Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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158 FXUS62 KRAH 101936 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 235 PM EST Sat Dec 10 2016 .SYNOPSIS... High pressure will settle overhead through tonight, then shift offshore Sunday. A warm front will push northward through the area Sunday night, and then a cold front will move through the region Monday night, before stalling out across the Carolinas through mid week. && .NEAR TERM /THROUGH TONIGHT/... As of 140 PM Saturday... Another quiet and cold night ahead as a portion of arctic high pressure slides across the Mid Atlantic region tonight. While the vast majority of the column is very stable and dry, areas of high level clouds from the mid Miss Valley will track within fast zonal steering flow eastward across VA and northern NC this evening into the overnight hours, yielding fair to briefly partly cloudy skies across the northern forecast area tonight. Some of these clouds may exhibit a period of orographic enhancement, although the moisture aloft may not be sufficient, and the upper level wind direction is a bit more westerly than is ideal. Otherwise, these high clouds should be mostly thin with limited coverage, and as such will have minimal impact on radiational cooling with otherwise mostly clear skies and very light winds. Lows 18-25, coldest in rural Piedmont areas. -GIH && .SHORT TERM /Sunday through Sunday night/... As of 235 PM Saturday... The surface high will shift off the Mid Atlantic coast Sunday with frontogenesis taking place along the Carolina coast. Moist overrunning flow focused on the 285-290K layer will surge northward through the area Sun afternoon, resulting in a south-to-north trend to mostly cloudy skies, which will last through Sun night. The precip details are tough to resolve, given the lack of agreement among the large scale models as to the coverage and amounts through Sun night. The NAM brings very light precip into the NC Foothills Sun afternoon, whereas the GFS has patchy light rain over the Sandhills, and the ECMWF is dry. Heading through Sun night, the ECMWF remains mostly dry (sandwiched between showers and the coast and light rain in the NC/VA Foothills), while the GFS brushes light precip over our far eastern sections and the NAM -- which has much deeper saturation -- drops heavier rain farther west to Highway 1. The SREF QPF plumes show most members have no precip or just very light amounts, around 0.01". Given the expected presence of dry air above the freezing level and fairly shallow nature of the moist upglide, have kept pops mostly in the slight chance range, for light rain or drizzle, although I have retained a period of 25-30% pop in the east for a portion of Sun night. Expect highs of 45-51 Sun, coolest NW and warmest SE, followed by a "low" of 39-47 Sun night, with temps dipping early in the evening then holding steady or rising slightly overnight as the warm air just aloft spreads in. -GIH && .LONG TERM /MONDAY THROUGH SATURDAY/... As of 240 AM SATURDAY... The general upper level patter in the GFS and ECMWF are very similar, however there are continued differences between the two with respect to precipitation chances and timing. Monday to Wednesday: Monday, an upper level shortwave will traverse the Great Lakes while the associated cold front will approach central NC from the north or northwest. Southwest flow ahead of the front will result in warm advection into the area during the day. The result will be fairly mild/above normal highs in the mid 50s NW to mid 60s SE. The front is expected to get hung up in the vicinity of the NC/VA border Monday Night through Tuesday Night as the parent surface low moves away to the northeast. Meanwhile, a strengthening low aloft will move eastward through Central Canada, while the flow over the Eastern U.S. will become more zonal but slightly troughed. This will contribute to the stalled southward progression of the front. There is still a bit of uncertainty regarding the southward progression of the front and thus the temperatures, particularly across the north, during this time. As a result, confidence in temperatures is below average. Will hold off on moving the front through until late Wednesday or Wednesday night, which will result in gradually lowering highs in the mid 50s to around 60 degrees Tuesday to low to mid 50s Wednesday. Lows Monday and Tuesday nights will be similar, upper 30s north to mid 40s south. Wednesday Night through Saturday: As the aforementioned upper low strengthens and slides further to the east-southeast, over Southeast Canada by Wednesday Night, the trough over the Eastern U.S. will become more amplified. The cold front will finally push through Central NC Wednesday Night and subsequent high pressure will move through the OH valley and into New England through Friday and ridge southward into NC. Latest model runs indicate strong CAD setting up for Friday Night into Saturday. The problem comes Friday night as moisture advecting into the region in southwest flow aloft may result in some p-type issues. For now will keep precipitation chances just below slight until there is a bit more model consistency and agreement, however wintry precipitation is not out of the question at the end of the period. Temperatures through the extended will be below normal with highs in the low to mid 40s Thursday and Friday, potentially dropping into the mid 30s to low 40s for Saturday. Lows will generally be in the mid 20s to low 30s. && .AVIATION /18Z Saturday through Thursday/... As of 100 PM Saturday... High confidence in VFR conditions through at least 15z Sun. High pressure will settle over the region today into tonight, before shifting off the Mid Atlantic coast on Sunday. Deep dry air remains in place, and any clouds through daybreak Sunday will be very high (above 15,000 ft AGL) with unrestricted vsbys and light surface winds. Then, as a warm front begins to push northward into the region, MVFR clouds will start to spread into NC from south to north after about 15z. Cigs are expected to drop to MVFR at FAY near the very end of the TAF valid period, but cigs should stay VFR elsewhere through 18z Sun. Looking beyond 18z Sun, MVFR cigs will continue spreading northward through NC Sun afternoon. Cigs should then drop to IFR after sunset, with a good chance for low level wind shear developing after midnight, as 1500-1800 ft AGL winds will be from the SW at 35-40 kts but under 10 kts at the surface. Areas of light rain will also develop overnight, with period MVFR vsbys along with the IFR cigs, as the warm front stalls over the area. Unsettled sub-VFR conditions should dominate from Mon into Wed as the front stalls out over the Carolinas with weak waves of low pressure tracking along it, although the details on timing of such adverse conditions are highly uncertain. The front should finally push back well to our south early Thursday, with a trend back to VFR as high pressure pushes in from the north. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...Hartfield SHORT TERM...Hartfield LONG TERM...KC AVIATION...Hartfield

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