Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 181510 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 1110 AM EDT Fri Aug 18 2017 .SYNOPSIS... A weak cold front will exit the area this morning taking any remaining showers and low clouds with it. A noticeable drop in humidity is expected but temperatures will remain warm through the weekend as high pressure builds across the Ohio Valley. A weakening weather system will cross the area on Saturday with a threat for showers and thunderstorms, particularly north of the Ohio River. Dry weather is then expected Sunday and into early next week as high pressure reasserts itself. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Isolated shower activity will be possible across extreme eastern portions of the forecast area through early afternoon, however expect shower activity to then move out of the area as the cold front pushes to the east. Went warmer than conshort, but on the cool side of guidance for today with weak CAA. Also with CAA expect cu to develop across the region today. Winds will pick up with some wind gusts around 20 mph.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY NIGHT/...
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Although cloud cover will decrease at the beginning of the short term period, expect an increase in clouds during the overnight hours in advance to a decent upper level disturbance approaching the region. This feature will be the focus for precipitation during the later parts of Friday night into the day on Saturday. Models are in agreement on bringing precipitation to the region with this feature, with less likelihood along and south of the Ohio River. Given the support with this system and model agreement, increased precipitation chances especially across northern portions of the region. Went close to conshort for highs which is close to the cool side of guidance values. With extensive cloud cover expected with this system and the timing of this system, believe that most locations will be limited to the upper 70s to low 80s. Locations along and south of the Ohio River where there will be less cloud cover and precipitation will see potentially higher temperatures around the middle 80s. There is some instability, although not overly impressive, with this system and therefore have a chance thunderstorm mention in the forecast. Cannot rule out an isolated damaging wind gust or large hail across extreme eastern portions of the forecast area since the system will be moving through that location during a more favorable time of day. More likely scenario would be small hail and some gusty winds. Winds will pick up during the afternoon as the system begins to pass through and some wind gusts around 20 mph outside of thunderstorms will again be possible. Winds will quickly diminish during the evening hours and cloud cover will begin to decrease. This will allow for temperatures to drop down into the upper 50s to low 60s across the area.
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&& .LONG TERM /SUNDAY THROUGH THURSDAY/... Guidance is in fairly good agreement for the start of the long term period, showing surface high pressure parked right over the heart of the Ohio Valley region in the wake of Saturday/s system. With ample subsidence, expect dry conditions Sunday as mid level ridging begins to nudge back northward into the area. With mostly sunny skies and a strengthening upper level ridge over the southeastern U.S., trended temps up a degree or two across the board -- with highs in the mid to upper 80s expected. By Monday, the high will have shifted east of the immediate Ohio Valley region, with return flow once again becoming established in the area. With this, and the midlevel ridging aloft, highs will top out several degrees warmer than Sunday -- with the potential for highs near 90 degrees for the southern half of the FA Monday afternoon. The main item of interest for Monday will be extent /or lackthereof/ of cloud cover for the impending solar eclipse. While the GFS is currently showing some cirrus working into western parts of the FA during the afternoon, the ECMWF shows all thick cirrus remaining well to the north/west of the immediate area. Even with the uncertainty regarding coverage or thickness of cirrus, it appears likely that Monday will be pcpn-free for the entire area. Even with some thin cirrus, diurnally-driven FEW to SCT Cu are possible during the eclipse timeframe. With increasing southerly flow and the corresponding increase in low level moisture, expect a warm Monday night period, with lows generally around 70 degrees. By early Tuesday, increasing low level moisture and the slow approach of a cold front will allow for the introduction of slight chance PoPs, especially for northwestern portions of the FA. PoPs will slowly increase during the day on Tuesday as low level destabilization occurs in the pre-frontal environment. Even with this, model solutions are in remarkable agreement (this far out) showing the front (and corresponding highest PoPs) moving through Tuesday night (NW to SE). Although it currently appears that best forcing will hold off until early Tuesday night, any shift in timing may act to increase or further decrease alignment/overlap with peak diurnal instability Tuesday. Nevertheless, any mid level disturbances ahead of the surface frontal boundary may be enough to initiate storm activity during the afternoon on Tuesday before the arrival of the front itself. Behind the front, a big change in airmass will occur as upper level troughing becomes more amplified east of the Great Lakes region. Unseasonably chilly temperatures aloft are forecast midweek and beyond, suggesting a period of below normal surface temperatures for the second part of the long term period. It appears probable that the area will see at least one or two days where temperatures do not make it out of the 70s Thursday and/or Friday. && .AVIATION /15Z FRIDAY THROUGH TUESDAY/... Cold front has pushed to just about DAY/CVG/LUK as of 11Z and is slowly pushing band of IFR stratus eastward. So all TAFs start this morning with some temporary IFR cigs and MVFR potential visibilities before drier air overtakes the sites and ceilings scatter out and lift as drier westerly flow picks up and becomes a little gusty. Expect diurnal cumulus to form pretty quickly once the stratus shifts out owing to very moist boundary layer, and this is likely to be VFR, though there is some concern that if forms earlier than anticipated it could come in MVFR. Right now playing the bulk of the afternoon as a scattered VFR cumulus deck, but will need to watch the 15Z-18Z timeframe for potential for cumulus to reform lower/thicker than currently expected. Overnight expect slowly thickening mid/high clouds as wave approaches from the west. Some showers or a thunderstorm possible at KDAY/KCMH/KLCK Saturday morning but likely after 12Z. OUTLOOK...Thunderstorms are possible on Saturday, and again on Tuesday. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Binau NEAR TERM...Novak SHORT TERM...Novak LONG TERM...KC AVIATION...Binau

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