Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 251512 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1112 AM EDT WED MAY 25 2016 .SYNOPSIS... 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. && .NEAR TERM /THROUGH TONIGHT/...
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As of 1100 AM EDT Wednesday... 12Z/8AM RNK sounding was dry... PWAT 0.48. Models indicate moistening forecast throughout the afternoon, but little or no precip threat unless you reside west of I-77. Deeper moisture is advancing across the OH/TN valleys...associated with scattered showers...so our far western CWA may encounter the eastern fringe of this activity during the late afternoon and evening. As the high country of NC warms, the meso models are also indicating some build-ups there with widely scattered showers and possibly a thunderstorm after 3PM. 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. 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/... 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. && .LONG TERM /SUNDAY THROUGH TUESDAY/... 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. && .AVIATION /15Z WEDNESDAY THROUGH SUNDAY/... As of 735 AM EDT Wednesday... Generally VFR conditions expected through the TAF valid period...with a few exceptions...mainly in the form of late night/early morning fog. Fog this morning limited to the Greenbrier Valley with KLWB briefly seeing IFR-LIFR vsbys. Any fog will dissipate quickly in the 13Z-14Z time frame. Through the day...main focus will be on short wave ejecting from broad upper low in the southwest U.S. Moisture and instability will increase in advance of this system through the afternoon...which may support scattered showers and isolated thunderstorms across the Alleghanys...far southwest VA...and northwest NC mountains late afternoon. Any activity could linger through the evening and overnight as the disturbance tracks northeast through the OH valley...so will carry VCSH KBLF...KLWB...and KBCB through the night. Will refrain from mentioning TSRA at this time as confidence in such given limited instability is low. Fog development early Thursday questionable...but late night rainfall and light winds could contribute to such in the KLWB and KBCB area. For the most part...cigs are expected to remain aoa050 through the TAF valid period...but BKN050 cigs a good bet west of the Blue Ridge this afternoon and overnight in association with upstream disturbance. Winds...mostly SW 5-8kts daytime...3-5kts or less at night. Medium to High Confidence in cigs through the TAF valid period. Medium to High Confidence in vsbys through the TAF valid period. High Confidence in wind dir/spd through the TAF valid 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/PM SHORT TERM...RAB LONG TERM...PM/RAB AVIATION...DS/MBS/RAB

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