Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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920 FXUS62 KRAH 292344 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 744 PM EDT Sat Apr 29 2017 .SYNOPSIS... A warm moist southerly flow will continue through the rest of the weekend, as a strong high pressure remains anchored off the Carolina coast. A cold front will cross the region Monday afternoon and evening. && .NEAR TERM /THROUGH TONIGHT/... As of 250 AM Saturday... A quiet but warm/muggy night ahead. Experimental GOES-16 red visible band imagery reveals cloud streets over the western and southern CWA, and batches of thin cirrus that emanated from the now- dissipating MCS activity just north of the Ohio River. But cloud cover remains mostly scattered/thin, allowing for strong heating and temps soaring to well above normal readings. The strong mid level anticyclone centered just off the Carolina coast combined with the Bermuda high pressure extending across the Southeast continues to prompt mean subsidence and a fairly dry column, so despite decent lapse rates around 7 C/km and current MLCAPE of 3000-4000 J/kg, any convection chances for the rest of the day appear slim. With the strong cap holding in place in the 950-850 mb layer, we`ll have another round of stratus form overnight, leading to a trend to mostly cloudy skies and patches of fog. We should once again see lows in the upper 60s to lower 70s, over 15 degrees above normal lows. -GIH && .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 /MONDAY THROUGH SATURDAY/... As of 305 PM Saturday... The latest run of the ECMWF model has brought more clarity to the long term forecast this afternoon. There is higher confidence in a frontal system moving through the area on Monday into Tuesday and then a strong upper level trough digging down into the southwestern U.S. that will help provide dynamics for two separate low pressure systems later in the week. The northern half of th upper trough will become more progressive and help develop a low that will cross the mid-Atlantic states on Thursday night and Friday. The southern half of the upper trough will become cutoff and develop a very slow moving low pressure system over the deep south that will provide moisture to central NC through next weekend and beyond. At this time the main precipitation periods will be Monday and Tuesday when showers and thunderstorms will be possible with a high shear/low CAPE scenario playing out. Most storms should remain sub- severe with a marginal risk for severe weather, mainly over the western half of the state. Later in the period, the nature of the slow moving low pressure system and the continued moisture transport into the area will again bring about concerns for an extended period of precipitation with rain heavy at times, and thus flooding becoming a primary concern late in the period. A frontal zone setting up between the exiting mid-Atlantic low and the near stationary deep south system will be the primary area of concern but it is too early to tell where or for how long that zone will be over any particular area. Monday will be the warmest day of the period with temperatures topping out in the mid 80s across the east with upper 70s in the NW Piedmont. With the exception of Wednesday, temperatures should gradually decrease through the period back through the 70s and possibly only topping out in the upper 60s by Saturday. && .AVIATION /00Z SUNDAY THROUGH FRIDAY/...
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As of 743 PM Saturday... 24-Hour TAF period: Will continue with the persistence forecast for tonight with high pressure and abundant low-level moisture remaining over the area. Fairly high confidence that cigs in the 800-1500 ft range will develop after midnight and fluctuate within that range through the early morning hours. Cigs should gradually lift after sunrise and scatter out in the afternoon Sunday, resulting in a return to VFR conditions for the rest of the day Sunday. Generally south-southwest winds should stay in the 5-10 kt range tonight, increasing some during the day with some gusts to around 20 kts possible at most sites. -KC Looking ahead: VFR conditions and dry weather will hold through Sun evening, with development of MVFR to IFR stratus once again after midnight, lasting through sunrise Mon with slow improvement to VFR Mon morning. A band of showers and storms expected to cross the area late Mon afternoon through Mon evening may bring a period of sub-VFR conditions and breezy/gusty winds from the SSW. Dry weather and VFR conditions should follow behind a front late Mon night through Wed. Chances will increase for showers/storms and sub-VFR conditions Wed night and especially Thu. -GIH
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...WSS/GIH NEAR TERM...Hartfield SHORT TERM...Hartfield LONG TERM...Ellis AVIATION...KC/Hartfield

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