So far, the humid Tuesday afternoon has yielded us no storm activity. But that has been a very different story across SE Iowa and Central Illinois. Our focus now turns well Northwest where our next potential round of storms has begun developing in the Northern Plains.
Our main 3 windows for storm chances in the next few days set up like this. We are watching trends to the Northwest for our next waves of storms as they move through the unstable environment to see where and when they may reach our general vicinity. Same deal for Wednesday as the afternoon looks dry as of now once lingering storms from the morning round clear out. This will produce the hot and humid weather like what we saw on Tuesday. Our next upper air wave looks to move in by the early overnight hours, producing our next chance at some storms. By Thursday, we will see better forcing with an upper level low ahead, leading to scattered storm chances during the afternoon, some of which may be strong to severe.
Ahead of the storms developing in the Northern Plains Tuesday evening, a tricky environment is set in place. There is still a lot of instability set up across the area for these storms to work with, but there is not a lot of upper air support to steer them. Because of this, the exact track and timing of these storms reaching the Stateline is still in serious question. The best chance for them arriving would be just before dawn tomorrow, as I currently favor a dry forecast through 5AM. These storms may be capable of damaging winds and heavy rain when they arrive.
Following the overnight/early morning round of storms, the environmental looks to destabilize for Wednesday afternoon, leading to more storm threats into the late evening again. With the lack of storms during the daytime, heat and humidity will build up, with heat indices likely near the triple digits again. This will be the fuel for the storms later in the evening. The exact timing of when this round of storms initiates to the West is still uncertain, but likely would be between 8PM-2AM window before progressing East through the Stateline shortly after initiation. Stay tuned with the forecast for this threat heading into tomorrow!
Another round of storms may be possible Thursday afternoon with the upper level low nearby. Any daytime heating between lingering morning storms and afternoon initiation will determine how strong the storms would be. As of now, the threat appears to be highest to the South and East of the Stateline, closer to Indiana, but this is subject to change based on how things trend between tonight and tomorrow night.
Note, so far all of the storm complexes have followed a very similar track just to our Southwest and South. There is a chance this could happen with both the chances Tuesday night and Wednesday night, which would keep us completely dry through Thursday morning. Nonetheless, I maintained our storm chances mainly during the evening and nighttime hours Tuesday night and again Wednesday night, with scattered storms possible Thursday into Friday as the upper low swings overhead. We dry out a bit into the weekend, but temperatures do not fall far, only back into the low/mid 80s.
Disclaimer: Forecasting multiple complexes of storms in weather environments like this one is not easy. Particularly with computer modelling, one of the biggest tools used to predict storms like these. In situations featuring extreme instability and multiple storm complexes, computer models can very quickly get off track. Think of it like a row of dominoes. Each complex of storms is a domino cascaded on by the previous round. It is difficult for the computer model to determine how quickly the atmosphere may recover following a round of storms, and this is only exasperated when there are multiple rounds of storms each throwing a wrench into the weather model that just ran based on current conditions as of an hour ago. Sometimes even miniscule details such as a change of a dew point temperature by 1-2° can set the line of dominoes on a completely different path, throwing off the entire rest of the forecast. That is where good human forecasting comes into play. A good forecaster looks at all the different scenarios based on current radar data and makes a determination of what might actually happen.
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