Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 210654 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 254 AM EDT Fri Apr 21 2017 .SYNOPSIS...
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A cold front is crossing the region early this morning, bringing cooler and drier air into the area today. Cooler conditions will continue into the weekend, with some chances for rain, as the front stalls south of the area. Warmer conditions are expected from Sunday into next week.
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&& .NEAR TERM /THROUGH TODAY/...
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Current surface analysis indicates that the incoming cold front, at least in terms of wind shift, is roughly halfway through the ILN CWA (moving from NW to SE). Areas of precipitation still being observed are ahead of the front, but do not appear to be directly tied to it, at least as a surface feature. There is likely some weak upper support helping this precipitation to persist (on the south side of 500mb/300mb wind maxima across the Great Lakes) and to take advantage of what little elevated instability is still in place. PoPs were raised slightly for the far southeastern counties over the next few hours, but otherwise, precipitation is expected to end as previously forecast once these showers have cleared through the region. Entering a regime of NW flow and cold advection, a generally dry day is expected across the ILN CWA on Friday, with the exception of a few showers getting into the far south late in the day (covered in the short term discussion). Clouds were somewhat difficult to pin down, with widespread overcast conditions still over the CWA, but a dry slot located just upstream behind the cold front. Additional stratocumulus over the Great Lakes is starting to look unlikely to really make it into the area, but even as 850mb moisture becomes sparse, additional high and mid clouds are likely to get into the region by late morning / early afternoon. Ultimately, the forecast for today will be generally mostly cloudy, but with an expectation that some areas (especially in the western / northwestern CWA) may break out clear for several hours in the morning.
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&& .SHORT TERM /TONIGHT THROUGH 6 PM SATURDAY/...
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Based on theta-e / MSLP analysis, the Friday morning cold front is expected to stall and pivot just south of the ILN CWA by late Friday and into Saturday morning. Precipitation chances through Friday night and Saturday will be tied to mid and upper level support moving eastward across this front, ultimately ending up with a surface low passing south of the region at some point on Saturday. Regarding all of the above features, model timing/placement agreement is disappointingly and remarkably poor. If there has been any trend with the 00Z runs, it has been for a slightly more southerly frontal position. This -- if nothing else -- will help to limit the potential for instability or more significant deep-layer moisture, limiting the threat for heavy rainfall. Models are not unanimous on this, however -- the 00Z ECMWF remains further north with the front and thus with its axis of greater QPF. The 00Z NAM is at the other end, keeping the majority of the CWA dry after an initial batch of rainfall on Friday night. WRF-ARW/WRF-NMM/NSSL Realtime WRF forecasts are similarly split on details but not as dissimilar on the overall picture, helping to paint a picture for PoPs based on a compromise scenario. Based on the majority of the model guidance, along with relatively unimpressive SPC SREF probabilities for >1" rainfall, the heavy rain mention will be removed from the forecast. Thunder was also removed from the grids, with even elevated instability expected to remain south of the area -- though, it should be noted, the elevated frontal boundary will be slightly further north than the surface front. PoPs were raised slightly with an initial wave of generally lighter precipitation late Friday evening into the overnight, with the greater chance for more persistent rainfall across the southern CWA at some point on Saturday. On the north side of the surface boundary, and in a regime of NE flow, Saturday will be a notably cool day -- with max temps at least 10 degrees below normal, only forecast to reach the lower to mid 50s. Obviously, the way the precipitation forecast plays out will have a role in these temperatures, making this a little lower confidence than normal. A rainier day on Saturday might keep temps closer to 50, but areas that escape the rain could get a little warmer.
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&& .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
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Rain chances will gradually diminish Saturday night into Sunday as the system works east. Weak high pressure is forecast to bring dry conditions Monday into Tuesday. A wave of low pressure traveling through the Great Lakes may result in a few more showers Tuesday night into Wednesday. Additional showers could affect mainly northern locations Thursday when a warm front is forecast to develop across the Great Lakes. Temperatures will start below normal for Saturday, with highs in the mid 50s limited by clouds, precip, and cold advection on a northeast low level flow. A rebound to near normal upper 60s can be expected by Monday due to warm advection and reduced cloud cover, with further warm advection making above normal 70s probable Tuesday through Thursday.
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&& .AVIATION /07Z FRIDAY THROUGH TUESDAY/... A few showers (perhaps with brief MVFR ceilings) may persist at the TAF sites for another few hours. After that, drier conditions are expected to move into the region, with VFR ceilings and WNW winds. These conditions will likely continue through most of the day on Friday, with mostly mid/high clouds, and northwest winds of around 10 knots. On Friday night, clouds will thicken from south to north, as chances for precipitation gradually begin to increase. Forecast confidence for Friday night into Saturday is very low, with regards to specific precipitation timing, so there may need to be changes to what is currently in the TAFs as it becomes more clear when (or if) rain ends up forecast to move into the area. It does appear that rain is more likely to occur at the southern TAF sites (CVG/LUK) through this time period. OUTLOOK...MVFR ceilings and visibilities possible Saturday with rain. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Hatzos NEAR TERM...Hatzos SHORT TERM...Hatzos LONG TERM...Coniglio AVIATION...Hatzos

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