Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 250805 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 405 AM 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 400 AM Saturday... Little change in the forecast of warm SSWly flow and partly sunny conditions today, and mild and continued dry tonight. The models have trended slower with the lifting of a closed upper low now over OK, likely as a result of ridging within, and greater spatial separation from, the main belt of the nrn stream westerlies along the Canadian border. Nonetheless, the upper low will likely maintain a steady, albeit slower, NEwd progression to near KSTL by 12Z Sun, as an upstream "kicker" shortwave trough amplifies through the Four Corners region, from the CA coast this morning. While low amplitude perturbations in SSWly flow aloft will spread E of the main upper low and result in weak (10-20 meter) height mid level falls over NC today, preceding sub-tropical ridging centered over the wrn Atlantic --and associated subsidence drying and capping influence Wwd into the Carolinas-- will continue to dominate our weather today. RAP temperatures have performed better than other guidance with dry adiabatic mixing through 900-850 mb in recent days; and see no reason to deviate from this guidance that favors high temperatures in the middle to upper 70s today. 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. && .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 FRIDAY/... As of 400 AM Saturday... With split flow persisting over the western US, yet another shortwave is forecast to eject east across the Mid-South Monday and Tuesday. Better destablization is expected each day as the low-levels continue to moisten around the Bermuda high, though limited forcing makes it hard to see more than isolated showers and storms on Monday. The relatively weak upper wave will cross NC late Monday night and Tuesday, and should result in a better chance of storms as it interacts with better instability on Tuesday. Highs both days will be in the upper 70s to lower 80s. The ridge aloft will then build back over the region Wednesday ahead of another upper low moving into the central Plains. meanwhile, a cold front is progged to push backdoor into NC Wednesday night and Thursday on the heels, though its still unclear how far south the front will get given the presence of the upper ridge. the GFS is much more aggressive with the front but also has a much more amplified northern stream flow. Temps will be knocked back into the 60s and lower 70s, with a possible cold air damming scenario setting up as high pressure migrates across the Great Lakes and the aforementioned low pressure system moves through the Midwest. && .AVIATION /08Z SATURDAY THROUGH WEDNESDAY/... As of 215 AM Saturday... VFR conditions are expected for most of the TAF period, with a couple of exceptions. The first will be a chance of radiation fog around daybreak at RWI and FAY, where winds will be lightest in proximity to offshore high pressure, and also where surface dewpoints around 50 degrees are maximized relative to areas to the west. In addition, morning to midday heating of a seasonably moist air mass around Bermuda high pressure will favor the development of a field of stratocumulus that will initially develop around 2500- 3000 ft, and may be briefly broken at that time. Otherwise, SSWly surface winds will increase into the 6-12 kt range after 14Z, with occasional gusts into the teens kts, then lessen after sunset. Outlook: Late night-early morning fog and/or stratus, then MVFR range cloudiness as that moist layer is heated through midday, will be possible each day through early next week. Otherwise, a chance of showers and associated sub-VFR conditions mainly at Piedmont TAF sites will exist Sun, then again forecast area-wide on Tue. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...SMITH LONG TERM...SMITH AVIATION...MWS

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