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Area Forecast Discussion
Issued by NWS Central Illinois
Issued by NWS Central Illinois
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264 FXUS63 KILX 040442 AFDILX Area Forecast Discussion...Updated Aviation National Weather Service Lincoln IL 1142 PM CDT Wed Jul 3 2024 .KEY MESSAGE... - A couple rounds of showers and storms are expected Thursday; one during the morning and a second during the late evening and overnight. There is increasing confidence in a relative lull in precip coverage during the late afternoon and evening. && .UPDATE... Issued at 913 PM CDT Wed Jul 3 2024 While a stationary frontal boundary remains draped across central Illinois this evening, the effective boundary is much further south from the Ozarks into the Ohio River Valley where a broken line of convection has developed. Other than an isolated shower or two south of I-70, the majority of the KILX CWA will remain dry for the balance of the evening and through a good portion of the overnight hours. Clusters of thunderstorms currently developing on the tail end of the stationary front across Nebraska/western Kansas in association with a short-wave trough ejecting out of the Rockies will track/develop eastward overnight. Latest runs of the HRRR/RAP continue to suggest convection reaching locations along/southwest of a Rushville...to Shelbyville...to Robinson line before dawn Thursday. As the wave approaches, showers and storms will overspread much of central Illinois after sunrise...before shifting eastward into Indiana by midday. Have updated hourly PoPs to better reflect current obs and expected trends tonight. Have also added patchy fog to the forecast tonight as calm winds and dewpoint pooling in the vicinity of the front will be conducive for fog. CAMs have been slow to catch on, but the most recent runs of the HRRR and GFSLAMP are trending foggier. Barnes && .DISCUSSION... Issued at 209 PM CDT Wed Jul 3 2024 This afternoon, synoptic cold front is located roughly near the I-55 corridor, while effective front from earlier convection just barely clips the southeastern forecast area near Lawrenceville. Temps jump from the low 80s north of the effective boundary to around 90F south. Anticipate this to be the main focus of convection as we head into the mid to late afternoon hours. Latest RAP suggests around 1500J/kg or higher MLCAPE is in place on the warm side of the boundary, but deep layer shear is marginal/sub- marginal around 20-30kt. Storms should begin to increase in coverage in this vicinity by late afternoon or early evening, and a few could be strong to marginally severe. Latest HRRR keeps this activity a county or two south of the forecast area which lines up well with current location of the front. Overnight into Thursday morning, a pair of shortwave troughs will move across central Illinois resulting in an increase in showers and a few storms. Weakening surface front will likely stay stalled across portions of southern Illinois with weak/negligible instability in place north of the front across central Illinois which will keep the threat for severe storms out of the local area. After the shortwave exits central Illinois early Thursday afternoon, there is growing confidence in a relative lull in precip later Thursday afternoon and at least early evening before a stronger shortwave digs across the Upper Midwest later Thursday evening into Friday. Despite passage of the weaker shortwave midday Thursday, mid level height falls will persist across central Illinois through the day in advance of the next deeper wave, contributing to at least some spotty convection during the afternoon/early evening, but coverage should be fairly isolated at this point, and should allow many locales to kick off their Independence Day celebrations. By mid to late evening, moderate instability (MUCAPE 1000-1500 J/kg) begins to lift back north into portions of central Illinois coinciding with the arrival of the deeper wave / closed 500mb low into the Midwest. Storm coverage will increase in response. Unfavorable diurnal timing should keep the severe threat low Thursday night into Friday morning, but a few stronger storms are possible, especially west of I-55, with seasonably strong deep layer shear overspreading central Illinois. As upper wave begins to depart the region Friday, strong cold air advection will overspread central Illinois in its wake and scour out some of the low level moisture. There will be a brief respite from the precip chances once this occurs and will persist into Friday. Temps will be lower, too, with afternoon highs generally in the upper 70s to lower 80s Friday and Saturday. Surface ridge axis will shift across the area Saturday afternoon with return flow overspreading the area Sunday. Heat and humidity will begin to creep back up in response and broad upper troughing over the Great Plains will be in place with several shortwaves ejecting across the region Sunday through the first half of next week bringing additional chances for showers and storms. Deubelbeiss && .AVIATION... (For the 06z TAFs through 06z Thursday Night) Issued at 1142 PM CDT Wed Jul 3 2024 A thick layer of mid-level cloud cover at around 12,000ft will persist through the night before a cluster of thunderstorms currently developing across southern Nebraska into Kansas spreads E/NE into central Illinois early Thursday morning. 00z CAMs show an appreciable spread concerning the exact track of the convection...with the bulk of the models preferring a more southern track along and south of the I-70 corridor. The HRRR remains the furthest north, and based on the current location of the stationary frontal boundary from south of KIKK to near KUIN, think it has the best handle on the situation. Have therefore added predominant thunder at KSPI between 12z and 15z and at KDEC/KCMI between 13z and 17z. Further north, confidence for thunder is lower, so have only gone with showers at KPIA and KBMI. Both NAM and HRRR forecast soundings suggest ceilings lowering to MVFR during the precip and remaining there for a couple hours afterwards. Have scattered the MVFR ceilings at all terminals after the 18z-21z time period. Winds will be light/variable through the entire 06z TAF period. Barnes && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$