Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 261141 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 741 AM EDT Fri Aug 26 2016 .SYNOPSIS... High pressure will be the dominant weather feature through the upcoming weekend...becoming centered directly overhead by Saturday. A cold front may slowly slide southward into the area by the middle of next week. A tropical low will gradually strengthen off the southern tip of Florida early next week and then possibly move off the coast through the week. && .NEAR TERM /THROUGH TONIGHT/... As of 300 AM EDT Friday... Mostly clear skies with light winds has resulted in patchy low clouds and fog this morning. Strong subtropical ridge of high pressure will remain across our region today and tonight. An isolated shower or thunderstorm may be possible this afternoon mainly over the southern Blue Ridge. It will be hot and humid this afternoon. Heat indices in the Piedmont should stay just below the century mark. High temperatures will range from the lower 80s in the northwest mountains to the mid 90s in the Piedmont. Clear to partly cloudy conditions expected tonight with areas of fog, especially in the western mountain valleys. Low temperatures tonight will drop into the lower 60s in the west to the lower 70s in Piedmont. && .SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/... As of 400 AM EDT Friday... A strong 596dm upper ridge will be centered over the region yet Saturday, with the center actually very near KROA or KBCB. Expect strong subsidence with warm temperatures aloft, +20C to +22C at 850mb and -4C to -5C at 500mb. The old cold dissipating cold front will likely lie across central NC into northern GA at this point. Most models develop a fair amount of convection and associated QPF around the western and southern periphery of the upper high as well as near the front, but especially across northwest NC and northeast TN. This appears overdone given the synoptic pattern in place, so have stuck with slight chance/20% pops mainly along and west of the Alleghany front/Blue Ridge, or primarily west of of I-77. In addition, models hang on to convection too long after 00Z as with no dynamics, activity will almost entirely be diurnally driven and dissipate quickly with the loss of daytime heating. Am not advertising pops in the 06Z to 12Z time frame. Temperatures will remain very warm Saturday and a good 10 degrees above normal, both lows and highs, with abnormally high dewpoints as well for late August. Look for highs still in the low to mid 90s across the Piedmont, with mostly 80s west. Lows will still only be in the 60s west to lower 70s east with dewpoints still hovering in the 60s to lower 70s same areas. For Sunday, the upper ridge shows signs of weakening and shifting just south of the area, but nonetheless remains the underlying theme of the synoptic pattern across the eastern U.S. A new weak cold front is evident across the OH valley into western PA/NY. This will be too far north of the RNK CWA to have any impact on our sensible weather at this point. There should again be diurnally driven convection mainly across the mountains and along the western periphery of the upper high, namely southern WV southward through eastern TN and western NC. Overall coverage should be on par with Saturday to perhaps less, with little to no activity across the Piedmont. Again, convection should weaken quickly with the loss of daytime heating. With upper heights and 850mb temps dropping a tad, expect daytime max temps to overall drop 1-2F across the CWA, yet still leaving readings well above seasonal normals. By Monday, the ridge continues to weaken slightly, yet remains the dominate feature for much of the mid latitudes of the U.S. A new west-east oriented weak cold front beings to drift toward the region from the north. As a result, most models indicate a slight uptick in convection across northern WV/northern VA toward the I-64 corridor by afternoon. Dynamics remain weak, but slight cooling aloft may provide for slightly better coverage northern areas than expected over the weekend. Southern parts of the CWA should remain mostly rain free. Temperatures will remain above normal, but instead of 10 degrees above normal, should be more on the order of 7-8 degrees above normal. Minimum temps will continue to show the greatest positive departures from normal, in the mid 60s west to lower 70s east. && .LONG TERM /TUESDAY THROUGH THURSDAY/... As of 430 AM EDT Friday... As with previous days, the main concern during the extended periods continues to revolve around a potential southeastern U.S. tropical system. Models continue to exhibit notable differences, but the general trend is toward a weak tropical low to drift into south Florida early to mid part of next week, then move northeast along the FL/GA/SC coast. The ECMWF has shown the most deviation from previous forecasts, now advertising a much weaker system than previous runs, and much closer to what the GFS has been advertising for the past several runs. This leave the RNK CWA largely unaffected on the northwest/dry side of the system with the main concern being the aforementioned front lingering across the region. It is quite possible that the RNK CWA will have no impact at all from this tropical system, but the exact solution remains to be seen. The trend to a weaker and further east tropical system is largely driven by a deeper trough now progged to develop across the northeast U.S. during the mid and later part of next week. This would tend to shunt the effects of a tropical system further east and quicker out to sea. Another feature of note that all models are picking up on is a weak tropical system now slated to develop along the TX Gulf Coast early next week. The moisture from this system could track north and northeast along the weak southward moving frontal boundary and enhance precipitation. However, for now, this appears to mainly be a concern for the Midwest, not here. Despite these changes, there is still not clear consensus to advertise anything greater than slight chance to low chance pops with weak forcing and limited synoptic systems of importance through this period. Maximum temperatures should continue to slowly cool during the period with a tendency toward upper troughing and lowering upper heights. Increased cloud cover will also help. Maximum temperatures will be mostly in the 80s through the period, except 70s mountains. However, PWAT/RH values will remain high and minimum temperatures will remain well above normal in the 60s mountains to lower 70s Piedmont. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/...
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As of 735 AM EDT Friday... High pressure both surface and aloft will control our weather today and tonight. Outside of morning fog and very isolated convection mainly along the western periphery of the CWA, great flying weather is expected. This morning, the combination of light winds and abundant low level moisture has produced patches of dense fog. KLWB and LBCB both seeing LIFR-VLIFR conditions in localized dense fog and VV cigs. KLYH and KDAN have MVFR conditions. Fog and associated cigs will burn off within a couple of hours after sunrise. For the remainder of the day, just sct VFR CU expected with strong subsidence aloft in place. Any convection too isolated and likely west of any of the TAF sites. Only site that may see convection nearby should be KBLF. Models do show a period of mid clouds traversing the region during the mid to late afternoon, so have introduced some 080-100kft clouds as a result. Fog and associated ceilings will likely develop again after 06Z in the usual spots, namely KLWB, KBCB, and KLWB in the very moist, stagnant air mass. Winds will be light NW-NNE through the TAF valid period at 4-7kts, becoming mostly calm after 00Z. Medium to high confidence in cigs and vsbys through the TAF valid period. Medium to high confidence in wind direction through the TAF valid period, with high confidence in wind speed through the TAF valid period. Extended aviation discussion... Strong ridging to hold tight on Saturday with continued VFR and again only isolated late day mountain shra/tsra resulting in possible brief MVFR. A weak front will drift into the area Sunday. Isolated to scattered diurnal showers and thunderstorms still possible into Sunday evening. Coverage will be limited in area and duration. Monday high pressure bubbles in but still a very humid airmass to keep isolated mountain storms around in the afternoon, but mainly VFR. Another front situated north of us Tuesday could enhance convective threat, mainly over the mountains and north of ROA/LYH.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...KK NEAR TERM...KK SHORT TERM...RAB LONG TERM...PM/RAB AVIATION...JH/KK/RAB

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