Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 301907 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 305 PM EDT Thu Mar 30 2017 .SYNOPSIS... Weak high pressure will extend into the area from the north today, then move offshore tonight. A storm system will approach from the west tonight, cross the area Friday, then move off the coast Friday night. High pressure will build in from the north over the weekend. Another storm system will affect the region Monday into Tuesday. && .NEAR TERM /through tonight/... As of 305 PM Thursday... The latest surface analysis has the departing surface high shifting over and just off the NE and Mid Atlantic coast, with the residual stable pool covering much of central and eastern NC, and the warm frontal zone extending from central OH through WV and W NC to SW SC. A band of showers and storms along this frontal zone, from near SAV to CAE to just west of CLT/INT, is being supported in part by moist upglide, low level mass convergence, and weak upper divergence, situated along an 850 mb moisture ridge. This convection will continue shifting to the ENE over the next several hours, decreasing in coverage and intensity as it encounters the drier and more stable air over the eastern Piedmont/Sandhills and Coastal Plain, beneath the eastward-moving mid level ridge. Will retain a trend to good chance/likely pops but with light QPF over the far western CWA only into the early evening, followed by a short relative lull before the more substantial mid level DPVA, now supporting convection over S AL into the Gulf, and the attendant upper divergence maximum (in the left exit region of the 120+ kt STJ) shift to the NE into the Carolinas later tonight. Based on extrapolation of these features and the timing of high-res models, coverage is expected to ramp up to categorical over the western and far southern CWA overnight, with lower-end likely in the NE CWA. While forecast hodographs tonight will be long and curved with very high 0-1 km helicity of 200-300 m2/s2 and strengthening 850 mb SSW flow, the lingering low level stable air and marginal mid level lapse rates may yield too little CAPE to work with overnight. But with the strengthening dynamic forcing for ascent late tonight, including a band of strong upper divergence and DPVA, there may be enough overlap with the retreating surface frontal zone to bring about a concern for isolated tornadoes with any discrete or embedded cells, most likely after 3 am. Expect lows of 51-60. -GIH && .SHORT TERM /THURSDAY NIGHT AND FRIDAY/... As of 420 AM Thursday... Attention will turn to the southwest on Thursday night as a warm front surges in and temperatures should actually begin to rise overnight at most locations. Good isentropic lift in the west will begin to encourage precipitation over the western portion of the CWA between 0-6Z Friday. Model forecast soundings are virtually saturated throughout the column with PW values near 1.3 inches. The low level jet structure is fairly unorganized early Friday morning and there are several small disturbances in the flow so expect several smaller waves of precipitation which could be scattered in nature at times. As the precipitation pushes eastward it could become a bit more organized into more multicellular or broken lines but shear will be decreasing at this time particularly in the lower levels as winds become southwesterly and more unidirectional with height. Instability will increase slightly with peak heating and a dynamic push from the left exit region of a 500 mb jet could cause a storm or two to become severe. SPC has the eastern half of the area in a marginal risk for severe wx with damaging winds the most likely threat. With decent moisture in this system expect rainfall totals anywhere from a half of an inch on the low end to about an inch on the high end. Temperatures will be tricky on Friday given the convection but with central NC in the warm sector for much of the day expect highs in the low to mid 70s in most locations. && .LONG TERM /SATURDAY THROUGH THURSDAY/... As of 215 PM Thursday... An energetic Pacific jet will send a series of significant shortwave perturbations into the west-central U.S., where the models indicate they will amplify toward the Four Corners/Srn Plains region and interact with an equally energetic southern stream. That interaction will ultimately shear the perturbations ENEwd into the Middle Atlantic states, with associated episodes of precipitation/convection, about every 72 hours in central NC. Saturday into Sunday: Beneath longwave ridging bulging northward from the Caribbean to central Canada, the weekend is expected to be dry, and mild, with a reinforcing dry frontal passage (the leading edge of a Pacific high) Sat night. Periods of stratocumulus may bubble beneath a strong, 5 k ft subsidence inversion, but not with enough coverage to significantly impact temperatures through the period. Highs in the upper 60s to 70s, warmest ahead of the reinforcing front on Sat. Lows, coolest Sun morning in the 40s, and about a category higher in return SEly flow and increasing deep moisture by Mon morning. Monday into Thursday: The next couple of strong shortwave perturbations will follow on schedule and cross central NC late Monday into Tuesday morning and again on Thursday. The result will be another batch of showers and thunderstorms late Monday into Monday night and again Thursday into Thursday night. It will otherwise be mild through the period, with maximum temperatures mostly in the 70s and minimum temperatures in the 50s. && .AVIATION /18Z Thursday through Tuesday/... As of 1230 PM Thursday... MVFR cigs over the far W (INT/GSO) will lift to VFR during the mid afternoon, while farther east at RDU/FAY/RWI, VFR cigs will hold for the rest of the daylight hours. Scattered showers will move into INT/GSO after 21z, however VFR vsbys and cigs should persist, with only brief MVFR conditions within short-lived heavier showers through this evening. Cigs are likely to drop back to MVFR then IFR around midnight (04z) at INT/GSO, after 2 am (06z) at RDU/FAY, and after 4 am (08z) at RWI, all as a storm system approaches from the W and SW tonight. Widespread MVFR to IFR vsbys within showers and thunderstorms are expected starting late tonight, tracking eastward through early Fri afternoon, ahead of an eastward moving cold front. The showers/storms and sub-VFR conditions are expected to push east of INT/GSO after 15z Fri, and RDU around 18z. Ahead of the front, through tonight, surface winds will be from the SSE, shifting to SW Fri morning, then to WSW with frontal passage at western sites late in the TAF valid period. Looking beyond 18z Fri: The trend from MVFR to VFR will progress eastward through RDU/RWI/FAY prior to 21z, as a cold front crosses the area. VFR conditions are expected to dominate through Sun as high pressure builds in from the north, although the moist low level flow from the NE may bring a short period of MVFR cigs mainly at RWI 03z-12z Sun (Sat night). Another storm system will bring a good chance of sub-VFR conditions and strong/shifting winds with height starting after 06z Mon (Sun night), dominating until Tue morning, when the system will move to our east with a trend back to VFR by Tue afternoon. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...Hartfield SHORT TERM...Ellis LONG TERM...MWS/Franklin AVIATION...Hartfield

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