Multiple sounding forecasts suggest this event will be held down by a slight capping inversion. As you may recall, a capping inversion involves a situation where the air at the surface is unable to rise due to a layer of warmer air just above the surface. However, as soon as that capping inversion breaks (which is expected to occur in the evening hours of April 9th), air attempting to rise and create thunderstorms will have over 1500 j/kg of instability available. From here, this rising air will form updrafts, which will then turn into weak (and likely rotating) thunderstorms. These initial storms will feed on upper air support and continuing availability of moderate instability to mature into supercells. With elevated helicity and high amounts of atmospheric spinning in the immediate vicinity of the mature supercells, tornadoes should begin to become a real concern as the 7:00 PM (central) hour comes to a close.
Forecaster Jon Davies indicates values above 2.5 are conducive for supercells and are favorable for tornadoes. That said, the projected EHI value of 3.6 is quite high and great for tornado development and propagation. There are several other parameters we could look at for guidance into forecasting this event, but from the aforementioned factors, I have a pretty good idea of what to expect.
A tornado outbreak is expected over eastern Oklahoma, Arkansas, portions of northeast Texas and southern Missouri. The cells should initiate in the evening hours and mature to supercell status in the later hours of the night. Tornadoes are likely in the aforementioned areas, and more than one of them could be long-tracked and strong. Further clarification is anticipated by tomorrow's new Storm Prediction Center outlook
Things to note:
-Storm Action Day has been declared for April 9th. Upgrade to a Critical Storm Action Day may be needed.
-Storm Action Day is possible on April 10th. Decision will be made in coming days.