Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 260743 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 343 AM EDT TUE JUL 26 2016 .SYNOPSIS...
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Broad surface high pressure will linger over the Southeast, before sliding offshore as a surface low develops and moves northeast across the Midwest and Great Lakes regions. A surface front will remain off to our north and linger within a region between the Ohio Valley, lower Great Lakes, and Mid-Atlantic regions. This front may finally move into our area early next week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As of 315 AM: Rainfall occurred across or near KAND/KGMU/KGSP/KHKY yesterday, should see patchy light fog around dawn. Early morning water vapor loop indicates a west-east band of rich moisture across the central Appalachians and mid Atlantic states. As the H5 ridge slowly slides SE over the western Atlantic, the southern edge of the moisture band is expected to reach the I-40 corridor this afternoon. The environment should feature higher PWs, moderate instability, and LFCs around 5.5 kft, supporting sct coverage of deep convection. I will forecast TSRAs to develop initially across the high terrain, then slide SE with the sfc trof over the Piedmont during the late afternoon to early evening. DCAPE values are forecast to range between 1000-1300 J/kg across the foothills and Piedmont this afternoon. It is possible that a few storms will result in locally damaging wind gusts. Otherwise, the headline for this afternoon will be the hot conditions. I will forecast high temperatures ranging from 90 degrees within the mtn valleys to mid to upper 90s east. The hot temperature will combine with afternoon RH values in the mid to upper 40s, resulting in Heat Index values between 100 to 104. We will mention the hot heat index values and thunderstorm potential in the HWO. Tonight, NAM indicates that deep convection will begin to gradually dissipate during the mid evening. Coverage of TSRAs/SHRAs east of the mtns should come to an end one to two hours after midnight. A few SHRAs may linger across the western NC mtns well into the late night hours. Low temperature are forecast to range from the upper 60s within the mtn valleys to the mid 70s along and east of I-85.
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&& .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
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As of 300 PM Tuesday: The subtropical ridge will remain the dominant feature across much of the southern half of the Conus at the start of the short term period, with an upper level high centered near the SC Coast, and a weakness in the ridge across the lower Miss Valley. A weak tropical disturbance is expected to develop within this weakness, and become absorbed in the westerlies by mid-week, as an area of height falls spreads into the northeastern quadrant of the country. On Wednesday, a weak lee trough and differential heating/ridge top convergence are expected to provide the primary sources of lift for initiating deep convection. Forecast soundings are seasonably unstable Wed afternoon, especially across the mountains and the northern zones. However, the GFS and to a lesser extent the NAM depict very poor lapse rates and weak instability across the southern half of the forecast area, closer to the upper ridge axis. That being the case, and with mean cloud-bearing flow that would tend to take high terrain convection toward the E/NE, there is virtually no model QPF response across the Piedmont of Upstate SC and northeast GA Wed afternoon. Since there still is some degree of buoyancy, a slight chance pop is retained in those areas, but 30-50 pops (along with ridge top likelies) are reserved for the mountains and the NC foothills and Piedmont. By Thursday AM, frontal zone associated with aforementioned northern stream height falls and tropical moisture plume are expected to extend from the lower Miss Valley into the eastern Ohio Valley and Central Appalachians. As vorticity max(es) lift west and north of the forecast area, the boundary may make a run at the NC mtns by the end of the day, supporting solid chance to likely pops. East of there, strengthening deep layer SW flow responding to height falls to our west actually works to advect even weaker mid-level lapse rates, lower than 5 C/km per a consensus of model guidance into the Piedmont. This is bad news for the parched areas of the Upstate and northeast GA, where probability of precip appears to be 20 percent at best once again Thu afternoon, only made worse by the fact that a plume of tropical moisture will be taunting the area from only a couple of hundred miles away. It appears the severe weather potential will remain low through the period, limited to perhaps a small chance of a microburst or two from pulse-y cells Wed afternoon. Increasing wind fields on Thursday would yield better chances for upscale organization along cold pools, but again the weak lapse rates aloft may well preclude adequate instability for robust convection, even in those areas where chances for convection are decent. Temps will remain at least a category above climo through the period.
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&& .LONG TERM /FRIDAY THROUGH MONDAY/...
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As of 330 AM Tuesday...Unfortunately for those of us desperate for rain, a clear consensus exists in the global models that would maintain a mean upper trough west of the forecast area, with perhaps even a slight retrogression into the early part of the weekend. This would spell little eastward movement of the front during this time, and guidance essentially dries up the deeper moisture with time. Thus, by the time the front finally does push into area, perhaps late in the weekend, it just doesn`t have much left to work with. Nevertheless, with ridge becoming increasingly suppressed into the western Atlantic, the synoptic pattern will become more conducive to lift and the boundary should support enhanced coverage of convection in most areas on Sunday and Monday afternoon/evening. Lower thickness values should also shave a couple of degrees off of this week`s hot temperatures.
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&& .AVIATION /08Z TUESDAY THROUGH SATURDAY/...
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At KCLT and KHKY: Rainfall at KHKY should yield MVFR fog from 10z to 12z. Morning water vapor loop indicates a west-east band of rich moisture across the central Appalachians and mid Atlantic states. As the H5 ridge slowly slides SE over the western Atlantic, the southern edge of the moisture band is expected to reach the I-40 this afternoon. The environment of higher PWs, moderate instability, and LFCs around 5.5 kft should yield sct coverage of deep convection. I will forecast TSRAs to develop initially across the high terrain, then slide SE with the sfc trof over the Piedmont during the late afternoon to early evening. I will highlight the period of convection with a PROB30 at KHKY from 19z-01z and KCLT 0z-5z. Otherwise, the forecast will feature steady winds from the SW and CU bases around 6 kft. Elsewhere: Rainfall occurred across or near KAND/KGMU/KGSP yesterday, expected to result in dawn mvfr fog. Otherwise, conditions should remain similar as discussed above. The potential for TSRA will develop earliest near KAVL between 18z-21z, then spreading to the I-85 corridor between 21z-1z. Outlook: A plume of deep moisture will gradually build across the western Carolinas and NE GA through the late week. SCT SHRAs and TSRAs will be possible each afternoon and evening, coverage the greatest across the mtns. Pre dawn fog and low clouds will be possible over areas of recent rainfall. Confidence Table... 07-13Z 13-19Z 19-01Z 01-06Z KCLT High 100% High 100% High 100% High 100% KGSP High 100% High 100% High 100% High 100% KAVL High 96% High 100% High 100% High 100% KHKY High 100% High 100% High 100% High 100% KGMU High 100% High 100% High 100% High 100% KAND High 100% High 100% High 100% High 100% The percentage reflects the number of guidance members agreeing with the scheduled TAF issuance flight rule category. Complete hourly experimental aviation forecast consistency tables and ensemble forecasts are available at the following link: www.weather.gov/gsp/aviation
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&& .CLIMATE...
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RECORDS FOR 07-26 MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 94 1949 72 1911 71 2012 49 1911 1940 2010 KCLT 100 2005 74 1920 76 1992 60 1904 1940 1940 1914 1936 KGSP 99 2010 76 1920 76 2005 53 1911 1995 1940 1987
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&& .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...JDL NEAR TERM...NED SHORT TERM...JDL LONG TERM...JDL AVIATION...NED CLIMATE...

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