FXUS63 KILX 161100 AFDILX Area Forecast Discussion National Weather Service Lincoln IL 557 AM CDT Thu Apr 16 2026 .KEY MESSAGES... - There is currently an Enhanced Risk (Level 3 of 5) for areas near and west of the Illinois River on Friday where a significant, all-hazards severe weather outbreak looms. - Much cooler temperatures return this weekend, with an attendant frost risk both Saturday night and Sunday night. && .DISCUSSION... Issued at 355 AM CDT Thu Apr 16 2026 A mid-level shortwave trough is currently situated over east- central Iowa, visible on early morning water vapor imagery. A significant plume of moisture extends from central Arkansas into the lower Great Lakes, coinciding with an area of mostly stratiform rain. Occasional convective activity, indicated by cooling cloud tops and 40 dbz radar echoes, is embedded within this rain shield. This activity is expected to move slowly eastward and exit Illinois shortly after sunrise as the upper trough progresses into north-central Illinois and the low-level jet weakens. Synoptic-scale subsidence and increasing height tendencies will build across central Illinois by midday, effectively ending precipitation chances for most, if not all, of the forecast area. With clouds lifting and breaking behind the departing shortwave, temperatures will warm into the mid-to-upper 70s. While the primary forecast calls for a clear day without further convection, a slight chance of isolated storms exists near and south of Interstate 70 late this afternoon. This is associated with a separate, trailing mid-level shortwave wobbling across the eastern Ozarks and into far southern Illinois. In this area, thermodynamic profiles become more favorable, with steepening mid-level lapse rates boosting MLCAPE values into the 1000-2000 J/kg range. However, the potential for widespread, vigorous convective development is limited by fleeting kinematics. As the upper jet core continues its eastward departure, deep layer shear around the time of potential initiation is only forecast to be about 20-25 kts. Consequently, portions of southern Illinois are outlooked for general thunderstorms today, but not for severe thunderstorms. Widespread thunderstorm activity is forecast to return Friday. This development is associated with subtle shortwave energy ejecting from the Central Plains toward the Mid-Mississippi Valley, occurring ahead of a more potent trough pivoting across the north-central U.S. A highly volatile environment is expected to evolve by Friday afternoon. The advection of an Elevated Mixed Layer (EML) ahead of a cold front will contribute to increasing mid-level lapse rates and overall buoyancy, with MLCAPE around 2500 J/kg. There is some uncertainty regarding the initial storm mode. Some 00z CAMs indicated the potential for isolated supercells to develop well ahead of the cold front, primarily over southeast Iowa and far west-central Illinois late in the afternoon. This activity would be triggered by the subtle shortwave energy and occur near a diffuse dewpoint gradient or pseudo warm front. If such isolated activity develops juxtaposed with an increasing kinematic field (bulk shear of 35 kts), an all-hazards risk could ensue ahead of the main cold front. This is not the most likely scenario. It's important to note that the main area of convective initiation is expected to occur well to our west along the cold front. And, with the orientation of the deep-shear vectors becoming parallel to the main forcing, supercells that develop on the cold front are anticipated to gradually grow upscale into a linear MCS, which would enter our area later in the evening. As the linear MCS moves into west-central Illinois, a continued risk for severe weather is anticipated, lasting well into the overnight hours. Residual supercell structures may persist initially, driven by an increasing low- level jet that elongates the low-level hodograph and enhances 0-3 km SRH. However, consolidating cold pools, amid strong low-level CAPE and shear, should support a transition to a mature QLCS. This mature QLCS will likely feature embedded bowing segments and mesovorticies that pose a substantial risk for straight- line wind damage and brief tornadoes as it progresses eastward. A significant cooling trend is forecast to begin by Saturday as the cold front moves through and displaces the warm, moist air mass from the previous week. Temperatures are expected to exhibit a non-diurnal trend, with highs likely occurring earlier in the day. The latest NBM guidance raises concern for widespread frost, with low temperatures anticipated to fall into the 30s Saturday and Sunday nights. By the middle of next week, temperatures are forecast to quickly rebound into the lower 70s. This warming trend is due to an upper-level pattern exhibiting some blockiness, allowing an amplified ridge axis to build into the region. && .AVIATION /12Z TAFS THROUGH 12Z FRIDAY/... Issued at 524 AM CDT Thu Apr 16 2026 Low-level clouds will lift and break for sun prior to 18z behind a departing disturbance. VFR conditions will then dominate the remainder of this TAF cycle. Breezy west winds will diminish by sunset, becoming light and variable overnight into Friday. && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$ KEY MESSAGES...MJA DISCUSSION...MJA AVIATION...MJA