Scientific Forecaster Discussion

000 fxus62 krah 222029 afdrah Area forecast discussion National Weather Service Raleigh NC 330 PM EST Fri Feb 22 2019 Synopsis... chilly high pressure will build southward into central NC through Saturday, resulting in another prolonged episode of appalachian cold air damming. A cold front will cross the region on Sunday, followed by tranquil weather and seasonable temperatures for early next week. && Near term /through tonight/... as of 330 PM Friday... Unsettled weather pattern to continue during the near term with extensive cloudiness and periods of rain/drizzle continuing tonight through early Saturday. A series of perturbations in the SW flow aloft will continue to stream from the lower MS valley into the Tennessee Valley/central Appalachians. Meanwhile, a chilly sfc high centered over New England will build southward into the Carolina Piedmont, setting up a classical cold air damming episode. The warm moist air overrunning the cold stable air near the surface will maintain the extensive cloud cover and periods of light rain/drizzle. The low level northeast flow will continue to advect cold air into the region overnight. By early Saturday, temperatures should vary from the upper 30s/near 40 north to the lower 40s south. Bulk of the precipitation will occur across the northern counties which will be in closer proximity to the better lift associated with the perturbations and the upper jet lifting over the Ohio Valley into southern New England. && Short term /Saturday and Saturday night/... as of 330 PM Friday... Little change in the overall weather pattern Saturday into Saturday night as periods of rain will persist with the greatest coverage across the northern counties. Expect little change in the temperatures throughout the day with the diurnal trend likely no more than 3-5 degrees. Currently appears that a lull in the precipitation may occur late in the day Saturday into Saturday evening though patchy drizzle and areas of fog appear highly probable. Later Saturday night, the approach of a strong cold front associated with a deep low pressure system lifting across the upper Midwest will induce a sly near sfc wind flow over our coastal plain counties, eventually spreading into the Piedmont toward daybreak Sunday. This flow will spread a warm air over the cool sfc, leading to the development of fog, some of which may be dense. Currently, the dense fog potential appears highest for locations south and southeast of Raleigh. In addition, should start to see an increase in rain or shower activity toward daybreak Sunday in the western Piedmont attributed to the convergence ahead of the approaching sfc cold front. Overnight temperatures will hold steady through the bulk of the evening, then slowly rise, especially southeast of Raleigh, after midnight. && Long term /Sunday through Thursday/... as of 300 PM Friday... Sunday and Sunday night: the surface low will deepen as it accelerates northeastward through the western Great Lakes on Sunday. Since the low (and thus best forcing) will be well to the north, the front will slow as it impinges on the Appalachians. The big question is how long The Wedge will hold and how far northwest the warm front advances through the area. The latest models suggest The Wedge could break just prior to the arrival of the front early Sunday. Best chances for convection will be along and ahead of the front between 12z Sunday and 00z Monday. The front should be through the area by Sunday evening. Somewhat low confidence in the high temperature forecast as it will depend on whether/how long The Wedge holds and the timing of the front. For now generally expect highs in the mid 60s northwest to mid 70s southeast. Lows behind the front in the mid 30s to around 40 degrees Sunday night. Monday through thursday: surface high pressure will build into and through the region behind the front, with dry, seasonable conditions expected through Tuesday night. The upper level trough amplifies Tuesday night into Wednesday as the surface high pushes offshore. A weak shortwave could pass over the area, however chances for any precipitation with that are small. The southerly return flow at the surface on Wednesday may contribute to increasing chances for rain, primarily across the south, on Wednesday. Forecast confidence for Wednesday and Thursday is very low at this time. && Aviation /18z Friday through Wednesday/... as of 1255 PM Friday... Widespread adverse aviation conditions expected across central NC through 12z Sunday. Southerly flow a few thousand feet above the surface will continue to pull a warm moist air mass over the cool stable air near the surface, resulting in widespread low clouds, mainly IFR/low end MVFR with pockets of LIFR, along with periods of light rain and drizzle. Areas of fog are also possible during the nighttime through early morning hours. Aviation conditions are expected to improve Sunday as a cold front crosses the region from the west. Currently anticipate improving aviation conditions west-to-east after 18z Sunday. In the wake of the front, sfc winds are expected to be windy with gusts upward of 35kts probable. VFR conditions should occur across central NC Sunday night through the first half of the work week. && Rah watches/warnings/advisories... none. && $$ Synopsis...wss

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