Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 062343 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 305 PM EST Wed Dec 6 2017 .SYNOPSIS... A cold front along the North Carolina coast early this afternoon will continue moving eastward through tonight. Cold high pressure will follow and extend across the Carolinas through Thursday. Meanwhile, a series of disturbances will pass overhead in southwesterly flow aloft. && .NEAR TERM /THROUGH TONIGHT/... As of 110 PM Wednesday... Satellite and upper air data depict a positively-tilted trough from Hudson Bay to srn CA, with an associated 100-150 kt upper level jet extending from the southern Plains to the Northeast. The jet stream is forecast to migrate enewd and across the srn and cntl Appalachians late this afternoon and tonight. Meanwhile, a series of northern branch polar and arctic stream shortwaves were evident from the upper Great Lakes and westward along the US/Canadian border. The shortwaves are forecast to amplify a new, positively-tilted longwave trough from the Great Lakes to the Four Corners region by early Thu. At the surface, a cold front was along the North Carolina coast at 18Z. A cP high pressure will follow and expand from the srn Plains today, to the srn Appalachians and Carolinas by tonight. The remainder of this afternoon should remain mostly dry. There will be some virga falling from a mid-high level overcast, particularly late this afternoon when the upper jet now over the southern plains moves to just northwest of our region. Tonight looks to be a classic, upper jet and mid level Fgen- generated light precipitation event, with precipitation falling from cloud bases mostly above 10 thousand ft. Mostly light rain should spread across roughly the southeastern half of the area, with the Triangle likely on the northwestern edge of the measurable precipitation shield. Low temperatures should dip relatively uniformly to around 40 degrees, with a small diurnal range governed by widespread cloud cover, and to a lesser degree evaporational cooling perhaps into the upper 30s where light rain occurs. && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... As of 110 PM Wednesday... Forecast remains nearly unchanged with a persistent southwesterly flow aloft, deep moisture, and multiple disturbances riding northeast over a baroclinic zone off the southeast coast. Light rain is expected on Thursday and Thursday night across the Coastal Plain and Sandhills, mainly south and east of Raleigh. With colder air working into the region, there is a chance that some of the precipitation will mix with or change to snow. It`s important to note that the pattern suggests an active period with widespread precipitation across coastal NC and decreasing amounts and coverage to the north and west in the more climatologically colder region of the northwest Piedmont. In addition, there is no well defined surface high to support the delivery of cold and dry air into central NC to support more than a low end event. Still, partial thickness values and forecast BUFR soundings support some wet snow across the northwest and northern Piedmont including the Triad area Thursday night with surface temperatures dropping into the 32 to 36 range. But given these areas are on the northwest fringe of the precipitation shield and PoPs are in only the chance range, no snow accumulation is expected. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... As of 305 PM Wednesday... ...Increasing chance of snow across portions of Central NC between midnight and 7 AM Saturday, with some accumulation on elevated and grassy surfaces possible... Friday and Friday Night: Central NC will be under the influence of deep southwesterly flow aloft as a strong upper level trough to the west swings eastward toward the region. Disturbances in the flow aloft will move over the area, resulting in periods of heavier precipitation. At the surface, Central NC will be sandwiched between the stalled front off the Mid-Atlantic coast and high pressure ridging eastward from the west. With the high in an unfavorable location, the best push of cold air will likely get hung up along the mountains. Expect much of the precipitation to fall as rain, especially early on. Despite the delayed CAA, strong lift in a saturated dendritic growth zone will likely result in precipitation rates strong enough for snow to occur where temperatures are in the 32-36 degree range. This will be an event where the cold air is chasing the precipitation, thus expect most of the precipitation to fall as liquid. Liquid equivalent precipitation totals will range from less than a quarter of an inch in the northwest to nearly 1.75 inches in the southeast. Given the warm ground and boundary layer, snow will have a difficult time accumulating except for on elevated and grassy surfaces and under high precipitation rates. Generally less than an inch of snow is expected at this time, primarily between midnight and 7 AM Saturday. Best chances for accumulating snow along a line from Lexington to Burlington to Roanoke Rapids, generally be along and west of US-1. Highs on Friday in the low to mid 40s with overnight lows in the upper 20s NW to mid 30s SE. Temps are not expected to fall below freezing in the Triad until after midnight. Saturday through Wednesday: As the strong upper disturbance swings through the region Saturday morning, the main precipitation axis will shift east of the area. At the surface, in the wake of the disturbance aloft, west-northwest flow will advect strong cold air into Central NC ahead of a secondary strong vort max aloft diving southward over the area. Saturday and Sunday will be the coldest days Central NC has had in a while, with highs in the low to mid 40s and overnight lows in the low to mid 20s (possibly dipping below 20 in outlying areas Sunday night). Generally dry weather expected for the remainder of the period although a few sprinkles/flurries early next week cannot be ruled out. Temperatures will moderate a bit Monday and Tuesday before another cold front moves through the area. && .AVIATION /00Z THURSDAY THROUGH MONDAY/...
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As of 645 PM Wednesday... 24-Hour TAF period: Light rain showers, including a few reports of light sleet continue across the forecast area as a short wave continues to push NE across central North Carolina. VFR+ conditions are expected to continue tonight, with rather stable CIGS above 5K Feet and P6SM VSBYS expected to remain in place at all TAF Sites. Expect the light rain showers to slowly diminish, exiting east of the FAY/RWI before sunrise Thursday. Moderate confidence in this forecast, with slightly lower confidence in overall precipitation timing. -JJM Outlook: An upper level trough will amplify west of the Appalachians, with associated periods of precipitation and sub-VFR conditions Thu night through early Sat. Some of that precipitation may mix with or change to snow briefly at Piedmont sites, particularly at RDU and GSO, Fri morning and again Friday night- early Sat. VFR Sunday and Monday in a dry westerly flow.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS/Franklin NEAR TERM...MWS/Franklin SHORT TERM...BLAES/Franklin LONG TERM...KC AVIATION...JJM/Franklin

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