Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 210007 AAA AFDJKL AREA FORECAST DISCUSSION...UPDATED National Weather Service Jackson KY 807 PM EDT Thu Jul 20 2017 .UPDATE...
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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 00Z TAFS through 00Z Friday evening) ISSUED AT 807 PM EDT THU JUL 20 2017 A neaby upper level ridge will maintain VFR conditions across the region throught majority of the period, besides some MVFR or worse fog to contend with between 06 and 12z. Given the increased low level moisture, did carry some temporary IFR at SME between 11 and 12z. Building heat and humidity on Friday will allow for a threat of isolated convection during the afternoon. Winds will remain light and variable through the overnight, before increasing to around 5 kts out of the west by Friday afternoon.
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&& .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...GEOGERIAN SHORT TERM...JP LONG TERM...KAS AVIATION...GEOGERIAN

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