Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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802 FXUS62 KRAH 292328 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 728 PM EDT FRI JUL 29 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 330 PM Friday... 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 1130 AM Friday... Stormy weather early in the work week should give way to quieter weather later in the week. The broad mid level trough axis will be oriented along the East Coast Mon, with surface troughing extending down through central NC. It still appears that the best convection chances will be across the SE half of the CWA Mon/Mon night, with lingering chances in the extreme SE Tue as the weak shear axis slides ESE through the area, although even these shower/storm chances should be largely to our east given the weak mid level flow from the WNW and NW over W and central NC and post-trough subsidence taking place. Heights aloft will continue to rise as the mid level trough shifts further out over the Atlantic with strong ridging building into and over the eastern CONUS during the mid-late week, yielding low, below-climo precip chances Wed-Fri. The 00z/29 ECMWF does favor some MCS activity riding from the OH Valley southeastward through NC late Wed/Wed night and lingering through Thu with widespread convection, however this is far from certain and lacking support from other models, so prefer to stay with a tranquil forecast for now. Models agree on low level thicknesses slipping to near to just below normal Mon through Wed, then rebounding back to near or just above normal for Thu/Fri as the surface high pressure ridge extending overhead gradually modifies with steady warming aloft. -GIH && .AVIATION /00Z Saturday through Wednesday/...
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As of 725 PM Friday... 24-Hour TAF period: High confidence that VFR conditions will prevail through the TAF period, especially through tonight and Saturday morning. The only exception will come Saturday aft/eve where/when showers and storms develop. Based on latest high-resolution model data, the best chances for storms will be at KRDU and KRWI from approx 20Z Saturday to 03Z Sunday. There is still a chance, albeit a bit lower, at KINT, KGSO (16Z-19Z), and KFAY (21Z-00Z). Storms will bring the usual heavy rain with reduced visbys and gusty winds where they develop. -KC Looking ahead: There will be a better-than-usual chance for sub-VFR conditions in showers/storms Sun into Mon as the upper trough settles overhead with a series of disturbances crossing the region. MVFR or IFR fog is possible each morning as well. Storm chances will decrease Tue into Wed with VFR conditions becoming dominant once again. -GIH
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&& .RAH WATCHES/WARNINGS/ADVISORIES... Heat Advisory today until 8 PM EDT this evening for NCZ011-027-028-042-043-077-078-085-086-088-089. && $$ SYNOPSIS...Hartfield NEAR TERM...Hartfield SHORT TERM...Hartfield LONG TERM...Hartfield AVIATION...KC/Hartfield

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