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Area Forecast Discussion
Issued by NWS Central Illinois
Issued by NWS Central Illinois
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663 FXUS63 KILX 111912 AFDILX Area Forecast Discussion National Weather Service Lincoln IL 212 PM CDT Sun Aug 11 2024 .KEY MESSAGES... - Rain will move into the region tomorrow morning, with off-and-on showers lingering into early Monday evening before tapering off. The best chances (+ 70%) and highest rainfall amounts (+ 0.50") are expected to occur west of a Galesburg-to-Springfield line. - Multiple rounds of thunderstorms will pass through the region between Wednesday night and Friday afternoon, perhaps affecting central Illinois directly. The severe weather potential remains low at this time, but torrential rainfall will accompany these storms. && .DISCUSSION...(through next Saturday) Issued at 1232 PM CDT Sun Aug 11 2024 Afternoon water vapor imagery depicts shortwave energy digging across the Black Hills, with regional radar mosaics revealing areas of showers and thunderstorms developing in the vicinity of this disturbance. Short-term, hi-resolution guidance is in excellent agreement that this activity across the Northern Plains evolves into an organized MCS tonight as it pushes across the Corn Belt, eventually making it across the Mid-Mississippi valley by dawn. While the general trend is for this MCS to decay on arrival (hostile low- level dry air and little- to- no instability), there remains some notable variance among hi- res guidance with respect to (a) areal extent of precip; (b) starting/ending time; and (c) the most reasonable range of rainfall estimates. Regarding the areal coverage of precip, the FV3 and ARW stand together in bleeding 0.10" rainfall north to the I-74 corridor and east to the I-57 corridor. Meanwhile, the HRRR, NSSL WRF and NAMNEST confine measurable rainfall west of a Galesburg-to- Springfield line. While both trends are viable outcomes, I tend to favor the further south/west solution. Experience and pattern recognition would suggest that decaying MCS`s tend to dive southward toward the instability gradient, which in this case, will be positioned in Missouri along a loose baroclinic zone. At this point, hi-res guidance is fairly consistent with rain entering our far west between 5-8am, with the bulk of rainfall occurring before Noon, but with scattered, warm-advection showers then lingering into the early evening hours before tapering off. Thinking most locations will receive between 0.01" - 0.25" tomorrow. What could separate the wheat from the chaff is any mesoscale banding that occurs. Whether this happens beneath a speculative MCV or is the result of transient frontogenetic enhancements from strong warm advection--I`m not sure--but there are hints of banding in some of the hi-res guidance. In such case, there could be a few narrow corridors of 0.75"- 1.0" -- again favoring areas west of a Galesburg-to-Springfield line. Skipping ahead, the Wednesday to Friday timeframe has the look of a busy pattern for central IL. From a synoptic viewpoint, there will be a warm front lifting across the region Wednesday night into Thursday, theoretically providing the needed buoyancy for thunderstorm activity. This, in tandem with multiple shortwaves traversing the area, should provide the necessary forcing and shear for an organized storm threat. Admittedly, the GEFS is much less bullish on the severe weather potential, but when added among EPS and GEPS guidance, probabilities increase for the late Wednesday night through Thursday evening period. Additional chances for showers and storms bleed into early next weekend, but these will be highly dependent on what evolves in the western Atlantic with regards to a tropical disturbance. If this disturbance drifts too far west, we could be stuck beneath low clouds and sprinkles. If it stays far enough east, it could be a dry and seasonably warm weekend. MJA && .AVIATION... (For the 18z TAFs through 18z Monday Afternoon) Issued at 1201 PM CDT Sun Aug 11 2024 High pressure will move across central Illinois this evening and overnight. Light W/NW winds in place today will become light and variable or calm overnight, then set up out of the SE Monday. Meanwhile, showers and thunderstorms will develop to our west this evening and approach central Illinois overnight, arriving Monday morning in a weakening phase. Confidence in precip on station is highest in the SW (at SPI) and lowest to the NE (CMI). Deubelbeiss && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$