Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 301825 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 225 PM EDT Sun Apr 30 2017 .SYNOPSIS... Bermuda high pressure will extend across the Southeastern states today. A cold front will approach the Appalachians tonight, then cross the region late Monday afternoon through Monday evening. Warm high pressure will build in from the southwest Tuesday through Wednesday. && .NEAR TERM /THROUGH TONIGHT/... As of 225 PM Sunday... Latest analysis shows a ridge off the SE coast and a closed trough over the middle of the country. S-SE flow over our area and moist BL has promoted shallow to moderate cu in the unstable BL. A few isolated showers have developed to our south and are current moving across SC border and into our southern zones. The HRRR and other CAMs have picked up on this and they show these isolated showers moving north across mainly our piedmont zones through the rest of the afternoon and dissipating by evening. Have updated the grids to include a 20 pop across most of our CWA south and west of the Triangle for the rest of this afternoon. For tonight, the trough over the Plains will lift slowly newd. As this system approaches, look for the pres gradient to tighten across our area, resulting in breezy s-sw winds. This will also maintain a warm moist BL, which when combined with the aforementioned winds, should result in sct-bkn low clouds. Lows in the mid 60s. && .SHORT TERM /Monday and Monday night/... As of 335 AM Sunday... A cold front associated with the mature cyclone lifting newd across the upper Midwest Monday will approach from the west late in the day and cross central NC late Monday night. The air mass ahead of the front will become convectively unstable with MLCAPE values off of the GFS in the 500-1000J/Kg range (and this model is typically too stable in this type of set-up). Meanwhile adequate shear for organized convection will be in place thanks to a low level jet around 40-45kts crossing overhead Monday afternoon. The latest convective allowing models suggest isolated-scattered showers/isolated t-storms crossing the Piedmont late Monday morning through early afternoon, with an increasing threat for a broken line of organized convection crossing the Piedmont late Monday afternoon- Monday evening, and into the coastal plain and Sandhills Monday evening-Monday night. At this time, a few strong/severe storms will be possible, primarily across the Piedmont due to the favorable timing of late afternoon when low level instability is maximized. Appears the main severe weather threats with the stronger storms will be large hail and damaging straightline winds. Breezy south-sw winds will occur ahead of the front Monday afternoon with gusts 25-30 mph probable across the region. High temperatures Monday dependent upon shower extend in the late morning-early afternoon and thickness of cloud cover. Feel fairly confident that locations along and east of highway 1 will reach the low-mid 80s due to later arrival of showers. Favor max temps in the west in the upper 70s-lower 80s though if shower coverage is much less than expected, high temps 80-84 will be more probable. Bulk of showers and storms should be east of highway 1 by 03Z, and exit the coastal plain counties of central NC by 06Z-08Z. Cooler more stable air will gradually filter into our region after 06Z, though not likely reaching our eastern periphery until close to daybreak. May see a 10 degree spread in the overnight temperatures, ranging from the mid 50s in the west to the low-mid 60s along the I- 95 corridor. && .LONG TERM /Tuesday through Saturday/... As of 315 AM Saturday... Tue/Tue night: A strong mid level low will track from the northern Great Lakes NE over E Canada as it fills Tue/Tue night. The surface front will be pushing off the NC coast early Tue, with falling lapse rates, much drier air, and a shift in low to mid level flow to westerly by Tue night. A very dry and stable column, with weak mild high pressure building in from the SW, will ensure plenty of sunshine and good mixing. Thicknesses start out slightly below normal, countered by strong heating, and expect near-normal highs of 75-81, with a WSW breeze. Passage of a weak mid level perturbation Tue night should bring some high cloudiness, but otherwise expect fair skies and lows in the lower-mid 50s. Wed/Wed night: By midweek, the fairly flat and westerly steering flow across the SE quarter of the CONUS will give way to a deep digging longwave trough