(5:15PM – 6/28/18) The third heat wave of the season is beginning to settle in across the region, and will be bringing several days of hot and humid conditions to the state…

The heat wave will be the product of a strengthening and building ridge that will be sweeping east across the region. Originating in the Plains, the ridge will pull very warm upper air temps from the West along with it as it slides to the east. With nice mixing of the atmosphere likely, this will translate to surface temps well into the 90’s across the state during the period. Additionally…Given recent heavy rains and flooding across the state the past few weeks, evapotranspiration from the maturing corn crop and a nice southerly flow in from the Gulf…High dew points are likely as well. Dew points will likely near or exceed 80 for many locations across the state during the period. The combination of the hot temps and high dew points will lead to oppressive heat indices, likely in the range of 100-115 during the period for most of the state.

Things have kicked off today across portions of the state, with highs into the low 90’s across portions of Southwest/Southern Illinois. A warm front currently across Southern Illinois will lift north across the state tonight, which will spread the hot temp and humid conditions for the coming days. The main focus is for Friday, Saturday and Sunday across the state. These days will likely feature similar conditions… High temps on these days will likely be into the mid-upper 90’s across much of the state. Peak heat indices will range from 100-115 during these three days as well. Low temps will likely stay in the 70’s for most areas as well, with more urban area likely staying closer to 80 (Such as St. Louis and Chicago). Record high and low temps will likely be in jeopardy for some locations during this period. A “cold front” will sweep across the state Sunday evening through Monday, which will bring the heat wave to an end. High temps into the low 90’s will likely linger into Monday for Southern Illinois, where the front will likely stall.

There is a wild card for some areas however…Some guidance is suggesting an complex of thunderstorms and/or outflow/cloud debris may try to push into portions of Northern Illinois Friday morning, which would lower high temps a bit for this area on Friday. It’s not a guarantee that it occurs, but it’s worth a mention as a possible scenario. Additionally, cloud debris could be issues for portions of Northwest/Western Illinois on Sunday, which could lower high temps a bit for that area on Sunday. Once again, it’s not a guarantee that either occurs, but worth a mention. Just a few fail points for some areas should other scenarios occur.

Additionally…A renewed period of heat will be likely across portions of the state next week, from Tuesday through Thursday. This will occur as the current ridge moving east ends up retrograding back west. Additional details on this will be posted in the coming days.