Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 272051 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 451 PM EDT Tue Sep 27 2016 .SHORT TERM...
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(This evening through Wednesday night) Issued at 405 PM EDT TUE SEP 27 2016 After the passage of a cold front yesterday, surface high pressure has set in across Kentucky. Meanwhile a strong upper level low remains in tact across the UP of Michigan, with a troughing in place across much of the eastern half of the conus. This is resulting in a strong pull of colder and drier Canadian air from Canada, southeast and into the Ohio River Valley. This combination of colder and drier air has resulted in clear conditions across the region through today, with afternoon temperatures cooling down to more seasonable normals. As we head into the overnight this high pressure should continue, with strong subsidence in place helping temperatures to drop off into the 40s once again by early morning. While dry air advection has been in play through the day, still expecting some of the deeper valleys to see some fog development overnight, especially near bodies of water. Also throughout the overnight, the upper level low will begin to make a southward push, reaching the southern extent of Lake Michigan by 12Z Wednesday. Heights will continue to lower aloft through the day Wednesday as the upper level low bowling balls itself southward, reaching central Indiana by 0Z Thursday. At the surface, a closed surface low will follow along the same southward path, moving into Kentucky during the afternoon hours Wednesday. From this low will sprout a secondary cold front, which is expected to traverse eastern KY tomorrow afternoon. Winds will become more southerly ahead of the frontal passage, which will pull some moisture into the region in the form of clouds ahead of the frontal system. Precipitation will accompany the frontal passage as well, with best chances moving across eastern KY late afternoon and into the first part of the overnight. A bit concerned about the coverage with this system. Overall I think the models are overdone with the moisture considering the overall upper flow is still pulling in an abundant amount of dry air aloft. Superblend gave likely pops, while many of the hi-res CAMs are showing a more scattered line of convection moving through the region. Ultimately decided to cap pops at high end chances given uncertainty, though further updates may deem increasing pops to be necessary. There is actually a small bit of instability with this frontal passage. While not much, it was enough concern to introduce some isolated thunder into the forecast for Wednesday afternoon/early evening. This instability should cease during the late evening after the frontal passage, cutting off any further thunder potential. Forecast soundings are showing llvl moisture sticking around through the end of the short term forecast period (the remainder of Wednesday night). There is enough moisture that light rainfall could continue through much of the night, so kept isolated to scattered pops in play. Wouldn`t rule out some drizzle in a few locations as well. Generally cloudy skies and ongoing precip will keep conditions insulated a bit more compared to tonight, despite the northerly wind shift after the cold frontal passage. Lows tomorrow night should bottom out in the upper 40s and low 50s. .LONG TERM...(Thursday through Tuesday) Issued at 450 PM EDT TUE SEP 27 2016 For the pattern being forecast, the models are in good agreement. A "bowling ball" of large, closed, nearly cut-off upper low will be situated over KY as the period starts. It will wobble for a couple days, before slowly heading back north and being absorbed into the westerlies. While it is here, the cold pool aloft will lead to instability, with a max during the heating of the day. The term heating is used loosely, as readings should not get out of the 60s on Thursday and Friday. Aside from diurnal trends, specifics for timing and placement of precip will depend on finer scale details of features rotating around the upper low. Have continued to use a somewhat broad brush approach due to a lack of confidence in the handling of these features. Models do show pockets of strong enough instability to support some thunder during the afternoon hours on Thursday and Friday. As the low heads back north over the weekend, dry weather should return for Sunday through Tuesday. No significant low level warm air advection is expected through the end of the period, but additional sunshine and mixing, along with warming temps aloft will allow for a slow warming trend.
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&& .AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon) ISSUED AT 149 PM EDT TUE SEP 27 2016 Surface high pressure has taken temporary control of the region after the passage of a cold front yesterday. Deep dry air flowing into the region from the west and northwest have allowed skies to remain clear across the region, while winds at the surface remain light and variable. This regime will last into the overnight, with some of the deeper valley locations expected to see fog development under the stable airmass. Not expecting the TAF sites to be affected for the most part, so continued to leave out of all but SME at this time. Tomorrow, a strong low pressure system to our north will begin to sink southward. This will push another weak cold front through Kentucky during the day. Winds will become more southerly throughout the day, promoting increasing cloud cover. However, clouds should remain well above VFR through the forecast period, and any precipitation associated with the front should hold off until after the forecast period as well. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...JMW LONG TERM...HAL AVIATION...JMW

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