Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 281336 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 936 AM EDT Tue Mar 28 2017 .SYNOPSIS... An upper-level disturbance and cold front will push across the region today, and offshore this evening. Weak high pressure will follow the front for tonight and Wednesday. Another storm system approach our area Thursday night and Friday, bringing another round of stormy weather. && .NEAR TERM /THROUGH TONIGHT/... As of 936 AM Tuesday... The main outflow boundary has already pushed through all of central NC and was moving toward the coast as of mid-morning. The back edge or trailing showers/iso thunderstorms were elevated and weak. This activity will end in the next few hours. We will adjust POP and WX to account for the expected break late morning and early afternoon. The main cold front and upper trough was already moving into the Northern Mountains of NC. We will have to rely on heating this morning into the early afternoon for the air mass to recover or destabilize. It appears that there will be an opportunity for that as there is a clear slot already developing behind our current band of showers and extensive cloudiness exiting the eastern and southern areas. There is a marginal risk for isolated severe thunderstorms this afternoon. Hi-Res models suggest widely scattered thunderstorms will develop along a wind shift line around 17z or 18z near the Triad region, then quickly move SE through the eastern Piedmont and Coastal Plain exiting the region by 22z or 23z. The favorable instability is expected to be mainly east of the Triad region; therefore, the isolated severe potential should be confined to the far eastern Piedmont to the coast 20z-23z or so. Even over these areas, MLCapes and many other severe weather parameters are only marginal given the turned over boundary layer - and lack of recovery time expected as the mid/upper trough timing is not optimal (too early by several hours). Otherwise, a partly sunny forecast this afternoon with SW winds becoming westerly as the wind shift moves through. A chance of showers and thunderstorms, one or two may reach near severe limits for wind and/or hail. Highs generally in the mid 70s to lower 80s. This action will shift offshore by sunset and dry/quiet conditions will return for tonight. Lows in the 50s. && .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/... As of 400 AM Tuesday... Quiet weather day on Wednesday as surface high pressure builds in from the north behind the exiting frontal system and an upper level ridge extends northward out of the southern Caribbean. A bit cooler with the airmass change with highs in the low 70s across the northeast to upper 70s in the southwest. Lows are expected to be in the mid 40s across the northeast to middle 50s in the southwest. && .LONG TERM /Thursday through Monday/... As of 345 AM Tuesday... Thu through Sat: The backdoor cold front is expected to settle just south of NC early Thu as cool high pressure noses in from the north. In the mid levels, a shortwave ridge shifts across the SE and Carolinas Thu, while a potent low pushes slowly eastward through the central and southern Plains. Major model differences start to emerge between the GFS and ECMWF Thu, resulting in a low confidence forecast. Both models take the mid level low and trough eastward through the Mid/Lower Miss Valley / Mid South / Gulf States and Carolinas / Southeast through early Sat, however the GFS digs energy into this low much more deeply than what is shown by the ECMWF, and this in part results in notable differences with the push of the front back north through NC, with the more southern-track GFS keeping the front to our south through Thu night (with a cool stable wedge regime in the NC Piedmont) followed by a slow northward push Fri, while the slightly weaker/more northerly ECMWF takes the milder air northward into central NC as early as late Thu. While the high to our northeast is not particularly strong nor is it being significantly reinforced aloft, this air mass should still be dense enough for the cool pool to stay lodged into the NC Piedmont through Thu. Will have highs Thu from the mid-upper 50s NW ranging to near 70 SE, with a slight chance of rain or drizzle in the west with overrunning flow strengthening over W NC as the 850 mb anticyclone shifts off the Carolina coast. As the mid level low/trough crosses the region with a negative tilt, it will be accompanied by a complex occluding surface frontal system, with a more southern track and less potential instability on the GFS (which develops strong forcing for ascent near the E Gulf Coast/FL Panhandle Thu/Thu night) and a more northern track with greater potential instability on the ECMWF. Have generally followed the slightly weaker ECMWF, although both models have been trending stronger with the shortwave trough in recent runs, so confidence remains low. There does appear to be enough moisture (PW of 1.25-1.5") and forcing for ascent, including DPVA, enhanced upper divergence, and low level mass convergence, for a continuation of likely pops, focused on Thu night through Fri evening, tapering down WSW to ENE Fri night into early Sat as the mid level shortwave trough and surface frontal system push to our east with a weak cool front settling southward through the area. Highs from the mid 60s to lower 70s Fri with cloudy skies and numerous showers/storms, and in the low-mid 70s Sat with partial sunshine and rising heights aloft as another mid level ridge axis approaches in the wake of the exiting trough. Sat night-Mon: Expect generally quiet weather Sat night/Sun as weak surface high pressure builds in from the north in tandem with the mid level shortwave ridging. Yet another shortwave trough crosses the S Plains into the lower Miss Valley Sun night into Mon, while the weak frontal zone to our south tracks back northward. Expect fairly seasonable temps Sun, perhaps still a little above normal as the incoming surface high will be cut off from a polar air source. Warmer thicknesses Mon, behind the weak warm front, will be offset with increasing clouds with the trough`s approach, so expect highs from the lower to upper 70s Mon. -GIH && .AVIATION /14Z TUESDAY THROUGH SATURDAY/... As of 930 AM Tuesday... 24 Hour TAF Period: Generally VFR conditions will return after the low stratus erodes in the KGSO/KINT areas, and the showers end down east at KRWI by late morning. Then, widely scattered strong thunderstorms are possible between 19z and 23z, mainly from KRDU eastward to the coast. VFR conditions expected tonight and Wednesday with weak high pressure. Long term: A low pressure system will cross the area on Friday through Friday night with the potential for showers and thunderstorms. High pressure with VFR conditions should return for the weekend. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Badgett NEAR TERM...Ellis/Badgett SHORT TERM...Ellis LONG TERM...Hartfield AVIATION...Ellis/Badgett

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