Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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510 FXUS62 KRAH 252357 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 655 PM EST Sat Feb 25 2017 .SYNOPSIS...
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A strong cold front currently crossing the area will move offshore this evening. Colder high pressure will move in from the west tonight, and linger through Sunday night, before moving offshore Monday. A warm front will approach from the south late Monday.
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&& NEAR TERM /THROUGH TONIGHT/... As of 330 PM SATURDAY... Deepening cyclone will lift north into Ontario and Quebec, with associated strong mid-upper trough over the OH and TN Valleys becoming negatively tilted as it progress eastward into the Mid- Atlantic States tonight. Attendant cold front currently approaching the Triad will advance east through central NC through 00 to 03z. It will remain breezy ahead of the front, with swly sustained winds of 15 to 18 kts, gusting to 25 to 30 kts, with similar magnitude west-northwesterly wind gusts in the wake of the front through 00 to 03z. Dry air and a strong boundary layer mixing is proving difficult to overcome and will continue to limit convective coverage across the area through 00z, though there still remains an isolated threat for a severe thunderstorm across the northern Piedmont and northern coast plain. Weak to moderate instability(MLCAPE 500-1000 J/Kg) has developed in response to steep low-level lapse rates from the unseasonably warm temperatures and mid-level lapse rates of 7.0 to 7.50 C/Km, left behind by the EML that pushed through the area earlier this morning. Impressive effective unidirectional shear of 50 to 60 kts, coupled with inverted-V sounding profiles and DCape values of 1000 to 1200 J/Kg from the entrainment of dry air aloft will make it possible for an isolated severe storm to produce damaging straight line winds across the northern/northeastern tier, with even 40 to 50 mph winds possible in the heaviest shower. Hail up to size of quarters is also possible. Convection should be exiting the area at or by 00z, with strong post- frontal dry cold air advection resulting in abrupt clearing and seasonable overnight lows in the lower 30s NW to upper 30s SE. && .SHORT TERM /SUNDAY AND SUNDAY NIGHT/... As of 315 PM SATURDAY... Flow aloft will become quasi-zonal flow in the wake of upper trough exiting the Mid-Atlantic region. High pressure building into the area from the west will quickly move offshore late Sunday night, but will maintain east to west surface ridging into Monday. This means that the cooler-more seasonable air will not stay around very long. Highs ranging from from mid 50s NW to around 60 SE. Sheared shortwave energy ejecting eastward across the Lower MS Valley in the progressive low-amplitude flow will bring an increase in high clouds late Sunday night/early morning and could temper low temps Sunday night. Lows in the 30s. && .LONG TERM /MONDAY THROUGH SATURDAY/... As of 200 PM Saturday... After the brief return to near normal high temperatures on Sunday, we will have a progressive warmup back into the 70s through midweek as high pressure moves offshore and southwest flow ensues. Moisture will be on the rise, as will cloud coverage and the chance of rain through the midweek period. Showers are expected as early as Monday night in the west as a weak upper disturbance lifts northeast in prevailing southwest flow aloft. It`s hard to find a really confident feature that might enhance coverage Tuesday night through Wednesday but we will be in the warm moist airmass with potential for any passing weak impulse to kick off spotty showers. Will maintain generally uniform low chance PoPs across the area pending later model resolution of these impulses. Temps will be rebounding on Monday into the 60s...with low to mid 70s on Tuesday and mid to upper 70s on Wednesday. A cold front driven by a rather strong shortwave moving into the Ohio valley will provide a focus for a line of convection Wednesday night in the west...with the convection moving east rapidly and offshore by Thursday evening. The convection will be east of central NC by early afternoon. This timing is not ideal to benefit from maximized diurnal instability, but strong upper diffluence and the low level convergence with a 50+ knot h85 jet will be sufficient for inclusion of at least a modest chance of thunderstorms at this point. Highs Thursday will be hampered by the onset of cold air advection fairly early in the day, with western areas topping out in the upper 50s...while the southeast might see some mid 60s. Dry weather and a cooler airmass will be in place Friday and Saturday, with highs both days mostly in the upper 50s to lower 60s. && .AVIATION /00Z Sunday through Thursday/...
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As of 655 PM Saturday... VFR conditions are highly likely for the next 24 hours. A cold front now moving through the area will be east of all central NC terminals by 04z. Strong and gusty surface winds are shifting with frontal passage to be from the WNW or NW. Speeds and gusts will diminish by 06z with sustained speeds trending down to under 10 kts. Scattered showers and storms will impact the northeast forecast area before 03z, however these should largely stay north of RWI. Winds Sun after 14z will be from the WNW or NW at 8-12 kts with a few gusts of 15-20 kts. Looking beyond 00z Mon: High pressure will build over the area from the west then move east and offshore Sun night, which will bring VFR conditions through Mon. The next chance for sub-VFR conditions will be Mon night, lasting through Tue night and perhaps into Wed, as southwest flow brings in low level moisture and an increased risk for showers, as well low stratus and fog, especially dusk through dawn. A cold front passage late Wed night or early Thu will bring a better chance for showers then. -GIH
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...CBL SHORT TERM...CBL LONG TERM...mlm AVIATION...Hartfield

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