The low level jet & overnight storm formation

During the summer months, overnight storm clusters become more common as low level winds increase ahead of storm systems which stall or move slowly across the Central Plains states. This pattern tends to set up in June through early July as cold fronts move in from the north and stall as they run into warmer air to the south, becoming nearly stationary across the north-central states.

Out ahead of these storm systems, low level winds increase after sunset as the atmosphere cools down. If conditions are fairly calm, a stable temperature inversion sets up where cool air aloft sinks to the ground and any leftover warm air sits on top of it. The stable air in an inversion acts like a nearly solid object and allows the air above it to flow rapidly past the inversion like wind blowing over water.

As a result, winds just a couple thousand feet above the ground will increase into a fast moving ribbon of air called the low level jet stream which transports moist air northward. If there is something to trigger storm development, the low level jet will fuel the storms, causing them expand and strengthen quickly into an MCC (mesoscale convective complex) which often brings heavy rain and strong, damaging winds to areas in it’s path.

We are seeing this pattern shape up again tonight. The forecast winds at around 3000 feet are expected to increase after 10 PM in western Missouri (see top image). At the same time a wave of lower pressure aloft (see related content) will move east causing storms to develop as the warm, moist air increases with the stronger southerly winds above the surface. Storm development is expected ahead of the strongest low level winds (see bottom image of related content). This pattern will likely repeat itself again Wednesday night with another round of storms likely in Mid-Missouri.