Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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452 FXUS62 KRAH 281430 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1030 AM EDT Fri Apr 27 2017 .SYNOPSIS... A warm moist southerly flow will continue through the weekend, as a deep high pressure ridge strengthens off the Southeast coast. && .NEAR TERM /Today and Tonight/... As of 1030 AM Friday... Forecast is on track. 12z GSO sounding reveals a cap in the 850-750 mb layer which has helped to trap moisture beneath it within a weak wind regime, resulting in stubborn stratus in the Triad and stratocu elsewhere. As surface winds strengthen across the area in the next few hours, horizontal dispersion should help mix out and lift the remaining low clouds, resulting in partly cloudy skies for much of the day areawide. Convection chances still appear slim, given the cap and falling PW values in the wake of the early-morning showers/storms now moving off the NE NC coast. But lapse rates aloft are fairly steep and projected to top out over 7 C/km this afternoon over the Coastal Plain, which could spur development of isolated storms in our far SE, although deep layer shear will be less favorable there (just 25 kts) compared to further west, thanks to the building ridge just off the coast. Recent runs of convection- allowing models support limited to no convection over central NC today. Will maintain a dry forecast, although an isolated cell or two remain possible where local effects can prompt sufficient mass convergence and forced ascent. Expect highs today in the mid 80s to lower 90s, except for lower 80s in the immediate Triad region where insolated will be reduced. -GIH Earlier discussion from 300 am: Extreme destabilization (3000-3500 J/Kg MLCAPE) is expected today as rich low-level moisture advects poleward beneath a modified elevated mixed layer /steep mid-level lapse rates/ in the presence of unimpeded insolation. Despite atypically favorable thermodynamics, a strong cap at the base of the EML combined with the absence of any discernible forcing is expected to preclude convective development. Convective inhibition will be greatest over western portions of the state where afternoon temps will top out in the mid 80s (versus ~90F in eastern NC). Unless a well-timed shortwave/MCV in SW flow aloft progresses across western NC or upstream convection propagates downstream into western NC (neither are likely based on the latest mesoanalysis/observational data and short term model guidance), convective development is highly unlikely. Erosion of CINH will be greatest in eastern NC this afternoon where weak low-level convergence will be present in assoc/w the seabreeze (assuming it penetrates inland). However, such weak/shallow forcing is unlikely to break the cap nor sustain updrafts in the presence of such a dry mid-level airmass. It is fortunate that deep convection is unlikely to develop considering that thermodynamic/kinematic profiles would strongly support robust supercells capable of producing destructive hail/microbursts. With a moist low-level return flow and expected development of stratus, expect overnight lows in the mid 60s to lower 70s. -Vincent && .SHORT TERM /Saturday and Saturday Night/... As of 300 AM EDT Friday... Thermodynamic conditions on Saturday will be very similar to today, though kinematic profiles are progged to be weaker. Regardless, a strong cap and lack of forcing is once again expected to preclude convective development. Expect above normal highs in the lower 90s with lows Sat night in the mid/upper 60s to lower 70s. -Vincent && .LONG TERM /SUNDAY THROUGH THURSDAY/... As of 325 AM EDT Friday... Sunday and Sunday night: Bermuda high shifts ever so slightly eastward on Sunday, with heights lowering a bit, especially across western NC. While not as hot as Saturday, highs Sunday will still be a good 7 to 10 degrees above normal. Highs in the lower 80s west to mid 80s east. The slight eastward shift of the ridge could also result in slightly higher pops in Ring of Fire fashion across the NC mtns and fthls. Will retain a slight/small chance pop across the western Piedmont, otherwise it will remain dry for much of central NC. Strengthening moisture advection with the approach of the front from the west Sunday night/early Monday morning will keep the chance of showers in the west overnight. Mild overnight lows in the mid to upper 60s. Monday and Monday night: A closed upper level low and associated deepening sfc low lifting through the Upper Midwest/Great Lakes will push a cold front into the area Monday evening/night. Attendant cold front will bring increasing chance of showers and storms to areas west of US 1 between 18 to 00z, delayed until after 00z across the east. With regards to severe potential, despite being well removed from the upper trough dynamics lifting off to the north and with models continuing to show limited/weak instability across central NC, impressive vertical shear anchored by a 50-60kt low to mid-level jet moving through the region warrants close monitoring of the system as we get closer in time. Breezy conditions are expected ahead of the front, with gusts of 30-35 mph possible. Thickening cloud cover and increasing pops from west to east during the afternoon will result in cooler temps. Highs ranging from mid/upper 70s west to mid 80s east. Tuesday through Thursday: Cooler/near normal temps will follow Tuesday and Wednesday in the wake of the cold frontal passage Monday night. By late next week, medium range models are actually in good agreement in showing the development of a highly amplified trough digging into the Deep South/SE US. This vigorous system has the potential to bring multiple weather hazards to the area, including heavy rain and severe storms to central NC. && .AVIATION /12Z Friday through Tuesday/... As of 640 AM EDT Friday... 24 Hour TAF Period: Sub-VFR ceilings and fog will gradually improve to VFR by mid/late morning in association with diurnal heating/ mixing. VFR conditions are expected to prevail through midnight, with SCT/BKN diurnal Cu based at 3-4 KFT this afternoon. IFR/LIFR stratus is anticipated to develop by the end of the TAF period at all terminals, between midnight and sunrise Sat. Looking Ahead: VFR conditions are expected to prevail through the weekend, aside from early morning stratus (IFR/LIFR ceilings). Convection appears unlikely until a cold front progresses eastward into the Carolinas late Monday into Monday night. -Vincent && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...Hartfield/Vincent SHORT TERM...Vincent LONG TERM...CBL AVIATION...Vincent

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