Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 280747 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 345 AM EDT Tue Mar 28 2017 .SYNOPSIS... An upper level trough will cross the region Tuesday, along with a trailing cold front. High pressure will build in from the north on Wednesday, then shift offshore Thursday. A strong storm system is expected to affect the region late in the week. && .NEAR TERM /THROUGH TONIGHT/... As of 945 PM Monday... Diurnally driven isolated convection across the southern piedmont earlier this evening has since died down with loss of heating. However, we will see an increase in pops late tonight(at least over the western piedmont) with the approach of the mid/upper level trough into the southern Appalachians aoa daybreak. Hi-Res models continue to show significant weakening of the upstream convection currently across TN as it crosses the mountains, encountering weak buoyancy in place across the area owing to nocturnal cooling. Will show high chance pops in the west, decreasing to small/slight chance pops in the east, given the potential for the convection to dissipate altogether as it reaches the eastern zones. It will be a very mild night with lows generally in the 60s. && .SHORT TERM /TUESDAY AND TUESDAY NIGHT/... As of 235 PM Monday... The latest Hi-Res convection allowing models suggest that only a few showers will remain from tonight`s convection that tries to cross the Piedmont. Regardless, the timing of the approaching mid/upper trough appears to be during the morning and early afternoon for the western Piedmont, which is essentially not diurnally favorable for strong or severe storms in the western zones. Models do favor redevelop of at least scattered showers and thunderstorms along the surface wind shift line that is forecast to move SE into central NC Tuesday afternoon. The favored lift area out ahead of the mid/upper trough is forecast to reach the eastern Piedmont into the Coastal Plain and Coastal Areas during the peak heating period. Convection may blossom as early as late morning or around noon near the wind shift line, and should spread and develop ESE during the afternoon. It appears that the most favored area for optional heating and destabilization should occur just to the east and south of the Triangle area, just before the convection develops in the early afternoon and tracks into the region. The earlier timing of the front and trough should limit the strong to severe threat in the NW Piedmont Triad region, with the focus in the eastern zones. Even in the east where the instability and shear is expected to be higher, most parameters for severe storms are forecast to be marginal. Highs in the upper 70s to lower 80s in the east, with dew points nearing 60, should lead to MLCapes near 1000 J/KG. Mid level lapse rates may still be in question but some subtle warming aloft may be a negative factor for organized severe storms. Still, look for at least scattered thunderstorms with the potential for wind gusts to 40-50 mph and possibly up to 1 inch hail in a few of the strongest storms. We will highlight areas east of the Triad area for this potential due to timing in the Hazardous Weather Outlook. The convection should be east of the region by around sunset or so, but the lagging wind shift line may aid in some weaker trailing storms into the evening in the east. Otherwise, partly cloudy with lows in the 50s expected. && .LONG TERM /Thursday through Monday/...
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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 strngthening 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
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&& .AVIATION /06Z TUESDAY THROUGH SATURDAY/... As of 135 AM Tuesday... 24 Hour TAF Period: A cluster of showers and storms is approaching the Triad at this time and although it appears to be weakening a bit, there is still lightning being observed in these storms. expect storms to pass over KINT and KGSO between 6-7Z and then continue off to the northeast and dissipate. Behind the first cluster of storms are two more lines of showers and storms that are expected to weaken as they move east, however given the behavior of last nights rain and the fact that there continues to be warm moist air to the east of the mountains, expect these showers and storms to hang on long enough to affect at least the Triad sites if not KRDU and potentially KFAY as well. Occurring later this would be between 8- 12Z. With these showers is the potential for some MVFR ceilings and visibilities. Expect rain to begin moving out of the Triad after 16z and gradually clearing out later in the day. Further east another round of showers and thunderstorms is expected Tuesday afternoon during peak heating with the potential for some storms to become severe. 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...CBL SHORT TERM...Badgett LONG TERM...Hartfield AVIATION...Ellis

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