Area Forecast Discussion
Issued by NWS Wilmington, OH

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376 FXUS61 KILN 231353 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 953 AM EDT Tue May 23 2017 .SYNOPSIS... A ridge of high pressure will exit east of the region today. Upper level low pressure in the Upper Midwest will strengthen as it moves southeast to the Tennessee Valley by Thursday morning. At the surface and lower levels, low pressure will be further north and settle in the Ohio Valley during this time. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Surface high pressure is departing the region to the northeast, with the ILN CWA currently in between two areas of greater moisture -- one ahead of the upper low moving southward along the Mississippi River, and the other moving through the southwesterly flow off the Gulf coast. Outside of these areas, the low-level flow remains fairly weak, so the advection process is not occurring particularly quickly in the middle Ohio Valley region. Generally light radar echoes have been observed over Indiana, with just a few reports of light rain so far. Over eastern Kentucky, an area of greater deep-layer moisture is advecting northeast, and 06Z model runs suggest this will clip the southeastern corner of the ILN CWA. There will be no more than a slight chance of light rain in either case, so most of the CWA will be kept dry in this forecast update. Some slight upward adjustments were made to temperatures, based on the current amount of clearing over the region, but clouds are expected to increase in coverage through the day. Previous discussion > Generally cloudy conditions will prevail over the region today with high clouds thickening and spilling in from the southwest. With the exiting surface high pressure ridge, dry conditions will be found. Temperatures will be fairly uniform and climb into the middle 70s.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY/... As the upper low digs south in the Upper Midwest tonight, southerly flow in the lower levels of the atmosphere will bring in moisture and wring it out in the broad upward motion found in the region. Scattered showers will become more prevalent later in the night and the increased chances will spread from west to east. Overnight lows will also be somewhat uniform over the region and drop to the middle and upper 50s. By Wednesday, some daytime insolation will be added to the mix and shortwave energy rotating north into Ohio will help to initiate more widespread showers and some embedded thunderstorms. Given the thicker cloud cover and expected rainfall, temperatures will be hard pressed to move past the 70 degree mark. Wednesday night should see precipitation move north as the upper level circulation remains well south of the area and the surface and lower level low circulation is along or just north of the OH/MI border. Though rainfall will be on the decrease and not much is expected, temperatures will once again drop into the low to mid 50s. Deeper moisture and the re-emergence of shower activity on Thursday will hamper temperatures once again, with middle 60s expected. The low pressure system will orient itself nw-se and move east of the region in the late day, with some cold-pool scattered instability showers possible in its wake. Ridging at the surface and aloft will take hold for Friday and a general drying pattern will be found as temperatures begin to rebound into the lower 70s. && .LONG TERM /FRIDAY NIGHT THROUGH MONDAY/... Models continue to trend on the quicker side both with the departure of the upper low Thursday night and additional precipitation chances beginning Friday night. Beyond that, model spread remains somewhat high for the weekend forecast, as a series of shortwaves is expected to move eastward across the region in the pseudo-zonal flow. At least initially, it is likely that some sort of surface boundary will exist across the region, with greater theta-e just to the south. Though this may eventually shift northward, this pattern is one that would support multiple rounds of showers and storms within an increasingly moist air mass. Thus, there will be at least some potential for both stronger storms as well as heavy / repeated rainfall for Saturday and Sunday. Within the GEFS suite and from run- to-run of the operational ECMWF/GFS, there are still big differences in wave amplitude/timing, negating the ability to forecast the specifics. For now, lower-end PoPs will be maintained through the entire weekend (though this has been increased from the previous forecast), with slightly above normal temperatures. This may come to an end with a cold frontal passage late Sunday into Monday, leading to drier conditions to start next week. && .AVIATION /14Z TUESDAY THROUGH SATURDAY/... Surface ridge centered to the northeast will continue to extend down across the tafs today. This will keep the low levels dry. Stubborn cirrus will provide broken to overcast ceilings into afternoon when it is expected to thin. After 00Z, the low levels start to moisten as vort max swings around the closed H5 low in the Mississippi Valley. There are still timing differences as to when the pcpn will start. Went with a consensus blend which brings scattered pcpn into the sw tafs around 09Z, then a steadier rain in around 12Z. OUTLOOK...MVFR ceilings and visibilities possible Wednesday into Thursday, and again Saturday. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Franks NEAR TERM...Franks/Hatzos SHORT TERM...Franks LONG TERM...Franks/Hatzos AVIATION...Sites

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