Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 171850 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 250 PM EDT Thu May 17 2018 .SYNOPSIS... An area of low pressure will drift slowly northward across the Southeast U.S. through Friday, bringing an increased threat for showers and few thunderstorms to central NC. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... As of 1000 AM Thursday... 12Z upper air analysis depict a deep sly flow over the SE U.S. thanks to a well organized area of low pressure over the Deep South. Perturbations rotating around this low will lift nwd across the Carolinas today, triggering/sustaining scattered-numerous showers and storms, especially this afternoon through mid evening. Based on latest meso-analysis, expect the highest coverage to occur across the Sandhills/southern Piedmont, northeastward into the Coastal Plain. The atmosphere contains abundant moisture with precipitable water values around 1.8 inches, well above normal for this time of year. Due to the moisture rich air mass, the showers and storms will be efficient at producing rainfall, leading to torrential downpours. The potential exists for some locations to receive between one-two inches of rain in an hour`s time, leading to minor flooding of streets and low lying areas. The extensive cloud cover and widespread showers will hold temperatures in check, recovering only into the upper 70s-lower 80s. Tonight, the bulk of the convection will dissipate with loss of heating, though cluster of showers and isolated storms will likely occur into the overnight due to favorable support aloft and the very moist atmosphere. Another muggy night with overnight temperatures in the upper 60s-lower 70s. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
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As of 310 AM Thursday... Deep tropical flow will tighten further on Friday as the mid level closed low over the mid Plains begins to lift northeast into the Ohio Valley. The ensuing southerly moisture tap into central NC will raise precipitable waters over the area to >2 inches, so precipitation efficiency will enhanced even given modest instability ahead of a weak low level surface wave which will be lifting north across the area Friday afternoon. Heading into Friday night, a belt of mid-to-upper level perturbations due to jetting around the stacked Bermuda high will be in the vicinity (the latest GFS lines it up over the Coastal Plain), which would enhance convection through Saturday as the closed low is slowly absorbed into the broader upper trof. The vestige of the low, a deamplifying short wave, looks to at last nudge the moisture plume east and offshore late Saturday or Saturday night. This appears to be the period with an enhanced chance for urban and small stream flooding, as heavy showers accompanying convection will have better potential for downstream re-development (potential ring- of-fire around the Bermuda high) and subsequent training in deep southerly flow. Rainfall amounts are expected to range from 1.5 to 2 inches Friday through late Saturday, but we could easily see those numbers doubled in a training environment. PoPs will be nudged upwards slightly, with a minimum of likely (>60%) PoPs area-wide through the period. Highs both days will be in the upper 70s to lower 80s after morning lows from 65 to 70.
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&& .LONG TERM /SATURDAY THROUGH THURSDAY/...
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As of 255 PM Thursday... The long term period will feature a gradual easing of the ongoing wet pattern into more scattered rain chances as we head into the middle of next week. The start of the long term period will feature an amplified pattern with the sub-tropical ridge off the southeast coast and a shearing trough across the OH and TN Valleys. A deep southerly flow will drive an axis of convection across central and eastern NC on Saturday that will shift east on Sunday. Fairly widespread showers and thunderstorms are expected on Saturday with a bit less coverage and a greater focus to the east on Sunday. While the trough departs early next week, a weakness aloft persists on Monday and Tuesday that will support more scattered, mainly afternoon and evening showers and storms. The approach of a backdoor cold front late Tuesday into Wednesday will support scattered storms with a drier air mass reducing storm coverage on Thursday. With very little air mass change, a good deal of cloudiness and at least scattered convection, highs will consistently range in the lower to mid 80s with low mainly in the mid to upper 60s. -Blaes
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&& .AVIATION /19Z THURSDAY THROUGH TUESDAY/... As of 155 PM Thursday... A moisture rich air mass coupled with a slow moving area of low pressure will contribute to an extended period of sub VFR parameters across central NC through Friday night, and potentially all the way to Sunday. Scattered to numerous showers and t-storms will produce MVFR ceilings and MVFR/IFR visibilities in heavy rain showers through 03Z Friday. While the bulk of the convection will diminish overnight, ceilings are expected to become low end MVFR/IFR. Another round of showers and storms with associated sub VFR ceilings and visibilities anticipated Friday and Friday night. The adverse aviation conditions expected to persist through Saturday, and possibly into Sunday. Improving aviation conditions anticipated Monday into Tuesday. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...WSS NEAR TERM...WSS SHORT TERM...MLM LONG TERM...BLAES AVIATION...WSS

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