Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 211531 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1030 AM EST Sun Jan 21 2018 .SYNOPSIS... High pressure will continue to drift offshore through tonight. A frontal system will approach from the west Monday, and cross central NC late Monday night through early Tuesday. A seasonably cool air mass will settle into the region for mid-week. && .NEAR TERM /THROUGH MONDAY/... As of 1030 AM Sunday... Current stretch of tranquil weather conditions will continue through tonight. Little change required to the near term forecast. 12Z area soundings depict a relatively dry and stable atmosphere across the region with precip water values around 0.60 inches. Water vapor imagery depicts an upper level low pressure system over southern GA lifting slowly though steadily to the east-ne. Meanwhile another area of low pressure was entering the central Plains. This system projected to strengthen and lift newd into the Great Lakes by Monday night. The system exiting to our south-southeast and the low pressure system over the central U.S. will induce a warm sly flow over central NC through Monday. This warm air advection is aiding to push temperatures across central NC into the 50s late this morning, and should yield temperatures in the low-mid 60s this afternoon. ~WSS Tonight and Monday: As the trough over the Rockies migrates ewd, the difluent exit region of the phased upr jets will likewise spread ewd, and across the cntl Appalachians and middle Atlantic states late tonight and Monday. Considerable high cloudiness will overspread cntl NC from the wsw late tonight and early Mon, likely peaking during the morning hours, before moving east during the afternoon. The surface ridge will have settled directly over cntl NC tonight, before then drifting offshore on Mon. Coastal frontogenesis will occur in return flow on the swrn periphery of the ridge; and this warm front --and associated more humid air mass characterized by the leading edge of surface dewpoints in the 50s-- is expected to retreat nwd across GA/SC on Mon, and into cntl NC by Mon evening- early Mon night. The approach of that boundary and associated low level warm/moist advection will result in both a nwd development of a shield of stratocumulus and cloudy or mostly so conditions during the mid-late afternoon and evening hours, and a slight chance of a shower over the far sern RAH CWFA by 00Z Tue. Any pre-(cold) frontal/warm conveyor convection should not arrive even in the wrn Piedmont until Mon night based on the latest model guidance. Despite the aforementioned increasing high clouds late tonight, strong radiational conditions beforehand and otherwise will favor lows mostly in the mid-upr 30s, with patchy fog. High temperatures Mon are expected to be similar to those of Sunday, though perhaps a degree or two warmer in the southeast and cooler in the west, owing to the presence and timing of the aforementioned cloudiness. ~MWS && .SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/... As of 225 AM Sunday... Fairly high confidence in a cold front approaching and moving through Central NC as all medium-range models indicate it. The uncertainty lies with the timing and intensity of precipitation as in moves through the area. The upper low that develops off the Rockies Sunday night will progress eastward through the Midwest on Monday before moving northeast into the Great Lakes region Tuesday. Meanwhile, the surface cold front will move eastward toward the Mid- Atlantic. The GFS is a bit more progressive/quicker with the fropa, while the ECMWF is slower, lagging 6-12 hours behind the GFS. For now, expect best chances for convection between midnight and noon on Tuesday. Winds are expected to strengthen ahead of the fropa, with sustained winds increasing to around 15 kts gusting into the 20-30 kt range Tuesday afternoon, although there is potential for some isolated higher gusts. Instability still appears to be limited and with the bulk of the convection currently expected overnight, chances for thunder will be somewhat limited across the western half of the area. There is a better, but not great, chance for some isolated thunder across the east late Tuesday morning, but confidence is still not terribly high at this time. Have included a slight chance for thunder with the latest forecast package. With the increasing southerly flow over Central NC Monday into Tuesday, lows Monday night in the upper 40s NW to mid 50s SE will likely occur at midnight Tuesday and increase through the night. High temperatures will range from upper 50s NW to mid 60s SE. With the front expected to be through Central NC by Tuesday night, clearing skies and cold advection in the wake of the front, expect lows in the low to mid 30s. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... As of 200 AM Sunday... Wednesday through Sunday: Expect dry weather through Saturday, 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 as another frontal system approaches the region, but details are still far from nailed down at this time. Highs will be generally in the 50s through Friday and lows in the upper 20s to low 30s Wednesday and Thursday night. High and low temperatures will increase Saturday and Sunday as the next system approaches. && .AVIATION /12Z SUNDAY THROUGH THURSDAY/... As of 620 AM Sunday... High pressure over the southeastern U.S. will result in mainly VFR conditions through the 12Z TAF period. The exception to VFR will be a chance of fog late tonight-Mon morning, but confidence in occurrence is below average given the latest trends in both observational and model data. Initially mainly clear skies may become scattered with high-based stratocumulus (5-6 k ft) later today, but these will be well within VFR range and with limited coverage and duration, with the greatest of both over the nrn Piedmont/near the VA border. Outlook: A high chance of IFR-MVFR ceilings will exist with the northward retreat of a warm front across cntl NC Mon evening and night. These conditions will persist until a cold front and accompanying band of showers cross cntl NC from west to east on Tue, with a subsequent return to VFR, generally between 12Z-15Z at Triad sites and around 18-20Z at ern ones. A very breezy swly wind will also develop behind the front, with gusts between 25 and 35 kts probable for at least a few hours on Tue. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...WSS NEAR TERM...WSS/MWS SHORT TERM...KC LONG TERM...KC AVIATION...MWS

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