Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 210013 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 813 PM EDT Sun Aug 20 2017 .UPDATE... Issued at 813 PM EDT SUN AUG 20 2017 A few mid-high clouds will continue to stream in this evening as decaying showers/storms push through the Midwest into the Ohio Valley downstream of an upper wave swinging through the Corn Belt and Great Lakes. Deep layer high pressure will hold supreme and keep precipitation nil across eastern Kentucky. Given the degree of mixing and drier air that materialized across portions of the Cumberland Valley this afternoon, reduced fog coverage outside of deeper river valleys where nocturnal drainage will allow for development later tonight. More widespread valley fog will be a better bet from the Bluegrass and Big Sandy regions through the remainder of the higher terrain where greater surface moisture and subsequently higher crossover temperatures reside. && .SHORT TERM...(This evening through Monday night) Issued at 309 PM EDT SUN AUG 20 2017 Afternoon surface analysis shows an area of high pressure in SW PA and warm front lifting north across the Ohio Valley. We will remain under the control of rising heights and surface high pressure. That said, we have CU developing across the region and some higher level cirrus streaming by at times this afternoon. These CU will dissipate tonight and we will see another night of mostly clear skies. This will lead to the potential for more patchy to areas of fog toward the overnight hours. This will dissipate through the morning on Monday. Monday will be a interesting day given the solar eclipse. There remains some question on how much this will affect many things such as clouds and temperatures. We will be watching how a MCS develops across portions of the Midwest and this could certainly send a few high clouds south. Another issue will be how much CU develops before the eclipse, but still think there will be a few despite the potential affects. However, do not think this will lead to major issues for viewing the solar eclipse. Do think the eclipse will lower temperatures around 18Z and then it should warm up again following the eclipse. Did keep temperatures in the upper 80s for most locations, as the recovery may be delayed enough to impact peak heating. After the eclipse all eyes do turn to the upper level trough across the Upper Midwest. This will begin moving SE toward the Ohio Valley. We will probably see some more clouds given this, but do not think we will see any precipitation before the end of the period. Overall limited the fog more so given the potential for some cloud cover. .LONG TERM...(Tuesday through Sunday) Issued at 400 PM EDT SUN AUG 20 2017 The models are in fairly good agreement aloft through the extended portion of the forecast. They all depict an amplifying trough pushing through the Upper Midwest and into the Great Lakes on Tuesday. This will spread lower heights south through the Ohio Valley and into Kentucky along with a strand of mid level energy. Heights will continue to fall through the day Wednesday as the core of the trough pivots into eastern Canada leaving northwest flow behind through the region and across Kentucky, though the bulk of the energy will remain well to the north. The pattern relaxes toward the end of the week with gradual height increases and advection that is more neutral at mid levels. However, by the latter part of the weekend, heights could be on their way back down as a new trough enters the picture from the northwest with a return of somewhat more substantial energy packets for the Ohio Valley, though the ECMWF is an outlier with its further south closed low for the Northern Plains. Given the model similarities and only minor differences during the first part of extended confidence initially is above average for the blended solution with lower confidence for the upcoming weekend as the model spread increases. Sensible weather will feature a cold front pressing southeast into the area as the main sfc low runs east into Quebec. This boundary will drop through eastern Kentucky Tuesday night into midday Wednesday as high pressure pushes in from the northwest. This front will need to be watched for a potential of severe weather owing to good instability Tuesday afternoon and evening as well as favorable winds aloft. Additionally, training of storms cells will be possible as the low level flow will be nearly parallel to the sfc boundary. Otherwise, once the front goes through cooler and less humid weather will follow through the bulk of the week, though a lingering shower or storm cannot be ruled out in the far southeast Wednesday afternoon and evening. Sfc high pressure will slip east Saturday and Sunday with return flow moisture and increasing heat leading to a potential for mainly diurnally driven storms for the latter half of the weekend. A stray convective cell cannot be ruled out on Saturday, but it looks unlikely at this point. Made only minor terrain based adjustments to the temperatures each night under the expectation of ridge to valley differences for most nights (aside from Tuesday night). As for PoPs - scaled them down quicker on the backside of the front as it drops south of the area on Wednesday. Also, held them back a tad on Saturday. && .AVIATION...(For the 00Z TAFS through 00Z Monday evening) ISSUED AT 813 PM EDT SUN AUG 20 2017 Showers and storms have remained west of a SDF to CVG line this evening, and do not anticipate any precipitation/CB migrating into the eastern Kentucky airspace with high pressure in full force. VFR conditions should hold for the most part through the next 24 hours across much of eastern Kentucky. The exception will be river valleys seeing degrading visibilities tonight into early Monday morning as fog develops, moreso from the Bluegrass region into the higher terrain of eastern Kentucky. SYM could see a period of MVFR visibilities develop again tonight, but JKL/SJS should remain above any fog. SME/LOZ should see lower chances as drier air mixed in at each site earlier today. Light and variable winds overnight will take on a southwesterly component by Monday afternoon at 5 knots or less. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...GUSEMAN SHORT TERM...DJ LONG TERM...GREIF AVIATION...GUSEMAN

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