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Area Forecast Discussion
Issued by NWS Central Illinois
Issued by NWS Central Illinois
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791 FXUS63 KILX 120838 AFDILX Area Forecast Discussion National Weather Service Lincoln IL 338 AM CDT Mon Aug 12 2024 .KEY MESSAGES... - Showers will spread across parts of central Illinois today. Rainfall will be light...with the highest amounts of 0.25 to 0.50 focused along/southwest of a Macomb to Springfield line. - Showers and thunderstorms will become more prevalent Wednesday night through Thursday night. While the severe weather risk will remain low (less than 5%), there is the potential for strong thunderstorms late Thursday afternoon into Thursday evening. && .SHORT TERM...(Today through Tuesday) Issued at 338 AM CDT Mon Aug 12 2024 A short-wave trough currently over South Dakota/Nebraska will track southeastward into the region today...spreading clouds and a few showers into central Illinois. 08z/3am radar mosaic shows clusters of showers/storms associated with the wave across central/western Iowa into northwestern Missouri. This activity will track E/SE and will spill into the Illinois River Valley after 11z/6am. With the nocturnal low-level jet weakening after sunrise and the showers pushing further east into a dry/subsident environment across Illinois, am expecting the precip to diminish in both intensity and areal coverage. Based on radar trends and latest HRRR/RAP runs, it still appears the most widespread showers will impact locations along/southwest of a Galesburg...to Lincoln...to Effingham line where high chance to likely PoPs are warranted. While the precip will tend to diminish toward midday, scattered showers will linger through the afternoon and into the evening as the wave traverses the area. Rainfall will be light...with the highest amounts in excess of 0.25 focused across the W/SW KILX CWA. Meanwhile, locations north of I-74 and east of I-57 may stay completely dry. Given extensive cloud cover and showers, temperatures will be suppressed today. Afternoon highs will range from the lower 70s across the W/SW where rain will be most likely...to the upper 70s to around 80 degrees near the Indiana border. Any lingering showers will come to an end this evening, followed by partial clearing and dry conditions overnight. With added boundary layer moisture in place and winds expected to be nearly calm, think fog will develop where rain occurs today. As a result, have added patchy fog to the forecast late tonight south of I-74 and west of I-57. After any early morning fog burns off, a partly sunny and dry day is anticipated for Tuesday with afternoon highs topping out in the upper 70s and lower 80s. Barnes .LONG TERM...(Wednesday through Sunday) Issued at 338 AM CDT Mon Aug 12 2024 As a more significant short-wave trough crosses the Rockies and pushes into the Plains, downstream upper ridging will nudge the primary baroclinic zone northward toward central Illinois by Wednesday. A few showers may spread into the far SW KILX CWA late Tuesday night, with scattered showers and storms anticipated everywhere along/west of I-55 on Wednesday. As has been advertised for the past several days, the most significant chance for widespread beneficial rainfall will arrive late Wednesday night through Thursday night as the Plains wave tracks further eastward into the region. With the warm front lifting northward and the nocturnal low-level jet strengthening from Oklahoma to Iowa, showers and thunderstorms will become widespread across Iowa, northern Missouri, and western Illinois Wednesday night. The storms will remain elevated, posing only a minimal risk for small hail/gusty winds late Wednesday night into early Thursday morning...primarily along/west of the I-55 corridor. Once the early day convection diminishes, a lull in rain chances will occur for a good portion of Thursday before an approaching cold front activates by late afternoon and evening. With low pressure progged to be over N/NE Iowa, central Illinois will be in the warm/unstable sector of the system. 00z Aug 12 GEFS shows a low probability (10-20%) of SBCAPEs exceeding 500J/kg and bulk shear increasing above 40kt. Given somewhat more favorable instability/shear parameters and the presence of a forcing mechanism during peak heating, think scattered strong thunderstorms will be a good bet late Thursday afternoon and evening...especially along/west of I-57. The Central Plains wave will slowly shift eastward through the region on Friday, continuing the chance for showers/thunder. Depending on the exact speed of the wave and its associated cold front, there may be another chance for strong thunderstorms Friday afternoon/evening along/east of I-57, but confidence in this scenario remains low at this time. After that, the strongest forcing will shift into the Ohio River Valley and drier weather will return for next weekend. Barnes && .AVIATION... (For the 06z TAFs through 06z Monday Night) Issued at 1104 PM CDT Sun Aug 11 2024 High pressure will remain perched over the area, resulting in calm to light/variable winds through Monday evening. Late tonight, fog is expected to form over eastern IL, and have included a few hours of MVFR visibility at KCMI. There is a 30% chance of IFR visibility in a 09-12z window. An upper level disturbance will move into central IL Monday morning, and linger into the evening. This will bring periods of -SHRA or sprinkles. Latest guidance shows ceilings and visibility remaining VFR across the central IL terminals. 25 && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$