Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 230435 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1235 AM EDT Wed May 23 2018 .SYNOPSIS... A warm and humid southwest flow will hold over the area today. A cold front will approach from the northwest late today, and then push southeast through North Carolina tonight. This front will settle across South Carolina Thursday through Friday, as high pressure builds in from the northeast. && .NEAR TERM /THROUGH TONIGHT/... As of 900 PM Tuesday... A mid/upper level trough will approach from the west tonight, allowing for a weakening band of showers and isolated thunderstorms to move into western/northern portions of the area late this evening/early Wednesday morning. However, the latest HRRR has trended towards very little of this activity making it into central NC. Given nocturnal stabilization and PW`s noticeably lower tonight, with the KGSO sounding showing PW`s of only 1.21 inches this evening, will lower pops some and only keep a low end chance across the far west and north late this evening into early Wednesday morning with a slight chance elsewhere. Low temps temps will remain warm though for this time of year, generally 65-70 degrees. && .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/... As of 345 PM Tuesday... At the base of a mid-upr low migrating ewd across Hudson Bay and Quebec, a series of minor perturbations will sweep across the Northeast and middle Atlantic Wed, then offshore by Wed night. Mid- upr lvl flow will consequently strengthen slightly and veer to nwly over cntl NC, with effective bulk shear values likely to increase into the 25-30 kt range. At the surface, a cold front will settle swd, in backdoor fashion, across VA during the day, then into the nrn NC Piedmont very late Wed afternoon and evening, where it will overtake a preceding, quasi- stationary lee trough over w-cntl NC. The front, modulated by convective outflow, will settle swd through cntl NC overnight. A somewhat drier/lee humid/cooler air mass will follow, as post- frontal high pressure ridges swd across the middle Atlantic region. Initially scattered showers and storms are likely to focus along remnant outflow from convection from the previous day/night; and also along the lee trough. This activity is expected to become numerous by late afternoon and early evening, as convergence/lift increase with the arrival of the surface front. Storms are likely to become semi-organized in a multi-cellular storm mode along common outflow, with an associated strong to isolated damaging wind threat as storm clusters propagate sewd, with the relative greatest potential where the aforementioned bulk shear should be maximized over the nrn Piedmont and nrn Coastal Plain. The chance of showers and storms will linger overnight, particularly over the srn half of the CWFA, as the (effective) frontal zone settles swd. Any earlier severe threat will have diminished owing to both nocturnal cooling and prior convective overturning. Generally persistence temperatures in the mid-upr 80s are expected on average, though modulated and shortened by convection/clouds, with lows in the mid 60s to around 70 degrees. && .LONG TERM /THURSDAY THROUGH TUESDAY/... As of 235 PM Tuesday... Progressive high pressure over the Great Lakes will make a stab at drying us out, pushing a front south of the area early on Thursday. With the front along or south of the area, will have only small chance PoPs along the southern tier counties Thursday into Thursday night. Highs will be only mildly influenced by the front due to strong insolation and should reach mostly mid 80s. The high moves off the New England coast, with return flow beginning to spread into the west Friday into Saturday. As such, chance category PoPs in the west Friday taper off eastward, with all areas in the low chance category on Saturday as we sit beneath an upper ridge conducive to airmass thunderstorms in the resulting unstable, but weakly forced environment. Highs both days will mostly reach mid 80s after mild morning lows in the mid and upper 60s. The moisture transport from the south returns once again for the late weekend aided by the Bermuda high and a developing low pressure system in the Gulf of Mexico. The moisture return will increase precip coverage Sunday and into early next week, and while there is a lot of uncertainty as to the timing of forcing mechanisms driving heavier convection, it will be diurnally influenced, and will maintain high chance to likely PoPs Sunday through Tuesday. Highs will show little variation from previous days, mostly mid 80s, with morning mins in the soupier airmass closer to 70 each morning. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... As of 1235 AM Wednesday... VFR conditions will dominate through the noon hour at all central NC terminals, although a period of MVFR cigs is possible 08z-12z this morning at INT/GSO within and behind a dissipating batch of light showers crossing the area. Otherwise, any other shower activity through the morning hours will be isolated and confined to the VA border region. By early afternoon, a band of scattered to numerous storms will develop across northern NC, sinking slowly to the SSE through the afternoon/evening as a cold front approaches from the NW. Storm chances will be greatest at INT/GSO/RDU/RWI 19z-01z and at FAY 22z-05z. Brief sub-VFR conditions with strong/shifting winds and hail are possible with any of these storms from mid afternoon through late evening. VFR conditions should then return after midnight as the cold front sinks just south of the area, allowing drier air to build in from the north. Looking beyond 06z Thu, there is a chance for brief late-night/early- morning stratus in the S (near FAY) early Thu, but otherwise VFR conditions and dry weather will rule over the region Thu into Fri as high pressure builds in from the N and NE. Early morning fog/stratus chances return Sat/Sun as the surface high moves out over the Atlantic, bringing a moist southerly return flow. Mainly afternoon/ evening shower/storm chances will resume Sat/Sun areawide. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...BSD SHORT TERM...MWS LONG TERM...mlm AVIATION...Hartfield

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