Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 220139 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 939 PM EDT Wed Mar 21 2018 .SYNOPSIS... Low pressure is moving east tonight, allowing high pressure and a drier airmass to build into the region Thursday and Friday. Low pressure will bring a mix of rain and snow to the region for Saturday. High pressure and dry air are forecast to return Sunday and Monday. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... Surface analysis suggests a surface trough is currently over the ILN CWA, extending from ESE-to-WNW, with a slight veering of winds behind the southward-moving axis. Precipitation has largely ended across the ILN CWA, with surface observations showing that clouds remaining over the area are generally in the mid-levels. The only exception, for the next hour or two, is the chance for some light flurries or freezing drizzle in southern Ohio / northeastern Kentucky, where a few pockets of low-level moisture still exist. RAP projections (mainly at 900mb and below) and a few light radar returns suggest this is the case, and also suggest that it will come to an end soon. A Special Weather Statement is in effect to highlight the potential for refreezing tonight, as any wet roads will become prone to becoming icy as temperatures fall into the 20s. The main change for this evening forecast update was to drop temperatures overnight, especially where the heaviest snow fell earlier -- mainly in the western half of the ILN forecast area. Temperatures were lowered by several degrees, especially as clearing is beginning to work into the region from the west. In fact, current HRRR/RAP runs suggest temperatures may fall even lower than even in this updated forecast -- possibly well into the teens. That is not out of the question given the aforementioned conditions. Previous discussion > Surface analysis shows low pressure to the east and high pressure to the west. ILN area is under a chilly northerly flow between these systems. Moisture and forcing associated with the low are diminishing and snow is ending. Still will see light snow for a few more hours especially in eastern locations, but little to no additional accumulation is expected. Clouds will linger this evening until clearing from the west arrives overnight with the high moving in. Temperatures will fall below guidance to the lower 20s, with these cold readings aided by snow cover. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/... Surface high pressure developing under a northwest upper flow will extend across the area Thursday and Thursday night. This will provide dry weather conditions and mostly clear skies through the period. Sunshine and modest warm advection will allow high temperatures in the low to mid 40s, still close to 10 degrees below normal. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... In a northwest flow aloft, our region will be between weak systems to our northeast and southwest on Friday. Surface high pressure will remain in place, and with sunshine, temperatures will warm into the 40s. Focus then turns to a low pressure system forecast to pass southeast through the lower Ohio Valley and the Tennessee Valley Friday night into Saturday night. Strong ascent in the form of a moist low level jet will spread precipitation east/northeast into the region Friday night into Saturday. There is an increasing signal for an accumulating snow event, perhaps significant, for locations along and north of the Ohio River. Many factors will play in how much snow will fall such as surface temperatures, thermal profiles, time of day, exact track of the low, and whether some locations along and north of the Ohio never mix with or change over to rain. We currently have a mix developing north of the Ohio with rain/snow changing to rain south of the Ohio. However, strong lift/dynamic cooling, along with a prolonged easterly flow in the low levels, may keep sounding profiles saturated near or below the 0 degree isotherm for points along and north of the Ohio River. Also, the strong vertical motion will likely occur in the favorable dendritic growth zone which will result in aggregate snowflakes. These types of snowflakes can result in heavy snow with rapid accumulation. So, until confidence increases in ptype and duration, have initially went with conservative in amounts, with the caveats mentioned above that could result in a heavier, more significant snow. This has been placed in the HWO. By Saturday night, the low pressure system will be pulling away to the southeast, allowing surface high pressure to build back into the region for Sunday. After lows between 25 and 30, highs will warm back into the 40s on Sunday. High pressure at the surface and aloft will remain over the region on Monday. Temperatures will continue to moderate with highs in the upper 40s to the lower 50s. For the remainder of the extended, an increasing moist, southwesterly flow will develop around the mid level ridge axis passing to the east. This will bring clouds and the potential for showers as we head into Tuesday. A frontal boundary will try to make inroads into the area by mid week, keeping the threat for rain in the forecast. Temperatures will continue to warm with 50s and perhaps 60s possible by next Wednesday. && .AVIATION /02Z THURSDAY THROUGH MONDAY/... With any remaining light snow departing the area early this evening, VFR conditions are expected through the rest of the TAF period. Ceilings have shifted to VFR, mainly with mid-level clouds, which should persist into the overnight hours before clearing out entirely. Clouds tomorrow will generally just be cirrus and some fair weather cumulus -- remaining VFR through the day. Winds will remain out of the northwest through the period, diminishing some this evening, but increasing to around 8-12 knots tomorrow afternoon. OUTLOOK...MVFR/IFR ceilings and visibilities are possible Saturday and Saturday night. MVFR ceilings are possible again on Monday. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Coniglio NEAR TERM...Coniglio/Hatzos SHORT TERM...Coniglio LONG TERM...Hickman AVIATION...Hatzos is the U.S. government's official web portal to all federal, state and local government web resources and services.