Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 200732 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 331 AM EDT Sat May 20 2017 .SYNOPSIS... A backdoor cold front will drop south into Virginia tonight and then into North Carolina late Saturday and Saturday night. Low pressure and a cold front will approach from the west Sunday and Sunday night. && .NEAR TERM /THROUGH TONIGHT/... As of 300 AM Saturday... Weakening upstream convection over SW Va and NC mountains may produce a brief passing shower or thunderstorm across the NW Piedmont and adjacent Va bordering counties across the northern Piedmont through daybreak, before dissipating as airmass undergoes further stabilization. A cold front, currently near the Mason-Dixon Line, will push south through Va this morning and will continue progress south, reaching Roanoke Rapids-Rocky Mount between 18-21z, Triangle and Triad between 21 to 00z, and then finally sagging south near the SC-NC state line between 00 to 06z, where it will briefly stall before retreating as a warm front late Sunday. Strong daytime heating within the warm sector should result in moderate destabilization with models showing MLCAPE values of 2000-2500 J/kg maximized along and north of HWY 64 corridor. Scattered to numerous showers and storms will be apt to develop within this highlighted area, with one or two severe storm clusters possible across much of the same area that experienced scattered thunderstorm damage yesterday afternoon(northern piedmont/northern coastal plain). The front will eventually sag near the SC/NC border Saturday evening/night with most of the convection waning around sunset owing to loss of heating. Post-frontal spotty rain/drizzle will be possible behind the front within an extensive stratus cloud deck. Highs today across the northern Piedmont and northern coastal plain will be largely dependent on the timing of the back-door cold front and attendant convection. Highs ranging from the lower 80s NE to lower 90s south. Low temperatures will range in the lower 60s north to upper 60s south. && .SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/... As of 245 PM Friday... Mid-level ridge axis over the area will shift east and offshore on Sunday, concurrent with scouring of weak cool air damming at the surface due to increasing southerly flow. Instability supportive of a few showers are expected along the periphery of the frontal zone...mainly west and south...during the morning, with increasing coverage areawide as the boundary retreats northeast during the afternoon. The slowly retreating frontal zone will produce a strong temperature gradient across the area...with the northern tier reaching upper 70s while central and southern sections reach low to mid 80s. && .LONG TERM /MONDAY THROUGH FRIDAY/...
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As of 331 AM EDT Saturday... An active first half of the week is shaping up for the long term period. First on Monday, a cold front is progged to cross central NC during the late afternoon and evening. Light to moderate rain ahead of the front will move in from the west as early as the early morning hours Monday, but the primary band of showers and tstms with the front expected to move across central NC during the late morning and afternoon hours, shifting to the coastal plain during the evening. Considerable cloudiness all day will slow heating, so with modest CAPE (< 500 j/kg), the risk for severe storms is low, but thunder can`t be ruled out. Highs around 80. The aforementioned front is expected to stall near the coast Monday night as a broad longwave trough sets up over the eastern half of the country and the front becomes aligned with sw flow ahead of the trough axis. This would set the stage for a potentially wet Tuesday/Tuesday Night period as deep moist sw flow, short wave energy in this flow, and subsequent low pressure waves along the front lift NE across the Carolinas. While both the GFS and ECMWF show this wet scenario, the ECMWF is more concerning given its emphasis on phasing northern stream energy with a southern stream jet streak moving across the deep south. Its resulting pattern features a strengthening 50+ kt low level jet moving NE across our CWA coupled with a farther inland position of sfc low (over the western Carolinas), all of which suggests a heightened risk for severe storms across our CWA late Tuesday. The GFS on the other hand keeps the sfc boundary pinned near the coast, which would keep the risk for severe storms mostly to our east. Temps will depend on cloud/rain coverage, but pattern suggests limited heating with highs in the upper 70s. The high likelihood for rain will continue late Wednesday and Wednesday night as the mid/upr trough axis begins to shift east, pushing a cold front across our area. It`s worth noting the strong jet streak and assoc deep layer wind field with this part of the system, so despite the low-CAPE environment, any thunderstorms that develop should have the potential to produce isolated strong wind gusts. The trough axis is expected to move across central NC during the day Thursday, so can`t rule out a few passing showers, but decreased coverage and intensity compared to previous days. Then dry Friday in the wake of the exiting trough axis. Temps near normal during the late-week period.
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&& .AVIATION /05Z SATURDAY THROUGH WEDNESDAY/... As of 1245 AM Saturday... Expect mainly VFR conditions overnight, with a few relatively short- lived exceptions at KINT and KGSO where a wet ground and a rain- cooled near surface layer from earlier storms could allow for some pockets of shallow fog. In addition, there will again be a chance of LIFR-MVFR ceilings and/or visibility restrictions over srn NC, including at FAY, in the few hours leading up to and around 12Z Sat. A back-door cold front will sag south into the area late Sat afternoon and into the evening. Scattered showers and storms will accompany the front, impacting RWI around 21Z, and KRDU, KGSO and KINT around 00z. Expect a brief period of post-frontal NELY wind gusts, with ceilings deteriorate rapidly, lowering to IFR-MVFR between 00 to 03z across the north to 06-09z at KFAY. Outlook: The back-door cold front will stall just south of the area on Sunday, before retreating NEwd as a warm front Sunday night. Ceilings are expected to remain sub-VFR through much of the day on Sunday with showers overspreading the area Sunday night as the warm front lifts north across the area. Another cold front, numerous showers and storms, and sub-VFR conditions, will move east across central NC Mon through early Mon night, followed by similar conditions in association with another frontal system on Wed. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...BLAES NEAR TERM...cbl SHORT TERM...mlm LONG TERM...np AVIATION...CBL

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