Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 160428 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1230 AM EDT Wed Aug 16 2017 .SYNOPSIS...
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A weak area of low pressure and a surface trough will linger near and off the Carolina coast through Wednesday night. A slightly drier air mass will move into the region on Wednesday. A back door cold front will drop into the region on Thursday and Friday before another cold front approaches from the northwest on Saturday.
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&& .NEAR TERM /THROUGH TONIGHT/... As of 955 PM Tuesday... Convection earlier this afternoon and through the evening has largely been driven by convective outflow boundaries, initially by a westward propagating surface cold pool and now by a SEWD propagating cold pool. While a weak vorticity shear axis moving over the area tonight could support an isolated shower overnight, it appears the bulk of activity will exit the eastern/southern zones aoa 06z. As has been the case the past several days, high PWAT airmass will support locally heavy rain over, with 1 to 1.5 inches in an hour or less resulting in high water on area roadways. Lows tonight once again in the lower/mid 70s with some patchy fog, potentially dense in some spots. && .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/... As of 239 PM Tuesday... Subsidence in the wake of shortwave energy progressing ESE of central NC tonight and early Wed will result in weak pressure rises over the central Appalachians, aiding the southward advection of a drier low-level airmass into central NC. A drier low-level airmass combined with warmer mid-level temperatures should act to mitigate diurnal destabilization and, most likely, preclude convective development. Will indicate dry conditions with highs in the upper 80s (N) to lower 90s (S). Lows Wed night in the low/mid 70s, warmest S/SE. -Vincent && .LONG TERM /THURSDAY THROUGH TUESDAY/... As of 239 PM Tuesday... Thursday and Friday...the risk for scattered showers/tstms remains in the forecast as a series of weak short waves move across in the wsw flow aloft. A more robust short wave trough is progged to approach on Saturday and lift by to our north on Sunday, and pushing a cold front down into the Carolinas in the process, and providing the synoptic scale support for additional rounds of scattered showers/tstms both Saturday and Sunday. With the upper trough pulling away and zonal or broad cyclonic flow left in its wake, the sfc boundary and moisture pool gets left behind across the Carolinas for early next week, thus continuing the daily risk for showers/tstms Monday and perhaps Tuesday, and also elevating the risk for the presence of clouds during the eclipse. Temps will run at or above normal through the period with no significant airmass changes. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
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As of 1230 AM Wednesday... Earlier showers/storms have exited central NC, leaving beyond VFR conditions but plenty of low level moisture both in the area and upstream. Weak low pressure over eastern NC and a trailing trough extending back along the NC/SC border will become more defined today, with low level flow becoming uniformly from the NNE/NE. Latest high resolution models show widespread IFR/LIFR stratus and MVFR/IFR fog drifting southward from VA and expanding, impacting central NC TAF sites between 07z and 16z this morning. RDU/RWI is likely to see the longest period of sub-VFR conditions early this morning, but such conditions are expected for at least a few hours at all sites. After about 16z, the low clouds will break up and lift, bringing VFR conditions to all sites, lasting through the end of the TAF valid period, with a couple of exceptions: First, there is a chance of a shower or storm, mainly in the SE (FAY), from around 19z to around 02z, which may bring a period of sub-VFR conditions and erratic winds. And, IFR conditions are likely to develop at RWI starting near the end of the forecast period, after 05z. Winds will be light (under 8 kts) from the NNE or NE today, becoming variable under 4 kts this evening through tonight. Looking beyond 06z Thu, IFR conditions are likely overnight into Thu morning in the NE (RWI), with just MVFR fog possible elsewhere. There is a good chance for showers and isolated storms both Thu and Fri afternoon, and sub-VFR fog/stratus are expected late Thu night into Fri morning and again late Fri night/Sat morning. Mainly afternoon and evening showers and storms are possible Sat through Sun as a cold front approaches from the NW. -GIH
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...JB NEAR TERM...CBL SHORT TERM...Vincent LONG TERM...np AVIATION...Hartfield

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