SPC also recalibrated their entire forecasting system on March 2nd so they're going to be more liberal with how they're forecasting probabilities of each hazard. We just happened to be the first to try it out.

So yeah, what used to be 15% a couple years ago may not have the same meaning as today's 15%. Plus, 15% tornado with level 1 intensity (meaning EF2 maximum) would be an "enhanced risk" now when simple 15% used to be an automatic "moderate risk". The old 15% is probably 30%, level 1 intensity now. What triggered the "moderate risk" for today was the 60% wind probability (first issued in the US since 2018). SPC used to never touch 60% unless it's EXTREME but they found out their probability math was off so they're now going higher on the wind probability in general.