Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 271736 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 136 PM EDT FRI MAY 27 2016 .SYNOPSIS... High pressure stays off the mid-Atlantic coast today into tonight expanding west toward the southern Appalachians by Saturday morning. A tropical low shifts northeast toward the South Carolina coast by Sunday morning, lingering across the Carolinas through the first part of next week. && .NEAR TERM /THROUGH TONIGHT/...
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As of 100 pm EDT Friday... Increased pops in the west for this afternoon lining up with the richer cu fields seen on Satellite images. Scattered showers starting to form along the blue ridge mountains in the warm unstable air. Raised high temperatures in the far western mountains for this afternoon. As of 940 am EDT Friday... Made some minor adjustments in temperatures using the latest sfc obs and lav guidance for this morning into this afternoon. The end result was to raise high temperatures in the east a few degrees. Modified pops for this morning into this afternoon leaning towards the RNK WRF ARW. Anticipating that showers and thunderstorms will once again develop along the Blue Ridge and Alleghanys this afternoon. With limited shear and instability, not expecting any severe weather this afternoon. More changes later... As of 350 am EDT Friday... Very little change in the forecast for today. Still expect most convection should fire along the Blue Ridge and Alleghanys at least by midday/early afternoon and drift north-northeast at 10 to 20 mph. As with yesterday will have to rely on low lvl outflow and convergence along the ridges to power the convection. There is some hint of weak upper forcing so have to account for that, but all in all still sitting at isolated to scattered coverage, with less east of the foothills. Expect sunshine to heat things up to the upper 70s to lower 80s across the mountains, while the east reaches the mid 80s. Tonight, seems convection weakens and ends after midnight, though cannot rule out isolated showers after midnight, but hard to pinpoint any one location. With moist low lvls and some clearing should see fog once again spring up in the valleys and where it rains during the afternoon/evening. Lows remain elevated in the lower to mid 60s areawide.
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&& .SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/... As of 400 am EDT Friday... Main concern continues to focus around a tropical system...not yet sure if it will be named...but nonetheless a low pressure area of tropical origin...that the models are in general agreement on drifting northwest from the Bahamas into South Carolina or eastern North Carolina by Monday. From that point...the GFS remains the outlier in keeping the system lingering across the Carolinas for several days through much of next week...not exiting the region until an upper trough arrives from the Midwest. A spiral band of preceding moisture is slated to reach the southeast part of the CWA by Saturday night/Sunday morning. In advance of this feature during the day Saturday...there is a very clear area of subsidence and a definite lack of precipitation. It appears that much...if any...convection that develops Saturday prior to the evening hours...would be across the Alleghanys...perhaps far southwest VA/northwest association with differential heating. Rain showers should then begin to 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 back across eastern SC/NC. Sunday is the day that most models agree will be the most active and wettest day across the CWA with the tropical low likely located across north central or northeast SC or perhaps southeast NC. PWATS move upwards into the 1.5 to 2.0 inch range depending on model...and an area of deep tropical moisture appears evident on most models from the tropical low northward across the Piedmont. There could be some enhancement of rainfall along and east of the Blue Ridge as well. With all of this in mind...have advertised likely to categorical pops east/along the Blue Ridge...with mostly chance pops to the west. Southeast West Virginia into far southwest VA will see the least rainfall from this pattern. The amount of thunderstorms is in question as instability is minimal given extensive cloud cover and a saturated atmosphere. So...have opted to just include slight chance thunder for now with moderate rain showers likely. By Monday...the ECMWF and Canadian begin to shift the deeper moisture and tropical low off the coast...while the GFS circulates the remnant low across SC. Abundant tropical moisture will remain in place across the region...but confidence in widespread heavy rainfall less than on Sunday...unless believing GFS solution. Have generally reduced pops to mostly high chance low end likely for this period. Low temperatures will be well above normal through the period...mainly in the 60s. Maximum temperatures will be mostly in the upper 70s to lower 80s...but it will be very humid through the period for sure. && .LONG TERM /TUESDAY THROUGH THURSDAY/... As of 420 am EDT Friday... As noted above...considerable uncertainty remains in the medium range forecast...hinged largely on the track...movement...duration of the southeast U.S. tropical low pressure area. Will it stall and linger per continued GFS solutions...or move out to sea by Tuesday per ECMWF and other models? A blocking upper ridge to the north will be the key. If the tropical system does linger for several days with non- existent steering currents and blocked upper flow, rainfall may become a concern as a result. The other key player in the extended period is a cold front and upper trough to the west, which travels slowly eastward during the period. Per the GFS...this may be the system that finally takes the tropical system remnants out of the region. Again...the strength of the upper ridge will determine how far the front makes it. In any case, we can expect scattered to perhaps numerous diurnal convection with warm/humid conditions through the period. In general, high temperatures will remain mostly in the 70s mountains to the 80s elsewhere. Low temperatures will be mainly in the 60s. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
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As of 136 pm EDT Friday... VFR ceilings will prevail this afternoon into tonight, with MVFR in convection and low clouds. Isolated convection starting to form in the warm unstable air across the higher terrain. Best focus for afternoon showers and thunderstorms will be across the mountains and west of the Blue Ridge. There are some capping aloft and the lack of a significant trigger which will hinder convection and its strength. Placed the mention of VCTS to BLF/BCB/LWB in the tafs with the best chance for MVFR thunderstorms this afternoon into this evening. Decided to add a VCSH to ROA with cloud development this afternoon. Overnight...any showers/thunderstorms will dissipate quickly after 00Z leaving SCT-BKN mid/high clouds. Fog will develop...mainly west of the Blue Ridge...and most likely in any areas that see late day rain. Winds...mostly SSW-SSE through the period...speeds 5-7kts or less. Medium to High confidence in cigs and vsbys through the TAF valid period. Medium to High confidence in wind spd/dir through the TAF valid period. Low to Medium confidence in thunderstorm potential. Extended discussion... Saturday the region will be in between systems with the upper low remaining west of the region and a tropical system developing off the SC coast. Little forcing and lift plus increased subsidence should confine any convection to the mountains...isolated to scattered diurnal activity at best. For the remainder of the period...the forecast will hinge heavily on the track of the tropical low pressure area...which at a minimum will bring increased moisture and shower chances to the area...which could linger well into next week. This will result in periods of mvfr- ifr cigs and greater potential for late night/early morning fog as well. Confidence in the evolution of the forecast past Sunday is low.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...WP NEAR TERM...KK/WP SHORT TERM...RAB LONG TERM...KK/RAB AVIATION...KK/RAB is the U.S. government's official web portal to all federal, state and local government web resources and services.