Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 191039 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 639 AM EDT Sat Aug 19 2017 .SYNOPSIS... A few showers and thunderstorms will be possible today as a weather system shifts through the Great Lakes. Skies will clear tonight as strong high pressure builds into the Ohio Valley, bringing several days of quiet weather. Temperatures will remain seasonable for mid August with highs in the 80s and lows in the 60s. A strong cold front will shift through the area on Tuesday evening with more showers and storms, before a much cooler and drier airmass moves in for the middle and end of next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Spent a great deal of time on today`s forecast given potential rain/thunderstorm chances and less-than-desired confidence on how things will evolve. At 07Z...sharp mid/upper level shortwave trough was crossing Lake Michigan with seasonably strong southwesterly mid level flow downstream over the Ohio Valley. 50-60m height falls /500mb/ were accompanying the trough and an area of thunderstorms had recently developed immediately downstream of the strongest PVA with the wave across northern Indiana with a trajectory towards northwest Ohio. Slowly thickening cirrus was spreading across the ILN forecast area, with mid cloud back along the mid-level trough axis. Using an amalgam of the most recent high resolution and convective allowing guidance and expected path of strongest height falls and synotpic forcing with the shortwave trough, expect area of storms over northern Indiana to track mainly east and perhaps brush far northern counties through sunrise hours as it weakens. Further south, modest low-mid level warm advection and moisture transport will continue to support a few showers from southern/central Indiana...and these should move across southeast Indiana/southwest Ohio in the hours just after sunrise with weakening toward mid-late morning. Thunder will be possible with this activity owing to weak elevated instability, but expect it to be isolated. By early afternoon, main shortwave energy will be pushing through northeast Ohio and pulling away from area. With lack of a respectable surface reflection of this system, boundary layer convergence will be hard to come by, but what semblance of a cold frontal structure that does eventually organize will focus its boundary layer convergence over central Ohio around 17Z...sinking slowly south/east through the afternoon. The result of this forcing should be a slowly organizing band of sct/bkn storms feasting on peak diurnal destabilization /MUCAPE around 1250 J/kg/ amidst modest effective shear /25-30kt/ which support some brief storm organization and severity. Expect highest threat area to be Scioto River Valley of central/south- central Ohio where a few gusty storms are likely before instability quickly is shunted south/east as the deeper northwesterly flow spreads in as the wave departs. Will continue to mention a few strong/severe storm possibilities in central Ohio mainly between noon and 4 PM which lines up well with new SWODY1 with likely a better focus of marginal severe threat east of the ILN area once storms exit and become a little better organized. There is considerable uncertainty how far west any afternoon development will occur. It`s possible some isolated updrafts may form as far west as ILN/CVG/DAY immediately along/ahead of the mid level trough axis ~18z, but convective allowing guidance is underwhelming and erratic on the likelihood of meaningful updrafts that far west. Overall, highest rain chances in central Ohio during the early-mid afternoon with much less chance further south/west. && .SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY NIGHT/... This will be a period of relatively quiet weather as the wave from this afternoon shifts rapidly east bringing an end to any early evening shower and thunderstorm threat. Should see clouds dissipate quickly as good subsidence moves in. Perhaps a little fog later tonight especially in the valleys as good radiational cooling signature develops as 1020mb surface high moves across Ohio with light flow and residual 60s dewpoints. Sunday to feature plenty of sun per forecast soundings from 19.00Z NAM/GFS. Most recent NAM runs however have been a little more robust on low level moisture suggesting some deeper cumulus is possible in the afternoon. But either way there should be ample sunshine with highs well into the 80s on light winds. Weak shortwave energy deamplifying as it crosses the Great Lakes Sunday night shouldn`t have much of an impact on an expected clear/mostly clear night. During this entire period, a bias-corrected MOS blend with minor adjustments should perform quite well given rather quiet/unchanging airmass, and this yields highs slightly above normal and lows around normal. && .LONG TERM /MONDAY THROUGH FRIDAY/... Models remain in good agreement showing a broad area of surface high pressure centered over the Mid-Atlantic region with its influence stretching westward into the eastern Ohio Valley on Monday. With the displacement of the high from the immediate area and increasing low level warmth and moisture, a very isolated afternoon shower/storm cannot be completely ruled out Monday -- particularly across the northwestern third or so of the FA. This being said, even with sufficient instability, there is not any notable forcing mechanism to initiate such activity (either at the surface or aloft), so maintained a dry fcst for now. The main item of interest for Monday will be the sky condition for eclipse viewing. In addition to development of an afternoon Cu field, do think there will be some thin cirrus streaming into western parts of the area by Monday afternoon. There continues to be some model variability on both the extent and thickness of such cirrus, but anticipate it to be fairly thin in nature given current data. Monday will likely be the warmest day of the week with lack of widespread dense cloud cover and the nudging of midlevel ridging into the Ohio Valley (particularly evident on ECMWF solutions). Highs in the upper 80s to around 90 degrees are expected area-wide. Past Monday afternoon, attention will turn to the next system that will impact the area on Tuesday. Model solutions continue to be in remarkable agreement with the broad-scale features of Tuesday/s system, including the general timing. 00Z solutions came in a bit faster than previous runs, showing precipitation entering northwestern parts of the FA as early as late Tuesday morning. This initial activity would be isolated to scattered in nature, but expect fairly substantial destabilization in the pre-frontal environment Tuesday afternoon and evening. Although wind profiles will be nearly unidirectional (WSW at sfc to W aloft) in nature, wind field magnitudes should be sufficient to support scattered to widespread thunderstorm development ahead of and/or along the advancing cold front. With this in mind, did maintain likely PoPs Tuesday afternoon and evening, but shifted time frame ahead by several hours. Pcpn should end from NNW to SSE very early Wednesday morning. The front will bring a big change in airmass to the region, with amplified upper-level troughing situated across the eastern third of the country by Wednesday. The coolest day of the week may end up being Thursday as a disturbance rotates around the broader-scale trough and unseasonably cool temperatures aloft filter into the region. Would not be entirely surprised to see near-record cool temperatures at some point late this week. However, some airmass modification is anticipated for Friday into next weekend. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
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Elevated showers falling out of a 8-10kft altocumulus deck are spreading across Indiana and western Ohio as of 11Z. While perhaps hitting a TAF site with sprinkles or light showers through about 14Z or so, these are not expected to have impact and conditions should remain VFR as they pass. As the mid deck begins to break up this afternoon, would expect a diurnally forced cumulus layer especially in central Ohio where convergence ahead of a weak cold front will be maximized. Still expecting a few showers/isolated storms to develop around 17-19Z in central Ohio which could impact the central Ohio terminals with MVFR conditions. Still a great deal of uncertainty on any updrafts further west/southwest along the front where convergence is less but at peak heating. This would include ILN/CVG/LUK but not enough confidence to put anything in these terminals yet. Any showers should shift quickly east and leave the area under diminishing clouds by late afternoon/evening. Expect a clear night tonight with river valley fog for KLUK and some light fog for central Ohio /LCK and CMH/ closer to the center of the high pressure system where winds will be lightest. OUTLOOK...Thunderstorms are likely on Tuesday into Tuesday evening.
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&& .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Binau NEAR TERM...Binau SHORT TERM...Binau LONG TERM...KC AVIATION...Binau

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