Area Forecast Discussion
Issued by NWS Blacksburg, VA

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254 FXUS61 KRNK 272349 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 749 PM EDT FRI MAY 27 2016 .SYNOPSIS...
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High pressure remains off the mid-Atlantic coast tonight and expands west toward the southern Appalachians by Saturday morning. A tropical depression shifts northeast toward the South Carolina coast by Sunday morning, lingering across the Carolinas through the first part of next week.
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&& .NEAR TERM /THROUGH SATURDAY/... As of 320 pm EDT Friday... A southwest flow of warm and moist air continues around the high pressure center off the Mid Atlantic coast this afternoon into Saturday. The combination of heating,instability and terrain creating scattered showers and thunderstorms this afternoon. SPC Mesoscale Analysis at 18z showed SBCAPE of 1000 to 2000 j/kg. SB LIs were minus 2 to minus 4 this afternoon. The best chance for showers and thunderstorms will occur along the Blue Ridge and Alleghanys this afternoon into this evening. With limited shear and instability, not expecting any severe weather this afternoon. However, slow moving thunderstorms in weak upper flow could produce locally heavy rains. Combined the HRRR and NAM for pops this afternoon, then shaped towards Superblend for tonight. With the loss of solar heating, convection weakens and ends after midnight. With moist low level and some clearing expect areas of fog to develop, especially in the valleys and where it rains during the afternoon/evening. Low temperatures remain mild with readings from the upper 50s in the mountains to the mid 60s in the Piedmont. For Saturday and beyond, the main concern continues to focus around a tropical system/low, that the models are in general agreement on drifting northwest from the Bahamas into South Carolina by early next week. In advance of this feature Saturday...there will be an area of subsidence and a definite lack of precipitation. However, with heating and some instability expected isolated to scattered showers and thunderstorms to develop in the northwest portions of the forecast area. High temperatures Saturday afternoon will range from the mid 70s in the mountains to the mid 80s in the Piedmont. && .SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/... As of 320 pm EDT Friday... Please refer to products and bulletins from the National Hurricane Center regarding tropical low. The ridge along the Mid Atlantic coast will start shifting east Saturday night as tropical disturbance/tropical storm makes landfall on the South Carolina coast. Rain showers should track into or develop across the southeast part of the Piedmont Saturday evening...but would expect rain overnight into early Sunday to focus more toward the core of the tropical system. Increased pops and QPF for Saturday night especially with upslope flow along the southern Blue Ridge mountains. Low temperatures on Saturday night will only drop into the upper 50s in the west to the mid 60s in the east. Sunday will be very unsettled with periods of rain across the forecast area. The rain will be heavy at times. Played the highest pops along the southern Blue Ridge with the upslope enhancement. PWATS climb upwards into the 1.5 to 2.0 inch range and an area of deep tropical moisture appears evident on most models from the tropical low northward across the Piedmont. The amount of thunderstorms is in question as instability is minimal given extensive cloud cover and a saturated atmosphere. Lowered high temperatures Sunday to around 70 degrees in the mountains to the upper 70s in the Piedmont. Showers and a few thunderstorms continue Sunday night with best chances along the Blue ridge mountains. Low temperatures Sunday night will vary from the mid 50s in the northwest mountains to the mid 60s in the piedmont. && .LONG TERM /MONDAY THROUGH FRIDAY/... As of 230 pm EDT Friday... Model guidance varies on the position and timing, but each offer a solution for an area of low pressure along the east coast Monday morning, somewhere between South Carolina and North Carolina. Moisture on the western flank of this system is progged to influence our region to various degrees through Tuesday, model dependent. The GFS and Canadian solutions are slow to eject the system northeast from the the SC/NC border. The GFS offers a solution that ejects a piece of the low northeast Monday, but with the main system remaining anchored near SC/NC. The European and NAM solutions eject the low a little more quickly towards the northeast. In different ways, both of these scenarios yield similar forecast solutions for the region. If the slower solution pans out, it will mean the bulk of the moisture will remain south of the forecast area, and the region will experience subsidence on the north side of the system. If the quicker solution pans out, any precipitation the area receives will be on the backside of the system, skirting the eastern portion of the region. Our forecast will reflect the best chances of precipitation across the southeastern portion of the area Monday into Tuesday, with limited or no precipitation across the far northwest. Tuesday night into Wednesday night, the low will continue to make slow progression to the northeast. The biggest difference will be with the European solution that started its progression just slightly sooner. At the same time, an upper trough will be approaching from the west. The uncertainty in the departure track of the low, plus increasing dynamics from the approaching trough, and a boundary layer rich with moisture will allow for isolated to scattered showers and storms across the forecast area. Chances gradually increase Thursday into Friday for one of two reasons. If the GFS solutions comes to pass, the upper trough will deepen, closed off, an stall across the center of the country. This would allow for plenty of moisture to stream north from the Gulf of Mexico into the region. Pieces of energy ejecting eastward from the main low will act as trigger mechanisms for daily convection. If the European solution is correct, precipitation chances will also increase as the upper trough remains progressive, and moves eastward along with its associated cold front into and through the region. Temperatures during this portion of the forecast will average above normal with upper 70s to around 80 common for highs across the mountains and low to mid 80s across the piedmont. Lows in the upper 50s to around 60 will be common across the mountains with low to mid 60s across the piedmont. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
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As of 735 PM EDT Friday... Radar showed isolated showers and thunderstorms this evening, mainly just northwest of KBLF and KLWB. Areal coverage was sparse enough to leave showers and thunderstorms out of these TAFs for the rest of the evening. Showers and thunderstorms will dissipate before midnight. Otherwise VFR conditions are expected for southwest Virginia and southeast West Virginia until midnight. High confidence that fog will again develop in the Greenbrier and New River Valleys with MVFR visibilities at KLWB and KBCB. LIFR fog is possible at KLWB. Any fog will dissipate quickly Saturday morning. VFR ceilings and visibilities are expected through the day. There is a small chance of showers and thunderstorms again the afternoon, northwest of KLWB and KBLF. Models have been consistent showing a band of drying and subsidence between showers and thunderstorms on the western side of the Appalachians and the leading edge of deeper moisture in advance on the tropical system approaching South Carolina. Medium confidence that any lower cloud cover or precipitation with the tropical system will not reach KDAN and southern Virginia until after the 00Z end of the TAF forecast period. Extended discussion... The forecast will hinge heavily on the track of the tropical system...which will bring increased moisture and shower chances to the area...which could linger well into next week. This will result in widespread showers by Sunday and periods of MVFR to IFR cigs, as well as a greater potential for late night/early morning fog. Confidence in the evolution of the forecast past Monday is low but pattern appears to remain wet for the Mid Atlantic region.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...KK/WP NEAR TERM...KK SHORT TERM...KK LONG TERM...DS AVIATION...AMS/KK

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