Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 170107 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 905 PM EDT Wed May 16 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 /THROUGH TONIGHT/...
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As of 905 PM Wednesday... Greater-than-usual shower chances will continue overnight. Observed vicinity and upstream PW remains quite high, 150-200% of normal, and close to the daily record at GSO. Widespread showers and isolated storms persist, focused over the N and W portions of the forecast area, with deep flow from the S and SSW allowing cells to train repeatedly over the same areas, elevating local rainfall amounts. Many areas have had 0.5-2.0" in the last several hours, with isolated higher totals near 3.0", but fortunately we`ve had relatively few problems. These widespread showers should continue translating to the N and NNW, following the mean steering flow, and most convection-allowing models suggest a comparative lull through the overnight hours, with just scattered showers. CAPE should continue to fall with loss of heating, and with poor mid level lapse rates, thunderstorm chances will continue to dwindle over the next few hours. Will taper down pops, holding onto scattered showers through late tonight. Pops should increase anew across the SE and far S CWA early Thu morning as a mid level disturbance and weak surface trough lift northward toward NC. Under overcast skies with patchy light fog, expect lows tonight in the upper 60s to lower 70s, again challenging record high min temps. -GIH Earlier discussion from 330 PM: A deep sly flow, a result of an upper level low over southern GA, will continue to funnel abundant moisture northward from the eastern Gulf into the Carolinas, maintaining precipitable water values well above normal for this time of year. Heating of this air mass has resulted in the development of scattered/numerous showers/t-storms across central NC this afternoon. Expect coverage to peak between 5 and 8 PM. After sunset, expect the convective coverage to diminish. A perturbation analyzed by the 12Z GFS and depicted on water vapor imagery crossing the far northern FL peninsula will continue to lift nwd. Based on the current track, this system may trigger a few showers prior to daybreak across sections of the southern Piedmont/Sandhills. Overnight min temps in the 67-72 degree range.
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&& .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... As of 330 PM Wednesday... Thursday and Thursday night, the remnants of the upper level low will interact with a mid level shear axis across the TN Valley- central Appalachians to cause periods of showers and thunderstorms across central NC. Due to the proximity of the upper level support, expect coverage to be greater than this afternoon, with bands of moderate-heavy rainfall probable, especially across the Piedmont where 925-850mb moisture transport expected to be maximized along with increasing divergence aloft. While not planning to issue a Flood Watch at this time, if it appears that a band of convection is going to set up over a urbanized location, or persist for more than 3-4 hours, than a watch may become necessary as precipitable water values hovering between 1.8-2 inches will make the showers/storms very efficient rain producers. Abundant cloud cover and anticipated convection will should limit afternoon temperatures to the 70s-lower 80s, warmest across the southeast half. Continued muggy Thu night with min temps in the upper 60s/around 70. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... As of 220 PM Wednesday... Longer range forecast remains on track. A tropical airmass will remain in place through Saturday. Deep southerly flow will keep high moisture content air to stream into the area with PWs generally in the 1.75 to 2.0 inches range which is between 2 and 3 standard deviations above normal. Surface high pressure over New England on Friday is expected to push a low level frontal zone southward into VA and possibly northern/northwestern NC. This may serve a low level focus for enhanced coverage of showers and thunderstorms. Mid/upper level flow is forecast to become more westerly Saturday night into Sunday, which should result in a decrease in the overall coverage and shifting the main focus of convection across the Coastal Plain on Sunday, along with more of a diurnal flavor to the convection. Chances for showers and thunderstorms will likely increase again early next week as the next cold front/surface trough is expected to move into the area from the north. High temperatures Sunday through Wednesday are expected to be in the 80s. Low temps will continue to remain warm, with lows in the mid to upper 60s to near 70. && .AVIATION /00Z THURSDAY THROUGH MONDAY/... As of 750 PM Wednesday... Showers and thunderstorms are evading all the TAF sites at this time but vicinity showers can be expected for the next several hours as convection begins to wind down for the evening. expect low ceilings to develop especially in the Triad with some sub-VFR visibilities mixed in as well, especially in areas that saw rain today. Winds will drop to light and variable overnight. More of the same Thursday afternoon with another round of convection expected and chances for sub-VFR conditions in those showers. Maybe a few gusts up to 20 kts in the KFAY area but all others should stay between 10-15 kts. Several days of showers and thunderstorms are expected through the end of the long term forecast bringing chance of adverse aviation conditions each day. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...WSS NEAR TERM...Hartfield/WSS SHORT TERM...WSS LONG TERM...BSD/Franklin AVIATION...Ellis

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