Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 270829 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 429 AM EDT FRI MAY 27 2016 .SYNOPSIS...
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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.
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&& .NEAR TERM /THROUGH TONIGHT/...
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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/...
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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 NC...in 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.
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&& .LONG TERM /TUESDAY THROUGH THURSDAY/...
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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.
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&& .AVIATION /08Z FRIDAY THROUGH TUESDAY/... As of 127 AM EDT Thursday... Mainly looking at VFR conditions at 06z, but looking at fog formation at LYH/LWB/BCB through 12z. Today should be similar to Thursday with models still favoring scattered shower or tsra coverage for the Blue Ridge and west to the WV. Will have VCTS at BLF/BCB per latest high-res radar depiction, but again overall coverage is lacking. Otherwise VFR through 06z/28th. 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. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...WP NEAR TERM...WP SHORT TERM...RAB LONG TERM...KK/RAB AVIATION...AMS/KK/WP

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