Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS62 KRAH 210610 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 210 AM EDT Fri Apr 21 2017 .SYNOPSIS...
-- Changed Discussion --
A pre-frontal surface trough will strengthen over west-central NC today, then linger tonight. Meanwhile, a cold front will approach from the northwest and move into NC on Sat. The front will settle slowly south Sat night and Sun, in advance of a slow-moving storm system will cross the Carolinas through Monday.
-- End Changed Discussion --
&& .NEAR TERM /THROUGH TONIGHT/... As of 10 PM Thursday... Isolated to widely scattered showers and storms that develop along a weak disturbance moving across the area this afternoon/evening have generally dissipate with nocturnal stabilization. Dry conditions are expected to generally continue with flat ridging holding over the area, with high pressure located offshore. The next disturbance and associated cold front will remain to the west of central NC overnight. Thus, expect a warm night, with low temps generally in the lower to mid 60s. && .SHORT TERM /FRIDAY THROUGH SATURDAY/... As of 330 PM Thursday... The aforementioned cold front is forecast to push southward into central NC Friday night, then stall in a west to east fashion Saturday. Models and ensembles continue to show a fair amount of spread with the location of the front Saturday, which will determine where the temperature/cloud gradient and the convection develops and/or is maintained along the north of the boundary. For now, the GFS and the EC operational solutions continue their recent trends (with the EC indicating the front to stall closer to the NC/VA border Saturday, and the GFS indicating the front will stall over southern NC). The surface high to the north is weak (forecast to be less than 1020 mb and centered well north) - suggesting the front will not "surge" southward as if propelled by a stronger high to the north. However, any organized pre-frontal convection may be the driving factor of where the front ends up Saturday, which could end up being either solution (or simply a solution in between the two), as the ensembles suggest. This will be an important forecast as the upstream strong system in the mid levels approaching later in the weekend from the west will bring deep moisture/strong lift and convergence for widespread rain and convection (see discussion below). For this package, we will continue to generally broad brush this forecast, then fine tune in later forecasts as models come into better agreement. There will be be large precipitation and temperature gradients with this front over the weekend - so any adjustment by 50 miles either north or south will have huge impacts on central NC`s sensible weather, QPF, and severe threat. Large differences in the models start late Friday afternoon into Friday evening, with the EC essentially dry, and the GFS very wet and stormy associated with the initial cold front over NW NC. Most Hi-res models suggest at least scattered thunderstorms between 400 PM and 800 PM in the Triad, and 600 PM to late evening over the Triangle. The EC appears to be well underdone with the initial convection QPF. We will continue to depict POP`s that show the best chance of convection northwest and north, and no POP south late Friday afternoon and evening. Highs Friday should reach the mid 80s, with lower 80s NW. Forecast Mlcape suggest at least a marginal risk of a severe storm with damaging wind the primary threat, mainly from Raleigh west and north Friday afternoon and evening. QPF will be around 0.50 NW, with amounts of less than 0.25 from Raleigh southward on Friday and Friday night. The initial convection should lay a boundary out over central NC late Friday night and Saturday. The higher POP should be along and just north of the exact boundary location. We will keep cooler temps/higher POP NW-N, lower to none over the SE Coastal Plain with temperatures well into the 80s. A marginal risk of a few severe storms should continue, and may be enhanced later in the day with the approaching energy from the west. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... As of 215 PM Thursday... Latest model guidance showing various outcomes for this period...leading to a low confidence forecast. A trough extends along and just offshore the west coast, and compromised of multiple embedded circulations/ perturbations. Some models split this trough into two pieces by mid week sending more troughing into the Ohio Valley. Other models hold lower heights farther to the west. Either outcome looks reasonable but will use continuity from previous forecast as a starting point. Using this scenario will slow down the closed low over the Southeast early in the week and place it further south. An associated surface cyclone will track ENEwd to Ewd along a frontal zone draped across the srn and central Appalachians and srn Middle Atlantic states late Sat through Sun, then to the coast of the Carolinas, where it will slow, by early Mon. That front, which will have slowed over srn VA Fri night, will likely sag Swd into at least the nrn NC Piedmont Sat, with an associated low level convergence axis provided by both the front and the aforementioned preceding outflow - likely near or just S of the VA state line. Convection will become diurnally-enhanced along and N of the front, with semi-organized storm multi-cell storm modes, and perhaps at least transient supercells in the vicinity of the low level convergence --and enhanced shear-- axis. Some slight NWd retreat of the boundary will be possible Sat night- early Sun afternoon, downstream of the aforementioned surface cyclone approaching from the west. That would suggest the better chances of convection would (briefly) pivot into the far NW portions of the area through early Sun. Another round of convection will then accompany the surface cyclone and attendant cold front as they cross the Carolinas Sunday afternoon. As the surface low slows beneath the aforementioned complex upper trough, deformation/stratiform rain and low overcast are likely Sun night into Mon. Temperatures on Monday will be in the 60s. Drying and warming conditions will return as the low finally moves away from the coast Tuesday, and return flow overspreads the Southeast Tuesday through Thursday. && .AVIATION /06Z FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --
As of 210 AM Friday... Mainly VFR conditions are expected, at least until scattered showers and storms develop in the vicinity of a pre-frontal surface trough centered over the NC Piedmont this afternoon. Brief sub-VFR conditions and gusty winds will result in/near these showers and storms. If storms merge into clusters and form a well-developed rain- cooled/outflow airmass in their wake, sub-VFR ceilings and visibilities may result later tonight. Outlook: A cold front and focus for showers and storms along and to the north of the boundary will settle south into central NC Sat, then southward yet to near the SC border Sat night and Sun. An area of low pressure will develop along the front and move slowly east across, then along the coast of, the Carolinas Sun through Mon night. This complex system will likely result in a prolonged period of rain and low overcast during that time (Sun-Mon night).
-- End Changed Discussion --
&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...BSD SHORT TERM...Badgett LONG TERM...MWS/Franklin AVIATION...MWS is the U.S. government's official web portal to all federal, state and local government web resources and services.