Area Forecast Discussion
Issued by NWS Jackson, KY

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398 FXUS63 KJKL 280018 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 818 PM EDT Thu Jul 27 2017 .UPDATE...
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Issued at 818 PM EDT THU JUL 27 2017 Best instability continues to shift south as showers and storms are ongoing in southern Kentucky. A ribbon of instability is also present across central Kentucky, but does not extend that far to the east, so no threat of this activity making it into the area. May see some dying rain showers put into a portion of the area through the evening hours, but most of the activity will be fairly isolated from this point forward, except in southern Kentucky where organized storms remain. Even in this area, activity will move on south over the next few hours with activity becoming more isolated overnight. Juicy airmass will remain through tomorrow, so a stray shower may pop up at anytime. Plan to see how rivers and creeks behave over the next few hours to see if we might need to evaluate the need for a flash flood watch for the expected shower and storm coverage expected on Friday with the cold front making its move southward. UPDATE Issued at 532 PM EDT THU JUL 27 2017 Numerous showers and storms continue to impact areas between I-64 in the north and the Hal Rogers Parkway in the south. Area is getting fairly well worked over as evident from the weakening complexes of showers and storms as they try to push east into areas that have seen the most activity earlier this afternoon. The best instability now is in areas that have not seen much rainfall today and that is across the southern 2 tiers of counties. Thus, expect any strength in the showers and storms to shift southward into that better instability with a lull working in from the north. As we lose the instability, we may not see much through the overnight period as the frontal zone will still be to our north with little forcing over the area. In fact, we may see a little subsidence build in on the north side of a MCV pushing southeast across western/central Tennessee. Thus, it looks like we may have seen the worst of the rain this evening for most areas with a general diminishing trend expected over the next several hours. Something I will be looking at over the next few hours is potential for fog tonight with the moist conditions with all the rainfall, we may see locally dense fog develop if we can maintain some clear skies tonight. Will be watching the cloud cover trends closely to determine if some dense fog needs to be inserted into the forecast tonight.
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&& .SHORT TERM...(This evening through Friday night) Issued at 440 PM EDT THU JUL 27 2017 The short term period is frustrating. We have a tropical-like air mass with weak forcing mechanisms. The result is thunderstorms popping at times, but with little available forecast skill as to exactly when/where the activity will occur. With high precipitable water and efficient rainers, there are some heavy amounts where storms train. A flash flood watch was contemplated, but with a lack of focus for convection, there`s a lack of confidence as to if/when/where problems might occur. However, the situation will need to be monitored to see if a more focused threat develops. The precip is being aided in general by a developing upper trough over the northeast CONUS, with warm/moist air advection underneath, and eventually a cold front impinging on the air mass. The cold front is expected to move through from northwest to southeast on Friday afternoon and evening, with the threat of significant rain ending after its passage. Drier air then begins to move in for the weekend. .LONG TERM...(Saturday through Thursday) Issued at 305 PM EDT THU JUL 27 2017 The extended portion of the forecast begins on Saturday with an upper level pattern that is typical of summer at this point. A stout ridge remains in place over the western CONUS with a longwave trough over the east. At the start of the period, a shortwave trough is swinging through the OH valley. At the surface, a cold front or boundary at this point will be slowly exiting KY through the southeast. Thus, with minimal CAPE and the weak boundary, there will still be a slight to low chance of showers and a thunderstorm or two by Saturday afternoon. This activity will come to an end by Saturday night as the last of the lift exits to the east. By Sunday, surface high pressure nudges into the area, coupled with the mid level ridge axis shifting east into the OH Valley as well. Given the lack of return flow and increased area of subsidence, a lengthy period of dry weather is on tap. Thus will go with a dry forecast on Sunday and continue through the end of the extended on Wednesday night. As well, the lower dew points expected and below average to average high temperatures through the period will make for pleasant weather during the extended. && .AVIATION...
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(For the 00Z TAFS through 00Z Friday evening) ISSUED AT 818 PM EDT THU JUL 27 2017 A mix of IFR/MVFR conditions will be present over the next several hours as showers and a few storms push on through the area. With activity becoming more isolated overnight, we may see conditions return to VFR for most of the area. However, given the recent rains, and potential clearing, we could see some valley fog develop overnight. Certainly a difficult aviation forecast with lots of uncertainty on how things evolve overnight. Thus, we could stay socked in with MVFR and IFR conditions through most of the night. For now, going to go optimistic with the TAFS except for the next few hours.
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&& .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...KAS SHORT TERM...HAL LONG TERM...SHALLENBERGER AVIATION...KAS is the U.S. government's official web portal to all federal, state and local government web resources and services.