Southwest Illinois had a pretty neat little mesoscale feature pass through this morning - a wake low. Right before 3am we had a significant pressure drop of about 7mb over the course of 15 minutes with 5mb falling in 1 minute (which is highlighted in the graph below from my weather station). That was quickly followed by strong wind gusts - I peaked at 36mph here at the house but I've seen reports of 60mph just across the river in Missouri.
So what is a wake low and what caused it to happen? A wake low is an area of lower pressure that we typically see on the backside of a squall line or in stratiform rain (much like we got this morning as you can see in the radar screenshot below). It appears as though the rain-cooled air built up a small region of higher pressure (several millibars higher than the surrounding air) as it moved through the area creating a strong pressure gradient over a short distance. Since nature is always working to be in equilibrium, that sharp of a pressure gradient is unsustainable. Eventually, this pressure bubble 'burst' in and when it did, it sent out a rush of strong winds that prompted numerous damage and high wind reports across the St. Louis metro and southwestern IL.
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