(10:30PM – 6/14/18) The second 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 a product of a strengthening ridge building northward into the region, which will pull in warm upper level temps from the Plains into the region. Conditions will be favorable for mixing of the atmosphere to reach these warm temps aloft, which translates to hot temps at the surface. Ridge placement such as we will see also tends to prevent thunderstorm development and limit cloud cover. Additionally, several days of southerly flow at the surface will help pull in higher dew points and humidity from the South. The final product ends up being a combination of hot temps, humid conditions, with high heat indices.
Hot and humid conditions started to impact a small portion of the state today (Thursday), with low-mid 90’s having occurred across portions of Southwest Illinois. Hot and humid conditions will expand across the state in coming days, lasting into early next week. For Friday, high temps will range from the upper 80’s across Northeast Illinois, to the low-mid 90’s across much of the rest of the state. Saturday through Monday will feature high temps in the mid-upper 90’s across most of the state. Low temps during this period will likely stay in the upper 60’s to mid 70’s for most areas, with urban areas (Such as Chicago and St. Louis) staying near 80.
High heat indices are likely during this period as well. The combination of high dew points in the upper 60’s to mid 70’s, and the aforementioned hot temps in the 90’s, will set the stage of heat index values ranging from 95-105 for many areas during the period.