Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 200655 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 155 AM EST Sat Jan 20 2018 .SYNOPSIS... High pressure will drift across the southeastern United States through the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 930 PM Friday... Just minor updates required with this evening update, mainly matching up temperature trends which were slower than expected across portions of the Triad and a bit faster across the sandhills of North Carolina. Still some concern with isolated fog development tonight, especially across the sandhills where the surface dewpoint depression is only 5 degrees in spots. Confidence is low though, mainly due to the high overhead and the dry airmass aloft, so have continued to leave it out of the weather grids for now. Previous Valid Discussion... Deep westerly flow over the eastern U.S. coupled with a sfc high anchored over the Deep South will maintain a weak lee side trough over the Piedmont tonight. While sfc winds will likely decouple around sunset, this sfc feature should induce a weak south-sw flow over central NC overnight just above the surface. Thus, should see overnight temperatures a few degrees warmer. Some members of the NAM hinting at possible low cloud/fog development above the snowpack as warmer air just above the surface overrides the colder air at the surface. Will continue to monitor but believe tomorrow night may be a better set-up for low clouds/fog. Still expect to see a disparity between locations where snow covers the ground and where snow is absent. Minimum temperatures should range from 17-21 where the snow depth is several inches deep, to the mid-upper 20s elsewhere. && .SHORT TERM /SATURDAY AND SATURDAY NIGHT/... As of 235 PM Friday... The atmosphere will continue to warm as the deep wly persists and the sfc high remains positioned over Southern GA/north FL. The relatively dry air mass will continue to promote wide diurnal temperature swings from sub freezing early morning lows to mild afternoon temperatures. Under sunny skies, expect afternoon temps in the upper 50s to around 60. The exception will be where snow several inches deep remains. The snow pack of this depth will continue to have an influence on the air temps, so afternoon temps in the lower 50s will be more likely. Saturday night, a moistening atmosphere aloft coupled with a persistent low level warm air advection should promote the development of fog or low clouds late Saturday night/early Sunday morning, primarily across the Piedmont where recent heavy snow fell. If the fog does develop, areas of freezing fog may occur as early morning temperatures will be slightly below freezing. Min temps 29- 33. && .LONG TERM /MONDAY THROUGH SATURDAY/... As of 200 AM Saturday... Monday and Tuesday: Fairly high confidence in the low pressure system approaching and moving through Central NC as all medium-range models are in good agreement. An upper low will develop off the Rockies on Monday, progressing east-northeastward through the Midwest and into the Great Lakes region through Tuesday. Meanwhile, the surface cold front will move eastward toward the Mid-Atlantic. With the increasing southerly flow over Central NC Monday into Tuesday, high temperatures will range from mid 50s NW to mid 60s SE. Lows Monday night in the mid 40s NW to low 50s SE. Of bigger concern than temperatures is the chance for precipitation and possibly some thunderstorms as the line of pre-frontal convection moves into and through the area. As of the latest model runs, MUCAPE appears to be less than 500 J/Kg and the surface low is displaced well to the north over the Great Lakes. There are still slight timing and intensity/amount of precip differences between the models, which will play a role in forecast for possible thunder. For now, given the uncertainty, will keep mention of thunder out of the forecast. Both models do indicate precipitation exiting the area by Tuesday night, with cold air starting to filter in behind the front. As a result, Tuesday night will likely be dry and temperatures quite a bit lower than the previous night, in the low to mid 30s. Wednesday through Saturday: This part of the forecast is likely to be dry, with a reinforcing dry cold frontal passage on Wednesday night/Thursday. Surface high pressure is expected to build into the area in the wake of the secondary cold front and remain over the area into Saturday. Chances for precipitation will increase over the weekend, but details are still far from nailed down. Highs will be generally in the 50s and lows in the upper 20s to low 30s Wednesday and Thursday night, increasing into the 30s Friday night. && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/... As of 1235 AM Saturday... High pressure over the southeastern US will result in mainly VFR conditions through the weekend. The exception will be a good chance of fog and associated ceilings/visibility restrictions between 05Z- 14Z Sun, with some lingering sub-VFR ceilings possible through the midday hours on Sunday, as that moist layer lifts and disperses with diurnal heating. Outlook: Sub-VFR conditions, and showers, are expected to affect cntl NC along and ahead of a cold front Mon evening through early Tue. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...JJM/WSS SHORT TERM...WSS LONG TERM...KC AVIATION...MWS is the U.S. government's official web portal to all federal, state and local government web resources and services.