Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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611 FXUS62 KRAH 150744 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 245 AM EST Fri Dec 15 2017 .SYNOPSIS... A pair of frontal zones will merge over south-central NC tonight, and along which an area of low pressure will develop and track, to off the srn middle Atlantic coast through Fri. High pressure will follow and migrate across the southeastern US through the weekend. && .NEAR TERM /FRIDAY/...
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As of 245 AM Friday... WV and 00z upper air datasets continue to show a positively tilted trough extending from the Great Lakes region south and west through the central/southern plains. At the surface, the forecast area finds itself between a building high currently situated along the Mason Dixon Line with a quasi-stationary front draped along the NC/SC state line with a backdoor front inching south and west inland from the Outer Banks. A strengthening low will begin to inch northeast along the stalled boundary before sunrise Friday, allowing a mid to upper level cloud deck to steep north gradually during the pre-dawn hours. Isentropic lift across the front will lead to stratus formation just prior to sunrise, especially across portions of the Triad and northern Piedmont Counties of North Carolina. This low to mid level deck will struggle to dissolve by mid day, with some guidance keeping the stratus layer in place past the end of peak heating. Thus, have trended down with temperatures for areas to the north and west with warmer values as you travel east toward the southern coastal plains, which should remain cloud free. Some concern with patchy fog in these areas, but likely not dense and very brief after sunrise. The aforementioned low will transition northeast throughout the day Friday, with combining northern and southern streams aloft assisting in enhancing the early stages of frontogenesis as it pushes offshore. Guidance continues to keep any and all precipitation well east of the area during this time period. .SHORT TERM /FRIDAY NIGHT AND SATURDAY/... As of 245 AM Friday... High pressure takes over by Friday night, keeping things calm, clear, and chilly as we progress into the weekend. Early morning temperatures saturday should be sub-freezing across the area, even as low as the mid 20s across the Triad and northern Piedmont Counties. Afternoon temperatures should be a bit warmer under a westerly breeze, settling near 50 for the northern portions of the forecast area, with mid 50s prevalent in the south and east. PoPs should remain near zero overnight saturday into sunday, with temperatures once again dipping just below freezing.
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&& .LONG TERM /SUNDAY THROUGH THURSDAY/... As of 235 AM Friday... The surface high will shift offshore on Sunday as a warm front lifts northward through the area Sunday eve/night, resulting in south- southeasterly return flow and warm advection into Central NC. Meanwhile aloft, the Southeast US will be under an upper level ridge, while a deep trough dominates over the Rockies and Southwest. A shortwave will break off from the low, migrating east-northeast through the Midwest toward the Mid-Atlantic. As of the latest model runs, the shortwave should ride the northern periphery of the ridge and stay north of the area Sunday/Sunday night. Temperatures will be on the rise, with highs in the mid to upper 50s and lows in the low to mid 40s. Although the models are in much better agreement with the overall upper level pattern, there are still some significant differences in the temperature and precipitation forecasts. The closed low over the Southwest US will become more of an open trough on Monday, gradually deamplifying as it lifts ENEward into the Midwest Tuesday/Tuesday night. The southwest flow into Central NC will increase during this time, increasing the moisture advection and thus chances of precipitation. Meanwhile, a cold front will drop southward toward and into Central NC Tuesday/Tuesday night. The highest chances for and amount of rain will be across the south, ahead of the front. The weakening trough turned shortwave may enhance the precipitation along the front Tuesday night as it passes near/over the area. Temperatures will be unseasonably warm Monday and Tuesday, with highs in the upper 50s to mid 60s and lows in the mid to upper 40s. Expect a slight decrease in temperatures for mid week, albeit still a bit above normal (highs in the mid to upper 50s and lows in the 30s Wed night and 40s Thu night). && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... As of 1230 AM Friday... VFR parameters should persist across central NC through 08Z. After 08Z, chances will increase for the potential for a deck of stratus to develop with MVFR ceilings 1500-2500ft probable, predominantly across the northern TAF sites. This deck of ceilings expected to persist until mid day, then gradually dissipate. Some isolated fog may also develop at FAY near daybreak, but low confidence, as mid to upper level cloud deck could dictate extent and/or duration. There is a high chance that VFR parameters will occur Friday night through Sunday morning. The next threat for sub VFR parameters is expected late Sunday into early next week as a low pressure system approaches from the west-sw. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...JJM SHORT TERM...JJM LONG TERM...KC AVIATION...JJM/WSS

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