Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 181700 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1200 PM EST Wed Jan 18 2017 .SYNOPSIS...An upper level ridge will build into the region from the west tonight as as a shortwave trough tracks offshore. Ridging aloft will prevail over the Carolinas and Mid-Atlantic on Thursday. && .NEAR TERM /THROUGH TONIGHT/... As of 1200 PM Wednesday... A clearing/drying trend will prevail this afternoon into tonight in association with subsidence in the wake of a compact upper low progressing offshore the DELMARVA coast. Given that skies cleared early in the day and that cold advection in the wake of the recent cold frontal passage will be delayed until later this afternoon, expect warmer highs than previously anticipated, in the upper 60s to lower 70s. Lows tonight will be driven by a combination of cold advection and radiational cooling, in the lower 40s. -Vincent && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... As of 1200 PM Wednesday... An upper level ridge and associated surface high building into the region from the west tonight will be situated directly over the Carolinas/Mid-Atlantic on Thursday. As such, expect a pleasant/ sunny day with above normal highs in the upper 50s to lower 60s. Widespread precipitation is expected to develop upstream over the Deep South/TN Valley during the day Thursday as a potent upper level low lifts NE through the Central Plains toward the Upper Great Lakes. As a result, clear skies will quickly give way to increasing cloud cover by sunset as mid/upper level ceilings advect downstream of the mountains. Southerly return flow will quickly strengthen over western portions of the Carolinas as shortwave energy rounding the base of the upper low in the Central Plains Thu afternoon ejects E/NE through the Deep South into the Carolinas Thursday night. Expect a further increase in cloud cover overnight as mid/upper level ceilings are complimented by low ceilings assoc/w strengthening warm advection. In fact, light rain will be possible by sunrise (09-12Z) Friday morning in the Western Piedmont as moisture deepens via warm advection in the presence of DPVA (assoc/w the aforementioned shortwave energy). Low temps Thu night may be met by Thu evening, particularly in the west, as a result of warm advection and thickening cloud cover. Expect temps ranging from the low/mid 40s E/NE to upper 40s W/SW. -Vincent && .LONG TERM /Friday through Tuesday/... As of 420 AM Wednesday... Model agreement with the general pattern continues to be better than usual through the weekend, although some important differences in the low level pattern are evident, and notable timing differences crop up by Mon/Tue. Models are overall trending wetter in this time frame. Temps will remain quite mild, with all cold air staying bottled up over northern Canada and the Arctic region. Fri/Fri night: The mid level trough extending from the Midwest through the Ohio Valley to SC early Fri will continue to pivot to the NE through NC and into the Mid-Atlantic and Northeast Fri, and will be followed by prominent shortwave ridging over the Southeast Fri night. Focused mid level DPVA and upper divergence associated with passage of the trough, along with high PW, will support a band of rain shifting through central NC Fri morning, with a west-to-east tapering down Fri afternoon, and dry but mostly cloudy conditions Fri night as low level moisture pools over the area with a light surface flow. Will go with likely pops Fri morning, trending downward Fri afternoon. The ECMWF/NAM bring today`s surface front back northward into NC, albeit in a very diffuse form, while the GFS is more defined in keeping the frontal zone near the NC/SC border, favoring thick low clouds and cooler temps, especially over northern NC. With well-above-normal thicknesses tempered a bit by the morning rain and lingering clouds late Fri into Fri night, expect above normal temps with highs from the mid 50s N to lower 60s S. Lows 45- 50. Sat/Sat night: What once appeared to be a fairly dry day now looks be trending wetter. Thanks to a powerful mid and upper jet from CA across the Desert Southwest and adjacent Mexico to TX, a strong low will be closing off over OK/TX before shifting to AR/LA through Sat night. Subtle perturbations ejecting from this low/trough will swing NE into the Carolinas Sat afternoon/night, while bands of enhanced upper divergence spread in from the SW, a product of ideally juxtaposed upper jetlets over the Ohio Valley and over the NE Gulf. Low level flow will be ramping up with an 850 mb jet nosing into the Carolinas, fostering moist isentropic upglide along/above the diffuse surface frontal zone. And models agree on PW staying well above normal as they generate precip over the area, mainly across the southern and western CWA Sat and areawide Sat night as heights aloft continue to fall with the approaching trough. Will bring in low chance pops mainly S on Sat, trending up to good chance Sat night. The rain and clouds will lead to a tighter diurnal temp range. Highs in the low-mid 60s Sat followed by lows in the mid 40s to lower 50s. Sun into Mon: The mid level low is expected to cross the lower Miss Valley, Gulf States, and Carolinas before moving into the interior Mid-Atlantic region through late Mon. This system will be accompanied at the surface by a complex but likely occluded frontal system, with vigorous deep forcing for ascent promoted by a 40-50 kt low level jet punching into the area, intense upper divergence within a zone of ascent between two ideally juxtaposed upper jets, and large mid level height falls. Confidence is high in a period of potentially heavy rain and embedded storms with strong kinematics and marginal instability and lapse rates, but the timing is less certain, as the GFS becomes much slower (farther SW) than the ECMWF with the upper low and trough as it swings ENE through our area with a negative tilt. Will lean toward the faster ECMWF, which has good agreement with its ensemble mean. Will have likely pops Sun/Sun night, with the best chance of heavy rain and storms Sun evening, followed by a SW-to-NE tapering down of pops on Mon as some drier mid level air works in from the SW. A strong storm or two remains possible given the energetic wind field, despite the weak instability noted by the models. Lingering instability showers and isolated storms will persist Mon with indications of high lapse rates and abundant moisture. Temps should remain above normal despite the clouds/precip. Tue: We should be on the west side of the departing low/trough shifting to our east and north, with yet another mid level ridge building in. Expect dry weather and a trend to fair skies. With no cold air available, temps will remain above normal. -GIH && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... As of 1200 PM Wednesday... 24-Hour TAF period: VFR conditions /clear skies/ will prevail through the TAF period, with winds becoming light/variable overnight as high pressure builds over the region from the W/NW. Long term: Sub-VFR conditions will be possible late Thu night or Friday morning as southerly return flow strengthens over the Carolinas. Adverse aviation conditions may prevail Fri through much of the upcoming weekend as a series of upper level disturbances track across the region. -Vincent && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Vincent NEAR TERM...Vincent SHORT TERM...Vincent LONG TERM...Hartfield AVIATION...Vincent

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