Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 300715 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 315 AM 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 850 PM SATURDAY... See climate section below for the Daily and Monthly Record High Minimum Records for Greensboro and Raleigh. Very warm temperatures are expected to continue tonight courtesy of the southerly flow around the Bermuda surface high pressure. Dew points are at record levels for late April, and this led to many areas having record high minimum temperatures April 28, 29, and for the expected lows tonight. Lows are expected to remain 70+ again for many areas as low stratus increases again late. Otherwise, the scattered diurnally driven scattered thunderstorms near the mountains will dissipate as they move northward (west of our region). && .SHORT TERM /Sunday and Sunday night/... As of 305 PM Saturday... The already-low convection chances for central NC look even lower on Sunday. While mid level heights do dip slightly during the day, mainly west, they remain anomalously high, with PW values falling further as a batch of deeply drier air tracks onshore and over the eastern Carolinas. Mid levels are also projected to warm a bit, most notable around 700-600 mb, which will cut down on the potential for the high CAPE values we`re seeing today. And with very weak deep layer shear over central NC, we are likely to see little to no showers or storm activity in our area, although there may be a few short-lived cells near the sea breeze, and a few more over the higher terrain where the wind field will be better. Otherwise, expect a lifting and mixing of morning stratus, yielding scattered to broken afternoon cumulus, along with some high clouds, especially west, ahead of the slowly approaching frontal zone and deep cutoff low moving from the Southern Plains into the Midwest. Highs 83-89, factoring in slightly lower low-level thicknesses and greater cloudiness. Clouds should increase further from the west Sunday night with strengthening warm air advection, which will also translate into an uptick in southerly winds overnight ahead of the front. Southwesterly steering flow increases Sun night and flattens, eventually becoming gently cyclonic, as weak perturbations track up over western NC overnight. With moisture deepening and PW again exceeding 1" in the west, will bring in a slight chance of showers late in the far western CWA. Lows mainly in the upper 60s. -GIH && .LONG TERM /Tuesday through Saturday/...
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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
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&& .AVIATION /06Z SUNDAY THROUGH THURSDAY/... As of 145 AM Sunday... Widespread IFR/low end MVFR ceilings will develop over central NC after 08Z and likely persist through much of the morning hours. Ceilings should lift dissipate in the 15Z-18Z time frame with a scattered cumulus cloud field highly probable this afternoon. Any showers that occur will be very isolated and limited to the Yadkin/Pee Dee River Valley. Low stratus expected to once again envelope most of central NC after 05Z Monday and linger into the first half of Monday morning. 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 25-30 mph probable Monday afternoon. The showers and storms should exit the coastal plain counties of central NC shortly after midnight. 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 April 30 / Greensboro... 64 (1970) Raleigh.......65 (2014) May 1 / Greensboro... 65 (2012) Raleigh.......67 (2012) ......................................................... The all time April Monthly Record High Minimum Temperatures at Greensboro and Raleigh... 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...Badgett SHORT TERM...Hartfield LONG TERM...Hartfield AVIATION...WSS CLIMATE...Badgett

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