765 FXUS63 KILX 022346 AFDILX Area Forecast Discussion National Weather Service Lincoln IL 646 PM CDT Wed Sep 2 2020 .SYNOPSIS... Issued at 248 PM CDT Wed Sep 2 2020 A frontal boundary will stall along the Ohio Valley tonight and tomorrow with a chance of showers and thunderstorms as far north as the I-70 corridor. Elsewhere in central Illinois expect dry weather through at least Saturday. && .SHORT TERM...(This evening through Thursday) ISSUED AT 248 PM CDT Wed Sep 2 2020 This afternoon, a cold front is located near the I-70 corridor and is slowly pushing south. Occasional showers are expected out ahead of the front and cannot rule out an isolated thunderstorm, though the overall threat is low with weak mid level lapse rates and cloud cover hampering afternoon destabilization. Further north, expect the rest of the area to be quiet through tonight as weak high pressure builds in from the southwest. On Thursday, another cold front is expected to push across the region. A very dry air mass will be in place with some sunshine helping to mix down surface dew points. The combination of lower dew points and continued weak mid level lapse rates will keep precip chances in check, but cannot rule out an isolated shower or storm across east central and southeast Illinois during and just after peak heating near the front. Otherwise, expect breezy conditions across the region on Thursday. Deep mixing will bring down stronger winds aloft with gust of 20 to 25 mph expected from late morning through the remainder of the daytime hours. .LONG TERM...(Thursday night through Wednesday) ISSUED AT 248 PM CDT Wed Sep 2 2020 Cold front will push across the Ohio Valley Friday while high pressure builds east from the central Great Plains to the mid Mississippi Valley. 850 mb thermal trough will be squarely overhead midday Friday resulting in the coolest day until at least early next week. After coming off morning lows in the 50s, highs on Friday will only be in the upper 70s to lower 80s. Overall a very dry column is expected Friday with steep low level lapse rates as the cooler air mass settles over the region. Winds will not be as breezy as Thursday, but still expect some gustiness to around 20 mph at times during the afternoon. Dew points will also mix down into the lower 50s and 40 with RH values bottoming out around or below 30 percent. This combination of drier air and breezy winds could pose some fire weather concerns Friday afternoon. Friday night into Saturday, surface ridge axis will settle along the Ohio Valley with return flow overspreading Illinois. Strengthening LLJ over the central Great Plains Friday night will result in showers and thunderstorms across portions of eastern KS into northern MO. This activity will be decaying as it moves east into Illinois Saturday morning, but could see some remnant cloud cover reach the local area. Dew points will inch back up into the mid to upper 50s Saturday afternoon while temperatures top out a few degrees warmer into the lower to mid 80s. LLJ strengthens again later Saturday, this time focused a little further northeast across portions of northern MO into IA. Resulting storms could ride the instability gradient into central Illinois Saturday night into Sunday. Early through the middle of next week, large scale pattern change is in the works, however, models continue to have large differences in the evolution of the increasingly amplified upper air pattern. Initial wave moving east across the Canadian Prairies will help drive a cold front across portions of the Midwest by Tuesday into Wednesday, though it remains uncertain how far south and how quickly the front will move. Meanwhile, a second stronger wave will dig across the PacNW early next week possibly cutting off over the Desert SW (ECMWF) or remaining open as it digs deep across the Great Plains (GFS). The GFS remains more progressive with the front dropping temperatures well below seasonal norms. Meanwhile, operational GFS does have reasonable support from ensemble members, although the GEFS mean is a bit slower in the eastward progression of the deep upper trough and colder air arriving locally. By Wednesday, differences between the ECMWF and GFS are around 40 degrees for afternoon highs. GFS indicates highs will only be in the upper 40s to lower 50s while the much slower ECMWF still has the area well into the 80s and lower 90s. Forecast generally takes the middle ground, so anticipate big changes up or down once better consensus is reached in how next week evolves. Stay tuned... && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) Issued at 645 PM CDT Wed Sep 2 2020 A cold front has pushed south of the TAF sites, with primarily SW winds occurring at the start of the 00z TAF period. Wind will become light overnight, backing to a more southerly direction or becoming variable. HRRR, RAP, NAMnest and GFS models are all pointing toward a band of dense fog forming from just south of SPI to DEC to CMI and south toward I-70 after 09z tonight. Have introduced some IFR fog at CMI and DEC for now, but may need to add SPI if model trends continue. Will monitor closely as the evening progresses. Fog should burn off by 14z tomorrow, then winds will become gusty out of the WSW by late morning. && .ILX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...Deubelbeiss SHORT TERM...Deubelbeiss LONG TERM...Deubelbeiss AVIATION...Shimon