Chance of Storms Gives Way to BIG July Cooldown

With hot and humid conditions, typical for the July, over Southern Illinois, it's hard to believe we may be talking about near record low temperatures in just a few days. As the result of Super Typhoon Neoguri curving away from Asia, it has caused a large "wrinkle" in the jetstream which is causing high amplitude waves which is now tracking east across the United States. With a large ridge baking the West, the flip side is a large trough which will bring unseasonably cool air south into eastern half of the United States.



Tuesday morning 300mb map showing large trough across the Midwest

A series of two surface cold fronts will begin the big push of cool air into Southern Illinois. With a upper-level high centered near Oklahoma Saturday afternoon, the first cold front is likely to "wash out" near Southern Illinois. With that being said, lift along the front, an increasing wind field, and warm, humid air ahead will likely result in scattered showers and storms in Southern Illinois late Sunday afternoon and into the evening. With the wind field increasing across Southern Illinois, a few storms may become strong to severe with primarily a wind threat. Precipitable water values will be quite high running near or above 2" which may result in some locations picking up heavy rainfall late Sunday into early Monday morning especially if storms "train" over the same areas. As the front washes out overnight, rainfall will taper off by Monday morning while we await the arrival of the stronger of the two fronts.

Tuesday morning, unseasonably strong cold air advection will be ongoing over Southern Illinois

While the second cold front is stronger, surface northerly winds behind the first front may limit moisture return and instability, though this will need to be monitored for potential of severe weather, especially south of the Ohio River.

With cold air spilling south, you'll likely wake up Tuesday morning with temperatures in the low 60's. This time of year, strong cold air advection typically results in a layer of clouds throughout the afternoon which may add to the cool air moving in keep temperatures in the mid to upper 70's. With surface high pressure settling in late Tuesday, Wednesday morning is likely to be the coolest as clouds also clear.

Wednesday's Record Low Temperature: 54º set in 1945

Wednesday's Forecasted Low Temperature: 55º