Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 290805 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 335 AM EDT MON AUG 29 2016 .SYNOPSIS... High pressure will persist over the Piedmont through tonight. An area of low pressure over the Atlantic will drift west toward the Carolina coast through Tuesday. && .NEAR TERM /THROUGH TONIGHT/... As of 330 AM Monday... No a lot of change in the synoptic pattern in the past 24-48 hours, with an upper ridge centered over the mid-Atlantic states, a upper low off the Southeast coast, and a dry air ridge in the low-levels extending into the region from the northeast. TD Eight is well to the east of ILM and is forecast to move slowly west toward the coast over the next 48 hours, strengthening a bit as in encounters more favorable shear/moisture and the Gulf Stream. Easterly flow around the aforementioned upper low will continue to supply moisture across the coastal plain, resulting in a strong moisture gradient over the Piedmont, with deeper mixing over the western Piedmont and dewpoints dropping into the lower 60s or even upper 50s, while dewpoints hover in the lower 70s in the coastal plain. Weak instability and moisture convergence will support scattered showers and a few isolated storms east of I-95, though most CAMs show less coverage than yesterday. Highs should be nearly identical to yesterday or a touch cooler given the abundance of mid clouds noted on IR imagery this morning; 87-90. Much like this morning, isolated showers and late-evolving stratus are expected in the coastal plain again tonight. Lows 66-72. && .SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/...
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As of 330 AM Monday... The upper low east of Savannah will stall on Tuesday, while TD Eight inches closer to the NC coast, awaiting an anticipated break in the sub-tropical ridge before moving north on Wednesday. Even with the storm moving closer to the coast, models show little impact inland with the dry air ridge remaining in place for another day. Thus, is appears just widely scattered showers/storms moving into the coastal plain again on Tuesday, with highs in the upper 80s to around 90. Interestingly, but still of little consequence, is the tendency for most models to generate another low off the Southeast, with 850mb PV denoting three distinct centers, including TD Nine in the GOMEX and TD Eight off the Carolina Coast. The next few days will certainly be interesting as these two or three systems respond to the synoptic flow and local environments. Lows Tuesday night, in the upper 60s and lower 70s.
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&& .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 /07Z MONDAY THROUGH FRIDAY/...
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As of 140 AM Monday... East-northeasterly low-level flow will continue to advect moisture inland this morning, resulting in low ceilings/vsbys across eastern NC. Meanwhile, a few showers will be possible around RWI. Confidence is high for IFR and LIFR conditions at RWI and FAY by 09Z. Expect low ceilings to reach RDU by 11Z, but confidence in low clouds at GSO and INT much lower given high clouds currently spread over the Piedmont and drier low-level air in place. Similar to yesterday, the low clouds will slowly disperse through 15z, with a chance of showers and storms confined mainly from RWI to FAY and east during the afternoon. Otherwise, conditions will be mostly VFR with a northeasterly wind that may periodically gust to 15-20kt. Similar conditions are expected tonight, with low clouds likely at RWI/RDU/FAY. Outlook: The approach for Tropical Depression 8 off the Carolina coast makes the aviation forecast for mid-late week a little uncertain, but at the moment it appears the impacts will be minor and VFR conditions will prevail, with overnight stratus possible over eastern NC.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...SMITH NEAR TERM...SMITH SHORT TERM...SMITH LONG TERM...Hartfield AVIATION...SMITH

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