The bringing information to the top, or near the top of the hierarchy based on some relevant change of mode or condition.
In this case we wanted to provide some additional value to the forecast, to tell not just what is going to happen, but why. To tell weather's story with a little more lore.
The test was to see if an informational tab that focused on an upcoming severe weather event (ie lightning) added to the forecast area garnered attention and increased time on page or provided a bump to other content types featured in the tab (photos, informational blog posts).
Debating placement, integration into an existing section, an interstitial addition or a contextual addition. The interstitial was rejected because the city page is already very content dense, and our users have experienced a good amount of change so adding a new module with limited testing was not a good choice, and the temporary contextual module seemed too disruptive, sometimes there, sometimes not. Making it's transitory nature make sense would be a challenge, and volatile interfaces have not tested well with our audience. The addition of a tab into the forecast graph puts in where it makes sense, the use of color and icon can be used to refine it's place in the hierarchy, and can be a/b tested without being as disruptive to the normal experience as the other options.