Area Forecast Discussion
Issued by NWS Blacksburg, VA

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021 FXUS61 KRNK 281141 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 741 AM EDT Sun Aug 28 2016 .SYNOPSIS... High pressure at the surface and aloft will remain over the region today. A weak cold front will begin to approach from the north Monday, then stall near the North Carolina border awaiting another front that will arrive from the north Thursday as high pressure aloft weakens. && .NEAR TERM /THROUGH TONIGHT/... As of 400 AM EDT Sunday... High pressure along the northern Mid-Atlantic coast has pushed a backdoor cold front toward the Alleghany front and northwest North Carolina Blue Ridge. The air mass across central and northern Virginia was drier and mostly void of low clouds/fog as a result. The location of the backdoor frontal boundary will be further west today as compared to Saturday. Thus, expecting any afternoon showers/storms to be confined to areas mainly west of the RNK CWA, but a few could develop or creep into the western periphery of the CWA, especially where the wedge normally tends to be weaker, say west of the I-77 corridor. Will maintain low pops in those areas, otherwise looking at a precipitation free day for the vast majority of the CWA along with mostly sunny skies. Any convection in the western areas will dissipate quickly with the loss of daytime heating. Temperatures will be slightly cooler today as 850mb temps fall back closer to +20C and the drier/slightly cooler air mass spreads southwest into the region from the northern Mid-Atlantic. The drop in dewpoints/RH values will likely be more noticeable than any temperature drop as the sun will still feel quite warm/hot this afternoon at any rate temperatures will still average about 8-10 degrees above normal. Overnight, a weak tropical low off the NC coast will drift northwest toward the coast and this will likely result in increasing RH values after midnight along with mid/high clouds into the Piedmont. To the north, a weak front will be nearing the PA/WV/MD border. Expect partly cloudy skies most areas with increased likelihood of patchy fog development as the wedge weakens and moisture begins to encroach from the southeast. && .SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/... As of 145 AM EDT Sunday... A persistent upper ridge will continue to rest across the Ohio River Valley eastward into northern Virginia through Monday. This will help maintain a prevailing easterly flow into and through the region that will bring with some Atlantic moisture. Trajectories will have their origin initially across New England before skirting the far western Atlantic then coming onshore once again. Look for the development of isolated to scattered afternoon showers and a few thunderstorms across western portions of the area. Here the impacts of any capping inversion will be least and orographical impacts and differential heating will lead to convection development. Any activity is anticipated to wane through the Monday evening hours. More of the same is expected on Tuesday. However, even a greater fetch of moisture off the Atlantic is anticipated. This will allow for a increased coverage of showers and storms as compared to 24 hours prior. The far southeast portion of the area may be hard pressed however to experience any convection. Convection will again wane through the evening hours, with some isolated coverage in the west into the early morning hours of Wednesday. Wednesday into Wednesday night, a cold front is progged to move southeast into, through and out of the area. Look for a trend of increasing showers and storms during the day Wednesday, with lingering showers across the eastern portion of the area during the evening and overnight hours. Temperatures during this portion of the forecast will trend slightly cooler each day. However, readings will still be above average for this time of the year. Highs will average around five degrees above average with the lows close to ten degrees above average. && .LONG TERM /THURSDAY THROUGH SATURDAY/... As of 400 AM EDT Sunday... General model consensus for the second half of the week is for the upper ridge to give way to some weak upper level troughing over the eastern CONUS, progressive flow across the northern tier states gradually whittling away at the eastern ridge. This should allow for another front to come through from the northwest during the period, although model uncertainty is high with respect to timing per unresolved solutions ongoing in the tropics. As such will keep the forecast pretty close to persistence with respect to precip probabilities, but shave a degree or two off the temperature per potential for drier air to infiltrate from the north later in the week, temperature trending closer to normal. && .AVIATION /12Z SUNDAY THROUGH THURSDAY/...
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As of 735 AM EDT Sunday... Mostly VFR conditions expected through the TAF valid period. A back door front will stall in the far western part of the CWA near the VA/TN/WV border during the period as another weak front approaches from the north Monday. Deeper moisture will be pushed mostly west of the CWA today by the developing drier east-northeast flow across the area from the weak surface high pressure off the northern Mid-Atlantic coast. Meanwhile, a strong ridge aloft will prevail over the region, centered across the Delmarva during the period. BKN low clouds mainly west of the Blue Ridge this morning could linger til around 15Z, then should dissipate. However, some low end VFR cigs could linger across southwest WV and far southwestVA, mainly west of I-77 into the early afternoon. Cannot completely rule out isolated shra/tsra western periphery of the CWA, including KBLF during the late afternoon, but feel that push of drier air should limit the threat to areas further west of the RNK CWA. Confidence to include in the KBLF TAF is too low at this point. Overnight and Monday morning, other than cirrus clouds spreading in from the southeast associated with a tropical disturbance off the SC/NC coast, cigs will be VFR. Fog development early Monday is in question as feel enough northeast-east wind will remain in place combined with the slightly drier air to preclude such. However, as always, KLWB and KBCB will be in question. Included a MVFR condition for KLWB, which could end up being none or the usual 1/4SM FG. Winds will be NE- ESE through the period at speeds of 5-8kts. Cannot completely rule out some low end gusts across the Piedmont from late morning through mid- afternoon, but have not advertised such at this time. Medium to high confidence in cigs and vsbys through the TAF valid period. Medium to high confidence in wind speed/direction through the TAF valid period. Extended aviation discussion... A weak west-east oriented front will drift south through the forecast area Mon. Isolated diurnally driven convection will be possible along the front toward the I-64 corridor Mon, then toward the NC/SC border by Tue. Coverage will be limited in duration and area on all days and have minimal impact on the TAF sites. Another front will move into the region Wed into Thu with a better chance for showers/thunderstorms, followed by cooler and drier air for Friday. Most of the period looks VFR at this point, outside of the usual late night/early morning fog/low clouds. At this time, it does not appear that any tropical systems will impact the CWA.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...RAB NEAR TERM...RAB SHORT TERM...DS LONG TERM...DS/PM AVIATION...RAB

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