FXUS63 KILX 251012 AFDILX Area Forecast Discussion...Updated Aviation National Weather Service Lincoln IL 512 AM CDT Sat Oct 25 2025 .KEY MESSAGES... - Spotty showers will overspread the region this weekend, resulting in little or no rainfall. - Additional rainfall chances emerge next week in the Tuesday- Wednesday timeframe. There is currently a medium (30-50%) chance of exceeding a 0.5" of new rainfall then. && .DISCUSSION... Issued at 309 AM CDT Sat Oct 25 2025 The synoptic pattern early this morning exhibits a split-flow regime, with a southern-stream trough positioned over the Texas Panhandle, and a northern-stream shortwave digging across the Upper-Mississippi Valley. Unfortunately, the northern-stream wave is undercutting the low-level moisture return coming up from the Gulf. This is illustrated nicely on our 00z sounding from last night, which depicts adequate mid- and upper-level moisture, but very dry air from the surface to about 10 kft. A quick glance at the current radar reveals a few echoes, which are being driven by some subtle warm advection processes, but given the moisture profile, these echoes are likely struggling to reach the ground. This is a trend that will continue through much of the weekend as the main storm track misses us to the south, with either virga or spotty, high-based showers occasionally showing up across central and southeast Illinois. The exception to this rule could come by Sunday near or south of I-70 where a few transient bands of FGEN may help squeeze out a soaking rain. For what it is worth, the more coarse NBM shows a higher probability of exceeding 0.1 inch of rainfall on Sunday compared to the finer HREF, with the NBM suggesting a 20-40% probability, while the HREF offers less than 10%. To be more succinct, we are forecasting little or no rain through this weekend. And, Monday has trended drier, too, as subsidence develops beneath the quickly evolving split-flow regime. Things start to get a little more interesting by Tuesday as strong shortwave energy digs across the Central Plains. While the overwhelming majority of available model guidance supports this shortwave evolving into a closed wave, there remains a high degree of uncertainty on its position into Wednesday. This uncertainty has implications on our rainfall potential through the mid-week period. Trends seen in the latest 00z suite of global deterministic guidance paint a phenomenon rarely seen in the US mid-latitudes by Wednesday, and that is the Fujiwhara effect. In essence, the closed, upper low emanating from the Plains is poised to briefly interact with a retrograding upper low coming from New England. These two cyclonic vortices will come into orbit of each other on Wednesday. This is more poetry than analysis at this point. Because frankly, here at 5 days out, it is very unlikely that NWP is cleanly resolving the interaction of these two waves. So rather than present scenarios A, B or C, it is more prudent to message the probability of a beneficial rainfall for portions of central and southeast Illinois. And to that point, the latest NBM offers a medium (30-50%) chance of exceeding 0.50" with the mid-week drama. Model guidance then comes into better consensus by Thursday with a ridge nosing in behind the departing upper-level lows. Fair, seasonal weather returns Thursday and extends into Friday before a frontal system drops into the region next weekend. MJA && .AVIATION... (For the 12z TAFs through 12z Sunday Morning) Issued at 409 AM CDT Sat Oct 25 2025 A slow-moving weather system will pass just to our south this weekend, keeping skies mostly overcast with occasional spotty showers. Model guidance is firm that ceilings will unlikely fall below 5 kft during this TAF period, meaning VFR conditions will persist. The wind, meanwhile, will maintain its east component with sustained speeds generally between 5-10 kts. MJA && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$