Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 171235 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 735 AM EST Sun Dec 17 2017 .UPDATE...
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Issued at 735 AM EST SUN DEC 17 2017 We continue to see some radar returns nearing the Lake Cumberland region this morning, but the dry air near the surface likely keeping this from reaching the ground. This idea is showing up well in the HRRR with coverage and amounts decreasing as this are of precipitation progresses northeast. Given this little changes are needed in the grids this update, but did freshen up grids with the latest obs and trends.
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&& .SHORT TERM...(Today through Monday) Issued at 421 AM EST SUN DEC 17 2017 The morning surface analysis shows an area of high pressure remains off to the southeast and we remain in control of this feature this morning. The feature of interest for the near term period will be a upper level closed low that is located across Kansas with the axis extending into the Arklatex this morning. The model soundings and time height analysis show a thick layer of drier air near the surface and this will be difficult to overcome today. There is a window this afternoon when we see the potential for deeper layer moisture connection. The other issue is the models have been in good agreement on the upper level shortwave dampening as it moves northeastward into the Ohio and Tennessee Valleys, and the weak low level jet remaining further south of the area. Given this and the fact that the guidance came in lower did lean toward lower POPs overall for today, with best chances residing in the Lake Cumberland region. Right now will lean closer to the better lift time for the better POPs and will continue to monitor radar trends for subsequent updates for POP timing. Overall for today with cloud cover and rainfall potential kept afternoon highs in the mid to upper 40s. This system will progresses east and flattens out as mentioned above for tonight. The caveat will be low level inversion will trap moisture near the surface and leave the potential for lingering stratus deck tonight. The models have also painted sporadic instances of omega and QPF at times and this will likely translate to patchy drizzle at times tonight. The temperatures tonight will remain uniform and generally in the mid to upper 30s given the lack of airmass change and cloud cover. Given the aforementioned persistent inversion and low level moisture did lean toward higher cloud coverage for Monday. Also a strengthening jet aloft could provide continuing support for patchy drizzle through the day on Monday and added this to the grids. The biggest caveat in this period will be the fact that the inversion is not as strong and this could put us at jeopardy for mixing out the inversion. For now, thinking this will remain in place and provide the platform for cooler temperatures than painted by the model blends. Therefore will lean toward afternoon highs topping out in the upper 40s to lower 50s. .LONG TERM...(Monday night through Saturday) Issued at 442 AM EST SUN DEC 17 2017 The models are in good agreement with a split-flow long wave pattern to start out across the CONUS into the middle of next week, with the Ohio and Tennessee valleys seeing more influence from the southern stream. The long wave pattern will then amplify significantly towards the weekend, with phasing taking place and a deep trough evolving across the center of the CONUS, bringing increasing confidence that colder air will eventually affect much of the lower 48 closer to Christmas. Details on the evolution of this trough and surface features continue to be lower confidence at this point, and will continue to rely on a blend of the guidance in order to mitigate model inconsistencies this far out. Skies look to be mostly cloudy across eastern Kentucky through Wednesday. Initially, we hang onto low clouds trapped under an inversion into Tuesday. A short wave trough will also move from the Desert Southwest to the Tennessee Valley through Wednesday, bringing reinforcing cloud cover as well as a decent chance of precipitation, mainly south of the Hal Rogers Parkway and Highway 80 corridors. Dry weather will return for Thursday, before a more significant cold front takes aim at the area Friday into Saturday. POP chances have increased for this time frame, peaking in the likely range by Friday night. Most of this precipitation looks to fall as rain; however, there is still some snow potential late Friday night into Saturday morning, as colder air races against the exit of the deeper moisture. Overall, temperatures through Saturday will average above normal, with colder air waiting to move in just beyond the forecast period. && .AVIATION...(For the 12Z TAFS through 12Z Monday morning) ISSUED AT 620 AM EST SUN DEC 17 2017 The period is beginning with high clouds and VFR conditions across eastern Kentucky. We continue to watch a upper level system approach from the southwest and this will bring an area of rainfall toward the region. WE are drier in the lower levels early and this will initially mitigate precipitation from making it to the ground. We will see best chances of precipitation and lowering CIGS to MVFR this afternoon. Then lingering low level moisture in the form of stratus deck will remain in place and descend through the TAF period. This will lead to the potential for drizzle and IFR or lower CIGs to round out the TAF period. The winds will remain light out of the south and southwest. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...DJ SHORT TERM...DJ LONG TERM...GEOGERIAN AVIATION...DJ

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