Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 270603 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 203 AM EDT Thu Apr 27 2017 .SYNOPSIS...
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A cold front will approach the mountains from the west late this afternoon and evening, then stall out and dissipate over the Mid- Atlantic tonight. A moist southerly return flow on the western periphery of a strengthening Bermuda high will prevail Friday through the weekend.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As of 910 PM EDT Wednesday... The skies had cleared across NC this evening. High pressure will be overhead tonight with light winds. There may be a bit more patch fog around sunrise that currently forecast due to the saturated ground under clear skies and light winds. We may have to add some patchy ground fog for later tonight, especially in the fog prone and soaked valley areas near the lakes, rivers, and even smaller creeks. The temperature / dew point spreads were already 5 degrees or less in many areas. Lows should fall into the 60-65 range, except upper 50s over the northern Piedmont.
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&& .SHORT TERM /Thursday and Thursday Night/...
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As of 335 PM EDT Wednesday... Skies will be generally sunny for much of Thu morning, with the mid level ridge axis sliding to our east, although high clouds will be increasing as the weakening line of convection approaches from the west, along with a weakening surface trough that brushes our W and N sections late Thu through Thu night before lifting up into the Mid Atlantic region. Warm and stable 850-600 mb air will inhibit convection in our area through early afternoon, despite surface dewpoints within a few degrees of 60, and this is further supported by the latest hi-res WRF-ARW/NMM runs which stay dry in our area through 18z. By mid afternoon, however, a weakened version of the convective line will be moving into the western CWA, accompanying a 30-40 kt 850 mb SSW jetlet, weaker than its previous state but still enough to support low level mass convergence over central NC, mainly from very late afternoon until shortly after midnight. Forecast soundings show mostly elevated instability increasing by evening, peaking in the 800-1200 J/kg range, and deep layer shear ranging from around 40 kts west to around 20 kts east, with column moistening as high PW values of 1.5-1.75" advect in from the SW. Detrimental to maintenance of this convection will be the lack of dynamic forcing for ascent, as any weak DPVA will track well to our NW, although models do indicate a pocket of enhanced upper divergence tracking NE through the area Thu evening, which may support greater storm coverage. For now, will hold onto low-end likely pops west, with lower chances through the central CWA and just small chances east, where deep layer shear and dynamic forcing for lift will be weaker closer to the departing ridge. With thicknesses higher than yesterday tempered by the increase in clouds, expect highs from near 80 NW to the mid 80s SE. Lows Thu night ranging from the low 60s NW to the upper 60s SE. -GIH
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&& .LONG TERM /Friday through Tuesday/...
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As of 325 PM EDT Wednesday... A weak surface tough associated with dying overnight convection is forecast to stall over the coastal plain and then retreat back to the west on Friday as the subtropical ridge amplifies off the Southeast coast. The ridge, and associated rising thicknesses will peak on Saturday (thicknesses of 1410-1420m), with highs accordingly peaking in the upper 80s to lower 90s, just short of record highs. Convection each day should mainly be tied to the seabreeze and higher terrain in southwesterly flow and no strong forcing. However, with strong instability forecast, owing to a plume of steep mid-level lapse rates off the Mexican Plateau, there could be a large hail and damaging wind threat, more so on Saturday when models suggest a shallow tropopause disturbance/jet moving lifting through the Deep South that could aid in triggering storms. Confidence in this feature and whether or not storms will be able to develop is still low at this point. The ridge will hold on Sunday and then give a little to a strong upper low forecast to lift from the Southern Plains to the Great Lake by Monday. POPs will increase on Monday as the associated cold front advances east across the mountains. Shear looks favorable for severe weather, but instability is questionable on Monday. Temps will accordingly be knocked back toward normal for the middle of next week.
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&& .AVIATION /06Z THURSDAY THROUGH MONDAY/...
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As of 145 AM EDT Thursday... 24 Hour TAF Period: VFR conditions associated with a dry/capped airmass will prevail through mid to late afternoon. Scattered convection (remnants of a squall line expected to cross the mountains this afternoon) will be possible 20-00Z at INT/GSO terminals and 00-04Z at eastern terminals, with the relative best chance at INT/GSO terminals given an increasingly dry/hostile airmass with eastern extent. SW/WSW wind gusts as high as 20G35KT will be possible in assoc/w any convection. Otherwise, calm or light SSW winds early this morning will increase to 10-15 knots a few hours after sunrise, with gusts as high as 20-25 knots this afternoon (after ~15Z), highest at the INT/GSO terminals. Outlook: Though VFR conditions will prevail through the majority of the upcoming weekend, adverse aviation conditions are periodically expected. Examples include IFR/LIFR ceilings expected to develop each morning Sat/Sun/Mon between 08-12Z, lifting/scattering out to VFR by 12-15Z. Additionally, isolated to scattered afternoon/evening (21-03Z) convection will be possible Fri/Sat. Should convection develop and/or propagate into the region Fri/Sat, environmental conditions would strongly support severe weather. Otherwise, expect the best overall potential for convection Monday evening/night in assoc/w a cold front /squall line/ progged to track eastward through the Carolinas. -Vincent
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Vincent NEAR TERM...Badgett SHORT TERM...Hartfield LONG TERM...Smith AVIATION...Vincent

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