In the late spring and summer, when a heat ridge builds in the atmosphere, there is often a concentration of strong thunderstorm clusters that rapidly rotate around the ridge. They feed off the heat in the ridge where subsidence caps convection. North of the ridge even weak disturbances in the flow can kick off thunderstorms that can organize into large clusters. They often produce heavy rains, hail, very strong winds and tornadoes.
This year given how wet the ground has been after a wet spring, there is plenty of moisture available to these storms. They often are nocturnal firing up very late in the day and continue into the following morning.
This ring of fire was very evident on June 17-18th when the heat ridge built north. Some areas to the north of the ridge saw three clusters in 24 hours.
Here is the heat dome mid-afternoon June 17th.
See the 24 hour rainfall ending the following morning (07:00am CDT). Several cluster developed especially at night into the following morning. Below is the 24 hour total precipitation from 7am CDT June 17th to 7 am CDT June 18th.
These heat ridges when they develop in the south central can help pump moisture from the Pacific and Gulf into the southwest and kick off the summer monsoon showers, also seen above in west Texas and New Mexico.
The storms also produced severe weather as seen here in this summary from the Storm prediction Center for the 17th.
These events last multiple days and indeed the SPC was showing more activity for the 18th.
Will this be the pattern for the summer? No, probably not. Usually patterns in June change as we move to July. Often these ridges this time of year retrogress (back up west) discontinuously. Models are showing this on the 18th. By the time this is posted, we will know for sure.
Ironically, this is very similar to the two most similar years with developing El Ninos following La Ninas, with an easterly QBO, near solar minimum and with a preceding Alaskan volcanic eruption.