Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 150744 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 344 AM EDT Sun Oct 15 2017 .SYNOPSIS...
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A cold front will move across the area today, bringing rain and gusty winds. Much cooler conditions are expected behind the front to start the new week, though as high pressure builds into the Ohio Valley, dry weather is expected. A gradual warming trend is expected through the rest of the week.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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The main issue for the weather today is the passage of a cold front through the Ohio Valley, and the concerns that will come along with it. Surface observations indicate that a surface low is located just south of Green Bay as of 07Z, with a cold front extending SW through the Quad Cities area and into Missouri. As the surface low tracks ENE ahead of a mid-level trough, the cold front will make relatively quick progress eastward as well. The wide band of precipitation near and behind the cold front at this hour is in a decaying phase, which is likely to continue based on the state of the diurnal cycle and supported by recent HRRR/WRF model runs. Though some of this weakening precipitation may make its way into the northwestern ILN CWA over the next few hours, the majority of the precipitation expected will not occur until the front is much closer. Though there are still some subtle timing differences, overall agreement is good on the passage of the cold front through the ILN CWA between 15Z-21Z. As time progresses through the day, and the front moves eastward, the air mass ahead of it will go from being almost completely void of instability to containing a small amount. This provides confidence in a scenario in which precipitation will be scattered and light as the front enters the CWA, but more focused and perhaps slightly convective as the front leaves the CWA. It is still a fair question to ask if there is enough instability to support the slight chance of thunderstorms currently in the grids, but a slight chance is just a slight chance, and the chances do look slightly higher in the southeastern third of the CWA by afternoon. Regardless, the potential for any convective-related hazards appears extremely low, and most places are unlikely to see any thunder. PoPs start out at 60 percent, increasing to 80 percent along the front with eastward extent. There is a fair amount of wind energy in the low levels, though the wind gust forecast (both in the synoptic flow on either side of the front and with the actual frontal passage) has remained fairly stable across the last few forecast cycles. Based on some recent HRRR/RAP BUFKIT soundings, numbers were increased just slightly. This still keeps the strongest gusts in the 30-35 knot range, below advisory criteria. To note -- the GFS seemed to be a high outlier with regards to wind gust strength in the northern sections of the ILN CWA. Nonetheless, one or two isolated gusts to around 40 knots with frontal passage could occur in a pattern like this. A few light showers will remain possible in the first hour or two behind the front, but dry conditions are expected heading into the evening, as cold/dry advection kicks in on the 300-320 degree flow. Clouds are a slightly more difficult forecast, and some stratocumulus could last into the overnight period. The temperature forecast for today required a bit of work, as conditions are steady/warming at this early hour, and the cold frontal passage will create significantly non-diurnal conditions through the morning and afternoon. A HRRR/RAP blend captured most of the day well, but some manual edits were needed this morning, as current obs and model analyses were not matching up perfectly.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...
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A gradual diminishing trend is expected in the winds behind the cold front, eventually leading to light NNW flow (10 knots or less) by early Monday morning. No question that the cold advection will lead to the coolest min temps in a while, with lower to mid 40s expected. Over the course of Monday, an expansive area of high pressure will build from the middle Mississippi Valley region into the Ohio Valley. With dry air in place, mostly clear conditions are expected, but the significant change in air mass will result in a big drop in temperatures -- with max temps only in the upper 50s to near 60.
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&& .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
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Surface high pressure will settle across the Ohio Valley Monday night. Winds will become light to calm across the eastern and southern zones, while a pressure gradient keeps winds up a tad over the northwest. With mainly clear skies, temperatures will fall into the mid and upper 30s over most locations of the east and south, especially in rural, sheltered, locations. Have expanded the frost potential to cover all by the northwest, where lows will be in the lower 40s. The frost potential has been included in the HWO product. For the period Tuesday into Wednesday night, surface high pressure will continue to extend across the Ohio Valley. Sunny days and clear nights are expected. Temperatures will modify with highs in the lower to mid 60s on Tuesday giving way to upper 60s to lower 70s on Wednesday. With a dry airmass in place and with light to calm winds at night, lows will drop into the upper 30s and lower 40s Wednesday morning, with mainly lower to mid 40s by Thursday morning. Mid level energy will be passing to our north Thursday into Thursday night, which may push a dry cold front into the southern Great Lakes by Friday morning. Otherwise, Thursday will see highs in the lower 70s all locations. For Friday and into the upcoming weekend, upper level riding will develop over the Tennessee Valley and will coincide with surface ridging across the region. This will keep the forecast dry and warm with highs in the mid 70s and lows in the mid 40s to the lower 50s.
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&& .AVIATION /07Z SUNDAY THROUGH THURSDAY/... The passage of a cold front today will be the main focus for impacts to aviation. This front will bring periods of gusty winds this afternoon (up to 30-35 knots) along with a wind shift from the SSW to the WNW in the 16Z-20Z time frame. This front is likely to bring showers to the area, along with a period of MVFR ceilings for all TAF sites. Going into the evening hours, ceilings should lift to VFR, and winds will diminish as they settle in to a NNW direction. Some low level wind shear is also possible this morning. There is also a very low probability of thunder at the TAF sites as the cold front moves through, and this is too low to include in the forecasts. OUTLOOK...No significant weather expected. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Hatzos NEAR TERM...Hatzos SHORT TERM...Hatzos LONG TERM...Hickman AVIATION...Hatzos

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