Area Forecast Discussion
Issued by NWS Wilmington, OH

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309 FXUS61 KILN 152349 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 749 PM EDT Tue Aug 15 2017 .SYNOPSIS... A weak frontal boundary will stall across the area this evening with a threat for isolated showers. After some morning fog, a disturbance approaching from the southwest will combine with the stalled boundary to produce another threat of showers and storms on Wednesday afternoon and night. A stronger frontal system will swing through the Ohio Valley on Thursday afternoon and evening bringing a higher chance of more widespread shower and thunderstorm activity. Wednesday and Thursday will be more humid than previous days, with noticeably warmer overnight lows. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... GOES 16 water vapor loop clearly shows shortwave trough progressing through the eastern Great Lakes into New York state. A slowing/weakening frontal boundary tied to this wave was approaching the far northern counties of the ILN forecast area, with some agitated/deepening cumulus per GOES16 visible imagery. A few showers are expected to develop in this area /basically along and north of I-70/ through early evening amidst weak CAPE /MLCAPE up to 500 J/kg/ and weak shear /effective shear <20kts/. Given the very weak instability, don`t think updrafts will be strong/deep enough for charge separation thus just running with low chance of showers. In addition, deeper moisture across northern Kentucky has prompted an isolated updraft or two this afternoon, and have a very low chance of an isolated shower across this area as well through peak heating. Overnight, there is a low chance that the stalled frontal boundary across the ILN CWA will foster an elevated updraft or two as very weak low/mid level warm advection/moisture transport begins downstream of stronger wave in the Central Plains. However, don`t think enough forcing is warranted for a PoP just yet. Think bigger overnight concern will be the boundary`s role in allowing fog development along/north of the feature. Thus, have lower visibility forecast over the northern ILN forecast area and higher fog coverage there too. Overnight lows will be relatively mild, especially in comparison to recent nights. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... While weather on Wednesday will be dominated by shortwave ridging moving across the Ohio Valley downstream of the wave approaching from the west, do have some concern for area of disturbed weather in Arkansas that is tied to a slowly dampening/opening mid level /700mb centered/ wave. As this feature is absorbed into larger scale backing mid-level flow downstream of stronger shortwave to the west, some of the deeper moisture and weak lift tied to the feature will lift northeast into the Tri-State later Wednesday afternoon and into the evening. The threat here will be for increasing chances of showers/storms from southwest to northeast through the mid-later afternoon hours and continuing into and through Wednesday night. This is particularly true as the night wears on and lower level convergence/warm frontal structure begins to develop and increase. Layered low-level moisture transport magnitudes and convergence support an increasing chance of showers and storms across the area as the night wears on. With near 70F dewpoints advecting into the area, think overnight lows will only fall into the lower 70s for most on Wednesday night. Little chance for severe weather is expected Wed afternoon/night as forecast soundings continue to show modest CAPE /weak mid- level lapse rates/ and effective shears. Suppose as forcing increases later Wednesday night that a stronger elevated updraft could develop but would expect primary threat to be locally heavy rain based on forecast soundings from NAM/GFS. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Period looks like it will begin with a warm front crossing the region and scattered showers and thunderstorms along the front. Later in the day, additional thunderstorms are expected as a cold front pushes east up the Ohio Valley. Kept likely PoPs Thursday ahead of the frontal passage. A low threat for severe thunderstorms remains Thursday as the atmosphere has some wind shear and instability. The 12Z models have slowed down the fropa, so kept PoPs up Thursday night, then there appears to be some lingering instability on Friday, for a few scattered storms, mainly in the east. Friday night looks dry, but models have now come together in swinging a descent H5 s/w through the Great Lakes Saturday. The GFS is a little slower than the ECMWF with this feature. Leaned towards the slightly quicker ECMWF. On Sunday through Monday, surface high pressure will be across the region. There is little forcing or deep moisture, so went with a dry forecast. By Tuesday, models drop energy into the region from the Great Lakes, bringing scattered storms. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
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We are still seeing a few showers along and north of Interstate 70 in association with a weak frontal boundary dropping down toward the area. Expect these to dissipate/decrease in coverage as we lose the daytime heating. Have left the northern TAFs dry but there is a slight chance that KDAY/KCMH/KLCK could see a brief shower in the next couple of hours. Otherwise, skies will go mostly clear overnight and with relatively light flow, areas of MVFR to locally IFR fog are expected to develop later tonight into early Wednesday morning. Any fog will lift through mid morning with scattered to broken cu developing. Increasing moisture through the day will combine with an approaching mid level short wave to produce an increasing chance of showers and thunderstorms from the southwest. Will therefore introduce a VCSH at KCVG to account for this as we head into the late afternoon and evening. OUTLOOK...Thunderstorms possible Thursday and Thursday night.
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&& .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Binau NEAR TERM...Binau SHORT TERM...Binau LONG TERM...Sites AVIATION...JGL

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