Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 211508 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1008 AM EST Sat Jan 21 2017 .SYNOPSIS... A mesoscale convective system will track across the region late this afternoon and evening. A potent upper level low and attendant low pressure system will track northeast from the Deep South into the Carolinas on Sunday, linger over the area on Monday, then gradually track offshore the Mid-Atlantic coast on Tuesday. && .NEAR TERM /THROUGH TONIGHT/...
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As of 400 AM Friday... ...Dense Fog Advisory now in effect through 11 AM for the Srn half of central NC... Widespread dense fog developed shortly after Midnight this morning and will be slow to dissipate due to the presence of low ceilings and unseasonable low-level moisture assoc/w 925-850 mb warm advection. Expect a slow/gradual improvement a few hrs after sunrise, with fog lifting by late morning. A few elevated showers cannot be ruled out late this morning and early this afternoon in the Sandhills and SW Piedmont (primarily near the SC border) in association with low-level warm advection and small amplitude waves in SW flow aloft. Otherwise, dry conditions are expected through mid afternoon in central NC. A large MCS (currently in LA/MS) is expected to track NE through the Deep South this morning, progress through upstate SC early this afternoon, then track NE/ENE across central NC late this afternoon through this evening. Warm advection, DPVA associated with a robust MCV and above normal moisture (PWAT ~1.50") will help maintain the MCS as it tracks into/across central NC. At the same time, a predominately stable airmass characterized by weak low/mid-level lapse rates and a near-sfc stable layer should temper the intensity of the system and keep convection elevated, precluding a severe potential, though lightning cannot be ruled out. Precipitation chances will be greatest between ~20Z this afternoon and midnight (~05Z) tonight, and rainfall amounts of ~0.50" are entirely reasonable, with locally higher amounts possible. Expect highs in the mid 50s to lower 60s (south) this afternoon and lows in the mid 50s tonight. -Vincent
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&& .SHORT TERM /SUNDAY/... As of 400 AM Saturday... Unseasonably rich moisture will surge N/NE from the GOMEX into the Carolinas on Sunday as low-level flow backs/strengthens in response to height falls in advance of a potent upper level low progressing east from the lower MS river valley into the Deep South. If an MCS develops over the Deep South tonight, it is possible that convection could affect portions of central NC Sunday morning, though confidence remains low with regard to the evolution/track of upstream convection that may develop later tonight. Otherwise, expect chances for convection to increase from SW-NE Sunday afternoon as small amplitude waves rounding the base of the upper low eject NE from the Deep South into the Carolinas amidst diffluent flow aloft and increasingly favorable thermodynamics as rich low-level moisture advects poleward underneath a modified elevated mixed layer characterized by H7-H5 lapse rates on the order of 7-8 C/km. If sufficient forcing is available to break the cap at the base of the EML and/or discrete convection develops upstream and propagates into central NC during the early/mid afternoon, the thermodynamic/kinematic environment would support supercells capable of producing all severe weather hazards. Otherwise, the primary severe weather threat will not unfold until late Sunday afternoon/evening when a strongly forced squall line is expected to propagate into central NC. Expect highs ranging from the lower 60s (NW) to the mid 70s (SE). -Vincent && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... As of 300 AM Saturday... Sunday night through Monday night: Based on latest model consensus, ongoing squall line/QCLS associated with the deepening upper low moving into the Southern Appalachians and attendant cold front moving through the area should be in the process of exiting the area late Sunday evening ~06z, bringing an end to the damaging wind and isolated tornado threat. The deepening upper low will take it`s sweet time lifting north into the Mid-Atlantic region on Monday, resulting in another unsettled/wet day across the area. So after the potential for a brief lull Sunday night as the dry slot overspreads the area, rain chances should increase once again as instability showers accompanying the upper low is expected to move through the area during the day on Monday. Cooler behind the lead front, aided by low clouds and showers. Highs Monday ranging from mid 50s NW to near 60 SE. As the system finally begins to pull away from the region Monday night/early Tuesday, lingering moisture/clouds are expected to clear out from SW to NE Monday night as the system exits the region. Lows Monday night in the 40s. Tuesday through Friday: Height rises over the region Tuesday and Wednesday will result in a return to near or just above normal temps. Shortwave energy moving through a positively-tilted trough setting up/sharpening over the Eastern US, could lead to scattered showers across the area late Wednesday night and Thursday as the attend cold front moves through the area. A colder pattern with below normal temperatures on Friday and into the weekend with good model agreement of a deep trough developing over the Eastern US. && .AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...
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As of 500 AM Saturday... Extremely Poor Aviation Conditions This Weekend... 24-HR TAF Period: Adverse aviation conditions are expected to prevail through the entire TAF period. VLIFR/LIFR visbys assoc/w dense fog and low ceilings are likely to prevail through ~15Z before conditions begin to improve. Observational trends along with the latest model guidance suggest dense fog will begin to lift by late morning, with visbys improving to IFR/MVFR and ceilings to IFR (500-1000 ft AGL) by early to mid afternoon, however, showers (and perhaps isolated thunderstorms) expected to track across central NC (from WSW- ENE) later this afternoon and evening will hamper further improvement. Conditions will deteriorate to LIFR/VLIFR in the wake of precipitation late this evening/overnight. Looking Ahead: Poor aviation conditions will persist Sunday/ Sunday night as a powerful upper level low and deepening sfc low pressure system track across the Deep South into the Carolinas. Low ceilings will persist at most terminals with episodic convection, some of which could become severe and produce damaging sfc wind gusts late Sunday afternoon/evening. The powerful upper level low and attendant sfc low will linger over the region Monday resulting in sub-VFR ceilings and scattered convection. Improvement should begin by Tuesday as the system tracks toward the Mid-Atlantic coast, though gusty NW winds are likely Tue afternoon. -Vincent
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&& .RAH WATCHES/WARNINGS/ADVISORIES...
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Dense Fog Advisory until 11 AM EST this morning for NCZ041-042- 073>078-083>086-088-089.
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&& $$ SYNOPSIS...VINCENT NEAR TERM...VINCENT SHORT TERM...VINCENT LONG TERM...CBL AVIATION...VINCENT

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