Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 261040 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 640 AM EDT Wed Apr 26 2017 .SYNOPSIS... A shortwave ridge aloft will build into the Carolinas from the west in the wake of the upper level low lifting northeast along the Mid- Atlantic coast. A moist southerly return flow on the western periphery of an offshore ridge and southwest flow aloft downstream of troughing over the central CONUS will prevail late this week through the weekend. && .NEAR TERM /Today and Tonight/...
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As of 345 AM Wednesday... A shortwave ridge aloft will build eastward over central NC today as an upper level low NE along the Mid-Atlantic coast. Although lingering low-level moisture (dewpoints in the lower 60s) and highs in the upper 70s to lower 80s may result in scattered diurnal Cu at 3000-4000 ft AGL, strengthening subsidence in the wake of the departing upper level low (and approaching shortwave ridge) will result in pronounced mid-level warming/drying and the development of a strong capping inversion over central NC this afternoon. This, combined with a thorough lack of forcing will result in dry conditions through tonight. Expect lows in the upper 50s to lower 60s. -Vincent
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&& .SHORT TERM /Thursday and Thursday Night/... As of 345 AM Wednesday... A strong subsidence inversion /cap/ will remain over central NC on Thu. As such, one would expect dry conditions to persist. A squall line over MO/AR at 06Z this morning is expected to propagate eastward into the TN valley by 12Z Thu as a potent (albeit deamplifying) shortwave trough lifts NE from the lower Midwest through the OH valley. Despite decreasing/departing forcing, the ongoing squall line in the TN valley Thu morning is expected to propagate eastward into the southern Appalachians during the aft/eve. An increasingly hostile thermodynamic environment with eastward extent over the Carolinas should result in rapid weakening (and eventual dissipation) of the squall line as it progresses over/east of the Appalachians, however, it is possible that lingering convection could affect portions of the western Piedmont between 21-00Z before dissipation occurs. Outflow assoc/w the remnants of the squall line could result in gusty westerly winds and a 10-15F temperature drop in the Foothills/western Piedmont late Thu afternoon, complicating the temperature forecast. Will indicate a chance for showers and thunderstorms in the western Piedmont during the late afternoon, with dry conditions elsewhere and highs in the 80s, coolest west and warmest (mid/upper 80s along/east of Hwy 1). Expect warmer low Thu night (mid 60s) in assoc/w low-level moisture advection from the SW and likely development of low stratus during the pre-dawn hours. -Vincent && .LONG TERM /THURSDAY THROUGH MONDAY/...
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As of 355 AM EDT Wednesday... Classic summertime pattern emerges for late week and into the weekend under the influence of a strengthening ~590 dm H5 ridge over the western Atlantic. By Saturday, low-level thicknesses are progged to peak between 1410-1420m(40m above normal) with H8 temps warming to around 18C. Highs Friday 85 to 90, followed by upper 80s to lower 90s on Saturday, when we could challenge the record high max at RDU. Heights are forecast to lower slightly on Sunday, with highs Sunday similar to Friday`s temps. Rain/convective chances through the weekend will be limited by the dominate ridge. Will retain slight/small chance pops across the western Piedmont, where initial convective development in the nearby higher terrain could propagate downwind into the area. If storms do develop or move east into the area on Saturday, strong instability ~3000 J/Kg aided by steep lapse rates aloft associated with a modified EML, coupled with deep layer shear of ~25kts could support some vigorous updrafts capable of producing large hail and damaging thunderstorm winds. A closed upper level low and associated deepening sfc low lifting through the Upper Midwest will push a cold front into the area Monday afternoon/evening. Attendant cold front will bring a chance for showers and storms to the area Monday-Monday night with cooler temps following on Tuesday.
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&& .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... As of 230 AM Wednesday... 24 Hour TAF Period: Challenging aviation forecast. Conditions ranged from VFR to LIFR across central NC at 06Z this morning. Expect MVFR/VFR ceilings at the Triad terminals with a potential for MVFR fog 09-12Z. Expect MVFR/IFR ceilings at eastern terminals this morning. Ceilings will lift to VFR (3000-4000 ft AGL) at all terminals by early afternoon. A westerly wind at 5-10 knots this morning will back to the SW/SSW at ~10 knots this afternoon, then become light/variable after sunset. Looking Ahead: Sub-VFR conditions assoc/w the remnants of a weakening squall line are expected to affect the western Piedmont (INT/GSO) late Thu aft/eve. With an offshore ridge, expect a persistent southerly return flow over the Carolinas through the weekend. As such, expect a potential for IFR/LIFR stratus each morning (08-13Z). A conditional potential for isolated severe thunderstorms will exist during the late afternoon hours Fri/Sat/Sun across western portions of the state, potentially affecting the INT/GSO terminals (should convection develop and/or propagate into the area). -Vincent && .HYDROLOGY... As of 230 AM Wednesday... Small creeks and streams will gradually recede over the next 24 hours. Main stem river flooding will likely persist for several more days. See water.weather.gov/ahps2/index.php?wfo=rah for the latest forecasts and for additional information. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Vincent NEAR TERM...Vincent SHORT TERM...Vincent LONG TERM...CBL AVIATION...Vincent HYDROLOGY..Vincent/MLM

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