Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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379 FXUS62 KRAH 271909 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 309 PM EDT Fri May 27 2016 .SYNOPSIS...High pressure will extend across the area through today. A low pressure system developing off the Southeast coast will drift toward the northwest, approaching the Carolinas and Southeast coast over the weekend. && .NEAR TERM /through Saturday night/... As of 1040 AM Friday... Little change required to the near term forecast. 12Z upper air analysis depicts a weak low-mid level trough across the western Piedmont. Meso-analysis has some moisture pooling along this feature. GSO sounding this morning depicts a mid level cap weaker compared to the past couple of days. With current parameters indicating a slightly better potential for isolated convection, have expanded the slight chance PoP farther to the south and east to encompass most of the southern and western Piedmont. Temperatures on track to reach well into the 80s to near 90 degrees. -WSS Tonight: Baggy mid level low pressure over the Bahamas (southwest of the offshore anticyclone) will begin a slow drift toward the FL coast, with a band of vorticity on its NNE side (in tandem with a deepening surface low center) rotating about the low toward the SE coast. This still-light-but-increasing flow aloft from the ESE will draw in high clouds from the offshore convection, such that skies will trend toward fair or partly cloudy tonight from SE to NW. Low 60-65. Sat/Sat night: Rain chances are expected to increase as the baggy mid level low shifts ashore over FL/GA/SC, while the surface low located NNE of the low progresses further to the NW, likely reaching the Southeast coast by Sun morning. This low has the potential to take on some tropical characteristics (see products and bulletins from the National Hurricane Center regarding this possibility), but regardless of its nature, the increased influx of low level Atlantic moisture particularly into the SE and southern CWA along with improving (yet still unfocused) upper divergence and rising PW to 1.5-2.0" should lead to increasing rain chances, focused on the southern CWA, on Sat and especially Sat night. Will trend pops up gradually from SE to NW starting Sat, reaching likely in the SE and good chance NW by late Sat night, with skies trending toward mostly cloudy. While this system could generate gusty winds and some locally heavy rainfall near its center, given that most models keep its center near or just off the GA or southern SC coast through Sat night, such impacts could easily be suppressed well to our south. That said, we`ll be closely monitoring this system as we head into the long holiday weekend. Expect highs Sat 82-86 and lows Sat night 64-69. -GIH && .SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/... As of 345 AM Friday... Increasingly wet/stormy for the latter half of the weekend. A strong vorticity max parent to a complex mid to upper-level low now centered near the Bahamas will, according to a preferred GFS/ECMWF consensus, be "kicked" out of the mean low position -- across the Carolinas-- by an upstream southern stream shortwave trough now over the Rio Grande. Meanwhile at the surface, the well- advertised low that the Air Force reserve Hurricane Hunter aircraft is scheduled to investigate this afternoon, is forecast to drift northwestward, to a position near the central SC coast by 12Z Mon. An inverted surface trough axis, likely in the form of a maritime tropical warm front, will extend northward from the low and bisect central NC. A deep southeasterly moisture plume, characterized by precipitable water values around 1.75 to 2 inches, will be directed into the Carolinas, between the mean upper low position near the Bahamas and a sub-tropical ridge centered near Bermuda. The presence of the moist axis will ripen the environment for numerous showers and storms, which will be aided by forcing for ascent accompanying the mid-upper level vorticity max, and focused by low level convergence along the aforementioned inverted trough/warm front. Despite the presence of the warm front, the low level flow and associated shear are expected to remain weak, at least comparatively so for a nearby tropical cyclone environment, so no heightened risk of severe weather is anticipated. Clouds and convection will yield high temperatures around 80 degrees, albeit with noticeably higher humidity levels driven by upper 60s to around 70 degree surface dewpoints east of the warm front. Lows 65 to 70 degrees. -26 && .LONG TERM /Sunday Through Friday/... As of 305 PM Friday... Sunday through Tuesday: The likely tropical/sub-tropical low is expected to be located very near the South Carolina coast Sunday morning, shown by nearly all of model guidance. However, where the sub-tropical/tropical/remnant low tracks after approaching/moving onshore is still in question. Given the approaching system and influx of tropical moisture into central NC, we should see numerous to widespread showers and thunderstorms on Sunday as the inverted surface trough pivots westward and into our area. This will lead to the potential of heavy rain with any showers and storms as PW`s are expected to surge to around/over 2 inches, along with at least some threat of at least isolated severe storms. With regard to the severe threat, there is still some uncertainty about how much instability we will have and how strong the deep and low level shear will be, with the eventual track and intensity of the system playing a major role. High temps Sunday should be limited to around 80 degrees thanks to the convection and mostly cloudy/overcast skies, but with quite humid conditions. The latest GFS and NAM shows the system lifting northward across the coastal plain of the Carolinas on Monday night into Tuesday and being absorbed in a passing northern stream s/w. The latest ECMWF is hinting at this potential now as well, which differ some from its previous run and has more of a drier solution across most of central NC by Monday, with any heavy rain/rain generally from the I-95 corridor and eastward. However, will maintain continuity for now with previous forecasts and still show at least likely pops across the eastern half of the area. Chances for showers and storms are expected to decrease further Monday night into Tuesday with any lingering trough axis located along the coast (higher chances east vs west for central NC). High temps on Monday and Tuesday are expected to be in the lower to mid 80s, with lows in the mid to upper 60s. Tuesday night through Friday: Will trend chances for showers and storms more towards climo with poor run to run model continuity, along with model differences. This will yield generally diurnal chance pops with high temps in the lower to mid 80s and lows in the 60s. && .AVIATION /18Z Friday through Wednesday/... As of 1240 PM Friday... High confidence that VFR conditions will persist across central NC through Saturday. An isolated shower or thunderstorm is possible in vicinity of KINT and KGSO between 20z-01z though confidence not high enough to mention in the TAF for either site. Also, after 08z, could see patches of fog, limiting the visibility to 2-5 miles in sections of the sandhills and the coastal plain. Aviation conditions deteriorate later Saturday as increasing low level moisture overspreads the region from the southeast. this will result in ceilings lowering into the MVFR category along with an increasing threat for showers. Adverse aviation conditions appear highly probable across central NC Saturday night through Sunday night. Low confidence in the forecast Memorial Day through Wednesday as weather conditions will be dictated by the position and movement of an area of low pressure in vicinity of the southeast U.S. Aviation conditions will vary between VFR and MVFR though tough to determine which category will be most likely during this period. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...WSS/Hartfield SHORT TERM...26 LONG TERM...BSD AVIATION...WSS is the U.S. government's official web portal to all federal, state and local government web resources and services.