Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 172030 AFDILN Area Forecast Discussion National Weather Service Wilmington OH Issued by National Weather Service JACKSON KY 430 PM EDT Tue Apr 17 2018 .SYNOPSIS...
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Surface high pressure will continue to build into the region this this evening and overnight. As clouds clear, expect many locations to drop below freezing across the CWA overnight. Clouds will also be on the increase late tonight and into the day Wednesday as a low pressure system tracks towards the area. This system will bring a rain showers to much of Ohio Wednesday and Thursday. A large area of high pressure will then build into the Great Lakes for the end of the week into next weekend providing dry weather conditions.
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&& .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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A brief area of high pressure will move across the CWA overnight as Ohio finds itself between an exiting surface low pressure system just north of New England and an approaching surface low moving across the central Plains this afternoon. As high pressure continues to settle in, dry air advection will erode away at the cloud deck that has plagued the CWA throughout the day, giving way to mostly clear skies by midnight. Winds at the surface will become light and variable, but the flow aloft will be quite strong out of the NW, pulling a colder northerly airmass into the region. This combination of light winds, clearing, and a colder airmass advecting into the region will allow temperatures to fall quite rapidly overnight. Furthermore, the ongoing cloud cover across the region today has resulted in temps that were quite a bit cooler than originally expected, with many places across the central and NE portion of the CWA still only in the upper 30s and low 40s. Meanwhile for points along and just south of the Ohio River where clearing has already taken place throughout the day, temperatures have risen into the upper 40s and low 50s.
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&& .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
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A warm front will push northward through Kentucky overnight, extending from the low pressure system approaching from the Plains. This will result in an influx of moisture in the form of clouds that will begin to impact the Ohio River by around midnight and then continue to extend northward across ILN into the second half of overnight. Expect that the influx of clouds will be slow enough across much of central and northern tiers of ILN that it shouldn`t play much of a factor into temps dropping below freezing. However for locations along and south of the Ohio River, warmer temps this afternoon (due to clearing that took place through the day), and the earlier influx of clouds overnight will prevent locations here from dropping below freezing. A freeze warning was issued for portions of the CWA from 3Z through 13Z. The far southern portion of the CWA was left out given borderline or above freezing temperatures forecast for overnight, while the northern half of the CWA is not currently within its frost/freeze program. The tier of counties just south of the warning could see borderline freezing temperatures, so will need to continue to monitor in case the warning needs to be extended further south. As we head into the day tomorrow, the center of low pressure is expected to shift eastward and traverse the ILN CWA during the late afternoon and evening. Winds will become more southerly and intensify throughout the afternoon ahead of this approaching system. This will also result in an influx of moisture and rain chances across the CWA throughout the afternoon as well. Rain should continue through the overnight Wednesday night, with northerly flow behind the exiting low taking hold and quickly dropping temperatures throughout the night. Overnight temps could fall to or just above freezing, especially in the northern portion of the CWA. Would not be surprised that lingering rainfall could mix with snow across the northern CWA during the late night (after 6Z). However, given the warm temps leading into this event, do not expect much impacts from this snowfall, unless we start to trend colder with the next model runs.
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&& .LONG TERM /THURSDAY THROUGH TUESDAY/...
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The extended begins with a fairly sharp trough axis swinging east across the Ohio Valley, with scattered rain showers diminishing from west to east across the area through the day. Another cool day will be on tap, with readings running 10 to 15 degrees below normal. Clouds will clear out Thursday night, with temperatures likely near or below the freezing mark by early Friday morning. A nice stretch of dry weather will continue into early next week as ridging maintains control across the region. Surface high pressure will gradually move from the Great Lakes region to just off the New England coast by Tuesday. North to northeast winds will keep temperatures averaging below normal through the first half of the weekend, before moderating to near or slightly above normal by early next week.
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&& .AVIATION /21Z TUESDAY THROUGH SUNDAY/...
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An elongated low pressure system continues to slowly shift NE across southern Quebec and New England. As it pulls away from the Ohio Valley, high pressure is beginning to move in from the west. This is advecting drier air into the region, which is cutting off the llvl cloud deck which has plagued Ohio for much of the day. That being said, this clearing trend is quite slow, with MVFR clouds likely linger in the NE TAF sites (KCMH and KLCK) into the evening. As clouds clear (which is already taking place at KCVG and KLUK), conditions are improving to VFR which they should remain through much of the night. Another low pressure system will shift into the Ohio Valley by tomorrow afternoon, bringing with it the return of southerly winds and moisture. Cloud cover will begin to overtake Ohio, starting from the south, before daybreak tomorrow (Wednesday) morning, lowering to MVFR at the southern most TAF sites through the first half of the day Wednesday. CIGS will continue to deteriorate with rain moving back into the region after the end of the TAF period late Wednesday afternoon and Wednesday night. West winds will continue to gust close to 30 kts at times through this afternoon. Winds will drop off tonight as the surface high builds into the area, but could increase again from the S (gusts 15 to 25 knots) during the afternoon Wednesday ahead of the approaching system.
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&& .ILN WATCHES/WARNINGS/ADVISORIES...
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OH...Freeze Warning from 11 PM this evening to 9 AM EDT Wednesday for OHZ060>065-070>074-080-082. KY...None. IN...Freeze Warning from 11 PM this evening to 9 AM EDT Wednesday for INZ050-058-059-066.
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&& $$ SYNOPSIS...JMW NEAR TERM...JMW SHORT TERM...JMW LONG TERM...GEOGERIAN AVIATION...JMW

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