Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 210740 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 340 AM EDT Fri Jul 21 2017 .UPDATE...
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Issued at 340 AM EDT FRI JUL 21 2017 An obs blend into the forecast was done. A more thorough update will follow shortly. UPDATE Issued at 1029 PM EDT THU JUL 20 2017 Forecast lows continue to look on track. The cooler valleys have dropped off into the mid 70s, with ridges holding at around 80 degrees. Cirrus has thinned somewhat this evening, but will continue to stick with partly cloudy skies, given the coverage still out there. Updates have been sent. UPDATE Issued at 807 PM EDT THU JUL 20 2017 Isolated showers have dissipated into the early evening, with mainly just some thicker cirrus hanging around. This should gradually dissipate over the next few hours, but did beef up the cloud cover initially to account for the latest satellite trends. Forecast lows look on target thus far, and have mainly adjusted the diurnal drop off over the next few hours to account for the slightly warmer readings still in place.
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&& .SHORT TERM...(This evening through Friday night) Issued at 420 PM EDT THU JUL 20 2017 As of mid afternoon, a ridge of surface high pressure extended into East KY from the southern MS Valley region. A weak surface trough is moving southeast across the area and along it some enhanced cumulus developed along it as well as some showers near the Daniel Boone Forest/escarpment. These showers have weakened over the past half an hour. At mid and upper levels, a ridge remains in place, centered over the Plains to MS Valley region. Meanwhile, south of an upper level low over the Hudson Bay region. A series of shortwave troughs are moving through the northern stream, the first is moving into the St Lawrence Valley and Upstate NY at this time and is helping send a cold front south of the Great Lakes. The upper level ridge will weaken from tonight through tomorrow with 594 dm heights or higher decreasing in areal extent though the center of the ridge should migrate to closer to the confluence of the OH and MS Rivers. At the same time, disturbances moving around the ridge will pass into parts of the OH Valley and Appalachian. Weak southerly flow between higher pressure over the southeast US and the nearly stalled front leading to a slight increase in surface dewpoints by Friday. Some of the model guidance brings some convective activity toward northeast KY late toward dawn including the HRRR. Confidence on convection that far south is not too high, though given the warm and moist airmass a couple of stray showers cannot be completely ruled out. Otherwise, with high pressure dominating and some passing clouds combined with generally higher dewpoints and crossover temps compared to yesterday afternoon and night, overnight lows should be a couple of degrees warmer on average for valley locations. At least patchy river valley fog if not greater coverage is also anticipated with it becoming dense in a few spots overnight. High pressure will again dominate on Friday though dewpoints should creep up another degree or two. This combined with similar max T to today and yesterday will yield greater coverage of the area with heat indices peaking at 100 or slightly above. In general, the current forecast has heat indices in the 88 to 103 range for most locations, but if dewpoints are a degree or two higher Heat Advisory Criteria will be approached. At this point, the heat is highlighted in the HWO and an SPS and later shifts will evaluate any need that might arise for a headline for a portion of the area. With higher dewpoints and the ridge weakening, and the potential for a cluster of convection to move into the area or send and outflow boundary into the area, the chances for convection during peak heating should be higher on Friday as compared to today. The warm and moist airmass lingering into Friday night with the boundary to the north and weak disturbances moving around the ridge, the threat for at least isolated convection will linger into Friday night. .LONG TERM...(Saturday through Thursday) Issued at 334 PM EDT THU JUL 20 2017 A slow moving cold front will push south Saturday into Monday, providing increasing shower and thunderstorm chances to the area. Best chances still look to be Sunday and Monday. This of cfront will wash out as it tries to push south of the area by early next week and may not do much to diminish moisture over the area. Thus, an afternoon shower or storm may remain possible into the midweek period. Heat and humidity will stay around through Sunday, but will see a slight cool down early next week with the front washing out just to our south. Thus, we will see a brief break from the heat. && .AVIATION...
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(For the 06Z TAFS through 06Z Friday night) ISSUED AT 340 AM EDT FRI JUL 21 2017 Fog is developing in valleys and will spread overnight. Most TAF sites should drop to at least MVFR conditions. VLIFR can be expected in the most fog prone valleys. Fog will dissipate on Friday morning, leaving VFR. A few thunderstorms are expected to develop on Friday afternoon, but overall coverage should still be sparse. With that in mind, have not included it in the TAFs.
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&& .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...HAL SHORT TERM...JP LONG TERM...KAS AVIATION...HAL is the U.S. government's official web portal to all federal, state and local government web resources and services.