724 FXUS61 KILN 192340 AFDILN AREA FORECAST DISCUSSION National Weather Service Wilmington OH 740 PM EDT Tue Oct 19 2021 .SYNOPSIS... High pressure will provide mostly sunny and warm conditions through Wednesday. Developing low pressure and an associated cold front will increase precipitation chances from Wednesday night through Thursday before cooler conditions return for late week. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... Surface high pressure centered over the southeast United States will continue to provide fair conditions this evening through tonight. Outside of a few thin cirrus clouds through late evening, clear skies will once again allow efficient radiational cooling. With this in mind, low temperatures should once again dip into the mid-40s. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... High pressure shifts off the Carolina coast Wednesday as developing low pressure moves east into Iowa. Outside of a few mid and high clouds, most of the signs of approaching low pressure will hold off until after sunset Wednesday. With steady southwesterly flow, temperatures will peak in the low 70s. Moisture increases over the Ohio Valley Wednesday night as the surface low slides into the Great Lakes. Latest guidance brings best chance of showers late in the period to the northern half of the CWA closest to the mid-level shortwave. Under increasing cloud cover and southwest flow ahead of the cold front, low temperatures will stay up in the mid to upper 50s. && .LONG TERM /THURSDAY THROUGH TUESDAY/... The period begins with a high confidence frontal passage on Thursday morning into early afternoon across the ILN forecast area, accompanied by a threat of showers and a few storms perhaps in the Scioto Valley with autumnal cooling to follow, and ends in an extremely low confidence pattern which may spell considerable warming. In the details, at 12Z on Thursday, a strong shortwave trough will be located over Lake Michigan with a cold front arcing south through Indiana. Out ahead of the front, an elevated band of showers may be moving through the western ILN CWA on Thursday morning in strong theta-e advection above the boundary layer. As the day progresses, there is some potential for these showers to become surface based to some degree by early-mid afternoon over the Scioto Valley, or perhaps surface-based shower development to occur along the front itself before exiting the forecast area. There is a narrow window among the various deterministic runs of enough surface based instability to develop in portions of the lower Scioto Valley to allow deep enough updrafts for thunder mention. This may need to be expanded northward a little in future forecasts. Given strong flow fields which will be unidirectional /southwesterly/ in nature, it is not out of the realm of possibility that some strong/gusty storms could occur in our southeast/eastern counties before the front exits, especially if the boundary ends up passing through an hour or two slower than expected. There will also be gusty winds in the wake of the front on Thursday afternoon particularly over western Ohio and eastern Indiana. Have moved winds and especially wind gusts higher for Thursday afternoon, but potentially not high enough as we may see some 30kt gusts at peak heating over the higher terrain areas /e.g., Bellefontaine Ridge./ Strong cold advection in the wake of the front on Thursday night, and a reinforcing secondary cold front on Friday, guarantee the eventual development of plenty of stratocumulus and light shower threat especially for Friday, where highs will only make the 50s to around 60. Uncertainly begins to rapidly increase over the weekend and into early next week as there is not good agreement on the path/strength of energy attempting to undercut high latitude blocking / longwave ridge moving east toward the Great Lakes. For right now am running a dry/cool Saturday with some modest increases in rain chances on Sunday as a warm frontal zone begins to set up over the Ohio Valley and attempt to push north. However, if energy runs along this boundary precipitation chances will need to greatly increase and temps may be too optimistic. Also am extending rain chances into Monday to account for the varied speed/latitude of the potential energy passing through the Great Lakes. This begins a period of high variability in the deterministic and ensemble members, with notable spread on 2m temp plumes Sunday->Tuesday. This comes to a head on Monday/Tuesday, with NBM temperature standard deviations maximized over the Ohio Valley indicating a great amount of uncertainty on warm frontal location as the longwave upper ridge moves in and weakening/undercutting energy moving out. While the NBM 50%ile and mean temps have risen considerably for Mon/Tue, it should be noted there are still a number of data which suggests robust warming will not occur to the level deterministic runs (e.g., the 10.19.12z GFS for example), thus considerable attention needs to be paid to this portion of the forecast for future adjustments. && .AVIATION /23Z TUESDAY THROUGH SUNDAY/... VFR conditions will continue at most TAF sites through the period. However, given the pattern the past couple of mornings, included MVFR vsby reduction and a tempo LIFR reduction due to river valley fog at LUK developing late tonight and continuing into the morning. Light southwest flow continues across the CWA with isolated gusts up to 20 kts Wednesday afternoon at ILN and DAY. OUTLOOK...MVFR ceilings and visibilities possible Thursday. MVFR ceilings possible Friday and Friday night. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Hogue NEAR TERM...Hogue SHORT TERM...Hogue LONG TERM...Binau AVIATION...Cornelissen