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Area Forecast Discussion
Issued by NWS Central Illinois
Issued by NWS Central Illinois
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762 FXUS63 KILX 170954 AFDILX Area Forecast Discussion...Updated Aviation National Weather Service Lincoln IL 454 AM CDT Sat Aug 17 2024 .KEY MESSAGES... - Scattered showers possible (30% chance or less) this afternoon along and north of a Davenport- to- Vincennes line. There could even be an isolated thunderstorm or funnel cloud, but severe weather is not anticipated. - Drier, cooler and otherwise low-impact weather is then forecast for the upcoming week. && .DISCUSSION... Issued at 1220 AM CDT Sat Aug 17 2024 Morning water vapor imagery shows an upper-level low positioned over the Great Lakes region, with multiple shortwaves embedded within the cyclonic flow. Short-term model guidance is in excellent agreement that this feature hangs around through the weekend, aiding periods of scattered showers through Sunday afternoon as various spokes of vorticity rotate through central IL. The latest 00z HREF guidance suggests shower chances (20-30%) largely remain confined along/north of a Davenport-to-Vincennes line today, and then east of Bloomington-to-Effingham line on Sunday as the upper-level low begins to pivot/depart eastward. Enough residual moisture and instability exists on the back side of the surface low for showers to be convective in nature, and with steep low-level lapse rates and a core of colder temperatures aloft, we could see a few funnel clouds today across the region. This idea is loosely supported by recent RAP13 guidance, which offers non-supercell tornado (NST) parameter values > 1 in areas along/north of I-74, with the highest values staying across the Chicagoland area. Another byproduct of steep low-level lapse rates today will be breezy conditions, as deeper boundary layer mixing helps achieve occasional gusts between 20-25 mph. Temperatures this afternoon will be held down by increasing clouds, as most locations across central Illinois hover around 80 degrees, while areas south of I-70 once again surge into the mid- to-upper 80s beneath less cloud coverage. A strong omega block appears to evolve by next week. The net effect will be lengthy stretch of dry and mild days across much of the Midwest. NBM deterministic guidance is providing afternoon highs between 76-82 degF and overnight lows between 55-60 degF each day between Monday and Thursday, with less than a 10% chance of rain. Eventually the anomalous ridge-axis portion of the omega block will nose across the Mid-Mississippi Valley, turning the heat up into the mid-to-upper 80s by late next week. At this point, it is difficult to target the next best chance for rain beyond the current weekend. A quick glance at the latest global deterministic solutions (GFS, ECMWF, and CMC) paint central Illinois beneath the core of the 594mb ridge, which would seemingly shunt any frontal or MCS precip well north of here. On the other hand, global ensembles such as the GEFS and EPS keep central Illinois more along the periphery of the 594mb ridge, perhaps offering a slightly better chance of tapping into frontal or MCS precip by next weekend. Either way, it`s hard to ignore the signal for an extended dry period across the Midwest, and this is supported by CPC`s increasing probability for below normal rainfall through August 30th. MJA && .AVIATION... (For the 12z TAFs through 12z Sunday Morning) Issued at 447 AM CDT Sat Aug 17 2024 Upstream observations indicate MVFR ceilings over northern Illinois this morning. Short-term forecast guidance supports these lower ceilings moving southward into portions of central Illinois after 14z/9am. Both PIA and BMI have the greatest chance of seeing these MVFR ceilings, eventually lifting and scattering to VFR early this afternoon. Elsewhere, VFR are expected to persist through the period. With the passage of another weak surface front this afternoon, winds will veer to the NW and gust to around 18-20 kts before diminishing around sunset. MJA && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$