Area Forecast Discussion
Issued by NWS Jackson, KY

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357 FXUS63 KJKL 230000 AAA AFDJKL AREA FORECAST DISCUSSION...UPDATED National Weather Service Jackson KY 800 PM EDT Tue Aug 22 2017 .UPDATE...
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Issued at 730 PM EDT TUE AUG 22 2017 Main band of strong to severe thunderstorms are sliding southeast through the area ATTM. The severe threat appears to be diminishing as the storms are moving into areas previous worked over with late afternoon storms. The remaining storms are just ahead of a cold front that will bring a change in air mass to the CWA by dawn. Look for the storms to gradually exit eastern Kentucky toward midnight, or shortly thereafter with a few lingering showers or an odd thunderstorm possible through 06z. As the new air moves in the pcpn threat will end from northwest to southeast. At this point it looks like the transition will be accompanied by some low stratus most places pre-dawn rather than fog, but will have to watch for that potential if the skies do manage to clear before sunrise Wednesday. Have updated the forecast to fine tune the PoPs and Sky cover well into the night with some tweaks to T and Td per the latest obs and trends. These have been sent to the NDFD and web servers. A new set of zones and HWO will follow as we clear the watch box behind the front before too long.
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&& .SHORT TERM...
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(This evening through Wednesday night) Issued at 340 PM EDT TUE AUG 22 2017 A cold front is presently pushing towards the Ohio river with some showers and thunderstorms developing just ahead of this feature. Other convection which fired along an outflow from overnight convection is now pushing its way across eastern Kentucky. Better bulk shear values remain across central/northern Kentucky, and as such, activity is really weakening as it outruns the better shear. After the present showers/storms push on through, will be a few hours before the next round with the front pushes on through. With lots of instability still present in central Kentucky, hesitant to let go of the severe thunderstorm watch yet. Thus, will hang on the watch for at least another hour or two to see how upstream convection behaves. Damaging winds will continue to be the main threat with the strongest storms. All of this activity and associated front will drop south and east overnight and be on the way out towards daybreak Wednesday. This will lead to a drier Wednesday along with much cooler conditions. Some cloud cover may hang on well into the afternoon before clearing late in the day. The clear skies will allow a cool night to set up for Wednesday night as temperatures fall back into the 50s. .LONG TERM...(Thursday through Tuesday) Issued at 450 PM EDT TUE AUG 22 2017 The models are in fairly good agreement aloft with the general pattern through the extended, though there are some significant difference with some of the smaller scale features. The core of the main trough residing over the eastern half of the continent will swing into the Ohio Valley on Thursday. The ECMWF actually closes off this part of the trough as it crosses northern Michigan while the other models are a tad weaker and more open with this feature. The trough bottoms out Thursday night with lower heights pushing south through Kentucky. The main trough will pull out this weekend with heights rebounding locally in its wake. As it does so, more energy packets will start to move across the area from the west with a hint of weak northwest flow established by Sunday. At this point, additional energy pours into the Upper Midwest with the next trough developing to our northwest. In this low flow environment at mid levels more energy will seep into Kentucky. Additionally, we will have to watch the upper level core of `Harvey` and how it eventually progresses onshore and creeps northeast into the Lower Mississippi Valley on Tuesday - more consolidated, but further south in the ECMWF and GFS than the CMC. The remnants of this tropical system could increasingly be a factor in the forecast for our area into the start of next week - but that also adds in an amount of uncertainty for the latter part of the forecast. Given the good agreement on the broad scale initially and increasing uncertainty/lower confidence later the blended solution looks like a reasonable starting point with minor adjustments. Sensible weather will feature very nice mid to late summer weather for the bulk of the week as cool Canadian high pressure settles into the region. This will make for dry and quiet weather with temperatures below normal through the period. Each night will likely see a moderate to large ridge to valley temperature split as the boundary layer decouples. Patchy valley fog can be expected to develop late at night and run through a couple of hours past dawn. Return moisture does come back into the picture by Sunday with diurnally driven air mass showers and through this evening and thunderstorms possible. Monday and Tuesday`s weather is quite questionable, though, as the remains of Harvey start to ooze this way as well as low pressure inbound from the northwest along with some mid level energy. As such, have brought better chances for showers and storms into the forecast though with low confidence in timing and amounts due to the tropical x-factor. Made mainly terrain based adjustments to the lows each night from the SuperBlend to account for an anticipated moderate to large ridge/valley temperature split. Also, adjusted the PoPs to better minimize any pcpn chances through the weekend and to be less specific with the threat Monday and Tuesday.
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&& .AVIATION...
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(For the 00Z TAFS through 00Z Wednesday evening) ISSUED AT 800 PM EDT TUE AUG 22 2017 A cold front is swinging south across eastern Kentucky tonight with a period of showers and thunderstorms. The convection will bring reductions in visibility and ceilings through midnight. As the front passes later tonight, some lower cigs could develop late bringing ceilings back into the MVFR category and possibly even IFR late. Look for the low clouds to dissipate by midday on Wednesday. VFR conditions then follow for quite some time. Winds will be light and variable through the period, outside of any storms this evening.
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&& .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...GREIF SHORT TERM...KAS LONG TERM...GREIF AVIATION...GREIF

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