Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 210758 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 358 AM EDT Mon Aug 21 2017 .SHORT TERM...
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(Today through Tuesday) Issued at 358 AM EDT MON AUG 21 2017 Surface high pressure is centered near the mid-Atlantic, with a quasi-stationary boundary aligned from the Great Lakes to the central Plains, with a secondary warm front extending southeast into the Ohio Valley. Aloft, an upper level ridge rules across the southeast CONUS, with flatter flow across the majority of the Mississippi Valley. A more vigorous short wave trough is moving southeast out of the southwest Canada, currently moving through the British Columbia/Alberta border. Eastern Kentucky is enjoying another most clear night, with areas of valley fog. Some debris high clouds have been making it into the area from the west, but these remain pretty thin. The next 24 hours will remain dry, as the upper level ridge to our southeast remains in control. Today still looks like an overall good viewing day for the full eclipse. Highs will peak in the upper 80s to near 90, with some cumulus and thinner high clouds to contend with during the day, but nothing extensive. Tonight, skies will remain mostly clear initially, as afternoon cumulus dries up. Meanwhile, the Canadian short wave trough will deepen and continue to move southeast, reaching the Great Lakes region by dawn Tuesday. Some high clouds will move in by early Tuesday morning, keeping fog a bit less extensive. Lows will generally range from 65 to 70 degrees. As the short wave trough continues to amplify across the U.S./Canadian border on Tuesday, low pressure will organize and deepen rapidly along the surface boundary to the east. The cold front will move southeast across the Ohio Valley Tuesday afternoon, with showers and thunderstorms breaking out along and ahead of the boundary. The blended POPs yielded likely values from the northwest during the afternoon, and given the forcing and instability, this seems reasonable. Additionally, stronger 0-6km bulk shear values than we have seen in a while will be on tap, supporting a severe thunderstorm threat, especially across the northwest half of the area. Will highlight this threat in the HWO. .LONG TERM...(Tuesday night through Sunday) Issued at 358 AM EDT MON AUG 21 2017 Forecast will start out with a cold front approaching the region Tuesday evening, and traversing from NW to SE Tuesday night and during the first half of the day Wednesday. Showers and thunderstorms will be possible throughout the night, but will peak during the day Wednesday just ahead of the frontal passage. That being said, once the front passes, winds will quickly shift to a more northerly direction and instability will drop off. Lingering precip on the back side of the frontal passage through the day Wednesday will therefore likely be in the form of rain, and should come to an end by Wednesday evening as the frontal boundary shifts southeast of the state. A large area of high pressure will take hold Wednesday night and through the rest of the work week. A strong troughing pattern will still be in place aloft, promoting NW flow across the state. This, in conjunction with northerly winds at the surface, will help to keep temperatures well below normal. Highs will generally be in the upper 70s with low humidity through Friday. By Saturday and Sunday, models are still in fair agreement showing the upper level troughing moving east of the region but some shortwaves developing and moving into the Ohio Valley under continued NW flow. That being said, they are not in good agreement as far as the exact timing and magnitude of these waves across the state. Surface winds also suggest a weak surface low passing across the region during the day Sunday. However, not confident on the exact location and timing given the uncertainty in models aloft. Regardless, there is the possibility for some unsettled weather during the weekend. Right now model consensus is for mainly diurnally driven isolated to scattered showers and thunderstorms, with best coverage during the day Sunday. Surprisingly both the GFS and ECMWF are both putting similar areas of coverage across far SE KY during the day Sunday as of now, so confidence was a bit higher here. But expect this forecast to continue evolving over the next few days.
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&& .AVIATION...(For the 06Z TAFS through 06Z Monday night) ISSUED AT 200 AM EDT MON AUG 21 2017 IFR or worse fog will be seen in the deeper river valleys through 13z, before dissipating. This should generally avoid the TAF sites, given the lower crossover temperatures from yesterday afternoon. Some cumulus at 5-6k feet agl will develop during the day, along with some passing high clouds. Winds will average less than 5 kts through the period. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...GEOGERIAN LONG TERM...JMW AVIATION...GEOGERIAN is the U.S. government's official web portal to all federal, state and local government web resources and services.