Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 101100 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 600 AM EST Sat Dec 10 2016 .SYNOPSIS... Cold high pressure will build across the area through tonight, then shift offshore Sunday. A cold front will approach from the west late Sunday and move through the area on Monday. && .NEAR TERM /THROUGH TONIGHT/... As of 300 AM Saturday... Cold start to the morning as Canadian high pressure noses into central NC, proving clear skies and a near calm sfc wind. Most places will start the day in the low-mid 20s with upper teens likely at the normally colder locations. Westerly flow aloft will eventually advect high level moisture into central NC later today, and more so tonight, leading to patches of cirrus. Still, expect plenty of sunshine today. Afternoon temps should recover into the 40- 45 degree range. Under clear-partly cloudy skies this evening, temperatures should cool off appreciably due to the relatively dry air mass and near calm winds. Overnight temps in the low-mid 20s will be common. && .SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/... As of 300 AM Saturday... Sunday, sfc high will drift offshore, leading to a sly low level return flow regime by late in the afternoon. this flow, originating offshore of Georgia/South Carolina will increase the presence of low level moisture. This should result in the formation of a low level cloud deck, spreading over the south half of central NC prior to sunset. Isentropic upglide increases appreciably bu sunset which should lead to a few patches of light rain over sections of the Sandhills and southern coastal plain. This upglide increases Sunday night, leading to a better chance for patchy light rain and/or drizzle over roughly the eastern half of the forecast area. With the lift and moisture confined to the lowest 10k ft of the atmosphere, expect rainfall to be very light, totaling no more than a few hundredths. Max temperatures Sunday dependent on some degree of sunshine, especially across the northern counties. If thicker cloud cover occurs sooner than expected ( by mid day or early afternoon versus later afternoon), then high temps may end up being 3-4 degrees cooler than currently forecast. High temperatures Sunday mid 40s north to around 50 south. Sunday night, expect temps to cool initially after sunset. After midnight, should see temperatures stabilize or slowly rise as a low level sly jet strengthens overhead and low clouds become thicker. Low temperatures mid-upper 30s north to the lower 40s southeast. && .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 /12Z SATURDAY THROUGH WEDNESDAY/... As of 600 AM Saturday... High confidence that VFR parameters will persist across central NC through 12Z Sunday as high pressure at the surface will be the dominate weather player. Westerly flow aloft will advect high level moisture across the area later today and tonight in the form of cirrus, which will thicken into an overcast layer tonight. The high will shift offshore Sunday. The return flow on the backside of the retreating high will advect low level moisture into central NC late Sunday and Sunday night, resulting in MVFR, and eventually IFR ceilings. In addition, patches of light rain should develop Sunday night. An increasing low level jet may produce marginal low level wind shear parameters Sunday night, mainly in the form of speed shear, as wind speed 35-40kts probable between 1500-2000ft. Variable aviation conditions expected Monday through Wednesday as a series of low pressure systems cross the southeast U.S. This will result in periods of MVFR or IFR parameters due to adverse ceilings. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Badgett NEAR TERM...WSS SHORT TERM...WSS LONG TERM...KC AVIATION...WSS

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