208 FXUS61 KILN 080007 AFDILN AREA FORECAST DISCUSSION National Weather Service Wilmington OH 807 PM EDT Thu Oct 7 2021 .SYNOPSIS... A cut-off low centered over Illinois will continue to weaken as it lifts northeast into the Great Lakes. The showery pattern associated with the low will transition into warm and dry conditions for the weekend into early next week as ridging builds into the Ohio Valley. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... Scattered shower activity over portions of the region are primarily located east of Cincinnati and then northward along the 68 corridor towards southeast Hardin County. A larger area of showers and embedded thunderstorms south of the CWA continue to push northward and will affect the northern KY counties over the next few hours. Trend is overall downward with existing showers with the exception that the central KY showers and storms will persist as they move into the CWA. Blended the current radar picture and used the HRRR and NAM12 to buffer into the immediate future of 2-3 hours, then took this trend of the earlier forecast and HRRR/NAM into the overnight hours. Mid- and upper-level low over Illinois remains cut-off from the flow as broad ridging over the eastern United States shunts the jet stream well north into northern Ontario and Hudson Bay. This low will continue to weaken as it slowly eases northeast into the Great Lakes tonight. These showers will shift to the northeast through the night with a weak disturbance ejecting in this direction from the parent low. Low temperatures will once again drop into the low to mid 60s. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/... The cut-off low will open into a trough by late Friday. While this occurs, its proximity to the west of the CWA along with afternoon heating will provide one more good chance of precipitation. The orientation of the trough leads to highest PoPs across the north, with gradually decreasing chances further south. By Friday evening heading into the overnight, guidance suggests conditions will begin to dry out from southwest to northeast. This will be accompanied by decreasing clouds as well. Low temperatures will drop into the upper 50s across most areas due to less cloud cover. && .LONG TERM /SATURDAY THROUGH THURSDAY/... The main themes in the long term period will continue to be above normal temperatures and relatively humid conditions. For the upcoming weekend, the remains of the pesky upper level low will continue to weaken and move northeast toward southeast Canada and the eastern Great Lakes. There could be a lingering low chance of a shower/storm across the far eastern zones, otherwise partly cloudy skies will prevail. Mid level ridging is expected to build into the Ohio Valley Saturday night and Sunday. A frontal system to our west and surface high pressure to the east will result in a modest surface pressure gradient setup which will increase low level southerly flow. This will allow temperatures to warm into the upper 70s to the lower 80s on Sunday. By early next week, aforementioned frontal system and its parent mid level trough will try to make in roads across the Great Lakes and Ohio Valley, weakening some as they try to suppress the mid level ridge to the east. Warm conditions on Monday will occur once again (upper 70s to the lower 80s). A chance of showers, perhaps a thunderstorm, will be introduced in the forecast from late Monday into Monday night as the cold front pushes east. Much of the activity is expected to be diminished in coverage by Tuesday. Mid level ridging is expected to bounce back northward into the Ohio Valley by mid week in advance of an even stronger mid level trough across the Intermountain West and Great Plains. Some timing issues exist at this juncture as to how fast/far east the associated cold front will get. Right now, a slower solution is preferred which brings the boundary during the Thursday into Friday time frame. Will forecast a chance of showers for now. High temperatures will remain in the 75 to 80 degree range. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... Overall weather pattern is sound, but the resultant shower activity resides in a muddled combination of convergent zones and shortwave energy. None of the deterministic models are providing enough evidence that their particular placement of QPF fields is favored over another. There are significant breaks and wide areas of zero QPF in one area or another for the next 24 hours. While a VCSH may be the truth as to a forecasting ability for all of the TAF sites, this approach is heavy handed and there could be a lot more dry periods such as what was experienced over the region today. ATTM, the best indications of rain occurs between midnight and daybreak, a little later between 08-09Z and daybreak for ILN CMH and LCK. Models were trying to indicate low stratus and IFR vsbys nearer sunrise, forecast of rain being more prevalent during these times had me leave the worst of the low cigs/vsbys out as just a possible outlying solution. During daylight hours on Friday, the better chance of activity will lie over the Scioto valley and then w-nwwd from metro Columbus to nearer Lima. However, this falls under the same caveats of the precip that is being forecast overnight - highly circumstantial and low confidence in placement/timing, slightly higher confidence in occurrence even given all of my hedging leading up to it. VFR cigs/vsbys will drop to MVFR cigs and rainfall will bring MVFR vsbys when it occurs. A drop in a category to IFR cigs/vsbys are possible, especially if any stratus develops later overnight. Given the weak <5kt winds shifting from ne to sly, this remains a potential that will need to be monitored for development. OUTLOOK...No significant weather is expected. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Hogue NEAR TERM...Franks SHORT TERM...Hogue LONG TERM...Hickman AVIATION...Franks