Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 201829 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 230 PM EDT Sun May 20 2018 .SYNOPSIS... A moist and slightly unstable air mass will remain entrenched across central NC through the middle of the week. && .NEAR TERM /THROUGH TONIGHT/... As of 1130 AM Sunday... The atmosphere has changed some during the past 24 hours. While the atmosphere remains abundantly moist with precipitable water values 1.5-1.8 inches, the flow has become more wly versus sly. This shift in the wind field is attributed to a minor mid/upper level trough passing overhead. A reflection of this feature is noted at 850mb, with a trough bisecting central NC. This feature will likely serve as a focus for the development of scattered convection this afternoon-early evening. Thus, currently anticipating the highest concentration of showers/t-storms south and east of Raleigh, along and ahead of the 850mb trough. Cannot rule out the potential for locally excessive rainfall, though steering current of 15-20kts should help to move convection steadily along. Partial sun this afternoon of duration of 2-4 hours should be enough to boost temperatures into the low-mid 80s. Tonight, bulk of convection will diminish with loss of heating, though a lingering low-mid level trough across the southern counties may serve to enhance low level convergence to maintain a few showers into the overnight. Continued warm/muggy with overnight temperatures in the upper 60s to around 70. && .SHORT TERM /MONDAY AND MONDAY NIGHT/... As of 310 AM Sunday... The Bermuda high will maintain its dominance into early next week, effectively stalling the southerly progress of a backdoor front on Monday and lifting a tropically tinged moisture plume northward into the stalled frontal zone. The returning moisture plume features PW`s of ~1.75" and will result in an increased chance of convection, with thunderstorms becoming more numerous as we approach max heating - especially across the northern tier of central NC, where instability will be higher north of the frontal zone due to steeper mid level lapse rates. Highs will be in the mid 80s, perhaps suppressed to the lower 80s if early precip coverage is more widespread. Convective activity will shift to the north overnight, with a lull in activity, especially over the southern tier, after midnight. Min temps will be persistence, 65-70 degrees, in the tropical airmass. && .LONG TERM /TUESDAY THROUGH SUNDAY/...
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As of 230 PM Sunday... Maritime Tropical airmass will remain over central North Carolina through Wednesday with dewpoints in the upper 60s to lower 70s. Diurnal heating and embedded disturbances in deep southerly flow will contribute to scattered convection each afternoon and evening with a lull in activity late night into early morning. Any convection will have potential to produce very high rainfall rates given above normal PWs . High pressure building across the Northeast Thursday may push a backdoor cold front into the area Thursday and Friday bringing a drier airmass and much lower chances for convection, especially from Triangle and points north and east. Southerly flow returns Saturday bringing tropical airmass back into central North Carolina for the holiday weekend. Diurnal heating and embedded disturbances will generate more convection Saturday and Sunday.
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&& .AVIATION /18Z SUNDAY THROUGH FRIDAY/... As of 210 PM Sunday... A moist and slightly unstable air mass will maintain marginal aviation conditions through mid week. MVFR-low end VFR ceilings expected across the region through Monday evening with the highest chances for adverse ceilings during the early morning hours, and in the afternoon in proximity of scattered convection. The atmosphere will support the development of scattered afternoon-evening showers and thunderstorms through mid week. This afternoon-evening, the highest concentration of scattered convection should occur to the south and east of Raleigh, primarily in vicinity of FAY. On Monday, it appears the highest concentration of convection will be across the northern Piedmont into the Coastal Plain, affecting most of the TAF sites. Scattered convection is fairly certain to occur each afternoon and evening through the remainder of the work week. In addition, patchy early morning low clouds will likely occur each morning. && .RAH WATCHES/WARNINGS/ADVISORIES... .None. && $$ SYNOPSIS...WSS NEAR TERM...WSS SHORT TERM...mlm LONG TERM...Franklin AVIATION...WSS

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