SMF Operating Northbound Wednesday

SMF normally operates Southbound. What what wind speed (against the
prevailing direction) does it take for an airport to change the direction of its operation?

I doubt there is an easy answer to this as many factors go into runway selection. For most aircraft, 10knts of tailwind is the limit, but in most cases the configuration would be changed to eliminate the tailwind. However, as in the case of SW1248, the controllers might select a configuration with a tailwind componet. In the SW case, RVR (runway visual range) minimums for the approach to 31C was higher than 13C, and that would allow more successful approaches (see Flying Mag. analysis).