Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 211052 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 652 AM EDT Fri Apr 21 2017 .SYNOPSIS... 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. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 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. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/... 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. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Upper level low will continue to dig south into the Tennessee Valley Saturday night into Sunday. As it does, it will gradually lose influence on the region. Clouds will decrease from the north but will remain some in the south with a lingering threat of showers. Temperatures should rebound into the lower and mid 60s on Sunday with the highest readings expected where more sunshine will occur. For Sunday night into Monday, upper level low will rotate southeast toward the southeast United States coastline. The threat for precipitation will end in the south with all locations expected to have sunshine on Monday. With airmass modification and solar radiation, temperatures will warm into the upper 60s to the lower 70s. Weak high pressure ridging at the surface and aloft will influence the regions weather Monday night into Tuesday. Dry weather and airmass modification will continue the warming trend with 70s expected on Tuesday. For the period Tuesday night into Wednesday night, upper level flow will allow a frontal system to push into the region from the northwest where it may briefly stall out by Wednesday night. This will bring at least a chance of showers to the northwest zones Tuesday night, and then a chance of showers and thunderstorms to all locations Wednesday into Wednesday night. By Thursday, models suggest that the upper level flow may begin to amplify. If this occurs, frontal boundary will lift north as a warm front into the Great Lakes on Thursday. This will eventually take the threat of precipitation with it. Temperatures will become above normal by this time with upper 70s to lower 80s expected. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/...
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Showers have ended at the TAF sites, and by 12Z, all of the airports are expected to be within a clear slot. While the clearing should be relatively short-lived, the clouds that move back in will likely be a mix of mid/high clouds (VFR) through the rest of the day. An MVFR stratocumulus deck is currently over northwest Ohio, but as of now this is not expected to make it to DAY/CMH/LCK before lifting. Winds are expected to be out of the northwest at around 10 knots. Tonight, clouds will thicken from south to north, as chances for precipitation gradually begin to increase. Forecast confidence for tonight into Saturday is 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 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, especially after midnight, with slightly greater chances for all TAF sites by Saturday afternoon. OUTLOOK...MVFR ceilings and visibilities possible Saturday with rain.
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&& .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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