Area Forecast Discussion
Issued by NWS Jackson, KY

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671 FXUS63 KJKL 201102 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 702 AM EDT Thu Jul 20 2017 .UPDATE...
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Issued at 653 AM EDT THU JUL 20 2017 Ended up tweaking lows down a few degrees based on temperature trends. As sun continues to rise, temperatures will quickly be on the increase from here on out. Pretty good fog development going on across eastern KY, especially in the river valleys. This too should continue to impact the region for the next hour or two before quickly dissipating with the rising temperatures. Also tweaked forecast for dew points and winds in the near term to make sure they were on track with current conditions. All updates have been updated and sent to NDFD/web.
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&& .SHORT TERM...(Today through Friday) Issued at 417 AM EDT THU JUL 20 2017 Upper level ridging will continue to build into the region today. It will dampen somewhat tomorrow in the northern portion of the state as a strong upper level low over Hudson bay allows for more WNW to ESE flow across the northern half of the U.S. to shift a bit southward into the northern Ohio Valley. That being said, even with this small shift, the upper level ridge will still have dominant control. At the surface, high pressure will also be large and in charge across the state today. The continued building heights will attribute to yet another day of well above normal temperatures, reaching 90 or maybe even topping it in most locations. A few fair weather cu will be possible during the afternoon, but otherwise conditions should remain dry under this regime. By Friday, however, a cold front will push towards the region from the north. Flow will become more S to SW, allowing more moisture to advect in from the south and boosting humidity levels a bit (though not a strong surge). This will cause two concerns. First, the presence of the frontal boundary just to our our north and a warm/more humid airmass in place, could spark isolated to scattered showers and thunderstorms during the day, especially in the afternoon. Best chances will be in the northern CWA and along the high terrain in the SE. Second, the S/SW flow will boost temps another degree or two, into the low 90s for highs. This will combine with the additional humidity in the atmosphere to produce heat indices just over 100 degrees in most locations. While we are still below heat advisory criteria based on the forecast, will go ahead and issue an SPS for heat concerns this day. .LONG TERM...(Friday night through Wednesday) Issued at 422 AM EDT THU JUL 20 2017 An upper level ridge will be over the Tennessee Valley, and surface high pressure over the lower Great Lakes and Appalachians at the start of the period. The high pressure at the surface and aloft will be weakening. In the upper levels, this will allow for slight cooling and a modest increase in wind as a northeast CONUS trough develops and the westerlies drop further south. At the surface, increased flow will help to bring Gulf of Mexico moisture into the area. The combined result will be an overall increase in shower/thunderstorm coverage as we move through the weekend. A cold front is expected to approach from the northwest Sunday and Monday, and this is when the highest POP will be carried. The GFS and ECMWF agree on the front passing through from northwest to southeast late Monday and Monday night, allowing for somewhat cooler and less humid air to move in to finish the period. Until then, conditions will be uncomfortably hot and humid. The hottest weather is expected on Friday, before an increase in clouds and precip starts to hold temperatures down. && .AVIATION...
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(For the 12Z TAFS through 12Z Friday morning) ISSUED AT 700 AM EDT THU JUL 20 2017 Surface high pressure and an upper level ridge building into the area will continue the rather stagnant weather pattern, with VFR conditions and light winds prevailing through much of the period. Fog has impacted all the TAF sites to some degree this morning (generally MVFR), but should be lifting and dissipating over the next couple of hours across all of East KY. Once fog dissipates, expect mostly clear skies with mainly diurnally driven CU developing in the afternoon, generally around 4k ft. High clouds will increase somewhat overnight, especially over the northern half of Kentucky, ahead of an approaching cold front. This should help keep fog impacts at bay somewhat overnight for this area, though some patchy valley fog will be possible in the southern half of the state. Winds will remain light and variable through the period.
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&& .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...JMW SHORT TERM...JMW LONG TERM...HAL AVIATION...JMW

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