Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 100740 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 240 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 815 PM Friday... 1040+ mb surface high pressure was centered over the Northern Plains states this evening. Bitterly cold air was associated with this high. The high pressure continued to build and extend SE to encompass much of the central and eastern United States. Even though the arctic air is greatly modified as it reaches our latitude, the temperatures were still around 15 degree below normal for mid- December with the air mass. These numbers seem almost mild if compared to the temperatures directly under the high pressure over MT/ND/MN, where readings were 25 to 35 degrees below normal. Cold air advection continued over our region with the NW flow. The pressure gradient will continue to weaken overnight as the core of the high shifts SE toward the mid-Mississippi Valley region. Clear skies are expected with good to excellent radiational cooling as winds die off to less than 5 mph. Dew points were already in the teens and lower 20s. Expect lows to fall to 20-25 except around 18 in the rural Piedmont locations. && .SHORT TERM /Saturday through Sunday night/... As of 335 PM Friday... Sat/Sat night: The surface high builds overhead through Sat night, as the mid level flow becomes more zonal. We should see an increase in high thin clouds, especially late Sat into Sat night, as weak perturbations and high level moisture move out of the Front Range and across the Mid-Atlantic region. Thicknesses will start out a bit cooler Sat morning than this morning, although this will be partially offset by some afternoon recovery, which should lead to highs similar to today, in the 40-45 range. Lows Sat night in the low-mid 20s, with light to calm surface winds and a veil of high thin clouds and patchy mid clouds overnight. Sun/Sun night: The 850 mb anticyclone will shift off the Southeast coast late Sat night into early Sun morning, inducing low level warm advection just above the slowly-departing surface high. This warm advection will strengthen over time Sun/Sun night, and models agree on increasing and deepening moist isentropic upglide, starting at 285K-290K, focused on the eastern CWA. Expect increasing clouds roughly from S to N Sun afternoon, trending to mostly cloudy areawide by sunset, and remaining cloudy Sun night. The column remains dry above the freezing level through Sun night, so any precip should be fairly light with pops no better than chance. With rising thicknesses balancing increasing clouds, expect still-cool highs in the 43-50 range. After a slight dip in temps Sun evening, readings should hold steady or rise a bit overnight. Lows 39-46. -GIH && .LONG TERM /MONDAY THROUGH SATURDAY/...
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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.
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&& .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/... As of 1230 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 an tonight in the form of patchy cirrus. 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 rather than directional 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...Badgett SHORT TERM...Hartfield LONG TERM...KC AVIATION...WSS

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