Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 171757 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 155 PM EDT Sat Mar 17 2018 .SYNOPSIS... A cold front will linger across central NC today. Meanwhile, an area of low pressure will cross the area tonight, suppressing the front to the south and allowing cooler high pressure to build into the Carolinas on Sunday. && .NEAR TERM /THIS AFTERNOON AND TONIGHT/... As of 1030 AM Saturday... Line of light showers from mid cloud deck is making rapid headway across central NC late this morning, although only a few locations have measured more than a trace due to deep dry air aloft. Meanwhile, low level southerly flow is on the increase as weak high pressure off the SE Virginia coast edges offshore and dew points will be rising rapidly ahead of a stronger system that will be moving through early tonight. Have generally tweaked trends to reflect ongoing advection and have modified weather grids tonight as the latest severe outlook boosts us into the slight risk category. Will be evaluating that further this afternoon. Previous Discussion: 08z Surface analysis shows a nearly stationary front draped west to east near the SC/NC state line. North of that boundary, high pressure continues to inch SE through the Ohio River Valley, likely to cross the Appalachians by sunrise before pushing off the Mid Atlantic Coast. This has allowed light and extremely dry northerly flow to be the primary controller overnight, keeping surface dewpoints in the teens (north) and twenties (south). This has allowed temperatures to dip a bit lower than originally forecast, with near to slightly below freezing temperatures witnessed across much of central North Carolina. Light reflectivity returns continue to push into the forecast area from the west, with little to no precipitation expected to reach the ground prior to sunrise, thanks largely to a rather impressive pocket of dry air in the low to mid levels, depicted nicely via the RNK/GSO 00z upper-air soundings. Winds will rebound after sunrise, as high pressure drifts offshore, allowing southerly/southwesterly flow to re-establish by mid morning. This will allow dewpoints to climb rather significantly through the mid afternoon, likely to reach the upper-40s to lower- -50s by supper. Temperatures should remain near normal, with a few 70 degree values in the south, with 60s prevalent north. Mid to upper-level cloud cover along with a few scattered showers will overspread the region from west to east thanks to an occluding surface low over the Ohio River Valley. Most of the precipitation with this surge will struggle to breach the dry air bubble at the surface, however, a secondary push from the remnants of the surface low will cross the area after dark, bringing about the possibility of more widespread showers and possibly even an elevated rumble of thunder. With impressive bulk shear and lapse rates in the late evening to overnight hours, a strong storm capable of producing isolated wind damage and small hail is not out of the question, especially north and west where a small amount of cape may remain. && .SHORT TERM /SUNDAY AND SUNDAY NIGHT/... As of 500 AM Saturday... A few showers or pockets of drizzle may linger pre-dawn Sunday, as high pressure moves into the region albeit briefly. Clouds will diminish throughout much of the day with northerly flow continuing across much of the region, keeping temperatures slightly below normal, rising into the mid 50s during the day and falling into the 40s overnight. The high will shift offshore in the evening, allowing southwesterly winds to return ahead of the next developing storm system, set to ride northeast into the Carolinas by Monday morning. && .LONG TERM /MONDAY THROUGH SATURDAY/... As of 430 AM Saturday... The medium range portion of the forecast continues to look unsettled, with a Miller B surface low configuration system expected late Monday into early Tuesday morning, with rain/showers expected to spread into the area on Monday, with precip chances expected to be maximized on Monday night/Tuesday early morning. This should result in a CAD air mass developing across the area, with potentially a few thunderstorms across far southern/southeastern portions of our area early Tuesday morning. As the coastal low begins to intensify and lift off to the north and east and becomes the dominate low on Tuesday morning chances for showers will begin to decrease. However, given high variability in recent model runs will keep chance pops in the forecast for Tuesday. Additional mid/upper level energy is expected to dive southeastward and into our area for Tuesday night into Wednesday. Model continue to struggle with how this system will evolve, but there remains the potential for a mix of rain/snow across northern/northeastern portions of the area on Wednesday/Wednesday evening. Dry weather is expected to generally return for late week with the mid upper level trough axis expected to shift to the east. Temps during the medium range are generally expected to remain below normal, with temps well below normal in the heart of the CAD (Piedmont) early this week and again on Wednesday with the threat of wintry precip. && .AVIATION /18Z SATURDAY THROUGH WEDNESDAY/...
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As of 130 PM Saturday... Intial surge of heavier mid cloudiness and patchy light rain has moved east of the area, with a clearing trend spreading east which will continue through around 00Z. Expect cloudiness to increase in from the northwest between 00-03Z as a low pressure area moves east along a stalled frontal zone across the area. This low will lead to a 4-6 hour window for showers (and potentially some stronger thunderstorms capable of producing some hail and damaging wind gusts), from 02Z-07Z in the Triad, and from 02-08Z at the eastern sites. Storms would be moving quickly and will not be extensive, so will not include in the TAFs at this point due to low confidence in the timing and just where they will track. MVFR/IFR ceilings will linger into early morning (12-14Z), with dry northeast flow scattering out the clouds to VFR late in the TAF period. VFR conditions are expected Sunday afternoon as high pressure settles into the area, then another threat of sub-VFR conditions arrives on Monday, with the sub-VFR threat persisting into the middle of next week as a series of disturbances passes overhead. Confidence is not high regarding timing of these disturbances, so aviation interests should check back for the latest thinking.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...WSS/mlm NEAR TERM...mlm/JJM SHORT TERM...JJM LONG TERM...BSD AVIATION...mlm is the U.S. government's official web portal to all federal, state and local government web resources and services.