Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 250846 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 446 AM EDT WED MAY 25 2016 .SYNOPSIS...
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High pressure will continue to build off the southeast coast and push warmer and more humid air into the region. This will bring well above normal temperatures to the appalachians and central mid Atlantic region...along with a chance for afternoon showers and thunderstorms...into the weekend. Then...a developing area of low pressure off the coast will begin moving in our direction and bring greater chances for precipitation for the latter portion of the Memorial Day weekend.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As of 430 AM EDT Tuesday... High pressure off the southeast coast will continue to push warmer and more humid air in our direction today. A combination of orographic effects from the Blue Ridge westward along with some upper level short wave energy looks like it will be enough to generate some low chance POPs for a late day shower. Meso guidance has trended these chances upward of late but do not have enough confidence in these wetter solutions at this time to go with higher POPs far west so will wait and see if the trend sticks around in later model runs and adjust upward if needed. However there does appear to be enough support to add a slight chance of thunder to the mix with this grid package. For tonight it looks like any convection will be tapering off early but there are indications that another impulse will keep some showers going overnight with some additional development spreading eastward into the piedmont. Will keep chance/slight chance pops going through the overnight period for most locations. With the influx of warmer air high temperatures will reach the middle and upper 80s east of the Blue Ridge with upper 70s/around 80 more common to the west. Lows tonight will generally be in the upper 50s to lower 60s.
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&& .SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/...
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As of 400 am EDT Wednesday... Synoptic pattern will continue to feature a deep and highly diffluent upper trough in the southwestern U.S. This system is not expected to move much at all through the period. Meanwhile...a downstream upper ridge will be located across the eastern half of the country. For Thursday...the main focus for our region will be on a short wave that is slated to eject northeast from the western U.S. upper low into the Ohio Valley Thursday...then toward New England by Friday. Ample moisture and instability will be present by Thursday afternoon to support scattered showers and thunderstorms...with the best focus west of the Blue Ridge closer to the upper support and better thermodynamics. Dynamics are weak at best...so expecting non-severe pulse thunderstorms. There is the potential for showers to be ongoing/developing early in the day Thu across the northwest...but the best coverage/intensity will be during the afternoon into the early evening. The aforementioned short wave moves northeast of the region Friday. The southwest U.S. upper low drifts slightly further east into the TX/OK region. As a strong short wave rounds the base of the upper trough...the upper flow amplifies with the flow becoming more meridional across the central and eastern U.S. Thus...it appears that this next short wave will largely lift northwest of the RNK CWA with upper ridging the dominate feature across our region. Showers/thunderstorms Friday will be highly diurnally driven and mainly focused across the Alleghanys and mountains of southwest VA/northwest NC. Areas east of the Blue Ridge may see a decrease in convection Friday as that area comes under increasing subsidence on the northwest side of a developing low pressure area across the Bahamas. For Saturday...the western U.S. upper low continues with a strong short wave lifting almost due north through the Midwest...thus having little to no effect on the RNK CWA. Our attention will be increasingly turning toward the southeast and a potential developing tropical system across the Bahamas. All models indicate strong potential for a tropical or subtropical system to develop across the Bahamas and drift northwest toward the SC/NC coast. The GFS remains one of the most aggressive models with this development...pushing deep tropical moisture well northwest into the RNK CWA by Sunday with PWATS into the 2+ inch range. The other models remain less aggressive with this deep moisture...tending to focus the effects of such closer to the NC/SC coast. This is in agreement with WPC thinking at this time. For Saturday...subsidence to the northwest of this developing low pressure area will likely suppress convection for much of the CWA...outside the Alleghanys and southeastern sections late in the day. One thing for sure during this period...our extended cool weather of recent will be gone. This entire period will feel much more like August with increasingly high humidity and temperatures in the 70s mountains and 80s elsewhere. Steadily increasing dewpoints/PWATS/RH values will result in some of the muggiest conditions we have experienced so far this year and will be in sharp contrast to the well below normal temperatures we have experienced most of May to this point. Low temperatures will tend to average 8-10 degrees above normal with max temps 5-8 degrees above normal. The increase in humidity will be the most notable part...however.
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&& .LONG TERM /SUNDAY THROUGH TUESDAY/...
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As of 430 am EDT Wednesday... This period will be dominated largely by the aforementioned tropical system slated to drift northwest into or near our region Sunday into Monday. The upper flow will remain quite stagnant with an upper high to our north and a broad upper low continuing in the western U.S. Therefore...if the tropical system does drift into the GA/SC/NC area as most models suggest...although there are notable differences in the distance it will track inland...it will likely linger for several days with non-existent steering currents and blocked upper flow. The upper high to the north could keep the system lingering in place for several days. Rainfall may become a concern depending on how far inland the system tracks. The ECMWF continues to paint the least ominous solution...keeping the bulk of the precipitation and higher PWATS closer to the coast. At a minimum...we can expect scattered diurnal convection with warm/humid conditions through the period. Max temps will remain mostly in the 70s mountains and 80s elsewhere...with lows mainly in the 60s. Have not made any drastic changes to the extended pops as there is still considerable uncertainty in exactly how much precipitation we will see.
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&& .AVIATION /08Z WEDNESDAY THROUGH SUNDAY/... As of 140 AM EDT Wednesday... Early in the TAF period we will have good conditions for radiational cooling and this will likely generate some fog toward daybreak. KLWB is most likely to see LIFR while KBCB may tempo to IFR and KLYH/KDAN may see a period of MVFR vsbys. Any fog/stratus will dissipate early Wednesday morning and leave sites with VFR conditions for the rest of the period. However as the circulation around high pressure off the southeast coast continues to pump warmer and more humid air into the region from the southwest...some showers may develop form the Blue Ridge west thanks to orographic effects and some upper level short wave energy. Will use VCSH west of the Ridge with no mention of precipitation to the east. Winds will be light through the period. Extended discussion... Wind flow through Friday will be out of the southwest with the weather pattern more reflective of summer conditions, primarily VFR except for widely scattered afternoon and evening showers during the peak heating part of the day. Nightime fog also possible in the mountain valleys, but mainly after midnight up until an hour or two after daybreak. Potential wind flow change is advertised by the models this weekend per development of a storm system off the southeast Atlantic Coast. Models differ quite a bit on timing and movement of this feature so low confidence forecast beyond Saturday attm. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...MBS NEAR TERM...MBS SHORT TERM...RAB LONG TERM...PM/RAB AVIATION...DS/MBS

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