with coolish overnights with some 40s mountains and 50s elsewhere. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/...
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As of 130 AM EDT Sunday... Backdoor front situated along the NC/VA border will slide south today. Lower ceilings already working as far southwest as ROA/MTV/SIF and points northeast. Question will be how far southwest this canopy of MVFR to IFR ceilings makes it. Think bCB will soon drop to MVFR as will LWB. BLF should stay out of the wedge clouds but could see some patchy IFR ceilings or vsbys after 09z. Models show this wedge slow to erode Sunday with MVFR or worse conditions prevailing most of the morning, and do not see LYH/DAN/BCB getting above 3kft at all this taf period while ROA may briefly rise above 3kft this afternoon only to fall back after 00z. Drizzle may impact LYH/DAN but overall should keep vsbys VFR, while ROA could see enhancement of drizzle this morning given some upslope component which will drop vsbys to MVFR. BCB/LWB vsbys will vary depending on how thick the low clouds get but do not foresee LIFR so keeping it more IFR at times. Needless to say not good flying conditions east of the Alleghany Front. Extended aviation discussion... The backdoor front will drift to just south of the area by Sunday night and stall. Overrunning will begin in earnest Sunday night into Monday in advance of a strong, but slow moving, cold front that will approach the area from the west late Monday. A healthy line of showers and a few thunderstorms can be expected in advance of the front as it moves through the region during this time frame. Widespread sub-VFR cigs/vsbys are expected in the wedge air mass Monday before the front arrives, which will also be accompanied by a period of sub-VFR cigs/vsbys. Conditions will improve by midweek, although as an upper low sinks southward over the Appalachians, conditions could become unsettled enough to continue periods of sub-VFR cigs and scattered showers.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH/WP NEAR TERM...JR/RAB/RCS/WP SHORT TERM...JH LONG TERM...JH AVIATION...RAB/WP

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