Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 251828 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 230 PM EDT Sat Mar 25 2017 .SYNOPSIS... Bermuda high pressure will extend west into the Carolinas and VA through the weekend. A weakening upper level disturbance will cross our region on Sunday. && .NEAR TERM /THROUGH TONIGHT/... As of 1050 AM Saturday... Little change to near term forecast as 12Z upper air analysis supports current forecast. An area of high pressure stretching west-to-east from the eastern Gulf and across the FL peninsula coupled with an area of low pressure lifting ne from the southern Plains into the mid MS Valley will result in a warm sw flow across central NC today and tonight. While the atmosphere overhead will gradually become more moist, most of the moisture advection is occurring in the lowest 5k ft of the atmosphere, and above 20k ft, with a bone dry mid layer. While skies will not be totally sunny due to the presence of patchy cirrus and scattered cu, the dry layer in the mid levels will permit partly sunny skies. Considering that most places are starting out 10-15 degrees warmer than Friday, and warm air advection will continue, should see afternoon temperatures solidly in the mid 70s with upper 70s probable east of highway 1. ~WSS Tonight: SSWly stirring around the wrn periphery of the sub-tropical ridge/Bermuda high, and considerable high clouds topping probable late-night stratus, should result in milder-than-guidance low temperatures, in the middle to upper 50s. While glancing forcing for ascent downstream of the lifting upper low will continue to pivot NEwd across central and wrn NC late tonight, associated forecast omega is centered in the mid levels where dry air from the subsident sub-tropical ridge will be maximized. As such, it seems unlikely that any band of upstream showers will survive and/or arrive even in the wrn Piedmont prior to 12Z, so the forecast will be a dry one through early Sun. ~MWS && .SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/... As of 400 AM Saturday... The upper low over the southern Plains states will lift to toward the Great lakes and weaken today through Sunday, while a Bermuda High continues to provide a warm southerly wind over the Carolinas. Ongoing convection in the Southern Appalachians Sunday morning should weaken as it moves out ahead of the primary cold front and the upper low, while becoming negatively tilted, weakens and passes well to our northwest. Aside form the western Piedmont, where 40-60m height falls appears to erode a fairly stout capping inversion, the rest of central and eastern NC remains capped by the sub-tropical ridge. Models continue to trend drier for most of central NC, and POPs have been adjusted down to just a chance west of US 1 on Sunday. Widespread cloud cover and possible showers will likely hold temps back a little in the west, but southerly flow should still allow highs to reach the mid 70s in the east. Models cranks out some light qpf Sunday night, but this looks over done, and stratus looks to be the only really issue, with mild lows in the mid and upper 50s. && .LONG TERM /MONDAY THROUGH SATURDAY/... As of 230 PM Saturday... A warm, moist airmass will be in place to kick off the work week. Precipitable water in excess of 1.2 inches and highs Monday through Wednesday reaching the mid 70s to lower 80s will provide modest instability and widely scattered showers Monday, with coverage ramping up somewhat on Tuesday as a progressive but relatively weak short wave moves east across the area. Timing of the short wave will be favorable to tap afternoon instability and a few thunderstorms will be possible in the afternoon...especially east where instability and upper diffluence are favorably aligned ~18-21Z. Dry and continue warm temperatures are initially on tap Wednesday as ridging aloft builds over the area ahead of another upper low moving into the central Plains. High presssure over the Great Lakes will surge south ahead of the Plains system, pushing a dry backdoor cold front south into the state later Wednesday, but highs will have time to reach the mid and upper 70s ahead of the cooler air. The "seasonally-adjusted" cold air damming setup will promote overrunning rain in the west as early as Thursday afternoon. PoPs will be ramping up Thursday night and lingering all the way through Friday night as low level southerly flow increases ahead of the Plains system. Low level instability will be meager at best, with no indication as yet that we might see a thermal moisture boundary encroach inland, As such, will have only a slight chance for elevated thunderstorms on Friday. Highs both Thursday and Friday will be mainly in the 60 to 65 range, with some lower 60s across the piedmont and northern coastal plain where cool air will be deeper. Lot of uncertainty as to how the Plains system evolves, i.e. the latest GFS re-establishes cool air advection with development of a coastal low, while the 00Z ECMWF was scouring out the cool airmass and allowing highs to rocket quickly back to the upper 70s...will go middle of the road 70 to 75 for now to await some consensus. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... As of 1240 PM Saturday... While VFR conditions will exist across central NC through Monday night, there will be occasional periods of MVFR/IFR ceilings late at night/early morning beginning tonight and again Sunday night. The adverse ceilings will be most likely in the 10Z-15Z time frame, with the chances higher across the western Piedmont (including the Triad terminals), and less so over the east. The highest threat for showers will occur mainly west and northwest of our region, though a stray shower or two may skirt in vicinity of the Triad terminals Sunday, and again Monday. The weather pattern will be unsettled through mid-week, suggesting that periods of sub VFR conditions are probable, primarily in the form of low ceilings during the overnight into the early morning hours. An approaching low pressure system will trigger scattered showers across central NC late Monday night through Tuesday. A backdoor cold front may drop into the region Wednesday, setting up a possible CAD event for the later half of the work week, and attendant sub VFR conditions. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...WSS/MWS SHORT TERM...SMITH LONG TERM...mlm AVIATION...WSS

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