Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 250757 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 350 AM EDT Wed Apr 25 2018 .SYNOPSIS... An upper level low, and related surface low pressure system, will track northeastward across central NC and southeastern VA early today. A weak cold front will then cross our region late this afternoon and tonight. && .NEAR TERM /THROUGH TONIGHT/... 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. && .SHORT TERM /THURSDAY THROUGH FRIDAY/...
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As of 350 AM Wednesday... A dry backdoor cold front will briefly sag south in the wake of the departing low as it lifts north into New England. This front will stall across the northern tier of central NC, stalling highs in the the upper 60s north, while the southern tier will reach mid 70s. The front will be quickly lifted back north of the area ahead of a vigorous southern stream closed low which will be moving east across the southern Plains into the Tennessee Valley Thursday night. This low will be accompanied by a rather impressive elevated mixed layer featuring mid level lapse rates of 6-7 K/km and at least modest upper diffluence complements of a 90Kt jetlet. Showers and scattered thunderstorms are expected to break out Thursday evening in the western Piedmont, with coverage increasing as the system lifts northeast up the Appalachians. As such, will raise PoPs to likely (~60%) category and transition the PoPs from the western Piedmont Thursday evening into the east after midnight. Activity will quickly taper off to scattered Friday morning as the system lifts northeast and is absorbed into the larger scale long wave trof migrating into the eastern CONUS. Should see some breaks in cloudiness on Friday with highs reaching low to mid 70s after mild morning lows in the mid 50s.
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As of 350 AM Wednesday... The longer range outlook is dry with a welcome warming trend on track to arrive early next week. A long wave trof will edge east across the Atlantic coast early this weekend, with cool air reinforced by a modest cold front Saturday night as the trof axis moves east of the area. Highs Saturday through Monday will be mostly 70 to 75 after morning lows mostly in the upper 40s. Surface high pressure will settle overhead on Monday as mid level ridging over the Plains begins moving east to produce height rises and warming early in the week. Stacked ridging will produce near-cloudless skies Tuesday and Wednesday with highs rising from upper 70s Tuesday to lower 80s on Wednesday.
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&& .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... As of 215 AM Tuesday... Widespread (L)IFR conditions will persist this morning from the Triad (INT/GSO) enewd to near and just north of RDU and RWI, in a residually cool/stable/saturated cold air damming air mass situated to the north of a nearly stationary front analyzed at 06Z from near VUJ to RDU to ECG. Given the close proximity of that boundary to RDU and RWI, occasional VFR conditions will be possible at those sites this morning. While some fog has recently developed to the south of the front, including at FAY, it is likely to be patchy and brief. Otherwise, an upr level low and associated cold temperatures aloft will track directly over cntl NC early today. A (deformation) MVFR cloud band and showers will accompany the passing upr lvl low; and some storms with small hail will also likely result as diurnal heating/destabilization occurs after 15Z centered around the RWI/IXA/ASJ vicinity, beneath the aforementioned cold temperatures aloft, this afternoon. Conditions will gradually improve to VFR from west to east as westerly flow ushers drier air into our region behind the low pressure. Outlook: An upr level trough and related surface low pressure system will track newd across the Carolinas Thu night. A period of sub-VFR conditions, showers, and a chance of thunderstorms, will result during that time. && .RAH WATCHES/WARNINGS/ADVISORIES... NC...None. && $$ SYNOPSIS...MWS NEAR TERM...Hartfield/WSS SHORT TERM...mlm LONG TERM...mlm AVIATION...MWS is the U.S. government's official web portal to all federal, state and local government web resources and services.