DISCUSSION
Issued at 333 AM CDT Sat Jul 27 2024

Surface analysis shows a large area of high pressure centered over the eastern Great Lakes Region. This will get shunted further east as an upper trough pivots toward the middle Mississippi Valley later today into Sunday. Precipitation chances increase tonight as the upper wave nears and a 25-30 kt LLJ set up, sparking the development of scattered showers and storms that will continue through most of the day on Sunday. Although severe weather chances are low this weekend, Gulf rich moisture air will aide in PWATs exceeding 2" in spots. This could lead to high rainfall rates with any heavier showers or storms.

Flow aloft transitions to west-northwesterly early in the week as ridging amplifies over the Plains states, putting us in the path for any ridge runner upper shortwaves/remnant MCS activity. The first of this series will arrive by Monday morning as a thunderstorm complex develops along the nose of a strong LLJ late Sunday night further west of here. There is some uncertainty on if this will maintain strength and pose a threat for any strong to severe impacts across central Illinois Monday morning. Another round is not out of the question by Monday evening along any remnant boundaries from earlier convection as strong instability 2000-3000 J/kg and effective shear of 40-45 kts will be in place. Because of the potential for both morning and evening severe weather, a marginal risk for severe storms has been introduced by the SPC.

Daily chances for showers and storms, including some severe storms, will exist through the end of the week underneath northwest flow aloft. Details of timing remain fuzzy, but the best parameters for any severe weather will be seen Tuesday and Wednesday which is when the best instability and bulk wind shear will coexist.
Precipitation amounts this upcoming week will vary areawide depending on where showers and storms occur, but ensemble probabilities show a 60%+ chance that most of the area will see at least 1 inch or more of rain through the end of the week.

In addition to a more active precipitation pattern, heat and humidity turn things dangerously hot for most of the central US as upper ridging further amplifies. High temperatures look to warm into the upper 80s to low 90s, with heat indices of 100 or higher from Tuesday through Thursday. Heat headlines look increasingly likely, but perhaps need to be taken day by day to account for showers/storms interfering with forecast temperatures/heat indices.

A stronger upper trough late in the week or weekend should bring some relief to the heat, but temperatures look to remain near or slightly above normal going into the following week.

NMA

AVIATION
(For the 12z TAFs through 12z Sunday Morning)
Issued at 546 AM CDT Sat Jul 27 2024

VFR conditions will be in place most of the day with light southeast winds. Shower and thunderstorm chances return later tonight into the overnight hours, so added PROB30 groups to account for this.
MVFR ceilings become likely going into Sunday morning with the highest probabilities (60%+) of <3k ft ceilings arriving before 12Z at KPIA and KSPI.

NMA

ILX WATCHES/WARNINGS/ADVISORIES
None.