I believe it is an annual event... its my first time hearing it as well, however this is my understanding of what it is. They simulate an evacuation from one of the Police Communications Centers and hand off all control to the alternate PCC. In the real world it would likely be because of a disaster, threat, fire etc.
I am listening to Wellington, Bruce, Grey Counties etc...It all got handed over to Orillia Comm, all calls and dispatching is how being handled from that center. I am not sure how big the event is if multiple comm centers are taking part tonight or if its just Orillia and London. I'll have to listen the next couple nights maybe Orillia will be handing off to London tomorrow night..... I am not sure how long it will stay in place for, likely only a couple of hours. Last I heard they were having issues logging officers in. Other than that it sounds like all has gone well so to speak up here.
There's a 10-3 in effect of course and several talk-groups have been patched together that normally are not.
That's my understanding of what's going on...
Mike