Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 250154 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 955 PM EDT Tue Apr 24 2018 .SYNOPSIS... An area of low pressure will track northeastward across the Carolinas and VA tonight. A weak cold front will cross our region late Wed and Wed night. && .NEAR TERM /THROUGH TONIGHT/...
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As of 955 PM Tuesday... High rain chances will persist overnight over the W and N sections of the forecast area, although the loss of heating has led to lowering CAPE and a resultant slow decrease in severe risk. The surface low is currently analyzed just SE of CLT, with an occluded front extending to its E across far SE NC, and weak troughs extending to its NW and SSW. Stacked cyclonic flow persists up through the mid levels over W NC, and this will move slowly eastward overnight, as the surface low tracks northeastward over central NC. The earlier strong to severe storms formed and moved into areas with effective shear over 30 kts, 200-300 m2/s2 of 0-1 km SRH, and LCLs under 750 m across all but far southern parts of central NC, north of the occluded front within the strong low level easterly flow. While mid level lapse rates did not exceed 6 C/km, MUCAPE was 500- 1000 J/kg along and south of the northward-pushing front, and a few cells which tracked NE or NNE along or at a small angle to the CAPE gradient exhibited tight gate-to-gate circulations, feeding on the high low level vorticity. The best low level shear has pushed further N into VA and CAPE has decreased (although moderate values hold over the central Coastal Plain), and the risk of severe storms should continue to dwindle. But the approaching mid level low and pockets of DPVA and upper divergence maxima (one of which is now tracking N over the W Piedmont) will continue to support convection overnight, and will maintain high chance pops across the W and N, shifting slowly WNW through daybreak Wed. This will include a threat for isolated strong dynamically-driven storms, with the potential for small hail. With clouds holding overnight (albeit with breaks across the SE sections) and high dewpoints, expect temps to drop minimally overnight, yielding lows in the mid-upper 50s. -GIH Previous discussion from 405 PM: Water vapor imagery depicts a well defined mature cyclone over the TN Valley with a couple of discernible s/ws rotating around it. One s/w is lifting newd across eastern TN/western NC, while another was noted crossing the Deep South. The lead s/w will lift across our region this evening, while the later should lift into our area late overnight/early Wednesday. These s/ws interacting with a available moisture will trigger/sustain numerous showers and a few thunderstorms late this afternoon through sunset. Bulk of thunderstorm activity will remain south-southwest of Raleigh. Narrow axis of instability and shear in vicinity of a nwd moving warm front will maintain a slight threat for a severe storm or two through 23Z across the southern Piedmont and Sandhills. May see a lull in the shower activity behind the initial s/w mid- late evening before showers start to increase in coverage across the western Piedmont ahead of the next s/w. This increase in shower activity should occur after 06Z. Potential for areas of fog to develop across the eastern counties, though most of the visibilities should be above a mile. Overnight temperatures in the 50s.
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&& .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
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As of 405 PM Tuesday... Wednesday, the upper level low will migrate east across the region. Expect showers to be concentrated near the center of this system in the morning then expand south and east in the afternoon. Will refrain from mention thunder at this time though an isolated rumble of thunder cannot be ruled out, especially east and southeast of Raleigh. With peeks of sun expected, it should be notably warmer across the northern counties compared to this afternoon. Highs should range from near 70 in the NW to the mid 70s south. Subsidence behind the departing upper low and loss of heating Wednesday evening should cause showers to quickly diminish in the early evening. Cloud cover will be slow to erode in the evening due to the cyclonic flow though this becomes more anti-cyclonic overnight. This should lead to partly cloudy skies. Min temps in the low-mid 50s.
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&& .LONG TERM /THURSDAY THROUGH MONDAY/... As of 335 PM Tuesday... As the mid- upper-level low lifts off to the northeast and gets absorbed into the low over the Great Lakes there will be a brief lull in precipitation chances over Central NC Thursday morning into Thursday Afternoon. Another shortwave low aloft will swing through the the Deep South and toward the Mid-Atlantic coast Thursday resulting in another chance for showers and thunderstorms across the region Thursday aft/eve into the overnight hours. As that second shortwave low moves through the area, a third shortwave will dive south through the ARKLATEX, elongating the parent longwave trough aloft. This third low may result in additional precipitation over the Carolinas, however there are some model differences in that regard at this time. Will continue to carry at least a slight chance for rain through Friday night, but confidence in rain occurring is not terribly high at this time. Meanwhile at the surface, a low will drift north-northeastward out of the Deep South and along the Eastern Seaboard toward New England. Temperatures Thursday through Saturday: Highs ranging from around 70 degrees in the NW to mid 70s SE and lows decreasing from mid 70s Thursday night to mid 40s NW to around 50 degrees SE Saturday night. Largely expect Sunday and Monday to be dry with highs in the low to mid 70s and lows in the mid 40s to low 50s. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... As of 810 PM Tuesday... 24 hour TAF period: Showers and thunderstorms continue to push northward through the northern two thirds of the forecast area. At this time KFAY is the only terminal that should remain dry at this point with all northern terminals still expecting another few hours where precipitation will be possible. Ceilings will continue to be at sub VFR level for much of the night. Expect mainly MVFR and IFR conditions across the forecast area overnight with some LIFR possible after 6z through sunrise. For the northeastern quadrant of the forecast area some fog will also be possible down to a half mile or less after 6z through sunrise. After sunrise expect rapid improvement in visibility and gradual improvement in ceilings back to VFR levels by late morning/early afternoon. Wind gusts have let up for the evening but expect some gusts of 15-20 kts again on Wednesday afternoon out of the northwest. Long term: After conditions return to VFR on Wednesday, expect VFR conditions through Thursday before another system moves in for Friday, presenting the next chance for sub-VFR conditions. && .RAH WATCHES/WARNINGS/ADVISORIES... NC...None. && $$ SYNOPSIS...MWS NEAR TERM...Hartfield/WSS SHORT TERM...WSS LONG TERM...KC AVIATION...Ellis

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