The Midwest is currently experiencing a classic "ring of fire" pattern as thunderstorm complexes ride over the top of the southwestern U.S. ridge bringing severe weather, sometimes of the destructive variety with damaging bow echos and derechos. It's the reason the region is known as derecho alley, and we're right in the heart of derecho season. This idea was laid out in my forecast discussion about the upcoming pattern over the weekend.
A thunderstorm cluster passed through portions of Illinois on Monday morning, July 29th. The atmosphere recovered and a few mini-supercells erupted across central Illinois during the evening, a few of which prompted tornado warnings and produced funnel clouds. Colin Davis and I ventured out and observed the tornado warned storm near Taylorville noting several rotating wall clouds and some cute structure.
Tornado warned mini-supercell with a wall cloud and circular updraft base near Taylorville, IL on Monday, July 29th, 2024:
When I went to bed on Monday night, most weather forecast models were showing a cluster of severe storms or a bow echo sweeping through portions of central Illinois during the afternoon and evening today (Tue, Jul 30). When I woke up and sat down at my desk this morning there was already a severe bow echo coming out of Iowa into western Illinois, about 9 hours ahead of schedule. There was also a trailing bow echo west of Des Moines.
As morning weather forecast data began to trickle in, I needed about five seconds before I realized it was all complete garbage. This is the comparison that I slapped together for social media this morning. One image shows the 3km NAM model, one of our more reliable, heavy-rotation models, and it's forecast radar reflectivity for 9 AM... (2 hours into the forecast that came out at 7 AM, mind you) and the other shows the actual radar for 9 AM.
Out of the gate, this model is completely ignoring two ongoing clusters of severe thunderstorms. To put it bluntly, if a weather model doesn't know what's happening NOW, it does not know what is going to happen LATER.
In a boom or bust pattern with a lethal combination of hot, humid air that is ready to rise and tons of little shortwaves embedded within the northwesterly jet stream flow that are ready to provoke it into erupting, what is one to do with no reliable help from computer weather forecast models?
You rely on your gut. It's easy for me to say at 8:45 PM, but I mentioned on social media this morning that the pit in my stomach that was there on the mornings of August 10th, 2020, June 29th, 2023, and July 15th, 2024 (all destructive derecho days in Illinois) was NOT there this morning. We had a thunderstorm complex ongoing at sunrise crossing from Iowa into Illinois, with that trailing thunderstorm complex hot on its heels. While the atmosphere did try to rapidly recover ahead of this trailing thunderstorm cluster, it wasn't going to be enough to restore the thermal profile to explosive, volatile levels. Sure enough, while it produced a smattering of severe reports, the second storm complex mostly struggled and sputtered as it trekked through the exhausted of the lead storms.
That was a lot of word salad to say, my gut told me that today would not be the day that we see a derecho manifest with 80-120 MPH wind gusts and embedded tornadoes race across the Midwest. There were a million ways I could have been wrong because of (gestures back up to the paragraph about explosive energy and provoking shortwaves) but that's all you've got when the computers don't have a clue. The meteorologist's brain and ability to rely on their own experience and pattern recognition is still crucial in these boom or bust scenarios.
I'll head to bed tonight giving the side eye to those burgeoning thunderstorm clusters in the Dakotas this evening. As the environment recovers tonight into tomorrow, we will probably be reassessing an entirely new severe weather threat with very little support from our computer friends.