Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 200527 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 127 AM EDT Thu Apr 20 2017 .UPDATE...
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Issued at 127 AM EDT THU APR 20 2017 WSR-88D radar showing a few left over showers are exiting far eastern KY this hour, but the thunder has now subsided with VII nill on the MRMS, cloud top warming, and no recent reports from the various lightning detection networks. Updated to deal with left over rain showers and blend in the latest obs and trends. UPDATE Issued at 1133 PM EDT WED APR 19 2017 The last of the showers and storms look like they are finally winding down. Will hold onto some isolated POPs for another hour or so matching the radar trends, with the rest of the night looking quiet. Clouds are much less prevalent tonight, compared to last several nights, so have played up the fog more, especially with pockets of locally heavy rainfall having occurred earlier. Lows will range from the mid 50s in the cooler spots, to around 60, where light southerly winds keep things a bit more mixed. Updates have been sent. UPDATE Issued at 755 PM EDT WED APR 19 2017 Mainly freshened up the hourly temperatures and dew points over the next few hours, as localized storms have cooled off places, including JKL. POPs were already in good shape, with a gradual diminishment expected through midnight. Only made a few minor adjustments to these based on the current radar trends.
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&& .SHORT TERM...(This evening through Thursday night) Issued at 433 PM EDT WED APR 19 2017 Scattered showers and thunderstorms have fired across the area this afternoon. These storms are not quick builders, the likely result of slight height rises and relatively weak instability to feed off of. Activity is expected to gradually die down through the late afternoon and early evening as sunset approaches. We will probably see some patchy fog develop through the overnight where precipitation has fallen late this afternoon and/or this evening. Added a mention of fog to the zones, particularly in the valleys. Otherwise, focus turns to a cold front that will drop into the region by late Thursday night into Friday. There is still considerable uncertainty with the details of this system. The GFS and NAM manage to take the boundary considerably further south than the ECMWF. This lowers confidence a bit with respect to sensible weather. Ramped up pops Thursday night as the front approaches but stayed close to model blends and guidance. For sensible weather, expect showers and thunderstorms to gradually die off through sunset. Skies will partially clear allowing for some reasonable radiative cooling. Preferred the inherited cooler valley temps over the warmer blends and model guidance for tonight. This will favor some patchy valley fog, which might tend to become more dense at times where late afternoon and evening precip occurs. Clouds will be on the increase late Thursday afternoon and gradually brought pops back into the picture late in the day. Showers and thunderstorms increase in coverage Thursday night with the cold front dropping into the area. Temperatures will climb to around 80 for much of the area Thursday. .LONG TERM...(Friday through Wednesday) Issued at 433 PM EDT WED APR 19 2017 Overall, there is good model agreement during the period. At the onset, a cold front will have entered KY from the northwest, and will be draped across the southeastern CWA as of Friday morning. It is expected to bring at least scattered showers and thunderstorms, especially east of the front, along the southeastern CWA where moist and warm southerly flow will still be occurring. The front will sag just southeast of KY during the day Friday, and remain in close enough proximity for an ongoing potential of precip on Friday, including some continuing thunder chances near the TN and VA borders. Loss of remaining instability overnight will cut off thunder chances by Friday night. Meanwhile, low pressure will be taking shape over the southern plains on Friday as well. This will be in response to an upper level wave (emanating from the upper low currently off the Pacific Northwest coast) moving southeast toward that region. The low pressure system will track eastward and draw the frontal boundary back north as a warm front toward far southern KY Friday night and Saturday. The GFS has remained further south with the eventual low track since yesterday, and is similar to the ECMWF which has remained nearly steady. This track takes the low near the KY/TN border, resulting in a wet start to the weekend, with a temperature contrast across the JKL forecast area. Rain is a good bet everywhere on Saturday. Thunderstorms will also be possible near the passing low, with surface based instability possible in far southern KY, and elevated instability further north. Heavy rainfall could be a concern, with 6 hour QPF values between 0.75 and 1 inch, and locally higher amounts possible. Latest trends show highest rainfall occurring along the far eastern KY border Sunday night. Significant rain should then pull out with the departing low by Sunday, but some light rain could linger. Ridging at all levels then builds in on Sunday night and brings decreasing clouds, with fair weather lasting through the rest of the period. && .AVIATION...(For the 06Z TAFS through 06Z Thursday night) ISSUED AT 120 AM EDT THU APR 20 2017 TAF sites are starting off the period VFR and should generally remain that way through the TAF period. The caveat will be the more valley sites could see fog, but right now will lean toward LOZ for MVFR VIS potential and leave out at other sites. Outside of TAF sites would think anywhere that saw convection and places that saw showers would have the chance of seeing fog through mid morning. While the convection this afternoon will be isolated in a weakly forced environment will mention VCTS for all the TAF sites. Winds will remain light out of the south to start the period, but deeper mixing into a modest LLJ could provide gusts of 15 to 20 knots through the afternoon. The better gusts would likely be in the Bluegrass and Lake Cumberland regions. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...DJ SHORT TERM...RAY LONG TERM...JMW AVIATION...DJ

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