Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 291735 RRA AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 135 PM EDT MON AUG 29 2016 .SYNOPSIS... An ENE to NE onshore flow will prevail through mid-week as Tropical Depression 8 approaches the Carolina coast from the ESE and high pressure shifts slowly east from the lower Great Lakes to the Mid- Atlantic coast. && .NEAR TERM /THROUGH TONIGHT/... As of 135 PM Monday... A dry low/mid-level airmass persists over the majority of central NC this morning, as sampled by the 12Z GSO RAOB (PWAT 1.11") and indicated by the latest 925/850 mb SPC mesoanalysis. Moisture increases rapidly as one progresses east of the I-95 corridor in the Coastal Plain where NE low-level flow has advected rich low-level moisture from the Atlantic into Eastern NC, as indicated by the 12Z MHX RAOB (PWAT 1.83"). Marginal destabilization (tempered by cloud cover and NE low-level flow) will be confined to areas along/east of I-95 this afternoon. Forcing for ascent will also be confined to areas along/east of I-95, in the form of weak DPVA assoc/w a shear axis extending N/NNE along the Southeast/Carolina coast, attendant a stalled upper level low offshore the GA/FL coast. With the above in mind, expect mostly cloudy skies and a slight chance of showers to along/east of the I-95 corridor this aft/eve, with partly cloudy skies and dry conditions elsewhere. Expect highs in the mid/upper 80s, coolest east of I-95. Lows tonight will range from the upper 60s (western and northern Piedmont) to lower 70s in the Coastal Plain, primarily east of I-95. -Vincent && .SHORT TERM /TUESDAY AND TUESDAY NIGHT/... As of 135 PM Monday... Moisture will increase over central NC on Tuesday as an E/NE onshore flow expands westward across the state, with PWAT values rising in comparison to today as , the shear axis extending N/NNW into the area (from a stalled upper level low offshore the GA/FL coast) today is expected to shift W/SW into western NC, upstate SC and northern GA. As a result, forcing will largely be absent Tue/Tue night. In fact, subsidence is likely to be present over portions of central/ eastern NC on the western periphery of TD #8 Tue aft/eve (progged to be a marginal tropical storm by then) as it approaches the NC OBX. With the above in mind, will indicate a dry forecast over central NC Tue/Tue night, with the best chance for precip along the Carolina/ Southeast coast. Expect partly cloudy skies with highs in the upper 80s to near 90F. Lows Wed in the upper 60s to lower 70s. -Vincent && .LONG TERM /Wednesday through Sunday/... As of 330 AM Monday... What is now TD8 is expected to be near or over the northern Outer Banks as a tropical storm early Wed, part of a broader shear axis extending from TD9 in the east central Gulf along the coastal Carolinas. Curiously, the NAM/GFS/Canadian also show a third surface low just off Hilton Head SC, this one perhaps spawned from current convection east of TD9 drawn to the NNW by the cold core upper low now spinning east of Savannah. While this sort of development between two existing tropical systems is a longshot, regardless, the better rain chances (25-35%) Wed/Wed night are apt to be over the SE CWA, along the mid level shear axis beneath upper divergence, with lower chances (10-20%) over the central/NW CWA where moisture will be much less (PW < 1.5") with mid level flow from the NW. Thicknesses will remain well above normal, supporting highs around 90 to the lower 90s with lows in the lower 70s. Now-TD8 is expected to move swiftly to the NNE away from NC late Wed. Attention then turns to the mid level polar stream trough that will dig and deepen over the Great Lakes and Northeast late Wed through Thu night, pulling a bonafide cold front into and through NC from the NW. While along-front moisture pooling appears meager, a few showers and storms may be generated as the front (and its accompanying upper divergence max in the right entrance region of a jetlet over/off the Northeast) encounters better moisture over the Piedmont late Thu, and will retain good chance pops (30-45%) Thu through Thu night, highest in the E half. Thicknesses remain elevated with a prefrontal thermal ridge in place, and expect highs from the upper 80s to lower 90s. The digging polar trough is expected to draw what is now TD9 to the NE across northern FL and off the SE coast Thu into Fri, allowing the front to progress fully to the SE through our area, with cool surface high pressure ridging building in from the Great Lakes/Ontario. Expect low precip chances Fri, likely extending through Sat/Sun, as the surface high pressure ridge narrows but continues to extend through central NC, while the mid level trough weakens and stalls near the mid-Atlantic and Southeast coast, keeping our area on the subsident side of the trough. As thicknesses drop to well below normal Fri and more so Sat/Sun, expect highs in the lower-mid 80s, with lows slipping into the 65-70 range. -GIH && .AVIATION /18Z MONDAY THROUGH SATURDAY/... As of 135 PM Monday... 24-hr TAF Period: With high pressure situated north across the Mid- Atlantic and Tropical Depression 8 offshore the Carolina coast, a relatively stable onshore (ENE) low-level flow will prevail through the TAF period. VFR conditions are expected to prevail at the INT/GSO/RDU terminals through the majority of the TAF period. At the FAY/RWI terminals, a small chance for MVFR ceilings attendant isolated showers will be possible this afternoon, and IFR/MVFR ceilings (stratus) will be possible for several hours around sunrise Tuesday morning, similar to this morning, with MVFR ceilings perhaps extending as far N/W as the RDU terminal. Looking ahead: Forecast confidence decreases mid-week due to uncertainty assoc/w the evolution of TD #8 offshore the Carolina coast and an upper level low offshore the Southeast coast. Forecast confidence remains low late this week into this weekend when a cold front approaching from the NW is progged to interact with TD #9 (located west of the FL Keys in the GOMEX this morning) as it tracks NE across northern FL and emerges offshore the Southeast coast. With the above in mind, VFR conditions are most likely to prevail at western terminals (INT/GSO), and eastern terminals (FAY/RWI) are most likely to see periodic showers and low ceilings mid/late week. -Vincent && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Vincent NEAR TERM...Vincent SHORT TERM...Vincent LONG TERM...Hartfield AVIATION...Vincent

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