over the Southern Plains, resulting in a backing of our mid level flow to SSW and an increased number of weak waves traversing the area. The most pronounced of these waves moves NE across W NC Wed night, helping to moisten the column above 600 mb overnight and foster a trend to mostly cloudy skies west, partly cloudy east. At the surface, a diffuse frontal zone is expected to dip southward into the Mid-Atlantic region but stay to our north as the weak surface high pressure drifts overhead and offshore, keeping NC within a light mainly southerly flow Wed night. Models continue to slow the progression of any prefrontal warm advection showers Wed night, although I still think isentropic and terrain-influenced upglide is possible near the mountains/foothills Wed night, resulting from a light but long-fetch low level Atlantic inflow, so have retained a slight chance of light showers over the far W Piedmont Wed night. Expect slightly warmer temps Wed, especially S, with highs of 77-83. Warm lows Sat night with the increase in clouds, 58-62. Thu-Sat: The weather becomes much more active, but forecast confidence in the details plummets. The GFS shows the aforementioned digging longwave trough cutting off over the mid and lower Miss Valley then drifting eastward over the Mid South and Gulf/Southeast states through Sat, before becoming phased with a northern stream trough and shifting east and offshore as a deeply amplified trough along the East Coast on Sun. The ECMWF, on the other hand, keeps its southern stream trough more open and nearly phased with the northern stream as it progresses more quickly over the E CONUS Thu-Sat. Both models have vacillated in recent runs between a more closed/slower/ deeper system and more open/faster one, and the GEFS mean is actually closer to the ECMWF than the GFS, thus confidence is lower than usual. But both operational models do focus the greatest chance of showers/storms Thu-Fri, so will place the highest pops then, with a lower chance Sat with expectations of the longwave trough axis either shifting overhead or just to our east as we head into the weekend. The risk of strong to severe storms appears to be greatest Thu afternoon/evening on the ECMWF and Fri on the GFS, with both showing DPVA ahead of the trough, focused upper divergence, mid level height falls, and strong deep layer shear, although potential instability may be marginal with mid level warming ahead of the longwave trough. Will monitor and wait for models to come into better agreement on timing. Expect warm highs in the low 70s to near 80 Thu, trending down to cooler than normal temps for Fri/Sat. -GIH && .AVIATION /18Z SUNDAY THROUGH FRIDAY/... As of 225 PM Sunday... Through Monday: VFR conditions attm across all of central NC, with cu and stratocu aoa 3500 ft agl. In this cu field, isolated showers have developed across SC and are moving nwd into south central NC. Thus, a few isold showers are possible across central NC the rest of this afternoon, but given limited coverage, for now have left them out of the TAFs. Steady S-SW low level winds coupled with moist BL will promote sct-bkn stratus after 01/06z, with MVFR and IFR conditions possible. Then, an approaching cold front will increase the threat for a few showers in the western Piedmont by late Monday morning. Showers and a few thunderstorms will increase in coverage across central NC Monday afternoon and Monday evening as the cold front is in our vicinity. MVFR ceilings/visibility highly probable in proximity to the heavier showers and storms. Proceeding the front, sfc winds will be gusty out of the south-southwest with gusts 20-30 mph probable Monday afternoon. The showers and storms should exit the coastal plain counties of central NC shortly after midnight. Beyond Monday: VFR conditions anticipated behind the cold front Tuesday into Wednesday. Another low pressure system will approach from the west-southwest by Thursday, increasing the risk for sub VFR ceilings and scattered showers. && .Climate... Daily Record High Minimum Temperatures May 1 / Greensboro... 65 (2012) Raleigh.......67 (2012) The all time April Monthly Record High Minimum Temperatures Greensboro... 68 set April 14, 1912 - then tied on April 23, 1920 and April 27, 2011. Raleigh.......71 set on April 14, 1922 - then tied on April 25, 1925. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...np SHORT TERM...WSS LONG TERM...Hartfield AVIATION...np CLIMATE...Badgett

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