Area Forecast Discussion
Issued by NWS Central Illinois
Issued by NWS Central Illinois
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302 FXUS63 KILX 250243 AFDILX Area Forecast Discussion...Updated National Weather Service Lincoln IL 943 PM CDT Mon Jun 24 2024 .KEY MESSAGES... - Hot and humid conditions on Tuesday will send heat indices as high as 105. A Heat Advisory has been introduced south of I-70. - Thunderstorms are possible (30-50%) north of I-72 Tuesday morning. Another round of storms could develop Tuesday afternoon into evening, though confidence in where/when will be dependent on the morning activity. && .UPDATE... Issued at 942 PM CDT Mon Jun 24 2024 Seeing a wide range of solutions for storm evolution the rest of tonight and Tuesday in the CAMs. The current clusters of storms over NE IL and approaching NE IL are struggling to maintain persistent deep updrafts. Some pulsing evident, but sub-severe intensity has been the rule this evening. Going forward, the consensus of the CAMs indicate a linear complex of storms will erupt somewhere in the S MN, N IA, SW WI area after midnight, and propagate to the south-southeast into central IL by sunrise. Timing and location are still quite uncertain, but SE oriented LLJ will be present as the warm front advances into IL from the west. That should be enough to support a late night storm system for at least our northern counties. The line is expected to be weakening as it reaches as far south as Lincoln and beyond, but isolated severe wind gusts and large hail will be possible with any sustained updraft through 7 am or so. The current forecast rain/storm chances generally follow that scenario, so only minor adjustments were needed to PoPs/Wx to account for the collaborated timing shifts. Overall, no other notable adjustments will be needed to the forecast this eve. Shimon && .DISCUSSION... Issued at 338 PM CDT Mon Jun 24 2024 Weak frontogenesis nosing into west-central IL late this afternoon has sparked a few isolated storms from Davenport, IA to Eureka, IL as of 3 pm. The NamNest is the only CAM that notes this activity, showing it ending around sunset. Added slight chance for PoPs to account for this over the next few hours. A surface low situated over the Northern Plains will track into the Upper Midwest tonight. Thunderstorms are expected to develop along the lows warm front/within the warm sector over Minnesota/Wisconsin tonight and track southeast along an instability gradient. CAMs show this activity approaching our northwest sometime between 10-14Z Tuesday morning. Although we will be capped, some elevated instability may support a few stronger storms capable of strong winds for a brief period of time before things begin to dissipate later in the morning as the LLJ wanes. There remains some uncertainty on how far south thunderstorm activity will make it Tuesday morning with current thinking keeping most of it north of I-72. Temperatures on Tuesday will likely be greatly impacted by morning convection, with very low confidence in high temperatures north of I-72. Ended up reducing highs by several degrees (upper 80s) from roughly a Champaign to Macomb line. Higher confidence for hot and humid conditions will be seen south of I-70 where air temperatures should reach the middle 90s with heat indices peaking around 105. A Heat Advisory has been issued for these counties from noon to 8 pm Tuesday. Outflow from morning thunderstorms will be the focus for additional activity later Tuesday afternoon into evening, though there remains uncertainty on where this will be situated. The 24.12Z HREF has instability peaking between 2000-3000 J/kg south of I-72, though wind shear will be on the weaker side (~20 kts). Strong to severe storms will be possible with any convection that does develop in the afternoon and evening, with damaging winds and large hail being the primary hazards. Although we can use the rain, some locally heavy rainfall could be seen with any storms on Tuesday with PWATs approaching 2 inches. The aforementioned low`s cold front will sag south through the area on Wednesday, bringing the return of more seasonable temperatures for Wednesday and Thursday. Temperatures steadily climb back into the upper 80s to low 90s by the end of the week ahead of the next system. A cold front will bring our next chance for precipitation Friday night into Saturday, with temperatures briefly turning cooler behind it. NMA && .AVIATION... (For the 00z TAFs through 00z Tuesday Evening) Issued at 632 PM CDT Mon Jun 24 2024 There remains uncertainty on placement and timing of showers and storms associated with the cold front tomorrow morning, but several models bring precip as far south as DEC and have included a prob30 in the forecast to account for this possibility of storms. Southwest winds will begin gusting to around 20 kt starting mid to late morning. Additional storms are likely later in the day beyond the current forecast period. Copple && .ILX WATCHES/WARNINGS/ADVISORIES... Heat Advisory from noon to 8 PM CDT Tuesday for ILZ066>068- 071>073. && $$