Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 300400 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1200 AM EDT SAT JUL 30 2016 .SYNOPSIS... A weak upper-level trough will become centered over the eastern U.S. through Saturday, bringing increased chances for showers and storms late Saturday through Monday, along with a trend toward more normal temperatures. && .NEAR TERM /THROUGH TONIGHT/... As of 920 PM Friday... Widely scattered convection will continue to develop in the west through midnight generated by advection of upstream perturbations in the west to southwest flow regime. Modest shear is available, but forcing is weak with waning instability...hence not expecting other than isolated thunder chances. Previous Discussion...Convection chances still appear small through tonight. Surface troughing holds over the area, with a weak vorticity axis spanning far western and northern NC within a weak southwesterly mid level flow. Poor mid level lapse rate and slightly lower temps and dewpoints have held down MLCAPE to less than 1500 J/kg so far, although effective deep layer shear is decent at 25-30 kts, enough to sustain organized convection. The latest HRRR takes the existing showers and isolated storms over northern GA and upstate SC eastward into the far SW CWA during the early evening hours in a weakened state, reasonable considering the lack of upper support and warm mid levels. Will maintain low chance pops, mainly in the SW, through the evening, dwindling with just an isolated shower or two overnight as the low levels stabilize. Heat indices in the heat advisory area have been generally under 105 so far, a result of the WNW low level flow across the area and resultant greater mixing and lower dewpoints. See little value in dropping the advisory now, so will leave it in place as is through early evening. Lows 70-75. -GIH && .SHORT TERM /Saturday through Sunday night/... As of 355 PM Friday... Convection chances will rise over the weekend as the baggy upper trough eases eastward through the Great Lakes and OH Valley, drawing the surface trough back westward over the western Piedmont. As the 850 mb trough axis over central/eastern NC washes out, low-mid level southwest flow will help pull greater PW over the area, with values climbing to near 2.0" in the east, setting the stage for increased shower/storm chances, greatest in the afternoon and evening. Will top out pops at 50%, due in large part to disagreement among the models on where the best location and timing of convection is apt to be, but based on the pattern and concentration of greatest moisture, we would expect areas along and east of Highway 1 to see the greatest coverage of showers and storms, and this area may need to be bumped up to likely pops or higher in future forecasts. The expected increase in clouds, both from convective debris mid and high clouds moving in from the MS and TN valley and from earlier diurnal cumulus formation, should hold temps down a bit both days, still above normal but yielding heat index values below advisory criteria. Will hold off on another advisory for now for Sat, and monitor trends tonight, but Sat could be the first day without a heat advisory or warning in central NC since last Sat, the 23rd. Highs both days 89-95, with morning lows in the lower-mid 70s.-GIH && .LONG TERM /Monday through Friday/... As of 1200 AM Saturday... Broad troughing aloft will prevail over the Carolinas and Mid- Atlantic early next week, transitioning to NW flow aloft mid-week as an upper level ridge re-strengthens over the lower MS river valley and Deep South, followed by ridging aloft mid/late next week as the aforementioned ridge builds E/NE over the Carolinas and Mid-Atlantic. With the above in mind, expect near normal temperatures early next week with temperatures rising above normal by mid/late week as the aforementioned ridge builds over the region. With broad troughing aloft, expect near or above-normal chances for convection early next week, with chances somewhat more ambiguous in NW flow aloft by mid- week, falling below normal (dry perhaps) late-week as the ridge builds over the region. With central NC situated on the southern periphery of the westerlies and eventually a period of NW flow aloft, a potential for organized severe weather may exist early to mid-week if small amplitude waves and/or upstream convection /MCVs/ progress into/across the region, particularly in vicinity of peak heating. -Vincent && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...MLM SHORT TERM...Hartfield LONG TERM...Vincent AVIATION...KC/Hartfield

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